Listing Endangered and Threatened Wildlife and Plants; Notice of 12-Month Finding on a Petition To List the Pacific Bluefin Tuna as Threatened or Endangered Under the Endangered Species Act, 37060-37080 [2017-16668]

Agencies

• DEPARTMENT OF COMMERCE
• National Oceanic and Atmospheric Administration

[Federal Register Volume 82, Number 151 (Tuesday, August 8, 2017)]
[Notices]
[Pages 37060-37080]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 2017-16668]


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DEPARTMENT OF COMMERCE

National Oceanic and Atmospheric Administration

[Docket No. 160719634-7697-02]
RIN 0648-XE756


Listing Endangered and Threatened Wildlife and Plants; Notice of 
12-Month Finding on a Petition To List the Pacific Bluefin Tuna as 
Threatened or Endangered Under the Endangered Species Act

AGENCY: National Marine Fisheries Service (NMFS), National Oceanic and 
Atmospheric Administration (NOAA), Commerce.

ACTION: Notice of 12-month petition finding.

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SUMMARY: We, NMFS, announce a 12-month finding on a petition to list 
the Pacific bluefin tuna (Thunnus orientalis) as a threatened or 
endangered species under the Endangered Species Act (ESA) and to 
designate critical habitat concurrently with the listing. We have 
completed a comprehensive status review of the species in response to 
the petition. Based on the best scientific and commercial data 
available, including the status review report, and after taking into 
account efforts being made to protect the species, we have determined 
that listing of the Pacific bluefin tuna is not warranted. We conclude 
that the Pacific bluefin tuna is not an endangered species throughout 
all or a significant portion of its range, nor likely to become an 
endangered species within the foreseeable future throughout all or a 
significant portion of its range. We also announce the availability of 
a status review report, prepared pursuant to the ESA, for Pacific 
bluefin tuna.

DATES: This finding was made on August 8, 2017.

ADDRESSES: The documents informing the 12-month finding are available 
by submitting a request to the Assistant Regional Administrator, 
Protected Resources Division, West Coast Regional Office, 501 W. Ocean 
Blvd., Suite 4200, Long Beach, CA 90802, Attention: Pacific Bluefin 
Tuna 12-month Finding. The documents are also available electronically 
at https://www.westcoast.fisheries.noaa.gov/.

FOR FURTHER INFORMATION CONTACT: Gary Rule, NMFS West Coast Region at 
gary.rule@noaa.gov, (503) 230-5424; or Marta Nammack, NMFS Office of 
Protected Resources at marta.nammack@noaa.gov, (301) 427-8469.

SUPPLEMENTARY INFORMATION: 

Background

    On June 20, 2016, we received a petition from the Center for 
Biological Diversity (CBD), on behalf of 13 other co-petitioners, to 
list the Pacific bluefin tuna as threatened or endangered under the ESA 
and to designate critical habitat concurrently with its listing. On 
October 11, 2016, we published a positive 90-day finding (81 FR 70074) 
announcing that the petition presented substantial scientific or 
commercial information indicating that the petitioned action may be 
warranted. In our 90-day finding, we also announced the initiation of a 
status review of the Pacific bluefin tuna and requested information to 
inform our decision on whether the species warrants listing as 
threatened or endangered under the ESA.

ESA Statutory Provisions

    The ESA defines ``species'' to include any subspecies of fish or 
wildlife or plants, and any distinct population segment (DPS) of any 
vertebrate fish or wildlife which interbreeds when mature (16 U.S.C. 
1532(16)). The U.S. Fish and Wildlife Service (FWS) and NMFS have 
adopted a joint policy describing what constitutes a DPS under the ESA 
(61 FR 4722; February 7, 1996). The joint DPS policy identifies two 
criteria for making a determination that a population is a DPS: (1) The 
population must be discrete in relation to the remainder of the species 
to which it belongs; and (2) the population must be significant to the 
species to which it belongs.
    Section 3 of the ESA defines an endangered species as any species 
which is in danger of extinction throughout all or a significant 
portion of its range and a threatened species as one which is likely to 
become an endangered species within the foreseeable future throughout 
all or a significant portion of its range. Thus, we interpret an 
``endangered species'' to be one that is presently in danger of 
extinction. A ``threatened species,'' on the other hand, is not 
presently in danger of extinction, but is likely to become so in the 
foreseeable future (that is, at a later time). In other words, the 
primary statutory difference between a threatened and endangered 
species is the timing of when a species may be in danger of extinction, 
either presently (endangered) or in the foreseeable future 
(threatened).
    We determine whether any species is endangered or threatened as a 
result of any one or a combination of the following five factors: The 
present or threatened destruction, modification, or curtailment of its 
habitat or range; overutilization for commercial, recreational, 
scientific, or educational purposes; disease or predation; the 
inadequacy of existing regulatory mechanisms; or other natural or 
manmade factors affecting its continued existence (ESA section 
4(a)(1)(A)-(E)). Section 4(b)(1)(A) of the ESA requires us to make 
listing determinations based solely on the best scientific and 
commercial data available after conducting a review of the status of 
the species and after taking into account efforts being made by any 
State or foreign nation or political subdivision thereof to protect the 
species.
    The petition to list Pacific bluefin tuna identified the risk 
classification made by the International Union for Conservation of 
Nature (IUCN). The IUCN assessed the status of Pacific bluefin tuna and 
categorized the species

[[Page 37061]]

as ``vulnerable'' in 2014, meaning that the species was considered to 
be facing a high risk of extinction in the wild (Collette et al., 
2014). Species classifications under IUCN and the ESA are not 
equivalent; data standards, criteria used to evaluate species, and 
treatment of uncertainty are not necessarily the same. Thus, when a 
petition cites such classifications, we will evaluate the source of 
information that the classification is based upon in light of the ESA's 
standards on extinction risk and threats discussed above.

Status Review

    As part of our comprehensive status review of the Pacific bluefin 
tuna, we formed a status review team (SRT) comprised of Federal 
scientists from NMFS' Southwest Fisheries Science Center (SWFSC) having 
scientific expertise in tuna and other highly migratory species biology 
and ecology, population estimation and modeling, fisheries management, 
conservation biology, and climatology. We asked the SRT to compile and 
review the best available scientific and commercial information, and 
then to: (1) Conduct a ``distinct population segment'' (DPS) analysis 
to determine if there are any DPSs of Pacific bluefin tuna; (2) 
identify whether there are any portions of the species' geographic 
range that are significant in terms of the species' overall viability; 
and (3) evaluate the extinction risk of the population, taking into 
account both threats to the population and its biological status. While 
the petitioner did not request that we list any particular DPS(s) of 
the Pacific bluefin tuna, we decided to evaluate whether any 
populations met the criteria of our DPS Policy, in case doing so might 
result in a conservation benefit to the species. Generally, however, we 
opt to consider the species' rangewide status, rather than considering 
whether any DPSs might exist.
    In order to complete the status review, the SRT considered a 
variety of scientific information from the literature, unpublished 
documents, and direct communications with researchers working on 
Pacific bluefin tuna, as well as technical information submitted to 
NMFS. Information that was not previously peer-reviewed was formally 
reviewed by the SRT. Only the best-available science was considered 
further. The SRT evaluated all factors highlighted by the petitioners 
as well as additional factors that may contribute to Pacific bluefin 
tuna vulnerability.
    In assessing population (stock) structure and trends in abundance 
and productivity, the SRT relied on the International Scientific 
Committee for Tuna and Tuna-Like Species' (ISC) recently completed 
peer-reviewed stock assessment (ISC 2016). The ISC was established in 
1995 for the purpose of enhancing scientific research and cooperation 
for conservation and rational utilization of HMS species of the North 
Pacific Ocean, and to establish the scientific groundwork for the 
conservation and rational utilization of the HMS species in the North 
Pacific Ocean. The ISC is currently composed of scientists representing 
the following seven countries: Canada, Chinese Taipei, Japan, Republic 
of Korea, Mexico, People's Republic of China, and the United States. 
The ISC conducts regular stock assessments to assemble fishery 
statistics and biological information, estimate population parameters, 
summarize stock status, and develop conservation advice. The results 
are submitted to Regional Fishery Management Organizations (RFMOs), in 
particular the Western and Central Pacific Fisheries Commission (WCPFC) 
and the Inter-American Tropical Tuna Commission (IATTC), for review and 
are used as a basis of management actions. NMFS believes the ISC stock 
assessment (ISC 2016) represents best available science because: (1) It 
is the only scientifically based stock assessment of Pacific bluefin 
tuna; (2) it was completed by expert scientists of the ISC, including 
key contributions from the United States; (3) it was peer reviewed; and 
(4) we consider the input parameters to the assessment to represent the 
best available data, information, and assumptions.
    The SRT analyzed the status of Pacific bluefin tuna in a 3-step 
progressive process. First, the SRT evaluated 25 individual threats 
(covering the five factors in ESA section 4(a)(1)(A)-(E)). The SRT 
evaluated how each threat affects the species and contributes to a 
decline or degradation of Pacific bluefin tuna by ranking each threat 
in terms of severity (1-4, with ``1'' representing the lowest 
contribution, and ``4'' representing the highest contribution). The 
threats were evaluated in light of the Pacific bluefin tuna's 
vulnerability of and exposure to the threat, and its biological 
response.
    Following the initial rankings of specific threats, the SRT 
identified those threats where the range of rankings across the SRT was 
greater than one. For these threats, subsequent discussions ensured 
that the interpretation of the threat and its time-frame were clear and 
consistent across team members. For example, it was necessary to 
clarify that threats were considered only as they related to existing 
management measures and not historical management. After clarification, 
and a final round of discussion, each team member provided a final set 
of severity rankings for each specific threat.
    There were three specific threats (Illegal, Unregulated, and 
Unreported fishing, International Management, and sea surface 
temperature rise) for which the range of severity rankings remained 
greater than one after they had been discussed thoroughly. For these 
threats the SRT carried out a Structured Expert Decision Making process 
(SEDM) to determine the final severity rank. In this SEDM approach, 
each team member was asked to apportion 100 plausibility points across 
the four levels of severity. Points were totaled and mean scores were 
calculated. The severity level with the highest mean was determined to 
be the final ranking. As will be further detailed in the Analysis of 
Threats and Extinction Risk Analysis sections of this notice, the SRT 
also used SEDM in steps 2 and 3 of its analysis.
    The purpose of decision structuring is to provide a rational, 
thorough, and transparent decision, the basis for which is clear to 
both the decision maker(s) and to other observers, and to provide a 
means to capture uncertainty in the decision(s). Use of qualitative 
risk analysis and structured expert opinion methods allows for a 
rigorous decision-making process, the defensible use of expert opinion, 
and a well-documented record of how a decision was made. These tools 
also accommodate limitations in human understanding and allow for 
problem solving in complex situations. Risk analysis and other 
structured processes require uncertainty to be dealt with explicitly 
and biases controlled for. The information used may be empirical data, 
or it may come from subjective rankings or expert opinion expressed in 
explicit terms. Even in cases where data are sufficient to allow a 
quantitative analysis, the structuring process is important to clearly 
link outcomes and decision standards, and thereby reveal the reasoning 
behind the decision.
    This initial evaluation of individual threats and the potential 
demographic risk they pose forms the basis of understanding used during 
steps 2 and 3 of the SRT's analysis.
    In the second step of its analysis, the SRT used the same ranking 
system to evaluate the risk of each of the five factors in ESA section 
4(a)(1)(A)-(E) contributing to a decline or degradation of Pacific 
bluefin tuna. This involved a consideration of the combination of all 
threats that fall under each of the five

[[Page 37062]]

factors. In the final step, the SRT evaluated the overall extinction 
risk for Pacific bluefin tuna over two timeframes--25 years and 100 
years.
    The SRT's draft status review report was subjected to independent 
peer review as required by the Office of Management and Budget (OMB) 
Final Information Quality Bulletin for Peer Review (M- 05-03; December 
16, 2004). The draft status review report was peer reviewed by 
independent specialists selected from the academic and scientific 
community, with expertise in tuna and/or highly migratory species 
biology, conservation, and management. The peer reviewers were asked to 
evaluate the adequacy, appropriateness, and application of data used in 
the status review report, including the extinction risk analysis. All 
peer reviewer comments were addressed prior to dissemination and 
finalization of the draft status review report and publication of this 
finding.
    We subsequently reviewed the status review report, its cited 
references, and peer review comments, and believe the status review 
report, upon which this 12-month finding is based, provides the best 
available scientific and commercial information on the Pacific bluefin 
tuna. Much of the information discussed below on Pacific bluefin tuna 
biology, distribution, abundance, threats, and extinction risk is 
attributable to the status review report. However, in making the 12-
month finding determination, we have independently applied the 
statutory provisions of the ESA, including evaluation of the factors 
set forth in section 4(a)(1)(A)-(E); our regulations regarding listing 
determinations (50 CFR part 424); our Policy Regarding the Recognition 
of Distinct Vertebrate Population Segments Under the Endangered Species 
Act (DPS Policy, 61 FR 4722; February 7, 1996); and our Final Policy on 
Interpretation of the Phrase ``Significant Portion of Its Range'' in 
the Endangered Species Act's Definitions of ``Endangered Species'' and 
``Threatened Species (SPR Policy, 79 FR 37578; July 1, 2014).

Pacific Bluefin Tuna Description, Life History, and Ecology

Taxonomy and Description of Species

    Pacific bluefin tuna (Thunnus orientalis) belong to the family 
Scombridae (order Perciformes). They are one of three species of 
bluefin tuna; the other two are the southern bluefin tuna (Thunnus 
maccoyii) and the Atlantic bluefin tuna (Thunnus thynnus). The three 
species can be distinguished based on internal and external morphology 
as described by Collette (1999). The three species are also distinct 
genetically (Chow and Inoue 1993; Chow and Kishino 1995) and have 
limited overlap in their geographic ranges.
    Pacific bluefin tuna are large predators reaching nearly 3 meters 
(m) in length and 500 kilograms (kg) in weight (ISC 2016). They are 
pelagic species known to form large schools. As with all tunas and 
mackerels, Pacific bluefin tuna are fusiform in shape and possess 
numerous adaptations to facilitate efficient swimming. These include 
depressions in the body that accommodate the retraction of fins to 
reduce drag and a lunate tail that is among the most efficient tail 
shapes for generating thrust in sustained swimming (Bernal et al., 
2001).
    One of the most unique aspects of Pacific bluefin tuna biology is 
their ability to maintain a body temperature that is above ambient 
temperature (endothermy). While some other tunas and billfishes are 
also endothermic, these adaptations are highly advanced in the bluefin 
tunas (Carey et al., 1971; Graham and Dickson 2001) that can elevate 
the temperature of their viscera, locomotor muscle and cranial region. 
The elevation of their body temperature enables a more efficient energy 
usage and allows for the exploitation of a broader habitat range than 
would be available otherwise (Bernal, et al., 2001).

Range, Habitat Use, and Migration

    The Pacific bluefin tuna is a highly migratory species that is 
primarily distributed in sub-tropical and temperate latitudes of the 
North Pacific Ocean (NPO) between 20[deg] N. and 50[deg] N., but is 
occasionally found in tropical waters and in the southern hemisphere, 
in waters around New Zealand (Bayliff 1994).
    As members of a pelagic species, Pacific bluefin tuna use a range 
of habitats including open-water, coastal seas, and seamounts. Pacific 
bluefin tuna occur from the surface to depths of at least 550 m, 
although they spend most of their time in the upper 120 m of the water 
column (Kitagawa, et al., 2000; 2004; 2007; Boustany et al. 2010). As 
with many other pelagic species, Pacific bluefin tuna are often found 
along frontal zones where forage fish tend to be concentrated 
(Kitagawa, et al., 2009). Off the west coast of the United States, 
Pacific bluefin tuna are often more tightly clustered near areas of 
high productivity and more dispersed in areas of low productivity 
(Boustany, et al., 2010).
    Pacific bluefin tuna exhibit large inter-annual variations in 
movement (e.g., numbers of migrants, timing of migration and migration 
routes); however, general patterns of migration have been established 
using catch data and tagging study results (Bayliff 1994; Boustany et 
al., 2010; Block et al., 2011; Whitlock et al., 2015). Pacific bluefin 
tuna begin their lives in the western Pacific Ocean (WPO). Generally, 
age 0-1 fish migrate north along the Japanese and Korean coasts in the 
summer and south in the winter (Inagake et al., 2001; Itoh et al., 
2003; Yoon et al., 2012). Depending on ocean conditions, an unknown 
portion of young individuals (1-3 years old) from the WPO migrate 
eastward across the NPO, spending several years as juveniles in the 
eastern Pacific Ocean (EPO) before returning to the WPO (Bayliff 1994; 
Inagake et al., 2001; Perle 2011). Their migration rates have not been 
quantified and it is unknown what proportion of the population migrates 
to the EPO and what factors contribute to the high degree of 
variability across years.
    While in the EPO, the juveniles make north-south migrations along 
the west coast of North America (Kitagawa et al., 2007; Boustany et 
al., 2010; Perle, 2011). Pacific bluefin tuna tagged in the California 
Current span approximately 10[deg] of latitude between Monterey Bay 
(36[deg] N.) and northern Baja California (26[deg] N.) (Boustany et 
al., 2010; Block et al., 2011; Whitlock et al., 2015), although some 
individuals have been recorded as far north as Washington. This 
migration loosely follows the seasonal cycle of sea surface 
temperature, such that Pacific bluefin tuna move northward as 
temperatures warm in late summer to fall (Block et al., 2011). These 
movements also follow shifts in local peaks in primary productivity (as 
measured by surface chlorophyll) (Boustany et al., 2010; Block et al., 
2011). In the spring, Pacific bluefin tuna are concentrated off the 
southern coast of Baja California; in summer, Pacific bluefin tuna move 
northwest into the Southern California Bight; by fall, they are largely 
distributed between northern Baja California and northern California. 
In winter, Pacific bluefin tuna are generally more dispersed, with some 
individuals remaining near the coast, and some moving farther offshore 
(Boustany et al., 2010).
    After spending up to 5 years in the EPO, individuals return to the 
WPO where the only two spawning grounds (a southern area near the 
Philippines and Ryukyu Islands, and a northern area in the Sea of 
Japan) have been documented. No spawning activity, eggs, or larvae have 
been observed in the EPO. The timing of spawning and

[[Page 37063]]

the particular spawning ground used after their return to the WPO has 
not been established. Mature adults in the WPO generally migrate 
northwards to feeding grounds after spawning, although a small 
proportion of fish may move southward or eastward (Itoh 2006). Some of 
the mature individuals that migrate south are taken in New Zealand 
fisheries (Bayliff 1994, Smith et al., 2001), but the migration pathway 
of these individuals is unknown. It is also not known how long they may 
remain in the South Pacific.

Reproduction and Growth

    Like most pelagic fish, Pacific bluefin tuna are broadcast spawners 
and spawn more than once in their lifetime, and they spawn multiple 
times in a single spawning season (Okochi, et al., 2016). They are 
highly fecund, and the number of eggs they release during each spawning 
event is positively and linearly correlated with fish length and weight 
(Okochi et al., 2016; Ashida et al., 2015). Estimates of fecundity for 
female tuna from the southern spawning area (Philippines and Ryukyu 
Islands) indicate that individual fish can produce from 5 to 35 million 
eggs per spawning event (Ashida et al., 2015; Shimose et al., 2016; 
Chen et al., 2006). Females in the northern spawning ground (Sea of 
Japan) produce 780,000-13.89 million eggs per spawning event in fish 
116-170 cm fork length (FL) (Okochi, et al., 2016).
    Histological studies have shown that approximately 80 percent of 
the individuals found in the Sea of Japan from June to August are 
reproductively mature (Tanaka, et al., 2006, Okochi et al., 2016). This 
percentage does not necessarily represent the whole population as fish 
outside the Sea of Japan were not examined.
    Spawning in Pacific bluefin tuna occurs in only comparatively warm 
waters, so larvae are found within a relatively narrow sea surface 
temperature (SST) range (23.5-29.5 [deg]C) compared to juveniles and 
adults (Kimura et al., 2010; Tanaka & Suzuki 2016). Larvae are thought 
to be transported primarily by the northward flowing Kuroshio Current 
and are largely found off coastal Japan, both in the Pacific Ocean and 
Sea of Japan (Kimura et al., 2010).
    As discussed above, spawning in Pacific bluefin tuna has been 
recorded only in two locations: Near the Philippines and Ryukyu 
Islands, and in the Sea of Japan (Okochi et al., 2016; Shimose & Farley 
2016). These two spawning grounds differ in both timing and the size 
composition of individuals. Near the Philippines and Ryukyu Islands, 
spawning occurs from April to July and fish are from 6-25 years of age, 
though most are older than 9 years of age. In the Sea of Japan, 
spawning occurs later (June to August) and fish are 3-26 years old.
    Pacific bluefin tuna exhibit rapid growth, reaching 58 cm or more 
in length by age 1 and frequently more than 1 m in length by age 3 
(Shimose et al., 2009; Shimose and Ishihara 2015). The species tends to 
reach its maximum length of around 2.3 m at age 15 (Shimose et al., 
2009; Shimose and Ishihara 2015). The oldest Pacific bluefin tuna 
recorded was 26 years old and measured nearly 2.5 m in length (Shimose 
et al., 2009).

Feeding habits

    Pacific bluefin tuna are opportunistic feeders. Small individuals 
(age 0) feed on small squid and zooplankton (Shimose et al., 2013). 
Larger individuals (age 1+) have a diverse forage base that is 
temporally variable and, in both the EPO and WPO, they feed on a 
variety of fishes, cephalopods, and crustaceans (Pinkas et al., 1971; 
Shimose et al., 2013; Madigan et al., 2016; O. Snodgrass, NMFS SWFSC, 
unpublished data). Diet data indicate they forage in surface waters, on 
mesopelagic prey and even on benthic prey. The SWFSC conducted stomach 
content analysis of age 1-5 Pacific bluefin tuna caught off the coast 
of California from 2008 to 2016 and found that Pacific bluefin tuna are 
generalists altering their feeding habits depending on localized prey 
abundance (O. Snodgrass, NMFS SWFSC, unpublished data).

Species Finding

    Based on the best available scientific and commercial information 
summarized above, we find that the Pacific bluefin tuna is currently 
considered a taxonomically-distinct species and, therefore, meets the 
definition of ``species'' pursuant to section 3 of the ESA. Below, we 
evaluate whether the species warrants listing as endangered or 
threatened under the ESA throughout all or a significant portion of its 
range.

Distinct Population Segment Determination

    While we were not petitioned to list a distinct population segment 
(DPS) of the Pacific bluefin tuna and are therefore not required to 
identify DPSs, we decided, in this case, to evaluate whether any 
populations of the species meet the DPS Policy criteria. As described 
above, the ESA's definition of ``species'' includes ``any subspecies of 
fish or wildlife or plants, and any distinct population segment of any 
species of vertebrate fish or wildlife which interbreeds when mature.'' 
The DPS Policy requires the consideration of two elements: (1) The 
discreteness of the population segment in relation to the remainder of 
the species to which it belongs; and (2) the significance of the 
population segment to the species to which it belongs.
    A population segment of a vertebrate species may be considered 
discrete if it satisfies either one of the following conditions: (1) It 
is markedly separated from other populations of the same taxon as a 
consequence of physical, physiological, ecological, or behavioral 
factors. Quantitative measures of genetic or morphological 
discontinuity may provide evidence of this separation; or (2) it is 
delimited by international governmental boundaries within which 
differences in control of exploitation, management of habitat, 
conservation status, or regulatory mechanisms exist that are 
significant in light of section 4(a)(1)(D) of the ESA. If a population 
segment is found to be discrete under one or both of the above 
conditions, its biological and ecological significance to the taxon to 
which it belongs is evaluated. Factors that can be considered in 
evaluating significance may include, but are not limited to: (1) 
Persistence of the discrete population segment in an ecological setting 
unusual or unique for the taxon; (2) evidence that the loss of the 
discrete population segment would result in a significant gap in the 
range of a taxon; (3) evidence that the discrete population segment 
represents the only surviving natural occurrence of a taxon that may be 
more abundant elsewhere as an introduced population outside its 
historic range; or (4) evidence that the discrete population segment 
differs markedly from other populations of the species in its genetic 
characteristics.
    Pacific bluefin tuna are currently managed as a single stock with a 
trans-Pacific range. We considered a number of factors related to 
Pacific bluefin tuna movement patterns, geographic range, and life 
history that relate to the discreteness criteria. Among the many 
characteristics of Pacific bluefin tuna that were discussed as 
contributing factors to the determination of ESA discreteness, three 
were regarded as carrying the most weight in the identification of 
DPSs. The strongest argument for the existence of a DPS was the spatial 
specificity of Pacific bluefin tuna spawning. The strongest arguments 
against the existence of a DPS included Pacific bluefin tuna migratory 
behavior

[[Page 37064]]

and genetic characteristics of the Pacific bluefin tuna.
    Based on the current understanding of Pacific bluefin tuna 
movements, Pacific bluefin tuna use one of two areas in the WPO to 
spawn. There is no evidence to suggest that these represent two 
separate populations but rather that, as fish increase in size, they 
shift from using the Sea of Japan to using the spawning ground near the 
Ryukyu Islands (e.g., Shimose et al., 2016). The spawning areas are 
also characterized by physical oceanographic conditions (e.g., 
temperature), rather than a spatially fixed feature (e.g., a seamount 
or promontory). This implies that the location of the spawning grounds 
may be temporally and spatially fluid, as conditions change over time. 
Given these considerations, the existence of two spatially distinct 
spawning grounds does not provide compelling evidence that discrete 
population segments exist for Pacific bluefin tuna. In addition, 
concentrations of adult Pacific bluefin tuna on the spawning grounds 
are found only during spawning times and not year-round.
    Catch data and conventional and electronic tagging data demonstrate 
the highly migratory nature of Pacific bluefin tuna. Results support 
broad mixing around the Pacific. While fish cross the Pacific from the 
WPO to the EPO, results indicate that they then return to the WPO to 
spawn. Furthermore, the limited genetic data currently available (Tseng 
et al., 2012; Nomura et al., 2014) do not support the presence of 
genetically distinct population segments within the Pacific bluefin 
tuna.

Pacific Bluefin Tuna Stock Assessment

    The ISC stock assessment presented population dynamics of Pacific 
bluefin tuna based on catch per unit effort data from 1952-2015 using a 
fully integrated age-structured model. The model included various life-
history parameters including a length/age relationship and natural 
mortality estimates from tag-recapture and empirical life-history 
studies. Specific details on the modelling methods can be found in the 
ISC stock assessment available at https://isc.fra.go.jp/reports/stock_assessments.html.
    The 2016 ISC Pacific bluefin tuna stock assessment indicated three 
major trends: (1) Spawning stock biomass (SSB) fluctuated from 1952-
2014; (2) SSB declined from 1996 to 2010; and (3) the decline in SSB 
has ceased since 2010 yet remains near to its historical low.
    Based on the stock assessment model, the 2014 SSB was estimated to 
be around 17,000 mt, which represents 143,053 individuals capable of 
spawning. Relative to the theoretical, model-derived SSB had there been 
no fishing (i.e., the ``unfished'' SSB; 644,466 mt), 17,000 mt 
represents approximately 2.6 percent of fish in the spawning year 
classes. It is important to note that unfished SSB is a theoretical 
number derived from the stock assessment model and does not represent a 
``true'' estimate of what the SSB would have been with no fishing. This 
is because it is based on the equilibrium assumptions of the model 
(e.g., no environmental or density-dependent effects) and it changes 
with model structures. That is, in the absence of density-dependent 
effects on the population, the estimate may overestimate the population 
size that can be supported by the environment and may change with 
improved input parameters. When compared to the highest SSB of 160,004 
mt estimated by the model in 1959, the SSB in 2014 is 10.6 percent of 
the 1952-2014 historical peak.
    It is important to note that while the SSB as estimated by the ISC 
stock assessment is 2.6 percent of the theoretical, model-derived, 
``unfished'' SSB, this value is based on a theoretical unfished 
population, and only includes fish of spawning size/age. Based on the 
estimated number of individuals at each age class, the number of 
individuals capable of spawning in 2014 was 143,053. However, total 
population size, including non-spawning capable individuals that have 
not yet reached spawning age, is estimated at 1,625,837. This yields an 
8 percent ratio of spawning-capable individuals to total population. 
From 1952-2014, this ratio has ranged from 28 percent in 1960 to 2.5 
percent in 1984, with a mean of 8 percent. The ratio in 2014 indicates 
that, relative to population size, there were more spawning-capable 
fish than in some years even with a similarly low total population size 
(e.g., 1982-84), and the ratio was at the average for the period 1952-
2014.
    The 2016 ISC stock assessment was also used to project changes in 
SSB through the year 2034. The assessment evaluated 11 scenarios in 
which various management strategies were altered from the status quo 
(e.g., reduction in landings of smaller vs. larger individuals) and 
recruitment scenarios were variable (e.g., low to high recruitment). 
None of these 11 scenarios resulted in a projected reduction in SSB 
through fishing year 2034.
    The stock assessment also indicates that Pacific bluefin tuna is 
overfished and that overfishing is occurring. This assessment, however, 
is based on the abundance of the species through 2014. As described in 
the following section on existing regulatory measures, the first 
Pacific bluefin tuna regulations that placed limits on harvest were 
implemented in 2012 with additional regulations implemented in 2014 and 
2015.

Summary of Factors Affecting Pacific Bluefin Tuna

    As described above, section 4(a)(1) of the ESA and NMFS' 
implementing regulations (50 CFR 424.11(c)) state that we must 
determine whether a species is endangered or threatened because of any 
one or a combination of the following factors: The present or 
threatened destruction, modification, or curtailment of its habitat or 
range; overutilization for commercial, recreational, scientific, or 
educational purposes; disease or predation; inadequacy of existing 
regulatory mechanisms; or other natural or manmade factors affecting 
its continued existence. We evaluated whether and the extent to which 
each of the foregoing factors contribute to the overall extinction risk 
of Pacific bluefin tuna, with a ``significant'' contribution defined, 
for purposes of this evaluation, as increasing the risk to such a 
degree that the factor affects the species' demographics (i.e., 
abundance, productivity, spatial structure, diversity) either to the 
point where the species is strongly influenced by stochastic or 
depensatory processes or is on a trajectory toward this point.
    For their extinction risk analysis, the SRT members evaluated 
threats and the extinction risk over two time frames. The SRT used 25 
years (~3 generations for Pacific bluefin tuna) for the short time 
frame and 100 years (~13 generations) for the long time frame. The SRT 
concluded that the short time frame was a realistic window to evaluate 
current effects of potential threats with a good degree of reliability, 
especially when considering the limits of population forecasting models 
(e.g., projected population trends in stock assessment models). The SRT 
also concluded that 100 years was a more realistic window through which 
to evaluate the effects of a threat in the more distant future that, by 
nature, may not be able to be evaluated over shorter time periods. For 
example, the potential effects of climate change from external forces 
are best considered on multi-decadal to centennial timescales, due to 
the predominance of natural variability in determining environmental 
conditions in the shorter term.

[[Page 37065]]

    The following sections briefly summarize our findings and 
conclusions regarding threats to the Pacific bluefin tuna and their 
impact on the overall extinction risk of the species. More details can 
be found in the status review report, which is incorporated here by 
reference.

A. The Present or Threatened Destruction, Modification, or Curtailment 
of Its Habitat or Range

Water Pollution
    Given their highly migratory nature, Pacific bluefin tuna may be 
exposed to a variety of contaminants and pollutants. Pollutants vary in 
terms of their concentrations and composition depending on location, 
with higher concentrations typically occurring in coastal waters. There 
are two classes of pollutants in the sea that are most prevalent and 
that could pose potential risks to Pacific bluefin tuna: Persistent 
Organic Pollutants (POPs) and mercury. However, the SRT also considered 
Fukushima derived radiation and oil pollution as independent threats.
    Persistent organic pollutants are organic compounds that are 
resistant to environmental degradation and are most often derived from 
pesticides, solvents, pharmaceuticals, or industrial chemicals. Common 
POPs in the marine environment include the organochlorine 
Dichlorodiphenyltrichloroethane (DDT) and Polychlorinated biphenyls 
(PCBs). Because they are not readily broken down and enter the food-
web, POPs tend to bioaccumulate in marine organisms. In fishes, some 
POPs have been shown to impair reproductive function (e.g., white 
croaker; Cross et al., 1988; Hose et al., 1989).
    Specific information on POPs in Pacific bluefin tuna is limited. 
Ueno et al. (2002) examined the accumulation of POPs (e.g., PCBs, DDTs, 
and chlordanes (CHLs)) in the livers of Pacific bluefin tuna collected 
from coastal Japan. They determined, as expected, that the uptake of 
these organochlorines was driven by dietary uptake rather than through 
exposure to contaminated water (i.e., through the gills). This research 
showed that levels of organochlorines were positively and linearly 
correlated with body length. Body length normalized values for PCBs, 
DDTs, and CHLs were calculated as 530-2,600 ng/g lipid weight, 660-800 
ng/g lipid weight, and 87-300 ng/g lipid weight, respectively. More 
recently, Chiesa et al. (2016) measured pollutants from Pacific bluefin 
tuna in the Western Central Pacific Ocean and found that 100 percent of 
the individuals sampled tested positive for five of the six PCBs 
assayed. Three POPs (specifically, polybrominated diphenyl ethers) were 
detected in 5-60 percent of fish examined. Two organochlorines were 
detected in 30-80 percent of samples. Unlike the findings of Ueno et 
al. (2002) from coastal Japan, no DDT or its end-products were detected 
in Pacific bluefin tuna in the Western Central Pacific Ocean.
    While POPs have been detected in the tissues of Pacific bluefin 
tuna (see above), much higher levels have been measured in other marine 
fish (e.g., pelagic sharks; Lyons et al., 2015). While there is a lack 
of direct experimentation on the potential impacts of POPs on Pacific 
bluefin tuna, there are currently no studies which indicate that they 
exist at levels that are harmful to Pacific bluefin tuna. Based on the 
findings in the status review, we conclude that POPs pose no to low 
risk of contributing to a decline or degradation of the Pacific bluefin 
tuna.
    Mercury (Hg) enters the oceans primarily through the atmosphere-
water interface. Initial sources of Hg are both natural and 
anthropogenic. One of the main sources of anthropogenic Hg is coal-
fired power-plants. Total Hg emissions to the atmosphere have been 
estimated at 6,500-8,200 Mg/yr, of which 4,600-5,300 Mg/yr (50-75 
percent) are from natural sources (Driscoll et al., 2013). In water, 
elemental Hg is converted to methyl-Hg by bacteria. Once methylated, Hg 
is easily absorbed by plankton and thus enters the marine food-web. As 
with POPs, Hg bioaccumulates and concentrations increase in higher 
trophic level organisms.
    As a top predator, Pacific bluefin tuna can potentially accumulate 
high levels of Hg. Several studies have examined Hg in Pacific bluefin 
tuna and reported a wide range of concentrations that vary based on 
geographic location. In the WPO, measured Hg concentrations ranged from 
0.66-3.23 [mu]g/g wet mass (Hisamichi et al., 2010; Yamashita et al., 
2005), whereas in the EPO they ranged from 0.31-0.508 [mu]g/g wet mass 
(Lares et al., 2012; Coman et al., 2015). The latter study demonstrated 
that in the EPO individuals that had recently arrived from the WPO 
contained higher Hg concentrations than those that had resided in the 
EPO for 1-3 years, including wild-caught individuals being raised in 
net pens. By comparison, concentrations of Hg in Atlantic bluefin tuna 
have been measured at 0.25-3.15 mg/kg wet mass (Lee et al., 2016). 
Notably, Lee et al. (2016) demonstrated that Hg concentrations in 
Atlantic bluefin tuna declined 19 percent over an 8-year period from 
the 1990s to the early 2000s, a result of reduced anthropogenic Hg 
emissions in North America. Tunas are also known to accumulate high 
levels of selenium (Se), which is suggested to have a detoxifying 
effect on methyl-Hg compounds (reviewed in Ralston et al., 2016).
    The petitioners suggest that since some bluefin products are above 
1 ppm, the U.S. Food and Drug Administration's (FDA) threshold, there 
is cause for concern with regard to bluefin tuna health. The FDA levels 
are set at the point at which consumption is not recommended for 
children and women of child bearing age and are not linked to fish 
health. While methyl Hg compounds have been shown to cause 
neurobiological changes in a variety of animals, there have been no 
studies on tuna or tuna-like species showing detrimental effects from 
methyl Hg. As with the POPs, other marine species have much higher 
levels of Hg contamination (Montiero and Lopes 1990; Lyons et al., 
2015). The SRT was unanimous in the determination that Hg contamination 
does not pose a direct threat to Pacific bluefin tuna.
    We find that water pollution poses no risk of contributing to a 
decline or degradation of the Pacific bluefin tuna. While we 
acknowledge that bioaccumulation of pollutants in Pacific bluefin tuna 
may result in some risk to consumers, the absence of empirical studies 
showing that water pollution has direct effects on Pacific bluefin tuna 
implies that water pollution is not a high risk for Pacific bluefin 
tuna themselves.
Plastic Pollution
    Plastics have become a major source of pollution on a global scale 
and in all major marine habitats (Law 2017). In 2014, global plastic 
production was estimated to be 311 million metric tons (mt) (Plast. 
Eur. 2015). Plastics are the most abundant material collected as 
floating marine debris or from beaches (Law et al., 2010; Law 2017) and 
are known to occur on the seafloor. Impacts on the marine environment 
vary with type of plastic debris. Larger plastic debris can cause 
entanglement leading to injury or death, while ingestion of smaller 
plastic debris has the potential to cause injury to the digestive tract 
or accumulation of indigestible material in the gut. Studies have also 
shown that chemical pollutants may be adsorbed into plastic debris 
which would provide an additional pathway for exposure (e.g., Chua et 
al., 2014). Small plastics (microplastics) have been documented as the 
primary source of ingested plastic materials among fish species, 
particularly opportunistic planktivores

[[Page 37066]]

(e.g., Rochman et al., 2013; 2014; Matsson et al., 2015). Few studies 
have examined microplastic ingestion by larger predatory fishes such as 
Pacific bluefin tuna and results from these studies are mixed.
    Cannon et al. (2016) found no evidence of plastics in the digestive 
tracts of skipjack tuna (Katsuwonis pelamis) and blue mackerel (Scomber 
australensis) in Tasmania. Choy and Drazen (2013) found no evidence of 
plastic ingestion in K. pelamis and yellowfin tuna (Thunnus albacares) 
in Hawaiian waters, but found that approximately 33 percent of bigeye 
tuna (Thunnus obesus) had anthropogenic plastic debris in their 
stomachs. While no specific studies on plastic ingestion in Pacific 
bluefin tuna are available, a study of foraging ecology in the EPO 
found no plastic in over 500 stomachs examined from 2008-2016 (O. 
Snodgrass, NMFS, unpublished data).
    We find that plastic ingestion by Pacific bluefin tuna poses no to 
low risk of contributing to a decline or degradation of the Pacific 
bluefin tuna. This was based in large part upon the absence of 
empirical evidence of large amounts of macro- and micro-plastic 
directly impacting individual Pacific bluefin tuna health.
Oil and Gas Development
    There are numerous examples of oil and gas exploration and 
operations posing a threat to marine organisms and habitats. Threats 
include seismic activities during exploration and construction and 
events such as oil spills or uncontrolled natural gas escape where 
released chemicals can have severe and immediate effects on wildlife.
    Unfortunately, there is limited information on the direct impacts 
of oil and gas exploration and operation on pelagic fishes such as 
Pacific bluefin tuna. Studies looking at the impacts of seismic 
exploration on fish have mixed results. Wardle et al. (2001) and Popper 
et al. (2005) documented low to moderate impacts on behavior or 
hearing, whereas McCauley et al. (2003) reported long-term hearing loss 
from air-gun exposure. Risk associated with seismic exploration would 
likely be less of a concern for highly migratory species that can move 
away and do not use sounds to communicate. Reduced catch rates in areas 
for a period of time after air guns have been used are considered 
evidence for this avoidance behavior in a range of species (Popper and 
Hastings 2009).
    The effects of seismic exploration on larval Pacific bluefin tuna, 
however, could be greater than on older individuals due in part to the 
reduced capacity of larvae to move away from affected areas. Davies et 
al. (1989) stated that fish eggs and larvae can be killed at sound 
levels of 226-234 decibel (dB), which are typically found at 0.6-3.0 m 
from an air gun such as those used during seismic exploration. Visual 
damage to larvae can occur at 216 dB, levels found approximately 5 m 
from the air gun. Less obvious impacts such as disruptions to 
developing organs are harder to gauge and are little explored in the 
scientific literature; however, severe physical damage or mortality 
appears to be limited to larvae within a few meters of an air gun 
discharge (Dalen et al., 1987; Patin & Cascio 1999).
    The most relevant study, for the purposes of the SRT, is an 
evaluation of the impacts of oil pollution on the larval stage of 
Atlantic bluefin tuna. Oil released from the 2010 Deepwater Horizon oil 
spill in the Gulf of Mexico covered approximately 10 percent of the 
spawning habitat, prompting concerns about larval survival (Muhling et 
al., 2012). Modeled western Atlantic bluefin tuna recruitment for 2010 
was low compared to historical values, but it is not yet clear whether 
this was primarily due to oil-induced mortality, or unfavorable 
oceanographic conditions (Domingues et al., 2016). Results from 
laboratory studies showed that exposure to oil resulted in significant 
defects in heart development in larval Atlantic bluefin tuna (Incardona 
et al., 2014) with a likely reduction in fitness. A similar response 
would be expected in Pacific bluefin tuna. Consequently, an oil spill 
in or around the spawning grounds has the potential to impact larval 
survival of Pacific bluefin tuna. Previous spills near the spawning 
grounds have mostly been from ships (e.g., Varlamov et al., 1999; Chiau 
2005), and have resulted in much smaller, more coastally confined 
releases into the marine environment than from the Deepwater Horizon 
incident. However, offshore oil exploration has increased in the region 
in recent years, potentially increasing the risks of a large-scale 
spill. Despite these considerations, the overall risks to Pacific 
bluefin tuna associated with an oil spill were considered to be low for 
a number of reasons: (1) Large oil spills are rare events; (2) Pacific 
bluefin tuna larvae are spread over two spawning grounds with little 
oceanographic connectivity between them, reducing risk to the 
population as a whole; and (3) the population is broadly dispersed 
overall.
    Oil and gas infrastructure may have beneficial impacts on the 
marine environment by providing habitat for a range of species and de 
facto no fishing zones. California has been a prime area of research 
into the effects of decommissioned oil platforms. Claisse et al. (2014) 
showed that offshore oil platforms have the highest measured fish 
production of any habitat in the world, exceeding even coral reefs and 
estuaries. Caselle et al. (2002) showed that even remnant oil field 
debris (e.g., defunct pipe lines, piers, and associated structures) 
harbored diverse fish communities. This pattern is not unique to 
California. For example, Fabi et al. (2004) showed that fish diversity 
and richness increased within the first year after installation of two 
gas platforms in the Adriatic Sea, and that biomass of fishes on these 
platforms was substantial. Consequently, oil platforms may provide 
forage and refuge for Pacific bluefin tuna.
    In summary, we consider oil and gas development to pose no to low 
risk of contributing to a decline or degradation of the Pacific bluefin 
tuna.
Wind Energy Development
    Concerns about climate impacts linked to the use of petroleum 
products has led to an increase in renewable energy programs over the 
past two decades. Offshore and coastal wind energy generating stations 
have been among the fastest growing renewable energy sectors, 
particularly in shallow coastal areas, which generally have consistent 
wind patterns and reduced infrastructure costs due to shallow depths 
and proximity to land.
    Impacts of wind energy generating stations on marine fauna have 
been well studied (see K[ouml]ppel, 2017 for examples). There have been 
some studies predicting negative effects on marine life, particularly 
birds and benthic organisms, but few empirical studies have 
demonstrated direct impacts to fishes. Wilson et al. (2010) reviewed 
numerous papers discussing the impacts of wind energy infrastructure 
and concluded that while they are not environmentally benign, the 
impacts are minor and can often be ameliorated by proper placement.
    Studies on wind energy development and its impact on fishes has 
largely focused on demersal species assemblages. Similar to oil and gas 
platforms, wind energy platforms have been shown to have a positive 
effect on demersal fish communities in that they tend to harbor high 
diversity and biomass of fish populations (e.g., Wilhelmsson et al., 
2006). Following construction of ``wind farms,'' one particular concern 
has been the effects of noise created by the operating mechanisms on 
fish. Wahlberg and Westerberg (2005) concluded that wind

[[Page 37067]]

farm noise does not have any destructive effects on the hearing ability 
of fish, even within a few meters. The major impact of the noise is 
largely restricted to masking communication between fish species which 
use sounds (Wahlberg and Westerberg, 2005). Given that Pacific bluefin 
tuna are not known to use sounds for communication, the impact of noise 
would be minimal if any. Additionally, wind farms are likely to serve 
as de facto fish aggregating devices and may prove beneficial at 
attracting prey and thus Pacific bluefin tuna as well. Also, given the 
highly migratory nature of Pacific bluefin tuna and their broad range, 
wind farms would not take up a large portion of their range and could 
be avoided.
    We find that wind energy development poses no to low risk of 
contributing to a decline or degradation of the Pacific bluefin tuna. 
This was based largely on the ability of Pacific bluefin tuna to avoid 
wind farms and the absence of empirical evidence showing harm directly 
to Pacific bluefin tuna.
Large-Scale Aquaculture
    Operation of coastal aquaculture facilities can degrade local water 
quality, mostly through uneaten fish feed and feces, leading to 
nutrient pollution. The severity of these issues depends on the species 
being farmed, food composition and uptake efficiency, fish density in 
net pens, and the location and design of pens (Naylor et al., 2005). 
There are several offshore culture facilities throughout the world, 
most being within 25 kilometers (km) of shore.
    The petition by CBD highlights a proposed offshore aquaculture 
facility in California as a potential threat to Pacific bluefin tuna. 
The proposed Rose Canyon aquaculture project would construct a facility 
to raise yellowtail jack approximately 7 km from the San Diego coast. 
The high capacity of the proposed project (reaching up to 5,000 mt 
annually after 8 years of operation) has raised concerns about 
resulting impacts to the surrounding marine environment. As the 
proposed aquaculture facility would act as a point source of 
pollutants, the potential impacts to widely distributed pelagic species 
such as Pacific bluefin tuna will depend on oceanographic dispersal of 
these pollutants within the Southern California Bight (SCB) and 
surrounding regions.
    Data from current meters and Acoustic Doppler Current Profilers 
(ADCPs) near Point Loma have recorded seasonally reversing, and highly 
variable, alongshore flows (Hendricks 1977; Carson et al., 2010). 
However, cross-shelf currents were much weaker. Similarly, Lahet and 
Stramski (2010) showed that river plumes in the San Diego area 
identified by satellite ocean color imagery moved variably north or 
south along the coast until dispersing, but were not advected offshore. 
Recent studies using high-resolution simulations of a regional oceanic 
modeling system have also shown limited connectivity between the 
nearshore region off San Diego and the open SCB (Dong et al., 2009; 
Mitari et al., 2009). This suggests that pollutants resulting from the 
proposed Rose Canyon aquaculture facility would likely be dispersed 
along the southern California and northern Baja California coasts 
rather than offshore. Pacific bluefin tuna are distributed throughout 
much of the California Current ecosystem, and are often caught more 
than 100 km from shore (Holbeck et al., 2017). Tagging studies have 
also shown very broad habitat use of Pacific bluefin tuna offshore of 
Baja California and California (Boustany et al., 2010). It should be 
noted that any aquaculture facilities in the United States are 
subjected to rigorous environmental reviews and standards prior to 
being permitted.
    We find that habitat degradation from large-scale aquaculture poses 
no to low risk of contributing to population decline or degradation in 
Pacific bluefin tuna over both time-scales largely due to the very 
small proportion of their habitat which would be impacted as well as 
the absence of empirical evidence showing harm directly to Pacific 
bluefin tuna.
Prey Depletion
    As highly migratory, fast-swimming top predators, tunas have 
relatively high energy requirements (Olson and Boggs 1986; Korsmeyer 
and Dewar 2001; Whitlock et al., 2013; Golet et al., 2015). They 
fulfill these needs by feeding on a wide range of vertebrate and 
invertebrate prey, the relative contribution of which varies by 
species, region, and time period. Pacific bluefin tuna in the 
California Current ecosystem have been shown to prey on forage fish 
such as anchovy, as well as squid and crustaceans (Pinkas et al., 1971; 
Snodgrass et al., unpublished data). As commercial fisheries also 
target some of these species, substantial removals could conceivably 
reduce the prey base for predators such as Pacific bluefin tuna. 
Previous studies have used trophic ecosystem models to show that high 
rates of fishing on forage species could adversely impact other 
portions of the ecosystem, including higher-order predators (Smith et 
al., 2011; Pikitch et al., 2012).
    Biomass of the two main forage fish in the California Current, 
sardine and anchovy, has been low in recent years (Lindegren et al., 
2013; Lluch-Cota 2013). This likely represents part of the natural 
cycle of these species, which appear to undergo frequent ``boom and 
bust'' cycles, even in the absence of industrial-scale fishing 
(Schwartzlose et al., 1999; McClatchie et al., 2017). Pacific bluefin 
tuna appear to be generalists and consequently are less impacted by 
these shifts in abundance than specialists. Pinkas et al. (1971) found 
that Pacific bluefin tuna diets in the late 1960s were mostly anchovy 
(>80 percent), coinciding with a period of relatively high anchovy 
biomass. In contrast, more recent data from the 2000s show a much 
higher dominance of squid and crustaceans in Pacific bluefin tuna 
diets, with high interannual variability (Snodgrass et al., unpublished 
data). Neither study recorded a substantial contribution of sardine to 
Pacific bluefin tuna diets, but both diet studies (Pinkas et al., 
Snodgrass et al., unpublished data) were conducted during years in 
which sardine biomass was comparatively low.
    This ability to switch between prey species may be one reason why 
Hilborn et al. (2017) found little evidence that forage fish population 
fluctuations drive biomass of higher order consumers, including tunas. 
This disconnect is clear for Pacific bluefin tuna. For example, in the 
1980s, Pacific bluefin tuna biomass and recruitment were both very low, 
but forage fish abundances in both the California Current and Kuroshio-
Oyashio ecosystems were high (Lindegren et al., 2013; Yatsu et al., 
2014). Hilborn et al. (2017) considered that a major weakness of 
previous trophic studies was a lack of consideration of this strongly 
fluctuating nature of forage fish populations through time. Predators 
have thus likely adapted to high variability in abundance of forage 
fish and other prey species by being generalists.
    However, although Pacific bluefin tuna have a broad and varied prey 
base in the California Current, the physiological effects of switching 
between dominant prey types are not well known. Some species are more 
energy-rich than others, and may have lower metabolic costs to catch 
and digest (Olson & Boggs 1986; Whitlock et al., 2013). Fluctuations in 
the energy content and size spectra of a prey species may also be 
important, as was found for the closely-related Atlantic bluefin tuna 
(Golet et al., 2015). It is

[[Page 37068]]

therefore not yet clear how periods of strong reliance on anchovy vs. 
invertebrates, for example, may impact the condition and fitness of 
Pacific bluefin tuna.
    We find that prey depletion poses a very low threat to Pacific 
bluefin tuna over the 25-year time frame, primarily because it is clear 
that they are generally adapted to natural fluctuations of forage fish 
biomass through prey switching. We also find that prey depletion may 
pose a low to moderate threat over the 100-year timeframe, albeit with 
low certainty. This was mainly because climate change is expected to 
alter ecosystem structure and function to produce potentially novel 
conditions, over an evolutionarily short time period. If this results 
in a less favorable prey base for Pacific bluefin tuna, in either the 
California Current or other foraging areas, impacts on the population 
may be more deleterious than they have been in the past.

B. Overutilization for Commercial, Recreational, Scientific or 
Educational Purposes

    Potential threats to the Pacific bluefin tuna from overutilization 
for commercial, recreational, scientific or educational purposes also 
includes illegal, unregulated and unreported fishing. Each of these 
potential threats is discussed in the following sections.
Commercial Fishing
    Commercial fishing for Pacific bluefin tuna has occurred in the 
western Pacific since at least the late 1800s. Records from Japan 
indicate that several methods were used prior to 1952 when catch 
records began to be taken in earnest and included longline, pole and 
line, drift net, and set net fisheries. Estimates of global landings 
prior to 1952 peaked around 47,635 mt (36,217 mt in the WPO and 11,418 
mt in the EPO) in 1935 (Muto et al., 2008). After 1935, landings 
dropped in response to a shift in maritime activities caused by World 
War II. Fishing activities expanded across the North Pacific Ocean 
after the conclusion of the war, and landings increased consistently 
for the next decade prior to becoming more variable (Muto et al., 
2008).
    There are currently five major contributors to the Pacific bluefin 
tuna fisheries: Japan, Korea, Mexico, Taiwan, and the United States. 
Each operates in nearshore coastal waters in the Pacific Ocean while a 
few also operate in distant offshore waters. In modern fisheries, 
Pacific bluefin tuna are taken by a wide range of fishing gears (e.g., 
longline, purse seine, set net, troll, pole-and-line, drift nets, and 
hand line fisheries), which target different size classes (see below). 
Among these fisheries, purse seine fisheries are currently the primary 
contributor to landings, with the Japanese fleet being responsible for 
the majority of the catch. Much of the global purse-seine catch 
supports commercial grow-out facilities where fish aged approximately 
1-3 are kept in floating pens for fattening prior to sale.
    Estimates of landings indicate that annual catches of Pacific 
bluefin tuna by country have fluctuated dramatically from 1952-2015. 
During this period reported catches from the five major contributors to 
the ISC peaked at 40,144 mt in 1956 and reached a low of 8,627 mt in 
1990, with an average of 21,955 mt. Japanese fisheries are responsible 
for the majority of landings, followed by Mexico, the United States, 
Korea and Taiwan. In 2014, the United States reported commercial 
landings of 408 mt, Taiwan reported 525 mt, Korea reported 1,311 mt, 
Mexico reported 4,862 mt, and Japan reported 9,573 mt. These represent 
2.4 percent, 3 percent, 7.7 percent, 28.4 percent, and 56 percent of 
the total landings, respectively. Landings in the southern hemisphere 
are small and concentrated around New Zealand.
    The commercial Japanese Pacific bluefin tuna fisheries are 
comprised of both distant-water and coastal longline vessels, coastal 
trolling vessels, coastal pole-and-line vessels, coastal set net 
vessels, coastal hand line vessels, and purse seiners. Each fishery 
targets specific age classes of Pacific bluefin tuna: Coastal trolling 
and pole and line target fish less than 1 year old, coastal set net and 
coastal hand-line target ages 1-5, purse seiners target ages 0-10, and 
the distant-water and coastal longline vessels target ages 5-20. The 
distant water longline fisheries have operated for the longest time 
while the coastal longline fisheries did not begin in earnest until the 
mid-1960s. Between 1952 and 2015, total annual catches by Japanese 
fisheries have fluctuated between a maximum of approximately 34,000 mt 
in 1956 and a minimum of approximately 6,000 mt in 2012, and they have 
averaged 15,653 mt.
    The Japanese troll fleet harvests small, age-0 Pacific bluefin tuna 
for its commercial aquaculture grow-out facilities. From 2005-2015, the 
harvest of Pacific bluefin tuna for grow-out by the troll fishery has 
averaged 14 percent of Japan's total landings (approximately 8.5 
percent of global landings) by weight.
    Nearly all commercial Pacific bluefin tuna catches by U.S. flagged 
vessels on the west coast of the United States are landed in 
California. Historically, the commercial fisheries for Pacific bluefin 
tuna focused their efforts on the fishing grounds off Baja California, 
Mexico, until the 1980s. Following the creation of Mexico's EEZ, the 
U.S. purse seine fisheries largely ceased their efforts in Mexico and 
became more opportunistic (Aires-da-Silva et al., 2007). Since 1980, 
commercial landings of Pacific bluefin tuna have fluctuated 
dramatically, averaging 859.2 mt with two peaks in 1986 (4,731.4 mt) 
and 1996 (4,687.6 mt). The low catch rates are not caused by the 
absence of Pacific bluefin tuna, but rather the absence of a dedicated 
fishery, low market price, and the inability to fish in the Mexican 
EEZ. In 2014, commercial landings of Pacific bluefin tuna in the United 
States were 408 mt, representing 2.4 percent of the total global 
landings.
    Mexico's harvest of Pacific bluefin tuna is dominated by its purse 
seine fisheries, which dramatically increased in size following the 
creation of Mexico's EEZ. While most of the purse seine fisheries 
target yellowfin tuna (the dominant species in the catch) in tropical 
waters, Pacific bluefin tuna are caught by purse seine near Baja 
California. Since 1952, reported landings in Mexico have ranged from 1-
9,927 mt with an average of 1,766.7 mt (ISC catch database https://isc.fra.go.jp/fisheries_statistics/). Since grow-out 
facilities began in Mexico in 1997, the purse seine fishery for Pacific 
bluefin tuna almost exclusively supports these facilities. These 
facilities take in age 1-3 Pacific bluefin tuna and ``fatten'' them in 
floating pens for export and represent virtually all of Mexico's 
reported capture of Pacific bluefin tuna. From 2005-2015, Mexico's 
harvest for its grow-out facilities has averaged 26.8 percent of the 
global landings.
    The Korean take of Pacific bluefin tuna is dominated by its 
offshore purse seine fishery with a small contribution by the coastal 
troll fisheries. The fisheries generally operate off Jeju Island with 
occasional forays into the Yellow Sea (Yoon et al., 2014). The purse 
seine fisheries did not fully develop until the mid-1990s, and landings 
were below 500 mt prior to this. Landings gradually increased and 
peaked at 2,601 mt in 2003, but have declined since then, with 676 mt 
landed in 2015. Since 1952, the average reported Korean landings of 
Pacific bluefin tuna has been 535 mt (data not reported from 1952-
1971).
    Historically, the Taiwanese fisheries have used a wide array of 
gears, but since the early 1990s the fisheries are largely comprised of 
small-scale longline vessels. These vessels are targeting fish on the 
spawning grounds

[[Page 37069]]

near the Ryukyu Islands. The highest reported catch was in 1990 at 
3,000 mt; however, landings declined to less than 1,000 mt in 2008 and 
to their lowest level of about 200 mt in 2012. Landings have since 
increased and the preliminary estimate of Pacific bluefin tuna landings 
in 2015 was 542 mt. Since 1952, Taiwanese landings of Pacific bluefin 
tuna have averaged 658 mt.
    We acknowledge the Petitioner's concern that a large proportion of 
Pacific bluefin tuna caught are between 0 and 2 years of age. The 
petition states that 97.6 percent of fish are caught before they have a 
chance to reproduce, and argues that this is a worrisome example of 
growth overfishing. The interpretation of the severity of this 
statement requires acknowledging several factors that are used to 
evaluate the production (amount of ``new'' fish capable of being 
produced by the current stock). Importantly, the estimate of production 
includes considering factors such as recruitment, growth of individuals 
(thus moving from one age class to the next and potentially reaching 
sexual maturity), catch, and natural mortality. Excluding all other 
parameters except catch results in erroneous interpretations of the 
severity of a high proportion of immature fish being landed on an 
annual basis. If all year classes are taken into account, the 
percentage of fish in the entire population (not just in the age 0 age 
class) that are harvested before reaching maturity is closer to 82 
percent. While we acknowledge that this is not an ideal harvest target, 
it is a more accurate representation of the catch of immature fish.
    Growth overfishing occurs when the average size of harvested 
individuals is smaller than the size that would produce the maximum 
yield per recruit. The effect of growth overfishing is that total yield 
(i.e., population size) is less than it would be if all fish were 
allowed to grow to a larger size. Reductions in yield per recruit due 
to growth overfishing can be ameliorated by reducing fishing mortality 
(i.e., reduced landings) and/or increasing the average size of 
harvested fish, both of which have been recommended by the relevant 
Regional Fisheries Management Organizations (RFMOs) and adopted for the 
purse seine fisheries in the western and central Pacific Ocean.
    We consider commercial fishing to pose the greatest risk to 
contribute to the decline or degradation of the Pacific bluefin tuna. 
Threat scores given by the BRT members for commercial fishing ranged 
from moderate to high (severity score of 2 to 3 with a mean of 2.29). 
While we acknowledge that past trends in commercial landings have been 
the largest contributor to the decline in the Pacific bluefin tuna, we 
find the population size in the terminal year of the ISC stock 
assessment (2014; >1,625,000 individuals and >143,000 spawning-capable 
individuals) as sufficient to prevent extinction in the foreseeable 
future. This is due to the fact that the population size is large 
enough to prevent small population effects (e.g., Allee effects) from 
having negative consequences. We also note that none of the scenarios 
evaluated in the ISC stock projections showed declining trends. This 
likely indicates that the proposed reductions in landings in the ISC 
stock assessment that were adopted by the relevant RFMOs and have been 
implemented by participating countries are likely to prevent future 
declines. Therefore, we consider commercial fishing to pose a moderate 
to high risk to contribute to the degradation of Pacific bluefin tuna.
Recreational Fishing
    Recreational fishing for Pacific bluefin tuna occurs to some extent 
in most areas where Pacific bluefin tuna occur relatively close to 
shore. The majority of recreational effort appears to be in the United 
States, although this may be an artifact of a lack of record keeping 
outside of the United States. From the mid-1980s onward, the majority 
of U.S. Pacific bluefin tuna landings have been from recreational 
fisheries. Along the west coast of the United States, the recreational 
fishing fleet for highly migratory species such as Pacific bluefin tuna 
is comprised of commercial passenger fishing vessels (CPFVs) and 
privately owned vessels operating from ports in southern California.
    The vast majority of recreational fishing vessels operate from 
ports in southern California from Los Angeles south to the U.S./Mexico 
border, with a large proportion operating out of San Diego. Much of the 
catch actually occurs in Mexican waters. The recreational catch for 
Pacific bluefin tuna is dominated by hook and line fishing with a very 
small contribution from spear fishing. The landings for Pacific bluefin 
tuna are highly variable. This variability is linked to changes in the 
number of young fish that move from the western Pacific (Bayliff 1994), 
and potentially regional oceanographic variability, and is not taken to 
reflect changes in overall Pacific-wide abundance.
    In addition to variability in immigration to the EPO, regulatory 
measures impact the number of fish caught. As mentioned, most U.S. 
fishing effort occurs in Mexican waters. In July 2014, Mexico banned 
the capture of Pacific bluefin tuna in its EEZ for the remainder of the 
year, reducing the catch by the U.S. recreational fleet. In 2015, while 
this ban was lifted, the United States instituted a two fish per angler 
per day bag limit and a 6 fish per multi-day fishing trip bag limit on 
Pacific bluefin tuna, lowered from 10 fish per angler per day and 30 
fish total for multi-day trips (80 FR 44887; July 28, 2015). It is 
difficult to quantify the effects of the reduced bag limit at the 
current time as there are only two years of landings data following the 
reduction (2015-16). This is further complicated by an absence of an 
index of availability of Pacific bluefin tuna to the recreational 
fishery. Anecdotal evidence in the form of informal crew and fisher 
interviews suggests that Pacific bluefin tuna have been in high 
abundance since 2012. CPFV landings in 2014-16 declined following an 
exceptionally productive year in 2013. Whether this was an effect of 
the reduced bag limit or an artifact of Pacific bluefin tuna 
availability is uncertain. While the petition raises the concern that 
the two fish per day per angler bag limit is insufficient as the 
fishery is ``open access'' (an angler may fish as many days as they 
wish), it is important to note that the number of anglers participating 
in CPFV trips has not increased dramatically since the late 1990s. It 
should also be noted that the average number of Pacific bluefin tuna 
caught per angler on an annual basis has never exceeded 1.4 (2013), 
thus the two fish per day per angler bag limit will effectively prevent 
a major expansion of the Pacific bluefin tuna recreational landings.
    Since 1980, the peak of the U.S. recreational fishery was in 2013 
when 63,702 individual fish were reported in CPFV log books, with an 
estimated weight of 809 tons. This was more than the total U.S. 
commercial catch in 2013 (10.1 mt), keeping in mind that commercial 
vessels cannot go into Mexican waters. The average recreational catch 
is far lower (264 mt average from 2006-2015). The peak recreational 
CPFV landings in the United States in 2013 represented 7 percent of the 
total global catch of Pacific bluefin tuna in that same year, whereas 
in 2015 it represented 3.2 percent of total global catch.
    Private vessel landings are more difficult to quantify as they rely 
on voluntary interviews with fishers at only a few of the many landing 
ports. In 2015, the estimated landings by private vessels was 6,195 
individual Pacific bluefin tuna, which represented approximately 30 
percent of all U.S.

[[Page 37070]]

recreational landings. Note, that these values are not included in the 
estimates above and represent additional landings.
    At 3.2 percent of the total global landings, we consider the U.S. 
recreational fishery to be a minor overall contributor to the global 
catch of Pacific bluefin tuna, and recent measures have been 
implemented to reduce landings. Given that recreational landings have 
been reduced through increased management, we consider recreational 
fishing as posing no or a low risk of contributing to population 
decline or degradation in Pacific bluefin tuna.
Illegal, Unreported, or Unregulated Fishing
    Illegal, Unreported or Unregulated (IUU) fishing, as defined in 50 
CFR 300.201, means:
    (1) In the case of parties to an international fishery management 
agreement to which the United States is a party, fishing activities 
that violate conservation and management measures required under an 
international fishery management agreement to which the United States 
is a party, including but not limited to catch limits or quotas, 
capacity restrictions, bycatch reduction requirements, shark 
conservation measures, and data reporting;
    (2) In the case of non-parties to an international fishery 
management agreement to which the United States is a party, fishing 
activities that would undermine the conservation of the resources 
managed under that agreement;
    (3) Overfishing of fish stocks shared by the United States, for 
which there are no applicable international conservation or management 
measures, or in areas with no applicable international fishery 
management organization or agreement, that has adverse impacts on such 
stocks;
    (4) Fishing activity that has a significant adverse impact on 
seamounts, hydrothermal vents, cold water corals and other vulnerable 
marine ecosystems located beyond any national jurisdiction, for which 
there are no applicable conservation or management measures or in areas 
with no applicable international fishery management organization or 
agreement; or
    (5) Fishing activities by foreign flagged vessels in U.S. waters 
without authorization of the United States.
    While there is likely some level of IUU fishing for Pacific bluefin 
tuna in the Pacific, no reports of substantial IUU fishing have 
emerged, thus the amount cannot be determined. However, improvements to 
catch document schemes in several countries have been proposed/
implemented in an effort to combat IUU harvest, and the most recent 
advice from the relevant RFMOs requires improvements to reporting. The 
SRT members had a range of opinions on the effects of IUU fishing on 
population decline or degradation for Pacific bluefin tuna, ranging 
from no impact to moderate impact. The SRT therefore performed a SEDM 
analysis to arrive at the conclusion that the magnitude of potential 
IUU fishing losses for Pacific bluefin tuna were likely low relative to 
existing commercial catches and thus not likely to increase 
substantially in the future; however, the certainty around this 
determination is low.
    Given the absence of estimates of IUU fishing losses for Pacific 
bluefin tuna, we have a low level of certainty for this threat. 
However, with the continued improvements in catch documentation and the 
assumption of low IUU take relative to the commercial harvest, we 
determined that IUU fishing represented a low to moderate risk of 
contributing to population decline or degradation in Pacific bluefin 
tuna.
Scientific and Educational Use
    Pacific bluefin tuna are used in scientific research for a range of 
studies such as migration patterns, stable isotope analysis, and 
feeding preference. The amount of lethal use of Pacific bluefin tuna in 
scientific and educational pursuits is negligible, as most tissues used 
in research (e.g. otoliths, muscle samples) are sourced from fish 
already landed by fishers. We therefore find no evidence that 
scientific or educational use poses a risk to contribute to the decline 
or degradation of Pacific bluefin tuna.

C. Disease and Predation

Disease
    Studies of disease in Pacific bluefin tuna are largely absent from 
the literature. Most studies involve the identification of parasites 
normally associated with cage culture. Parasites are often associated 
with mortalities and reduced production among farmed marine fishes 
(Hayward et al., 2007). Epizootic levels of parasites with short, 
direct, one-host life cycles, such as monogeneans, can be reached very 
quickly in cultured fish because of the confinement and proximity of 
these fish (Thoney and Hargis 1991). Among wild marine fishes, 
parasites are usually considered benign, though they can be associated 
with reduced fecundity of their hosts (Jones 2005; Hayward et al., 
2007).
    Munday et al. (2003) provided a summary of metazoan infections 
(myxosporeans, Kudoa sp., monogeneans, blood flukes, larval cestodes, 
nematodes, copepods) in tuna species. Many metazoans infect Thunnus 
spp., but not many are known to cause mortalities; most studies to date 
have focused on the health and/or economic importance of these 
diseases. For example, postmortem liquefaction of muscle due to 
myxosporean infections occurs in albacore, yellowfin tuna, and bigeye 
tuna (Thunnus obesus), and in poorly identified Thunnus spp. Lesions 
caused by Kudoa sp. have been found in yellowfin tuna and southern 
bluefin tuna (Langdon 1990; Kent et al., 2001). Munday et al. (2003) 
report that southern bluefin tuna have been found to be infected with 
an unidentified, capsalid monogenean that causes respiratory stress but 
does not lead to mortality.
    Young Pacific bluefin tuna are often infected with red sea bream 
iridoviral, but the disease never appears in Pacific bluefin tuna more 
than 1 year of age, and occurrence is restricted to periods of water 
temperatures greater than 24 [deg]C (Munday et al., 2003). Mortality 
rates rarely reach greater than 10 percent for young fish. The fish 
either die during the acute phase of the disease, or they become 
emaciated and die later.
    There is no evidence of transmission of parasites or other 
pathogens from captive Pacific bluefin tuna in tuna ranches. This is 
likely due to the fact that wild Pacific bluefin tuna are not likely to 
be in close enough proximity to pens used to house Pacific bluefin 
tuna.
    We find that disease poses no to low risk of contributing to 
population decline or degradation in Pacific bluefin tuna. This was 
based largely on the absence of empirical evidence of abnormal levels 
of natural disease outbreaks in Pacific bluefin tuna, the absence of 
observations of wild Pacific bluefin tuna swimming in close enough 
proximity to ``farms'' such that disease transmission is possible, and 
the absence of empirical evidence showing disease transmission from 
``farms'' to wild Pacific bluefin tuna.
Predation
    As large predators, Pacific bluefin tuna are not heavily preyed 
upon naturally after their first few years. Predators of adult Pacific 
bluefin tuna may include marine mammals such as killer whales (Orcinus 
orca) or shark species such as white (Carcharodon carcharias) and mako 
sharks (Isurus spp.) (Nortarbartolo di Sciara 1987; Collette and Klein-
MacPhee 2002; de

[[Page 37071]]

Stephanis 2004; Fromentin and Powers 2005). Juvenile Pacific bluefin 
tuna may be preyed upon by larger opportunistic predators and, to a 
lesser degree, seabirds.
    We find that natural predation poses no to low risk of contributing 
to population decline or degradation in Pacific bluefin tuna. This was 
based primarily on the limited diversity of predators and absence of 
empirical evidence showing abnormal decline/degradation of Pacific 
bluefin tuna by predation.

D. The Inadequacy of Existing Regulatory Mechanisms

    The current management and regulatory schemes for Pacific bluefin 
tuna are intrinsically linked to the patterns of utilization discussed 
in the previous section ``Overutilization for Commercial, Recreational, 
Scientific or Educational Purposes.'' The evaluation in this section 
focuses on the adequacy or inadequacy of the current management and 
regulatory schemes to address the threats identified in the section on 
``Overutilization for Commercial, Recreational, Scientific or 
Educational Purposes.''
    Pacific bluefin tuna fisheries are managed under the authorities of 
the Magnuson-Stevens Fishery Conservation and Management Act (MSA), the 
Tuna Conventions Act of 1950 (TCA), and the Western and Central Pacific 
Fisheries Convention Implementation Act (WCPFCIA). The TCA and WCPFCIA 
authorize the Secretary of Commerce to implement the conservation and 
management measures of the Inter-American Tropical Tuna Commission 
(IATTC) and Western and Central Pacific Fisheries Commission (WCPFC), 
respectively.
International Fisheries Management
    Pacific bluefin tuna is managed as a single Pacific-wide stock 
under two RFMOs: The IATTC and the WCPFC. Both RFMOs are responsible 
for establishing conservation and management measures based on the 
scientific information, such as stock status, obtained from the ISC.
    The IATTC has scientific staff that, in addition to conducting 
scientific studies and stock assessments, also provides science-based 
management advice. After reviewing the Pacific bluefin tuna stock 
assessment prepared by the ISC, the IATTC develops resolutions. Mexico 
and the United States are the two IATTC member countries that currently 
fish for, and have historically fished for, Pacific bluefin tuna in the 
EPO. Thus, the IATTC resolutions adopted were intended to apply to 
these two countries.
    The WCPFC has a Northern Committee (WCPFC-NC), which consists of a 
subset of the WCPFC members and cooperating non-members, that meets 
annually in advance of the WCPFC meeting to discuss management of 
designated ``northern stocks'' (currently North Pacific albacore, 
Pacific bluefin tuna, and North Pacific swordfish). After reviewing the 
stock assessments prepared by the ISC, the WCPFC-NC develops the 
conservation and management measures for northern stocks and makes 
recommendations to the full Commission for the adoption of measures. 
Because Pacific bluefin tuna is a ``northern stock'' in the WCPFC 
Convention Area, without the recommendation of the Northern Committee, 
those measures would not be adopted by the WCPFC. The WCPFC's 
Scientific Committee also has a role in providing advice to the WCPFC 
with respect to Pacific bluefin tuna; to date its role has been largely 
limited to reviewing and endorsing the stock assessments prepared by 
the ISC.
    The IATTC and WCPFC first adopted conservation and management 
measures for Pacific bluefin tuna in 2009, and the measures have been 
revised five times. The conservation and management measures include 
harvest limits, size limits, and stock status monitoring plans. In 
recent years, coordination among both RFMOs has improved in an effort 
to harmonize conservation and management measures to rebuild the 
depleted stock. The most relevant resolutions as they relate to recent 
Pacific bluefin tuna management are detailed below.
    In 2012, the IATTC adopted Resolution C-12-09, which set commercial 
catch limits on Pacific bluefin tuna in the EPO for the first time. 
This resolution limited catch by all IATTC members to 5,600 mt in 2012 
and to 10,000 mt in 2012 and 2013 combined, notwithstanding an 
allowance of up to 500 mt annually for any member with a historical 
catch record of Pacific bluefin tuna in the eastern Pacific Ocean 
(i.e., the United States and Mexico). Resolution C-13-02 applied to 
2014 only and, similar to C-12-09, limited catch to 5,000 mt with an 
allowance of up to 500 mt annually for the United States. Following the 
advice from the IATTC scientific staff, Resolution C-14-06 further 
reduced the catch limit by approximately 34 percent--6,000 mt for 
Mexico and 600 mt for the United States for 2015 and 2016 combined. The 
IATTC most recently adopted Resolution C-16-08. In accordance with the 
recommendations of the IATTC's scientific staff, this resolution 
maintains the same catch limits that were applicable to 2015 and 2016--
6,600 mt in the eastern Pacific Ocean during 2017 and 2018 combined. 
The final rule implementing Resolution C-16-08 was published on April 
21, 2017, and had an effective date of May 22, 2017. The most recent 
regulations represent roughly a 33 percent reduction compared to the 
average landings from 2010-2014 (5,142 mt). Resolution C-16-08 also 
outlined next steps in developing a framework for managing the stock in 
the long-term. This framework included an initial goal of rebuilding 
the SSB to the median point estimate for 1952-2014 by 2024 with at 
least 60 percent probability, and further specifies that the IATTC will 
adopt a second rebuilding target in 2018 to be achieved by 2030. The 
second Joint IATTC-WCPFC Northern Committee Working Group meeting on 
Pacific bluefin tuna, that will be held August 28-September 1, 2017, 
will discuss the development of a rebuilding strategy (second 
rebuilding target and timeline, etc.) and long-term precautionary 
management framework (e.g. management objectives, limit and target 
reference points, and harvest control rules).
    The conservation and management measures adopted by the WCPFC have 
become increasingly restrictive since the initial 2009 measure. In 
2009, total fishing effort north of 20[deg] N. was limited to the 2002-
2004 annual average level. At this time, an interim management 
objective--to ensure that the current level of fishing mortality rate 
was not increased in the western Pacific Ocean--was also established. 
In 2010, Conservation and Management Measure (referred to as CMM) 2010-
04 established catch restrictions in addition to the effort limits 
described above for 2011 and 2012. A similar measure, CMM 2012-06, was 
adopted for 2013. In 2014 (CMM 2013-09) all catch of Pacific bluefin 
tuna less than 30 kilograms (kg) was reduced by 15 percent below the 
2002-2004 annual average. In 2015 (CMM 2014-04) the harvest of Pacific 
bluefin tuna less than 30 kilograms was reduced to 50 percent of the 
2002-2004 annual average. The CMM 2014-04 also limits all catches of 
Pacific bluefin tuna greater than 30 kg to no more than the 2002-2004 
annual average level. The measure was amended in 2015 (CMM 2015-04) to 
include a requirement to adopt an ``emergency rule'' where additional 
actions would be triggered if recruitment in 2016 was extremely poor. 
However, this emergency rule was not

[[Page 37072]]

agreed to at the 2016 Northern Committee annual meeting. It is expected 
that it will be discussed again at the Northern Committee meeting in 
August 2017. Lastly, the measure was amended in 2016 (CMM 2016-04) to 
allow countries to transfer some of their catch limit for Pacific 
bluefin tuna less than 30 kg to their limit on fish larger than 30 kg 
(i.e., increase catch of larger fish and decrease catch of smaller 
fish); the reverse is not allowed. Unlike the IATTC resolutions for 
Pacific bluefin tuna, the current WCPFC Pacific bluefin tuna measure 
does not have an expiration date, although it may be amended or 
removed. Both the IATTC and WCPFC measures require reporting to promote 
compliance with the provisions of the measures.
    In summary, the WCPFC adopted harvest limits for Pacific bluefin 
tuna in 2010 and further reduced those limits in 2012, 2014, and 2016. 
The IATTC adopted harvest limits for Pacific bluefin tuna in 2012 and 
further reduced those limits in 2014 and 2016. Additionally, both RFMOs 
addressed concerns about monitoring harvest by adopting monitoring and 
reporting plans in 2010. Furthermore, the ISC stock assessment predicts 
that under all scenarios the current harvest limits will allow for 
rebuilding the abundance of Pacific bluefin tuna to targets by 2030.
    After thorough discussion, the SRT members had a range of opinions 
on the effects of international management on population decline or 
degradation for Pacific bluefin tuna, ranging from no impact to high 
impact. The SRT therefore used SEDM to arrive at the conclusion that 
inadequacy of international management poses a low risk of contributing 
to population decline or degradation in Pacific bluefin tuna over the 
short time period (25 years) and a moderate risk over the long time 
period (100 years).
Domestic Fisheries Management
    Domestic fisheries are managed under the MSA. The MSA provides 
regional fishery management councils with authority to prepare Fishery 
Management Plans (FMPs) for the conservation and management of 
fisheries in the U.S. EEZ. The MSA was reauthorized and amended in 1996 
by the Sustainable Fisheries Act (SFA) and again in 2006 by the 
Magnuson-Stevens Fishery Conservation and Management Reauthorization 
Act (MSRA). Among other modifications, the SFA added requirements that 
FMPs include measures to rebuild overfished stocks.
    The Pacific Fishery Management Council (Pacific Council) has 
purview over the U.S. West Coast fisheries, which catch the large 
majority of Pacific bluefin tuna caught by U.S. vessels. The Pacific 
Council makes recommendations on the implementation of the FMP for U.S. 
West Coast Fisheries for highly migratory species (HMS FMP) for 
consideration by NMFS. Additionally, the Pacific Council makes 
recommendations to NMFS on issues expected to be considered by the 
IATTC and WCPFC. During its November 2016 meeting, the Pacific Council, 
in response to a petition that NMFS received by the Center for 
Biological Diversity, recommended a review of domestic status 
determination criteria for Pacific bluefin tuna at upcoming meetings in 
March, June, and September 2017. The domestic status determination 
criteria, also commonly referred to as reference points, are targets 
for fishing effort and abundance of the population. At the March 2017 
meeting, NMFS provided a report to the Pacific Council that included 
domestic status determination criteria for Pacific bluefin tuna.
    The Pacific Council, in response to NMFS' 2013 determination that 
the Pacific bluefin tuna stock was overfished and subject to 
overfishing (78 FR 41033; July 9, 2013), recommended reducing the bag 
and possession limits for Pacific bluefin tuna in the recreational 
fishery. The Pacific Council recommended reducing the daily bag limit 
from 10 to 2 fish and the possession limit from 30 to 6 fish. Based on 
analyses conducted at the SWFSC, this was projected to reduce landings 
by 10.4 percent in U.S. waters and 19.4 percent in U.S. and Mexican 
waters combined (Stohs, 2016). We published a final rule in 2015 
implementing the bag limit of two fish per day and possession limit of 
six fish per trip (80 FR 44887, July 28, 2015).
    NMFS coordinates closely with the California Department of Fish and 
Wildlife (CDFW) to monitor the Pacific bluefin tuna fishery. The State 
of California requires that fish landed in California have a 
corresponding receipt, which indicates quantity landed. Together, NMFS 
and CDFW monitor landings to ensure catch limits agreed to by the IATTC 
are not exceeded.
    In summary, NMFS initially set limits for commercial and 
recreational harvest limits in 2010 and further reduced those limits in 
2012, 2014, and 2016. The CDFW monitors and reports commercial and 
recreation harvest to NMFS. When U.S. commercial catch limits are met, 
NMFS closes the fishery. Furthermore, the ISC stock assessment predicts 
that the current harvest limits will allow for stable or increasing 
Pacific bluefin tuna SSB. We expect the current harvest limits to be 
effective at reducing the impact of domestic commercial and 
recreational fisheries, and we will continue to monitor the 
effectiveness of those regulations. We find that U.S. domestic 
management of commercial and recreational fishing poses no or low risk 
of contributing to population decline or degradation in Pacific bluefin 
tuna.

E. Other Natural or Man-Made Factors Affecting Its Continued Existence

    The other factors affecting the continued existence of Pacific 
bluefin tuna that we analyzed are climate change, radiation 
contamination from Fukushima, and the risks of low abundance levels 
inherent in small populations.
Climate Change
    Over the next several decades climate change models predict changes 
to many atmospheric and oceanographic conditions. The SRT considered 
these predictions in light of the best available information. The SRT 
felt that there were three physical factors resulting from climate 
change predictions that would have the most impact on Pacific bluefin 
tuna: Rising sea surface temperatures (SST), increased ocean 
acidification, and decreases in dissolved oxygen.
Rising Sea Surface Temperatures
    Rising SST may affect Pacific bluefin tuna spawning and larval 
development, prey availability, and trans-pacific migration habits. 
Pacific bluefin tuna spawning has only been recorded in two locations: 
Near the Philippines and Ryukyu Islands in spring, and in the Sea of 
Japan during summer (Okochi et al., 2016; Shimose & Farley 2016). 
Spawning in Pacific bluefin tuna occurs in comparatively warm waters, 
and so larvae are found within a relatively narrow temperature range 
(23.5-29.5 [deg]C) compared to adults (Kimura et al., 2010; Tanaka & 
Suzuki 2016).
    Currently, SSTs within the theoretically suitable range for larvae 
are present near the Ryukyu Islands between April and June, and in the 
Sea of Japan during July and August (Caiyun & Ge 2006; Seo et al., 
2014; Tanaka & Suzuki 2016). Warming of 1.5-3 [deg]C in the region may 
shift suitable times to earlier in the year and/or places for spawning 
northwards. Under the most pessimistic (``business as usual'') 
CO2 emission and concentration scenarios, SSTs in the North 
Pacific are likely to increase substantially by the end of the 21st 
century (Hazen et al., 2013; Woodworth-Jefcoats et al., 2016). However, 
there is considerable spatial

[[Page 37073]]

heterogeneity in these projections. The southern Pacific bluefin tuna 
spawning area is projected to warm 1.5-2 [deg]C by the end of the 21st 
century, with particularly weak warming in the Kuroshio Current region. 
In contrast, the Sea of Japan may warm by more than 3 [deg]C compared 
to recent historical conditions (Seo et al., 2014; Scott et al., 2016; 
Woodworth-Jefcoats et al., 2016).
    The precise mechanisms by which warming waters will affect Pacific 
bluefin tuna larvae are not entirely clear. Kimura et al. (2010) 
assumed that the lethal temperature for larvae was 29.5 [deg]C. 
However, Muhling et al. (2010) and Tilley et al. (2016) both reported 
larvae of the closely-related Atlantic bluefin tuna in the Gulf of 
Mexico at SSTs of between 29.5 and 30.0 [deg]C. In addition, tropical 
tuna larvae can tolerate water temperatures of well above 30 [deg]C 
(Sanchez-Velasco et al., 1999; Wexler et al., 2011; Muhling et al., 
2017). Pacific bluefin tuna larvae may have fundamentally different 
physiology from that of these other species, or it is possible that the 
observed upper temperature limit for Pacific bluefin tuna larvae in the 
field is more a product of the time and place of spawning, rather than 
an upper physiological limit.
    Similar to other tuna species, larval Pacific bluefin tuna appear 
to have highly specialized and selective diets (Uotani et al., 1990; 
Llopiz & Hobday 2015). Smaller larvae rely primarily on copepod 
nauplii, before moving to cladocerans, copepods such as Farranula and 
Corycaeus spp. and other zooplankton. In the Sea of Japan region, the 
occurrence of potentially favorable prey organisms for larval Pacific 
bluefin tuna appears to be associated with stable post-bloom conditions 
during summer (Chiba & Saino, 2003). This suggests a potential 
phenological match to Pacific bluefin tuna spawning. Environmentally-
driven changes in the evolution of this zooplankton community, or the 
timing of spawning, could thus affect the temporal match between larvae 
and their prey. Woodworth-Jefcoats et al. (2016) project a 10-20 
percent decrease in overall zooplankton density in the western Pacific 
Ocean, but how this may relate to larval Pacific bluefin tuna prey 
availability is not yet known.
    Climate change may affect the foraging habitats of Pacific bluefin 
tuna. Adult and older juvenile (>1 year) Pacific bluefin tuna disperse 
from the spawning grounds in the western Pacific and older juveniles 
can make extensive migrations, using much of the temperate North 
Pacific. An unknown proportion of 1-2 year old fish migrate to foraging 
grounds in the eastern North Pacific (California Current LME) and 
typically remain and forage in this region for several years (Bayliff 
et al., 1991; Bayliff 1994; Rooker et al., 2001; Kitagawa et al., 2007; 
Boustany et al., 2010; Block et al., 2011; Madigan et al., 2013; 
Whitlock et al., 2015).
    Sea surface temperatures in the California Current are expected to 
increase up to 1.5-2 [deg]C by the end of the 21st century (Hazen et 
al., 2013; Woodworth-Jefcoats et al., 2016). Pacific bluefin tuna 
tagged in the California Current demonstrate a seasonal north-south 
migration between Baja California (10[deg] N.) and near the California-
Oregon border (42[deg] N.) (Boustany et al., 2010; Block et al., 2011; 
Whitlock et al., 2015), although some fish travel as far north as 
Washington State. The seasonal migration follows local peaks in 
productivity (as measured by surface chlorophyll), such that fish move 
northward from Baja California after the local productivity peak in 
late spring to summer (Boustany et al., 2010; Block et al., 2011). 
Uniform warming in this region could impact Pacific bluefin tuna 
distribution by moving their optimal temperature range (and thermal 
tolerance) northward. However, it is unlikely that rising temperatures 
will be a limiting factor for Pacific bluefin tuna, as appropriate 
thermal habitat will likely remain available.
    The high productivity and biodiversity of the California Current is 
driven largely by seasonal coastal upwelling. Although there is 
considerable uncertainty on how climate change will impact coastal 
upwelling, basic principles indicate a potential for upwelling 
intensification (Bakun 1990). Bakun's hypothesis suggested that the 
rate of heating over land would be enhanced relative to that over the 
ocean, resulting in a stronger cross-shore pressure gradient and a 
proportional increase in alongshore winds and resultant upwelling 
(Bakun et al., 2015; Bograd et al., 2017). A recent publication 
(Sydeman et al., 2014) described a meta-analysis of historical studies 
on the Bakun hypothesis and found general support for upwelling 
intensification, but with significant spatial (latitudinal) and 
temporal (intraseasonal) variability between and within the eastern 
boundary current systems. In the California Current, a majority of 
analyses indicated increased upwelling intensity during the summer 
(peak) months, though this signal was most pronounced in the northern 
California Current (Sydeman et al., 2014).
    To date, global climate models have generally been too coarse to 
adequately resolve coastal upwelling processes (Stock et al., 2010), 
although recent studies analyzing ensemble model output have found 
general support for projected increases in coastal upwelling in the 
northern portions of the eastern boundary current systems (Wang et al., 
2015; Rykaczewski et al., 2015). Using an ensemble of more than 20 
global climate models from the IPPC's Fifth Assessment Report, 
Rykaczewski et al. (2015) found evidence of a small projected increase 
in upwelling intensity in the California Current north of 40[deg] N. 
latitude and a decrease in upwelling intensity to the south of this 
range by the end of the 21st century under RCP 8.5. Pacific bluefin 
tuna are more commonly found to the south of the 40[deg] N. latitude 
mark. Perhaps more importantly, Rykaczewski et al. (2015) described 
projected changes in the phenology of coastal upwelling, with an 
earlier transition to positive upwelling within the peak upwelling 
domain. Overall, these results suggest a poleward displacement of peak 
upwelling and potential lengthening of the upwelling season in the 
California Current, even if upwelling intensity may decrease. The 
phenological changes in coastal upwelling may be most important, as 
these may lead to spatial and temporal mismatches between Pacific 
bluefin tuna and their preferred prey (Cushing 1990; Edwards and 
Richardson 2004; Bakun et al., 2015). However, the bluefin tuna's 
highly migratory nature and plasticity in migratory patterns may help 
to mitigate shifts in phenology.
    The information directly relating to food web alterations that may 
impact Pacific bluefin tuna is scarce. While changes to upwelling 
dynamics in foraging areas have been examined, it is still relatively 
speculative, and literature on the potential impacts of the projected 
changes is limited. Given their trophic position as an apex predator, 
and the fact that Pacific bluefin tuna are opportunistic feeders that 
can change their preferred diet from year to year, alterations to the 
food web may have less impact on Pacific bluefin tuna than on other 
organisms that are reliant on specific food sources.
    Climate change may affect the Pacific bluefin tuna's migratory 
pathways. Pacific bluefin tuna undergo trans-Pacific migrations, in 
both directions, between the western Pacific spawning grounds and 
eastern Pacific foraging grounds (Boustany et al., 2010; Block et al., 
2011). For both migrations, Pacific bluefin tuna remain within a 
relatively narrow latitudinal band (30-40[deg] N.) within the North 
Pacific Transition Zone (NPTZ), which is characterized by generally 
temperate conditions. This

[[Page 37074]]

region, marking the boundary between the oligotrophic subtropical and 
more productive subarctic gyres, is demarcated by the seasonally-
migrating Transition Zone Chlorophyll Front (TZCF; Polovina et al., 
2001; Bograd et al., 2004). Climate-driven changes in the position of 
the TZCF, and in the thermal environment and productivity within this 
region, could impact the migratory phase of the Pacific bluefin tuna 
life cycle.
    Under RCP 8.5, SSTs in the NPTZ are expected to increase by 2-3 
[deg]C by the end of the 21st century (Woodworth-Jefcoats et al., 
2016), with the highest increases on the western side. The increased 
temperatures within the NPTZ are part of the broader projected changes 
in the central North Pacific Ocean, including an expansion of the 
oligotrophic Subtropical Gyre, a northward displacement of the 
transition zone, and an overall decline in productivity (Polovina et 
al., 2011). The impacts of these changes on species that make extensive 
use of the NPTZ could be substantial, resulting in a gain or loss of 
core habitat, distributional shifts, and regional changes in 
biodiversity (Hazen et al., 2013). Using habitat models based on a 
multi-species biologging dataset, and a global climate model run under 
``business-as-usual'' forcing (the A2 CO2 emission scenario 
from the IPCC's fourth assessment report), Hazen et al. (2013) found a 
substantial loss of core habitat for a number of highly migratory 
species, and small gains in viable habitat for other species, including 
Pacific bluefin tuna. Although the net change in total potential 
Pacific bluefin tuna core habitat was positive, the projected physical 
changes in the bluefin tuna's migratory pathway could negatively impact 
them. The northward displacement of the NPTZ and TZCF could lead to 
longer migrations requiring greater energy expenditure. The generally 
lower productivity of the region could also diminish the abundance or 
quality of the Pacific bluefin tuna prey base.
    A recent study of projected climate change in the North Pacific 
that used an ensemble of 11 climate models, including measures of 
primary and secondary production, found that increasing temperatures 
could alter the spatial distribution of tuna and billfish species 
across the North Pacific (Woodworth-Jefcoats et al., 2016). As with 
Hazen et al. (2013), this study found species richness increasing to 
the north following the northward displacement of the NPTZ. They also 
estimated a 2-5 percent per decade decline in overall carrying capacity 
for commercially important tuna and billfish species, driven by warming 
waters and a basin-scale decline in zooplankton densities (Woodworth-
Jefcoats et al., 2016). While there is still substantial uncertainty 
inherent in these climate models, we can say with some confidence that 
the central North Pacific, which encompasses a key conduit between 
Pacific bluefin tuna spawning and foraging habitat, is likely to become 
warmer and less productive through the 21st century.
Increasing Ocean Acidification and Decreasing Dissolved Oxygen
    As CO2 uptake by the oceans increases, ocean pH will 
continue to decrease (Feely et al., 2009), with declines of between 0.2 
and 0.4 expected in the western North Pacific by 2100 under the 
Intergovernmental Panel on Climate Change's Representative 
Concentration Pathway (RCP) 8.5 (Ciais et al., 2013). RCP 8.5 is a high 
emission scenario, which assumes that radiative forcing due to 
greenhouse gas emissions will continue to increase strongly throughout 
the 21st century (Riahi et al., 2011). Rearing experiments on larval 
yellowfin tuna suggest that ocean acidification may result in longer 
hatch times, sub-lethal organ damage, and decreased growth and survival 
(Bromhead et al., 2014; Frommel et al., 2016). Other studies on coral 
reef fish larvae show that acidification can impair sensory abilities 
of larvae, and in combination with warming temperatures, can negatively 
affect metabolic scope (Munday et al., 2009a,b; Dixson et al., 2010; 
Simpson et al., 2011). Surface ocean pH on Pacific bluefin tuna 
spawning grounds is currently higher than that in the broader North 
Pacific (8.1-8.2) (Feely et al., 2009). How this may affect the ability 
of Pacific bluefin tuna larvae (in particular) to adapt to ocean 
acidification is unknown. Recent studies have shown that future 
adaptation to rising CO2 and acidification could be 
facilitated by individual genetic variability (Schunter et al., 2017). 
In addition, transgenerational plasticity may allow surprisingly rapid 
adaptation across generations (Rummer & Munday 2017). However, these 
studies examined small coral reef fish species, so results may not 
transfer to larger, highly migratory species such as Pacific bluefin 
tuna. As well as incurring direct effects on Pacific bluefin tuna, 
ocean acidification is also likely to change the prey base available to 
all life stages of this species. Different organisms vary substantially 
in their sensitivity to the combined effects of acidification and 
warming (Byrne 2011). A shift in the prey assemblage towards organisms 
more tolerant to acidification is therefore likely in the future.
    Current projections estimate a future decline in dissolved oxygen 
of 3-6 percent by 2100 under RCP 8.5 (Bindoff et al., 2013; Ciais et 
al., 2013). This may be most relevant for spawning-sized adult Pacific 
bluefin tuna, which may be subject to greater metabolic stress on 
spawning grounds. While some studies exist on the effects of 
temperature on metabolic rates, cardiac function and specific dynamic 
action in juvenile Pacific bluefin tuna (e.g. Blank et al., 2004; 2007; 
Clark et al., 2008; 2010; 2013; Whitlock et al., 2015), there are no 
published studies on larger adults, or on larvae. While future warming 
and decreases in dissolved oxygen may reduce the suitability of some 
parts of the Pacific bluefin tuna range (e.g. Muhling et al., 2016), 
likely biological responses to this are not yet known.
    Another factor to include in considerations of climate change 
impacts is biogeochemical changes. Driven by upper ocean warming, 
changes in source waters, enhanced stratification, and reduced mixing, 
the dissolved oxygen content of mid-depth oceanic waters is expected to 
decline (Keeling et al., 2010). This effect is especially important in 
the eastern Pacific, where the Oxygen Minimum Zone (OMZ) shoals to 
depths well within the vertical habitat of Pacific bluefin tuna and 
other highly migratory species and, in particular, their prey (Stramma 
et al., 2010; Moffit et al., 2015). The observed trend of declining 
oxygen levels in the Southern California Bight (Bograd et al., 2008; 
McClatchie et al., 2010; Bograd et al., 2015), combined with an 
increase in the frequency and severity of hypoxic events along the U.S. 
West Coast (Chan et al., 2008; Keller et al., 2010; Booth et al., 
2012), suggests that declining oxygen content could drive ecosystem 
change. Specifically, the vertical compression of viable habitat for 
some benthic and pelagic species could alter the available prey base 
for Pacific bluefin tuna. Given that Pacific bluefin tuna are 
opportunistic feeders, they could have resilience to these climate-
driven changes in their prey base.
    The effects of increasing hypoxia on marine fauna in the California 
Current may be magnified by ocean acidification. Ekstrom et al. (2015) 
predicted the West Coast is highly vulnerable to ecological impacts of 
ocean acidification due to reduction in aragonite saturation state 
exacerbated by coastal upwelling of ``corrosive,'' lower pH waters 
(Feely et al., 2008). The most

[[Page 37075]]

acute impacts would be on calcifying organisms (some marine 
invertebrates and pteropods), which are not generally part of the adult 
Pacific bluefin tuna diet. While direct impacts of ocean acidification 
on Pacific bluefin tuna may be minimal within their eastern Pacific 
foraging grounds, some common Pacific bluefin tuna prey do rely on 
calcifying organisms (Fabry et al., 2008).
Climate Change Conclusions
    We find that ocean acidification and changes in dissolved oxygen 
content due to climate change pose a very low risk to the decline or 
degradation of the Pacific bluefin tuna on the short-term time scale 
(25 years), and low to moderate threat on the long-time scale (100 
years). The reasoning behind this decision for acidification centered 
primarily on the disconnect between Pacific bluefin tuna and the lower 
trophic level prey which would be directly affected by acidification as 
well as by the lack of information on direct impacts on acidification 
on pelagic fish. Conclusions by the SRT members on the rising SST due 
to climate change required SEDM, as the range of values assigned by 
each SRT member was large. Following the SEDM, the SRT concluded that 
SST rise poses a low risk of contributing to population decline or 
degradation in PBF over the short (25 year) and long (100 year) time 
frames. This decision was reached primarily due to the highly migratory 
nature of Pacific bluefin tuna; despite likely latitudinal shifts in 
preferred habitat, it would take little effort for Pacific bluefin tuna 
to shift their movements along with the changing conditions.
Fukushima Associated Radiation
    On 11 March, 2011, the T[omacr]hoku megathrust earthquake at 
magnitude 9.1 produced a devastating tsunami that hit the Pacific coast 
of Japan. As a result of the earthquake, the Fukushima Daiichi Nuclear 
Power Plant was compromised, releasing radionuclides directly into the 
adjacent sea. The result was a 1- to 2-week pulse of emissions of the 
caesium radioisotopes Caesium-134 and Caesium-137. These isotopes were 
biochemically available to organisms in direct contact with the 
contaminated water (Oozeki et al., 2017).
    Madigan et al. (2012) reported on the presence of Caesium-134 and 
Caesium-137 in Pacific bluefin tuna caught in California in ratios that 
strongly suggested uptake as a result of the Fukushima Daiichi 
accident. The results indicated that highly migratory species can be 
vectors for the trans-Pacific movement of radionuclides. Importantly, 
the study highlighted that while the radiocaesium present in the 
Pacific bluefin tuna analyzed was directly traceable to the Fukushima 
accident, the concentrations were 30 times lower than background levels 
of naturally occurring radioisotopes such as potassium-40. In addition, 
Madigan et al. (2012) estimated the dose to human consumers of fish 
from Fukushima derived Caesium-137 was at 0.5 percent of the dose from 
Polonium-210, a natural decay product of Uranium-238, which is 
ubiquitously present and in constant concentrations globally.
    Fisher et al. (2013) further evaluated the dosage and associated 
risks to marine organisms and humans (by consumption of contaminated 
seafood) of the caesium radioisotopes associated with the Fukushima 
Daiichi accident. They confirmed that dosage of radioisotopes from 
consuming seafood were dominated by naturally occurring radionuclides 
and that those stemming directly from Fukushima derived radiocaesium 
were three to four orders of magnitude below doses from these natural 
radionuclides. Doses to marine organisms were two orders of magnitude 
lower than the lowest benchmark protection level for ecosystem health 
(ICRP 2008). The study concluded that even on the date at which the 
highest exposure levels may have been reached, dosages were very 
unlikely to have exceeded reference levels. This indicates that the 
amount of Fukushima derived radionuclides is not cause for concern with 
regard to the potential harm to the organisms themselves.
    We find that Fukushima associated radiation poses no risk of 
contributing to population decline or degradation in Pacific bluefin 
tuna. This was based largely on the absence of empirical evidence 
showing negative effects of Fukushima derived radiation on Pacific 
bluefin tuna.
Small Population Concerns
    Small populations face a number of inherent risks. These risks are 
tied to survival and reproduction (e.g. Allee or other depensation 
effects) via three mechanisms: Ecological (e.g., mate limitation, 
cooperative defense, cooperative feeding, and environmental 
conditioning), genetic (e.g., inbreeding and genetic drift), and 
demographic stochasticity (i.e., individual variability in survival and 
recruitment) (Berec et al., 2007). The actual number at which 
populations would be considered critically low and at risk varies 
depending on the species and the risk being considered. While the 
Pacific bluefin tuna is estimated to contain at least 1.6 million 
individuals, of which more than 140,000 are reproductively capable, the 
SRT deemed it prudent to examine the factors above that are 
traditionally used to evaluate the impacts of relatively low population 
numbers. In the paragraphs that follow we discuss how small population 
size can affect reproduction, demographic stochasticity, genetics, and 
how it can be affected by stochastic and catastrophic events, and Allee 
effects.
    In small populations, individuals may have difficulty finding a 
mate. However, the probability of finding a mate depends largely on 
density on the spawning grounds rather than absolute abundance. Pacific 
bluefin tuna are a schooling species and individual Pacific bluefin 
tuna are not randomly distributed throughout their range. They also 
exhibit regular seasonal migration patterns that include aggregating at 
two separate spawning grounds (Kitigawa et al., 2010). This schooling 
and aggregation behavior serves to increase their local density and the 
probability of individuals finding a mate. This mating strategy could 
reduce the effects of small population size on finding mates over other 
strategies that do not concentrate individuals. It is unknown whether 
spawning behavior is triggered by environmental conditions or densities 
of tuna. If density of adults triggers spawning, then reproduction 
could be affected by high levels of depletion. However, the abundance 
of Pacific bluefin tuna has reached similar lows in the past and 
rebounded. The number of adult Pacific bluefin tuna is currently 
estimated to be 2.6 percent of its unfished SSB. The number of adult 
Pacific bluefin tuna reached a similar low in 1984 of 1.8 percent and 
rebounded in the 1990s to 9.6 percent, the second highest level since 
1952.
    Another concern with small populations is demographic 
stochasticity. Demographic stochasticity refers to the variability of 
annual population change arising from random birth and death events at 
the individual level. When populations are very small (e.g., <100 
individuals), chance demographic events can have a large impact on the 
population. Species with low mean annual survival rates are generally 
at greater population risk from demographic stochasticity than those 
that are long-lived and have high mean annual survival rates. In other 
words, species that are long-lived and have high annual survival rates 
have lower ``safe'' abundance thresholds, above which the risk of 
extinction due to chance demographic processes becomes negligible. Even 
though the percentage of adult Pacific bluefin tuna relative to 
historical levels is low, they still

[[Page 37076]]

number in the hundreds of thousands. In addition, the total population 
size in 2014 as estimated by the 2016 ISC stock assessment was 
1,625,837. The high number of individuals, both mature and immature, 
should therefore counteract a particular year with low survivorship.
    Small populations may also face Allee effects. If a population is 
critically small in size, Allee effects can act upon genetic diversity 
to reduce the prevalence of beneficial alleles through genetic drift. 
This may lower the population's fitness by reducing adaptive potential 
and increasing the accumulation of deleterious alleles due to increased 
levels of inbreeding. Population genetic theory typically sets a 
threshold of 50 individuals (i.e., 25 males, 25 females) below which 
irreversible loss of genetic diversity is likely to occur in the near 
future. This value, however, is not necessarily based upon the number 
of individuals present in the population (i.e., census population size, 
NC) but rather on the effective population size 
(NE), which is linked to the overall genetic diversity in 
the population and is typically less than NC. In extreme 
cases NE may be much (e.g. 10-10,000 times) smaller, 
typically for species that experience high variance in reproductive 
success (e.g., sweepstakes recruitment events). NE may also 
be reduced in populations that deviate from a 1:1 sex ratio and from 
species that have suffered a genetic bottleneck.
    With respect to considerations of NE in Pacific bluefin 
tuna, the following points are relevant. Although there are no 
available data for nuclear DNA diversity in Pacific bluefin tuna, the 
relatively high number of unique mitochondrial DNA haplotypes (Tseng et 
al., 2014) can be used as a proxy for evidence of high levels of 
overall genetic diversity currently within the population. With two 
separate spawning grounds, and adult numbers remaining in the hundreds 
of thousands, genetic diversity is expected to still be at high levels 
with little chance for inbreeding, given that billions of gametes 
combine in concentrated spawning events.
    Animals that are highly mobile with a large range are less 
susceptible to stochastic and catastrophic events (such as oil spills) 
than those that occur in concentrated areas across life history stages. 
Pacific bluefin tuna are likely to be resilient to catastrophic and 
stochastic events for the following reasons: (1) They are highly 
migratory, (2) there is a large degree of spatial separation between 
life history stages, (3) there are two separated spawning areas, and 
(4) adults reproduce over many years such that poor recruitment even 
over a series of years will not result in reproductive collapse. As 
long as this spatial arrangement persists and poor recruitment years do 
not exceed the reproductive age span for the species, Pacific bluefin 
tuna should be resilient to both stochastic and catastrophic events.
    Although Pacific bluefin tuna are resilient to many of the risks 
that small populations face, there is increasing evidence for a 
reduction in population growth rate for marine fishes that have been 
fished to densities below those expected from natural fluctuations 
(Hutchings 2000, 2001). These studies focus on failure to recover at 
expected rates. A far more serious issue is not just reducing 
population growth but reducing it to the point that populations 
decrease (death rates exceed recruitment). Unfortunately, the reviews 
of marine fish stocks do not make a distinction between these two 
important categories of depensation: Reduced but neutral or positive 
growth versus negative growth. Many of the cases reviewed suggested 
depensatory effects for populations reduced to relatively low levels 
(0.2 to 0.5 SSBmsy) that would increase time to recovery, 
but no mention was made of declining towards extinction. However, these 
cases did not represent the extent of reduction observed in Pacific 
bluefin tuna (0.14 SSBmsy). Thus, this case falls outside 
that where recovery has been observed in other marine fishes and thus 
there remains considerable uncertainty as to how the species will 
respond to reductions in fishing pressure.
    Hutchings et al. (2012) also show that there is no positive 
relationship between per capita population growth rate and fecundity in 
a review of 233 populations of teleosts. Thus, the prior confidence 
that high fecundity provides more resilience to population reduction 
and ability to quickly recover should be abandoned. These findings, 
although not providing examples that marine fishes exploited to low 
levels will decline towards extinction, suggest that at a minimum such 
populations may not recover quickly. However, Pacific bluefin tuna 
recently showed an instance of positive growth from a population level 
similar to the most recent stock assessment. This suggests potential 
for recovery at low population levels. However, the conditions needed 
to allow positive growth remain uncertain.
Small Populations Conclusion
    We find that small population concerns pose low risk of 
contributing to population decline or degradation in Pacific bluefin 
tuna over both the 25- and 100-year time scales, though with low 
certainty. This was largely due to the estimated population size of 
more than 1.6 million individuals, of which at least 140,000 are 
reproductively capable. This, coupled with previous evidence of 
recovery from similarly low numbers and newly implemented harvest 
regulations, strongly suggests that small population concerns are not 
particularly serious in Pacific bluefin tuna.

Analysis of Threats

    As noted previously, the SRT conducted its analysis in a 3-step 
progressive process. First, the SRT evaluated the risk of 25 different 
threats (covering all of the ESA section 4(a)(1) categories) 
contributing to a decline or degradation of Pacific bluefin tuna. The 
second step was to evaluate the extinction risk in each of the 4(a)(1) 
categories. Finally, they performed an overall extinction risk analysis 
over two timeframes--25 years and 100 years.
    In step one, the evaluation of the risk of individual threats 
contributing to a decline or degradation of Pacific bluefin tuna 
considered how these threats have affected and how they are expected to 
continue to affect the species. The threats were evaluated in light of 
the vulnerability of and exposure to the threat, and the biological 
response. This evaluation of individual threats and the potential 
demographic risk they pose forms the basis of understanding used during 
the extinction risk analysis to inform the overall assessment of 
extinction risk.
    Within each threat category, individual threats have not only 
different magnitudes of influence on the overall risk to the species 
(weights) but also different degrees of certainty. The overall threat 
within a category is cumulative across these individual threats. Thus, 
the overall threat is no less than that for the individual threat with 
the highest influence but may be greater as the threats are taken 
together. For example, some of the individual threats rated as 
``moderate'' may result in an overall threat for that category of at 
least ``moderate'' but potentially ``high.'' When evaluating the 
overall threat, individual team members considered all threats taken 
together and performed a mental calculation, weighting the threats 
according to their expertise using the definitions below.
    Each team member was asked to record his or her confidence in their 
overall scoring for that category. If, for example, the scoring for the 
overall threat confidence was primarily a function of a single threat 
and that threat had a high level of certainty, then

[[Page 37077]]

they would likely have a high level of confidence in the overall 
confidence score. Alternatively, the overall confidence score could be 
reduced due to a combination of threats, some of which the team members 
had a low level of certainty about and consequently communicated this 
lower overall level of confidence with a corresponding score (using the 
definitions below). Generally, the level of confidence will be most 
influenced by the level of certainty in the threats of highest 
severity. The level of confidence for threats with no to low severity 
within a category that contains moderate to high severity threats will 
not be important to the overall level of confidence.
    The level of severity is defined as the level of risk of this 
threat category contributing to the decline or degradation of the 
species over each time frame (over the next 25 years or over the next 
100 years). Specific rankings for severity are: (1) High: The threat 
category is likely to eliminate or seriously degrade the species; (2) 
moderate: The threat category is likely to moderately degrade the 
species; (3) low: The threat category is likely to only slightly impair 
the species; and (4) none: The threat category is not likely to impact 
the species.
    The level of confidence is defined as the level of confidence that 
the threat category is affecting, or is likely to affect, the species 
over the time frame considered. Specific rankings for confidence are: 
(1) High: There is a high degree of confidence to support the 
conclusion that this threat category is affecting, or is likely to 
affect, the species with the severity ascribed over the time frame 
considered; (2) moderate: There is a moderate degree of confidence to 
support the conclusion that this threat category is affecting, or is 
likely to affect, the species with the severity ascribed over the time 
frame considered; (3) low: There is a low degree of confidence to 
support the conclusion that this threat category is affecting, or is 
likely to affect, the species with the severity ascribed over the time 
frame considered; and (4) none: There is no confidence to support the 
conclusion that this threat category is affecting, or is likely to 
affect, the species with the severity ascribed over the time frame 
considered.
    Based on the best available information and the SRT's SEDM 
analysis, we find that overutilization, particularly by commercial 
fishing activities, poses a moderate risk of decline or degradation of 
the species over both the 25 and 100-year time scales. While the degree 
of certainty for this risk assessment was moderate for the 25-year time 
frame, it was low for the 100-year time frame. This largely reflects 
the inability to accurately predict trends in both population size and 
catch over the longer time frame. In addition, management regimes may 
shift in either direction in response to the population trends at the 
time.
    Over the short and long time frames, we find that habitat 
destruction, disease, and predation are not likely to pose a risk to 
the extinction of the Pacific bluefin tuna. Among the specific threats 
in the Habitat Destruction category, water pollution was ranked the 
highest (mean severity score 1.5). This was largely due to the fact 
that any degradation to Pacific bluefin tuna by water pollution is a 
passive event. That is, behavioral avoidance might not be possible, 
whereas other specific threats involved factors where active avoidance 
would be possible.
    We also find that based on the best available information and the 
SRT's SEDM analysis, the inadequacy of existing regulatory mechanisms 
poses a low risk of decline or degradation to the species over both the 
25- and 100-year time scales, given the stable or upward trends of 
future projected SSB over the short time scale from various harvest 
scenarios in the 2016 ISC stock assessment. The confidence levels were 
moderate for the 25-year time frame and low for the 100-year time 
frame.
    Lastly, we find that other natural or manmade factors, which 
included climate change and small population concerns, pose a low risk 
of decline or degradation to the species over the 25-year time frame 
and moderate risk over the 100-year time frame.

Extinction Risk Analysis

    As described previously, following the evaluation of the risk of 25 
specific threats contributing to the decline or degradation of Pacific 
bluefin tuna, the SRT then conducted step 2 and step 3 to perform an 
extinction risk analysis. In step two the SRT used SEDM to evaluate the 
contribution of each section 4(a)(1) factor to extinction risk. 
Finally, in step 3 the SRT performed an overall extinction risk 
analysis over two timeframes--25 years and 100 years.
    This final risk assessment considered the threats, the results from 
the recent stock assessment, the species life history, and historical 
trends. After considering all factors, team members were asked to 
distribute 100 plausibility points into one of three risk categories 
for the short term and long term time frames. The short-term time frame 
was 25 years and the long-term time frame was 100 years.
    The SRT defined the extinction risk categories as low, moderate, 
and high. The species is deemed to be at low risk of extinction if at 
least one of the following conditions is met: (1) The species has high 
abundance or productivity; (2) There are stable or increasing trends in 
abundance; and (3) The distributional characteristics of the species 
are such that they allow resiliency to catastrophes or environmental 
changes. The species is deemed to be at moderate risk of extinction if 
it is not at high risk and at least one of the following conditions is 
met: (1) There are unstable or decreasing trends in abundance or 
productivity which are substantial relative to overall population size; 
(2) There have been reductions in genetic diversity; or (3) The 
distributional characteristics of the species are such that they make 
the species vulnerable to catastrophes or environmental changes. 
Finally, the species is deemed to be at high risk of extinction if at 
least one of the following conditions is met: (1) The abundance of the 
species is such that depensatory effects are plausible; (2) There are 
declining trends in abundance that are substantial relative to overall 
population size; (3) There is low and decreasing genetic diversity; (4) 
There are current or predicted environmental changes that may strongly 
and negatively affect a life history stage for a significant period of 
time; or (5) The species has distributional characteristics that result 
in vulnerability to catastrophes or environmental changes.
    The SRT members distributed their plausibility points across all 
three risk categories, with most members placing their points in the 
low and moderate risk categories. Over the 25-year time frame, a large 
proportion of plausibility points were assigned to the low and moderate 
risk by some team members. Over the 100-year time frame, more points 
were assigned to the moderate risk category by all members and a few 
members assigned points to the high risk category. After the scores 
were recorded, the SRT calculated the average number of points for each 
risk category under both the 25 and 100-year timeframes. For both 
timeframes, the greatest number of points were in the low risk 
category. The average number of points for the low risk category was 68 
for the 25-year timeframe and 51 for the 100-year timeframe.
    There are a number of factors that contributed to the low ranking 
of the overall extinction risk over both the 25 and 100-year time 
frames. The large number of mature individuals, while small relative to 
the theoretical, model-derived unfished population, coupled

[[Page 37078]]

with the total estimated population size, was deemed sufficiently large 
for Pacific bluefin tuna to avoid small population effects. Harvest 
regulations have been adopted by member nations to reduce landings and 
rebuild the population, with all model results from the ISC analysis 
showing stable or increasing trends under current management measures. 
Also, the SRT noted that over the past 40 years the SSB has been low 
relative to the theoretical, model-derived unfished population (less 
than 10 percent of unfished), and it has increased before. While the 
SRT agreed that climate change has the potential to negatively impact 
the population, many members of the team felt that the Pacific bluefin 
tuna's broad distribution across habitat, vagile nature, and generalist 
foraging strategy were mitigating factors in terms of extinction risk.
    After evaluating the extinction risk SEDM analysis conducted by the 
SRT over the 25-year and 100-year timeframes, we considered the overall 
extinction risk categories described below:
    High risk: A species or DPS with a high risk of extinction is at or 
near a level of abundance, productivity, spatial structure, and/or 
diversity that places its continued persistence in question. The 
demographics of a species or DPS at such a high level of risk may be 
highly uncertain and strongly influenced by stochastic or depensatory 
processes. Similarly, a species or DPS may be at high risk of 
extinction if it faces clear and present threats (e.g., confinement to 
a small geographic area; imminent destruction, modification, or 
curtailment of its habitat; or disease epidemic) that are likely to 
create present and substantial demographic risks.
    Moderate risk: A species or DPS is at moderate risk of extinction 
if it is on a trajectory that puts it at a high level of extinction 
risk in the foreseeable future (see description of ``High risk'' 
above). A species or DPS may be at moderate risk of extinction due to 
projected threats or declining trends in abundance, productivity, 
spatial structure, or diversity. The appropriate time horizon for 
evaluating whether a species or DPS is more likely than not to be at 
high risk in the foreseeable future depends on various case- and 
species-specific factors. For example, the time horizon may reflect 
certain life history characteristics (e.g., long generation time or 
late age-at-maturity) and may also reflect the time frame or rate over 
which identified threats are likely to impact the biological status of 
the species or DPS (e.g., the rate of disease spread). (The appropriate 
time horizon is not limited to the period that status can be 
quantitatively modeled or predicted within predetermined limits of 
statistical confidence. The biologist (or Team) should, to the extent 
possible, clearly specify the time horizon over which it has confidence 
in evaluating moderate risk.)
    Low risk: A species or DPS is at low risk of extinction if it is 
not at moderate or high level of extinction risk (see ``Moderate risk'' 
and ``High risk'' above). A species or DPS may be at low risk of 
extinction if it is not facing threats that result in declining trends 
in abundance, productivity, spatial structure, or diversity. A species 
or DPS at low risk of extinction is likely to show stable or increasing 
trends in abundance and productivity with connected, diverse 
populations.
    The SRT evaluation of extinction risk placed the majority of 
distributed points in the low risk category for both the 25-year and 
100-year timeframes. The SRT members explained their assessment of low 
risk over those timeframes recognizing that the large number of mature 
individuals, while small relative to the theoretical, model-derived 
unfished population, coupled with the total estimated population size, 
was deemed sufficiently large for Pacific bluefin tuna to avoid small 
population effects. Harvest regulations have been adopted by member 
nations to reduce landings and rebuild the population, with all model 
results from the ISC stock assessment analysis (ISC 2016) showing 
stable or increasing trends under current management measures. Also, 
the SRT noted that over the past 40 years the SSB has been low relative 
to the theoretical, model-derived unfished population (less than 10 
percent of unfished), and it has increased before. While the SRT agreed 
that climate change has the potential to negatively impact the 
population, many members of the team felt that the Pacific bluefin 
tuna's broad distribution across habitat, its vagile nature, and its 
generalist foraging strategy were mitigating factors in terms of 
extinction risk.
    Based upon the expert opinion of the SRT and for the reasons 
described above, we determine that the overall extinction risk to 
Pacific bluefin tuna is most accurately characterized by the 
description of the low risk category as noted above.

Review of Conservation Efforts

    Section 4(b)(1) of the ESA requires that NMFS make listing 
determinations based solely on the best scientific and commercial data 
available after conducting a review of the status of the species and 
taking into account those efforts, if any, being made by any state or 
foreign nation, or political subdivisions thereof, to protect and 
conserve the species. We are not aware of additional conservation 
efforts being made by any state or foreign nation to protect and 
conserve the species other than the fishery management agreements 
already considered, thus no additional measures were evaluated in this 
finding.

Significant Portion of Its Range Analysis

    As the definitions of ``endangered species'' and ``threatened 
species'' make clear, the determination of extinction risk can be based 
on either assessment of the rangewide status of the species, or the 
status of the species in a ``significant portion of its range'' (SPR). 
Because we determined that the Pacific bluefin tuna is at low risk of 
extinction throughout its range, the species does not warrant listing 
based on its rangewide status. Next, we needed to determine whether the 
species is threatened or endangered in a significant portion of its 
range. According to the SPR Policy (79 FR 37577; July 1, 2014), if a 
species is found to be endangered or threatened in a significant 
portion of its range, the entire species is listed as endangered or 
threatened, respectively, and the ESA's protections apply to all 
individuals of the species wherever found.
    On March 29, 2017, the Arizona District Court in Center for 
Biological Diversity, et al., v. Zinke, et al., 4:14-cv-02506-RM (D. 
Ariz.), a case brought against the U.S. Fish and Wildlife Service 
(FWS), remanded and vacated the joint FWS/NMFS SPR Policy after 
concluding that the policy's definition of ``significant'' was invalid. 
NMFS is not a party to the litigation. On April 26, 2017, the FWS filed 
a Motion to Alter or Amend the Court's Judgment, which is pending. In 
the meantime, we based our SPR analysis on our joint SPR Policy, as 
discussed below.
    The SPR Policy sets out the following three components:
    (1) Significant: A portion of the range of a species is 
``significant'' if the species is not currently endangered or 
threatened throughout its range, but the portion's contribution to the 
viability of the species is so important that, without the members in 
that portion, the species would be in danger of extinction, or likely 
to become so in the foreseeable future, throughout all of its range.
    (2) The range of a species is considered to be the general 
geographical area within which that species can be found at the time 
NMFS

[[Page 37079]]

makes any particular status determination. This range includes those 
areas used throughout all or part of the species' life cycle, even if 
they are not used regularly (e.g., seasonal habitats). Lost historical 
range is relevant to the analysis of the status of the species, but it 
cannot constitute a SPR.
    (3) If the species is endangered or threatened throughout a 
significant portion of its range, and the population in that 
significant portion is a valid DPS, we will list the DPS rather than 
the entire taxonomic species or subspecies.
    When we conduct a SPR analysis, we first identify any portions of 
the range that warrant further consideration. The range of a species 
can theoretically be divided into portions in an infinite number of 
ways. However, there is no purpose to analyzing portions of the range 
that are not reasonably likely to be of relatively greater biological 
significance, or in which a species may not be endangered or 
threatened. To identify only those portions that warrant further 
consideration, we determine whether there is substantial information 
indicating that (1) the portions may be significant and (2) the species 
may be in danger of extinction in those portions or likely to become so 
within the foreseeable future. We emphasize that answering these 
questions in the affirmative is not a determination that the species is 
endangered or threatened throughout a SPR, rather, it is a step in 
determining whether a more detailed analysis of the issue is required. 
Making this preliminary determination triggers a need for further 
review, but does not prejudge whether the portion actually meets these 
standards such that the species should be listed.
    If this preliminary determination identifies a particular portion 
or portions that may be significant and that may be threatened or 
endangered, those portions must then be evaluated under the SPR Policy 
as to whether the portion is in fact both significant and endangered or 
threatened. In making a determination of significance under the SPR 
Policy we would consider the contribution of the individuals in that 
portion to the viability of the species. That is, we would determine 
whether the portion's contribution to the viability of the species is 
so important that, without the members in that portion, the species 
would be in danger of extinction or likely to become so in the 
foreseeable future. Depending on the biology of the species, its range, 
and the threats it faces, it may be more efficient to address the 
``significant'' question first, or the status question first. If we 
determine that a portion of the range we are examining is not 
significant, we would not need to determine whether the species is 
endangered or threatened there; if we determine that the species is not 
endangered or threatened in the portion of the range we are examining, 
then we would not need to determine if that portion is significant.
    Because Pacific bluefin tuna range broadly throughout their 
lifecycle around the Pacific basin, there was no portion of the range 
that, if lost, would increase the population's extinction risk. In 
other words, risk of specific threats to Pacific bluefin tuna are 
buffered both in space and time. To be thorough, the SRT examined the 
potential for a SPR by considering the greatest known threats to the 
species and whether these were localized to a significant portion of 
the range of the species. The main threats to Pacific bluefin tuna 
identified by the SRT were overutilization, inadequacy of management, 
and climate change. Generally, these threats are spread throughout the 
range of Pacific bluefin tuna and not localized to a specific region.
    We also considered whether any potential SPRs might be identified 
on the basis of threats faced by the species in a portion of its range 
during one part of its life cycle. We further evaluated the potential 
for the two known spawning areas to meet the two criteria for a SPR. 
The spawning areas for Pacific bluefin tuna are likely to be somewhat 
temporally and spatially fluid in that they are characterized by 
physical oceanographic conditions (e.g., temperature) rather than a 
spatially explicit area. While commercial fisheries target Pacific 
bluefin tuna on the spawning grounds, spatial patterns of commercial 
fishing have not changed significantly over many decades. The 
historical pattern of exploitation on the spawning areas was part of 
the consideration in evaluating the threat of overexploitation to the 
species as a whole, and was determined to not significantly increase 
the species' risk of extinction for the members utilizing that portion 
of the range for the spawning stage of their life cycle. Given that the 
species has persisted throughout this time frame and has experienced 
similarly low levels of standing stock biomass, it has shown the 
ability to rebound and has yet to reach critically low levels. 
Therefore, it was determined that this fishery behavior has not 
significantly increased the species' risk of extinction for this life 
cycle phase.

Significant Portion of Its Range Determination

    Pacific bluefin tuna range broadly throughout their life cycle 
around the Pacific basin, and there is no portion of the range that 
merits evaluation as a potential SPR. If a threat was determined to 
impact the fish in the spawning area, it would impact the fish 
throughout its range and, therefore, the species would warrant listing 
as threatened or endangered based on its status throughout its entire 
range. Based on our review of the best available information, we find 
that there are no portions of the range of the Pacific bluefin tuna 
that were likely to be of heightened biological significance (relative 
to other areas) or likely to be either endangered or threatened 
themselves.

Final Determination

    Section 4(b)(1) of the ESA requires that NMFS make listing 
determinations based solely on the best scientific and commercial data 
available after conducting a review of the status of the species and 
taking into account those efforts, if any, being made by any state or 
foreign nation, or political subdivisions thereof, to protect and 
conserve the species. We have independently reviewed the best available 
scientific and commercial information including the petition, public 
comments submitted on the 90-day finding (81 FR 70074; October 11, 
2016), the status review report, and other published and unpublished 
information, and have consulted with species experts and individuals 
familiar with Pacific bluefin tuna. We considered each of the statutory 
factors to determine whether it presented an extinction risk to the 
species on its own, now or in the foreseeable future, and also 
considered the combination of those factors to determine whether they 
collectively contributed to the extinction risk of the species, now or 
in the foreseeable future.
    Our determination set forth here is based on a synthesis and 
integration of the foregoing information, factors and considerations, 
and their effects on the status of the species throughout its entire 
range. Based on our consideration of the best available scientific and 
commercial information, as summarized here and in the status review 
report, we conclude that no population segments of the Pacific bluefin 
tuna meet the DPS policy criteria and that the Pacific bluefin tuna 
faces an overall low risk of extinction. Therefore, we conclude that 
the species is not currently in danger of extinction throughout its 
range nor is it

[[Page 37080]]

likely to become so within the foreseeable future. Additionally, we did 
not identify any portions of the species' range that were likely to be 
of heightened biological significance (relative to other areas) or 
likely to be either endangered or threatened themselves. Accordingly, 
the Pacific bluefin tuna does not meet the definition of a threatened 
or endangered species, and thus, the Pacific bluefin tuna does not 
warrant listing as threatened or endangered at this time.
    This is a final action, and, therefore, we are not soliciting 
public comments.

References

    A complete list of all references cited herein is available upon 
request (see FOR FURTHER INFORMATION CONTACT).

Authority

    The authority for this action is the Endangered Species Act of 
1973, as amended (16 U.S.C. 1531 et seq.).

    Dated: August 3, 2017.
Samuel D. Rauch III,
Deputy Assistant Administrator for Regulatory Programs, National Marine 
Fisheries Service.
[FR Doc. 2017-16668 Filed 8-7-17; 8:45 am]
 BILLING CODE 3510-22-P