Endangered and Threatened Wildlife and Plants; Proposed Endangered Status for Black Abalone, 1986-1999 [E8-335]

Agencies

• DEPARTMENT OF COMMERCE
• National Oceanic and Atmospheric Administration

[Federal Register Volume 73, Number 8 (Friday, January 11, 2008)]
[Proposed Rules]
[Pages 1986-1999]
From the Federal Register Online via the Government Printing Office [www.gpo.gov]
[FR Doc No: E8-335]


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DEPARTMENT OF COMMERCE

National Oceanic and Atmospheric Administration

50 CFR Part 224

[Docket No. 071128765-7769-01]
RIN 0648-AW32


Endangered and Threatened Wildlife and Plants; Proposed 
Endangered Status for Black Abalone

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

ACTION: Proposed rule; request for comments.

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SUMMARY: We, NMFS, have completed a review of the status of black 
abalone (Haliotis cracherodii) under the Endangered Species Act (ESA). 
After reviewing the best scientific and commercial information 
available, evaluating threats facing the species, and considering 
efforts being made to protect black abalone, we have concluded that the 
species is in danger of extinction throughout all of its range and are 
proposing to list the species as endangered under the ESA. This 
proposal is based on information indicating that: the disease known as 
withering syndrome has spread to areas throughout the range of the 
species, has been responsible for the local extirpation of populations 
throughout a large part of the species' range, and threatens remaining 
black abalone populations; low adult densities below the critical 
threshold density required for successful fertilization exist 
throughout a large part of the species' range; and, a number of 
interacting factors (e.g., suboptimal water temperatures, reduced 
genetic diversity, and illegal harvest) may further hamper natural 
recovery of the species. A critical habitat designation is being 
considered and may be proposed in a subsequent Federal Register notice. 
If the proposed listing is finalized, a recovery plan will be prepared 
and implemented.

DATES: Comments on this proposal must be received by April 10, 2008. 
Public hearing (s) will be held promptly if any person so requests by 
February 25, 2008. Notice of the location (s) and time(s) of any such 
hearing(s) will be published in the Federal Register not less than 15 
days before the hearing(s) is(are) held.

ADDRESSES: You may submit comments, identified by [RIN 0648-AW32], by 
any one of the following methods:
     Electronic Submissions: Submit all electronic public 
comments via the Federal eRulemaking Portal https://www.regulations.gov.
     Facsimile (fax): 562-980-4027, Attn: Melissa Neuman.
     Mail: Submit written comments to Chief, Protected 
Resources Division, Southwest Region, National Marine Fisheries 
Service, 501 West Ocean Blvd., Suite 4200, Long Beach, CA 90802-4213.
    Instructions: All comments received are a part of the public record 
and will generally be posted to https://www.regulations.gov without 
change. All Personal Identifying Information (for example, name, 
address, etc.) voluntarily submitted by the commenter may be publicly 
accessible. Do not submit Confidential Business Information or 
otherwise sensitive or protected information.
    We will accept anonymous comments. Attachments to electronic 
comments will be accepted in Microsoft Word, Excel, WordPerfect, or 
Adobe PDF file formats only.
    A draft black abalone status review report and other reference 
materials regarding this determination can be obtained via the Internet 
at: https://www.nmfs.noaa.gov. The draft status review report and list 
of references are also available by submitting a request to the 
Assistant Regional Administrator, Protected Resources Division, 
Southwest Region, NMFS, 501 West Ocean Blvd., Suite 4200, Long Beach, 
CA 90802-4213.

FOR FURTHER INFORMATION CONTACT: Melissa Neuman, NMFS, Southwest Region 
(562) 980-4115; or Lisa Manning, NMFS, Office of Protected Resources 
(301) 713-1401.

SUPPLEMENTARY INFORMATION:

Background

    Black abalone was added to the National Marine Fisheries Service's 
(NMFS') Candidate Species list on June 23, 1999 (64 FR 33466) and 
remained on this list after NMFS redefined the term ``candidate 
species'' on April 15, 2004 (69 FR 19975). We initiated an informal ESA 
status review of black abalone on July 15, 2003, and formally announced 
initiation of a status review on October 17, 2006 (71 FR 61021), at the 
same time soliciting information from the public. On December 27, 2006, 
we received a petition from the Center for Biological Diversity (CBD) 
to list black abalone as either an endangered or threatened species 
under the ESA and to designate critical habitat for the species 
concurrently with any listing determination. We published a 90-day

[[Page 1987]]

finding on April 13, 2007 (72 FR 18616), stating that the CBD petition 
presented substantial scientific and commercial information indicating 
that the petitioned actions may be warranted.
    In June 2007, we assembled a Status Review Team (SRT) to review the 
available information, assess the extinction risk and threats facing 
the species, and produce an ESA status review report for black abalone. 
The draft status review report (VanBlaricom et al., 2007) (hereafter 
``status report'') provides a thorough account of black abalone biology 
and natural history, and assesses demographic risks, threats and 
limiting factors, and overall extinction risk. The key background 
information and findings of the draft status report are summarized 
below.

Taxonomy and Species Description

    Abalone, members of the gastropod genus Haliotis, are marine 
gastropods that occur throughout most of the world (Cox, 1962). There 
are approximately 60 species (Geiger, 1999) found in temperate to 
tropical waters from the intertidal zone (i.e., the area of the 
foreshore and seabed that is exposed to the air at low tide and 
submerged at high tide) to depths of over 50 m. All are benthic, 
occurring on hard substrate, relatively sedentary, and generally 
herbivorous, feeding on attached or drifting algal material. There are 
seven species of abalone native to the west coast of North America 
(Geiger, 1999).
     The taxonomic classification of black abalone is as follows: 
Phylum Mollusca, Class Gastropoda, Subclass Prosobranchia, Order 
Archaeogastropoda, Superfamily Pluerotomariacea, Family Haliotidae, 
Genus Haliotis, Species cracherodii. Leach (1814) gave the first formal 
description of this shallow-living abalone (upper intertidal zone to 
subtidal depths of 6 m), describing the shell as smooth, circular, and 
black to slate blue in color. There are five to nine open respiratory 
pores that are flush with the shell's surface. Typically, the shell's 
interior is white (Haaker et al., 1986), with a poorly defined or no 
muscle scar (Howorth, 1978). Adults attain a maximum shell length of 
approximately 20 cm (throughout this document we use the maximum 
diameter of the elliptical shell as the index for individual body 
size). The muscular foot of the black abalone allows the animal to 
clamp tightly to rocky surfaces without being dislodged by wave action. 
Locomotion is accomplished by an undulating motion of the foot. A 
column of shell muscle attaches the body to the shell. The mantle and 
black epipodium, a sensory structure and extension of the foot which 
bears lobed tentacles of the same color (Cox, 1960), circle the foot 
and extend beyond the shell of a healthy black abalone. The internal 
organs are arranged around the foot and under the shell.

Historical and Current Distribution

    There is some debate regarding the northern extent of the historic 
range of black abalone. Many have cited the historic range as extending 
from Coos Bay, Oregon, USA to Cabo San Lucas, Southern Baja California, 
Mexico (Geiger, 2000). However, the northernmost documented record of 
black abalone (based on museum specimens) is from Crescent City (Del 
Norte County, California, USA; Geiger, 2004). Most experts agree that 
the current range of black abalone extends from Point Arena (Mendocino 
County, California, USA) south to Northern Baja California, Mexico. 
Black abalone may exist, but are considered extremely rare, north of 
San Francisco (Morris et al., 1980) to Crescent City, California, USA 
and south of Punta Eugenia to Cabo San Lucas, Baja California, Mexico 
(P. Raimondi, pers. comm.). Within this broad geographic range, black 
abalone generally inhabit coastal and offshore island intertidal 
habitats on exposed rocky shores where bedrock provides deep, 
protective crevice shelter (Leighton, 2005).

Population Structure

    Recent studies have evaluated population structure in black abalone 
(Hamm and Burton, 2000; Chambers et al., 2006; Gruenthal, 2007) using 
various methods. These studies indicate: (1) minimal gene flow among 
populations; (2) black abalone populations are composed predominantly 
of closely related individuals produced by local spawning events; (3) 
gene flow among island populations is relatively greater than between 
island and mainland populations; and (4) the overall connectivity among 
black abalone populations is low and likely reflects limited larval 
dispersal, and a low degree of exchange among populations.

Habitat

    Black abalone occur over a broad latitudinal range, though the 
range appears to have narrowed somewhat from historic times. This broad 
range, in addition to their small-scale distribution (high intertidal 
to 6 m depth), is associated with an evolved capability to withstand 
extreme variation in environmental conditions such as temperature, 
salinity, moisture, and wave action.
    Black abalone occur on a variety of rock types, including igneous, 
metamorphic, and sedimentary rocks at a number of locations. Complex 
surfaces with cracks and crevices in upper and middle intertidal zones 
may be crucial recruitment habitat and appear to be important for adult 
survival as well (Leighton, 1959; Leighton and Boolootian, 1963; 
Douros, 1985, 1987; Miller and Lawrenz-Miller, 1993; VanBlaricom et 
al., 1993; Haaker et al., 1995). Complex configurations of rock 
surfaces likely afford protection from predators, direct impacts of 
breaking waves, wave-born projectiles, and excessive solar heating 
during daytime low tides.

Movement

    Planktonic larval abalone movement is almost certainly determined 
primarily by patterns of water movement in nearshore habitats near 
spawning sites. Individual larvae may be able to influence movement to 
some degree by adjusting vertical position in the water column, but to 
our knowledge the ability of black abalone larvae to move in this way 
has not been documented. Movement behavior of post-metamorphic juvenile 
black abalone is likewise unknown. Leighton (1959) and Leighton and 
Boolootian (1963) indicate that black abalone larvae may settle and 
metamorphose in the upper intertidal zone, using crevices and 
depressions (including those formed by abrasive action of other 
intertidal mollusks) as habitat. Leighton and Boolootian (1963) suggest 
that young black abalone move lower in the intertidal zone as they 
begin to grow, occupying the undersides of large boulders. To our 
knowledge there is no published information on direct observations of 
movement behavior of small ( <20 mm) juvenile black abalone in the 
field. Qualitative (Leighton, 2005; VanBlaricom, unpublished 
observations) and quantitative (Bergen, 1971; Blecha et al., 1992; 
VanBlaricom and Ashworth, in preparation; Richards, unpublished 
observations) studies of movement in black abalone suggest that smaller 
abalone (<65 mm) move more frequently than larger abalone, movement is 
more frequent during night hours compared to daylight hours, and that 
larger abalone may remain in the same location for many years.

Diet

    Larvae are lecithotrophic (i.e., receive nourishment via an egg 
yolk) and apparently do not feed while in the plankton. From the time 
of post-larval metamorphosis to a size of about 20 mm, black abalone 
are highly cryptic,

[[Page 1988]]

occurring primarily on the undersides of large boulders or in deep 
narrow crevices in solid rocky substrata. In such locations the primary 
food sources are thought to be microbial and possibly diatom films 
(Leighton, 1959; Leighton and Boolootian, 1963; Bergen, 1971). At 
roughly 20 mm black abalone move to more open locations, albeit still 
relatively cryptic, gaining access to both attached macrophytes and to 
pieces of drift plants cast into the intertidal zone by waves and 
currents. As black abalone continue to grow, the most commonly observed 
feeding method is entrapment of drift plant fragments. Webber and Giese 
(1969), Bergen (1971), Hines and Pearse (1982), and Douros (1987) have 
confirmed the importance of large kelps in the diet of juvenile and 
adult black abalone. The primary food species are said to be 
Macrocystis pyrifera and Egregia menziesii in southern California 
(i.e., south of Pt. Conception) habitats, and Nereocystis leutkeana in 
central and northern California habitats.

Reproduction

    Black abalone have separate sexes and are ``broadcast'' spawners. 
Gametes from both parents are shed into the sea, and fertilization is 
entirely external. Resulting larvae are minute and defenseless, receive 
no parental care or protection of any kind, and are subject to a broad 
array of physical and biological sources of mortality. Species with a 
broadcast-spawning reproductive strategy are subject to strong 
selection for maximum fecundity of both sexes. Only through production 
of large numbers of gametes can broadcast spawners overcome high 
mortality of gametes and larvae and survive across generations. It is 
not uncommon for broadcast-spawning marine species, a group including 
many taxa of fish and invertebrates, to produce millions of eggs or 
sperm per individual per year. Broadcast spawners are also subject to 
other kinds of selection for certain traits associated with 
reproduction, including spatial and temporal synchrony in spawning and 
mechanisms that increase probabilities for union of spawned gametes.

Spawning Density

    As intertidal organisms on exposed rocky shores, black abalone 
typically release gametes into environments of extreme turbulence. As a 
consequence, eggs and sperm must be released from adults in relatively 
close spatial and temporal proximity in order to have any chance of 
union and fertilization before rapid dispersal and loss of opportunity.
    A central problem for conservation of black abalone is the dramatic 
reduction in densities over the past quarter-century in almost the 
entire geographic range of the species. Reductions in density are so 
extreme and widespread that considerable attention is now focused on 
assessment of critical density thresholds for successful reproduction, 
recruitment, and population sustainability. A review of critical 
density thresholds, below which recruitment failure occurs, for other 
marine, broadcast-spawning invertebrates (i.e., sea urchins, sea 
cucumbers, hard clams, scallops, giant clams, and geoduck clams) has 
revealed that critical density thresholds exist across a broad 
taxonomic range. However, despite apparent risks of local extinction 
when populations decline below critical density thresholds, there are 
several cases where combinations of circumstances allow populations to 
recover to densities above the critical thresholds. Thus, for black 
abalone the key conservation issues are identification of critical 
density thresholds and an understanding of circumstances, if any, that 
may allow escape from high risks of local extinction when thresholds 
are breached.
    Babcock and Keesing (1999) estimated critical density thresholds at 
0.15-0.20 m-2 for greenlip abalone (Haliotis laevigata). Tissot (2007) 
reviewed recruitment patterns in three long-term data sets for black 
abalone in California: in each case, recruitment failed when declining 
population densities fell below 0.75-1.1 m-2. Tissot (2007) noted that 
densities in most black abalone populations south of Cayucos, 
California, have fallen below the densities noted. Recent evidence 
suggests that disease-induced increases in the mortality rate of black 
abalone continue to move northward along the mainland coast of 
California (e.g., Raimondi et al., 2002; Miner et al., 2006). Thus, 
critical density thresholds are thought to have been violated for most 
of the black abalone populations in California, and because of the 
spread of the disease known as withering syndrome (as explained below), 
the number and geographic scope of populations with densities falling 
below sustainable levels is expected to increase.

Larval Settlement

    A sequence of studies and discoveries by Morse and colleagues 
(Morse et al., 1979; Morse and Morse, 1984; Trapido-Rosenthal and 
Morse, 1986; Morse, 1990; Morse, 1992), Douros (1985), and Miner et al. 
(2006) suggest that availability of crustose coralline algae in 
appropriate intertidal habitats may be significant to the success of 
the larval recruitment process in black abalone; and, that the presence 
of adult black abalone may facilitate larval settlement and 
metamorphosis because the activities and presence of the abalone favor 
the maintenance of substantial substratum cover by crustose coralline 
algae. Although crustose coralline algae are ubiquitous in rocky 
benthic habitats along the west coast of North America, a mechanistic 
understanding of processes that sustain these algal populations has not 
been established to our knowledge. If the presence of black abalone 
facilitates the abundance of crustose coralline algae, it follows that 
the issue of critical density thresholds may take on added importance.

Larval Dispersal and Recruitment

    Indirect methods for assessing larval dispersal in abalone (Tegner 
and Butler, 1985; Prince et al., 1988; Hamm and Burton, 2000; Chambers 
et al., 2005; Chambers et al., 2006; Gruenthal, 2007) point to 
consistent results. Given that most abalone larvae are drifting in the 
water for a period of about 3-10 days before settlement and 
metamorphosis (e.g., McShane, 1992), abalone in general, including 
black abalone, have limited capacity for dispersal over distances 
beyond a few kilometers, and are able to do so only rarely.
    Tissot (2007) has estimated empirically that successful recruitment 
of black abalone requires the presence of local adult populations at 
densities of 0.75-1.1 m-2 or greater, and that the number of 
known populations of adult black abalone at or above putative threshold 
densities is diminishing over time in a geographically progressive 
manner. Tissot (2007) further noted that virtually all monitored black 
abalone populations continue to decrease in mean density over time. 
This combination of observations emphasizes the importance of critical 
density thresholds in the sustainability and conservation of black 
abalone populations throughout their range. Patterns of aggregation may 
mitigate effects of decline below a critical density threshold 
(VanBlaricom, unpublished data). However, only one or two populations 
in California that have sustained mass mortality due to withering 
syndrome are known to be increasing in numbers. Thus, even if an 
ability for black abalone to aggregate exists, it may not be sufficient 
to facilitate successful recruitment and population sustainability 
under current environmental conditions.

[[Page 1989]]

Growth and Maximum Size

    Available data on black abalone growth suggest that young animals 
reach maximum shell diameters of about 2 cm in their first year, then 
grow at rates of 1-2 cm per year for the next several years. Growth 
begins to slow at lengths of about 10 cm, corresponding to an age range 
of 4-8 yrs. Beyond this point, growth is less predictable, shell 
erosion may become a significant factor, and size distributions for 
older animals may vary according to local conditions. Growth and 
erosion of shells may come into equilibrium in older black abalone, 
such that growth can be viewed as facultatively determinant.
    Maximum recorded shell length for black abalone was listed at 213 
mm by Wagner and Abbott (1990). Ault (1985) reported a maximum shell 
length of black abalone at 215 mm. Leighton (2005) indicated a shell 
length of 216 mm reported by Owen (unpublished observation). At least 
two black abalone of approximately 220 mm maximum shell length were 
known to be alive at San Nicolas Island in January 2007 (VanBlaricom, 
Neuman, and Witting, unpublished observations), but the cryptic 
locations of the animals have made measurements awkward and possibly 
not accurate. Monitoring and measurement of these individuals will 
continue in association with ongoing population surveys.

Mortality

    Mortality rates caused by withering syndrome appear to be sensitive 
to fluctuations in local sea surface temperatures (Friedman et al., 
1997; Raimondi et al., 2002; Harley and Rogers-Bennett, 2004; Vilchis 
et al., 2005). There is evidence that, in the short term, population-
scale mortality rates vary in space and time from near zero to high 
proportions of local populations. The available evidence suggests that 
mortality rates driven by withering syndrome are highest during periods 
following elevations in sea surface temperature (e.g., Raimondi et al., 
2002). Over the long term, all available evidence indicates substantial 
increases in mortality rates, and consequent reductions in densities, 
in populations throughout the range of black abalone that have been 
afflicted by withering syndrome (e.g., Tissot, 2007). More detail 
regarding the severe risk that withering syndrome poses to the future 
survival of the species is presented below (see Summary of Factors 
Affecting the Species and Population Modeling: Geographic Spread of 
Disease vs. Disease Resistance).
    Physical oceanographic conditions, predation by octopuses, 
lobsters, sea stars, fishes, sea otters, and shorebirds, competition 
with sea urchins, and food limitation may all impose mortality at 
varying rates depending on black abalone life stage. The draft status 
report (VanBlaricom et al., 2007) provides additional qualitative 
information regarding the relative importance of these sources of 
mortality. The importance of anthropogenic mortality (i.e., commercial 
and recreational harvest, illegal harvest, incidental losses, 
pollution) is also discussed in the draft status report and in other 
sections of this proposed rule (see Summary of Factors Affecting the 
Species).

Abundance

    There are two types of data that can be examined to provide a 
better understanding of variation in black abalone abundance over time: 
fishery-dependent and fishery-independent data. Based on a detailed 
examination of these two data types, Tissot (2007) evaluated trends in 
black abalone abundance over the last 3 decades.
Fishery-dependent Information
    An intertidal fishery focused on red (Haliotis rufescens Swainson, 
1822), green (Haliotis fulgens Philippi, 1845), and black abalone began 
in the 1850s in Central California and in the 1880s in Baja California, 
Mexico (Bonnot, 1930; Lundy, 1997). The fishery peaked at 1,860 mt in 
1879 (Cox, 1962). By 1913, the intertidal fishery was closed because of 
concerns regarding overfishing (Bonnot, 1930). From 1913-1928, 
commercial and recreational dive fisheries developed, but black abalone 
were not documented prior to 1940. During the 18\th\ and 19\th\ 
centuries, two predatory forces on black abalone populations in 
Southern California had been removed. First, the Native American 
Chumash and Gabrielino/Tongva cultures of the southern California 
Islands, who were known to have harvested black abalones in large 
numbers for food over periods of five to ten millennia, and fur hunters 
responsible for the elimination of southern sea otter populations south 
of Point Conception by the time of the U.S. Civil War. There is 
uncertainty regarding the ecological importance of sea otter predation 
on black abalone, but the potential for strong interactions is 
substantial given known effects of sea otter predation on red abalone 
(for more detailed information on the effects of sea otter predation 
see Summary of Factors Affecting the Species below).
    California Department of Fish and Game landings data (1940-1993) 
indicate that black abalone were intensively exploited only after other 
more marketable species had been largely depleted. Black abalone 
landings peaked in 1973 at 868 mt. During the peak decade of black 
abalone fishing from 1972-1981, Rogers-Bennett et al. (2002) estimate 
that approximately 3.5 million individuals were taken in the commercial 
fishery, and an additional 6,729 animals were taken in the recreational 
fishery. By 1993 both fisheries for black abalone were closed due to 
concerns regarding severe population declines (Haaker et al., 1992).
    Rogers-Bennett et al. (2002) estimated baseline abundance, prior to 
overfishing and mass mortalities due to withering syndrome (for more 
detailed information on withering syndrome see Summary of Factors 
Affecting the Species below), for black abalone using landings data 
from the peak of the commercial and recreational fisheries (1972-1981), 
assuming that the population was at least as large as the number taken 
in the fishery, that the fishery ``sampled'' all size classes, and that 
no new individuals were added to the population during the 10-year peak 
of the fishery. With these assumptions, the baseline minimum estimate 
of abundance for black abalone prior to overexploitation and withering 
syndrome was 3.54 million animals. This estimate provides a historic 
perspective on patterns in abundance, defines a relevant baseline 
abundance against which to compare modern day trends, and helps to 
assess the species' current status and risks. However, it should be 
noted that the estimate was calculated using data from a period of time 
when black abalone reached extraordinary abundance levels on the 
Channel Islands, possibly in response to the elimination of subsistence 
harvests by indigenous peoples, limited public access in modern times, 
and regional-scale extinctions of sea otters.
    The abalone fishery in Mexico dates to approximately 1860, but 
modern commercial harvests did not develop until the 1940s. The fishery 
is pursued by 22 fishing cooperatives, distributed across 4 management 
zones on the Pacific coast of the Baja California peninsula. Five 
cooperatives are present in management zone 1, which is the 
northernmost of the zones and extends from the U.S.-Mexico border to 
Punta Malarrimo, Baja California Sur.
    Reported commercial fishery data for black abalone during 1990-2003 
comes entirely from management zone 1. During this time period, the 
commercial

[[Page 1990]]

catch of black abalone in Mexico declined from a high of 28 mt in 1990 
to <0.5 mt in 2003, an overall decline of greater than 98 percent (J. 
Palleiro, unpublished data; Sierra-Rodriguez et al., 2006). These data 
suggest similar fishery declines to those in California. The decline in 
Mexico is attributed primarily to large mortality events associated 
with withering syndrome, rather than to overfishing.
Fishery-independent Information
    The earliest fishery-independent black abalone abundance estimates 
were generated beginning in 1975 at survey stations on the Palos Verdes 
Peninsula of Los Angeles County, California (Miller and Lawrenz-Miller, 
1993). Black abalone densities ranged from 1.0 to 6.8 m-2 
from 1975-1976, but declined during the remainder of the survey 
interval to less than 0.3 m-2 by 1987. Douros (1987) 
reported densities as great as 127 m-2 in certain surge channels at 
Santa Cruz Island in 1983-1984, but typical densities within a study 
site ranged from 30 to 90 m-2. Other field studies during the 1980s on 
Santa Cruz Island yielded black abalone densities of 0 to 50 
m-2 (Haaker et al., 1992). Tissot (1995), also studying 
black abalone populations on Santa Cruz Island, found averages of 43 to 
58 m-2 for surf-exposed and protected subpopulations, 
respectively, in 1987. These densities declined over the next 6 years 
due to withering syndrome, dropping to less than 1 m-2 by 
1993. As of this writing, only one site on Santa Cruz Island (Willows 
Anchorage) has experienced an increase in local density since 1993.
    Several studies monitoring black abalone abundance at other Channel 
Islands found similar declines through the late 1980s and early 1990s. 
From 1985 to 1989, mean densities for black abalone populations on 
Anacapa, Santa Rosa, Santa Barbara, and San Miguel islands were 
obtained annually along permanent transects established by the Channel 
Islands National Park (Richards and Davis, 1993). Densities ranged from 
20 to 50 m-2 on early visits, but fell to <10 m-2 
by 1989 for all islands except for San Miguel due to mass mortalities 
associated with withering syndrome. By 1996, local densities fell to 
1.0 m-2 or less on San Miguel Island.
    At San Nicolas Island, densities of black abalones averaged >10 
m-2 at nine monitored sites from 1981 to the early 1990s. 
Withering syndrome was first seen at San Nicolas Island in spring 1992 
(VanBlaricom et al., 1993), and densities declined during the middle 
1990s to <1 abalone m-2 at all sights except one 
(VanBlaricom, unpublished data. The highest local density of black 
abalone recorded among the several studies of island populations in the 
1980s was 296 individuals, primarily adults, in a single quadrat of 1 
m\2\ at San Nicolas Island on November 23, 1988, at site 7 
(VanBlaricom, 1993; unpublished data).
    In recent years, three fishery-independent surveys for black 
abalone have been conducted along the mainland coast and offshore 
islands of Baja California, Mexico. In 2002, a survey for black abalone 
was done at Bahia Tortugas, just south of Punta Eugenia and located at 
the north end of management zone 2. Only four individuals were found, 
ranging in maximum shell diameter from 121 to 152 mm (Sierra Rodriguez 
et al., 2006). A second survey was conducted in 2004. Black abalone 
were found at low densities where they occurred, with 98 percent of 
located animals measuring <120 cm in maximum shell diameter. No animals 
were found with symptoms of withering syndrome during the 2004 survey. 
Black abalone were found along the mainland coast of management zone 1, 
and on Isla Guadalupe and Isla San Jeronimo. The only black abalone 
found in Baja California Sur were at Bahia Tortugas (Sierra-Rodriguez 
et al., 2006).
    The third study was conducted in 2005 in regions of upwelling on 
rocky intertidal benches along the northern Baja California coast from 
Costa Azul to Punta Baja (Raimondi, unpublished data). Twelve sites, 
suspected to have been affected by withering syndrome, were surveyed 
for suitable habitat (rocky crevices) in the mid to low intertidal 
zone, and then timed searches were conducted for black abalone. Black 
abalone were not densely aggregated at any site surveyed in this study; 
however, a large proportion of the individuals found were small (<50 
mm). This evidence of recent recruitment in northern Baja California is 
promising given that there is no evidence of successful recruitment to 
mainland California sites affected by withering syndrome (south of Pt. 
Piedras Blancas in northern San Luis Obispo County). Raimondi 
(unpublished data) hypothesized that the discrepancy between the 
patterns of recruitment in the two regions may be because: (1) healthy 
populations exist somewhere in Mexico (perhaps on offshore islands), 
and these are seeding northern areas; or (2) recruitment dynamics are 
different for withering syndrome-impacted sites in Mexico versus those 
in California. Fresh shells, in some cases containing flesh, were found 
at three of the twelve sites, suggesting that withering syndrome may 
still be impacting areas of Northern Baja California. Large numbers of 
older shells were identified at a few sites, suggesting that black 
abalone were abundant in these areas in the past.

Consideration as a ``Species'' Under the ESA

    The ESA defines a species as ``any species or subspecies of 
wildlife or plants, or any distinct population segment of any species 
of vertebrate fish or wildlife which interbreeds when mature.'' Black 
abalone is a marine invertebrate and is not a subspecies; therefore, it 
may not be subdivided into a listable unit below the taxonomic species 
level.

Status of Black Abalone

    Black abalone have experienced major declines in abundance that 
prompted eventual closure of the commercial and recreational fisheries 
and resulted in local extinctions and low local densities in the 
majority of long-term monitoring studies in California. These declines 
have been particularly severe in the southern California Islands, which 
were major foci for the commercial fishery from 1970-1993 and where 
abalone densities were high (>40 m-2) as late as the mid-
1980s. Although the geographic range of black abalone extends to 
northern California, the vast majority of abalone populations have 
historically occurred south of Monterey, particularly in the Channel 
Islands (Cox, 1960; Karpov et al., 2000). Thus, black abalone 
populations have been severely reduced over an area that covers more 
than half of the species' geographic range, and black abalone from 
these areas historically comprised greater than 90 percent of the 
commercial fishery catch and the majority of the adult black abalone 
populations in California.
    Both the commercial fishery trends and long-term monitoring studies 
indicate that significant declines in black abalone abundance began in 
southern California in the mid-1980s. The first evidence of decline 
came from Palos Verdes in the late 1970s and early 1980s and at Laguna 
Beach in 1985-1986 (Tissot, 1988). However, in the case of Palos 
Verdes, the decline may have been due to other factors (Miller and 
Lawrenz-Miller, 1993). By 1986, declining populations and associated 
observations of withering syndrome had spread to the northern Channel 
Islands, starting at Anacapa, progressing to Santa Rosa, Santa Cruz, 
and Santa Barbara islands, and finally reaching San Miguel Island in 
1989 (Tissot, 1991; Davis et al., 1992; Tissot, 1995). By the early 
1990s, declines were observed on San Nicolas Island (VanBlaricom et 
al., 1993) and

[[Page 1991]]

north of Point Conception on the mainland to Government Point, Santa 
Barbara County (Altstatt et al., 1996). During the 1990s, declines in 
abundance were noted north of Government Point to Cayucos in San Luis 
Obispo County (Altstatt et al., 1996; Raimondi et al., 2002). Noted 
declines were also observed in central Baja California, Mexico, around 
Bahia Tortugas during El Nino events in the late 1980s and 1990s 
(Altstatt et al., 1996; Pedro Sierra-Rodriquez, personal communication) 
and may be linked to declines in the fishery that occurred in the 
1990s. Thus, the spread of withering syndrome is strongly associated 
with declines in abundance and with a pattern of increased northward 
expansion co-occurring with increasing coastal warming and El Nino 
events (Tissot, 1995; Altstatt et al., 1996; Raimondi et al., 2002).
    To our knowledge there are no data available on black abalone 
populations north of San Mateo County on the mainland coast of 
California. As a consequence, we lack information on the remaining 
stocks of black abalone not influenced by withering syndrome. The two 
northernmost sites have either not been studied since 1995 (Ano Nuevo; 
Tissot, 1995) or have only been recently established in large, 
dispersed areas (Pigeon Point; Raimondi and Miner, pers. comm.). 
Establishment of long-term monitoring studies in northern California 
(e.g., in San Francisco County and north of the Golden Gate) would 
serve an important need in documenting northward progression of 
withering syndrome and mass mortality in the northern limit of the 
geographic range of black abalone.
    Natural recovery of severely reduced abalone populations can be a 
very slow process (e.g., Tegner, 1992). This is largely due to the low 
reproductive efficiency of widely dispersed adult populations coupled 
with short larval dispersal distances (see Reproduction and Spawning 
Density above). Therefore, severely reduced populations, in addition to 
providing few reproductive adults, also experience reduced 
effectiveness of fertilization and eventual recruitment of larval 
abalone.
    Moreover, many studies have shown that abalone larvae generally do 
not disperse widely. For example, Prince et al. (1988) and McShane 
(1992) showed a strong correlation between the abundances of adult and 
newly recruited abalone at several sites in South Australia, which 
suggests that larvae are not dispersed very far from their point of 
origin. Similarly, Tegner (1992) showed that recruitment of juvenile 
green abalone was rare in Palos Verdes, California, where adult abalone 
were very uncommon even though abundant adult stocks were found less 
than 30 km away in the Channel Islands. Thus, although more abundant 
black abalone populations occur in central and perhaps northern 
California, decimated stocks in southern California are unlikely to 
receive significant recruitment from these distant populations (Hamm 
and Burton, 2000).
    Studies indicate that a local adult density ``threshold'' exists 
and influences local recruitment. Recovery will largely depend on the 
density of local brood stocks and whether this density is below the 
critical value necessary for successful recruitment (Tegner, 1992). 
Based on field experiments, Babcock and Keesing (1999) showed that 
recruitment failure occurred in greenlip abalone at adult densities of 
0.15-0.20 m-2. Based on empirical data from three long-term 
studies of black abalone in California, recruitment failure occurred 
below adult densities of 0.75-1.10 m-2. Given that the 
majority of populations south of Cayucos in central California are 
below this threshold, many significantly so, it seems unlikely that 
these populations will be able to recover naturally to their former 
abundances, at least in the near future. Moreover, given the continued 
decline of most populations and the continued northward expansion of 
withering syndrome with warming events (Raimondi et al., 2002), it 
seems likely that black abalone populations will continue to decline on 
a large scale.

Assessment of Risk of Extinction

Analysis of Demographic Risk

    The demographic risks that black abalone face were assessed by 
considering four criteria (abundance, growth rate/productivity, spatial 
structure/connectivity, and genetic and life history diversity) and 
other key risks (e.g., threats). These criteria provide a strong 
indication of the level of extinction risk faced by a species. A 
species at very low levels of abundance and with few populations will 
be less tolerant to environmental variation, catastrophic events, 
genetic processes, demographic stochasticity, ecological interactions, 
and other processes. Productivity or a growth rate that is unstable or 
declining over a long period of time may reflect a variety of causes, 
but indicates poor resiliency to future environmental variability or 
change. For species at low levels of abundance, in particular, 
declining or highly variable productivity confers a high level of 
extinction risk. A species with a geographic spatial structure that is 
not widely distributed across a variety of well-connected habitats will 
have a diminished capacity for recolonizing locally extirpated 
populations, and is at increased risk of extinction due to 
environmental perturbations and catastrophic events. A species that has 
lost locally adapted genetic and life-history diversity may lack the 
raw resources necessary to endure short- and long-term environmental 
changes.
    The SRT concluded that black abalone face high levels of risk in 
each of the four demographic criteria. The SRT unanimously scored the 
species' abundance as high risk due to critically low population 
abundance as indicated by local density levels. Severe declines in 
abundance (greater than 90 percent) have occurred at the majority (76 
percent) of long-term monitoring study sites, including all sites in 
southern California (Tissot, 2007). The high risk to abundance is 
attributable to population densities below the minimum threshold 
density necessary for successful fertilization (0.75 - 1.1 
m-2). Additionally, this factor contributes significantly to 
long-term risk of extinction, and, coupled with low spatial 
connectivity between populations (i.e., making recolonization unlikely) 
and the ongoing activity and expansion of withering syndrome, is likely 
to contribute to short-term risk of extinction in the foreseeable 
future.
    The majority of the SRT concluded that there is a very high risk of 
black abalone extinction due to low growth and productivity. Population 
growth is negative in all areas south of Cayucos, California, except 
for two locations in the southern California Islands. Furthermore, all 
sites south of Cayucos, but for the two isolated island locations, have 
exhibited recruitment failure because of local densities below the 
minimum threshold for successful fertilization. This high level of risk 
due to poor growth rate and productivity, by itself, likely indicates a 
high risk of extinction in the near future.
    The majority of the SRT concluded that black abalone are at high to 
very high risk because of compromised spatial structure and population 
connectivity. Dispersion data among local populations indicates that 
there is poor connectivity among populations. Such limited connectivity 
reduces the likelihood that disease resistance to withering syndrome, 
if it exists, will spread to other populations. Furthermore, the poor 
connectivity among populations makes it unlikely that populations 
extirpated by disease or catastrophic events will be recolonized in the 
foreseeable future.

[[Page 1992]]

    The SRT unanimously concluded that black abalone are at high 
extinction risk because of low genetic diversity. Genetic diversity in 
a population is determined by estimating the number of possible alleles 
that may exist at gene loci. Genetic diversity provides a mechanism for 
populations to adapt to their changing environment. Thus, the more 
genetic variation in a population, the better the chance that at least 
some individuals will have the capability to adapt to a new environment 
and will be able to pass this capability on to subsequent generations. 
Loss of genetic diversity in populations may occur because of factors 
that cause a major reduction in abundance and/or isolate a subset of 
individuals from the rest of the population. Genetic diversity has 
likely declined in black abalone populations because of catastrophic 
losses that the species has experienced throughout a large part of its 
range. As a result, populations have become small and more isolated, 
exacerbating the effects of naturally occurring low exchange rates 
between populations because of limited larval dispersal. Overfishing 
and disease have contributed to the loss of genetic diversity within 
black abalone populations, and, as a result, the ability of extant 
(i.e., currently existing) black abalone populations to exhibit 
resilience in the face of other threats, such as other diseases, has 
been compromised. Low genetic diversity, in combination with low 
spatial connectivity between populations, suggests that even if some 
genetic resiliency exists locally, it is not likely to spread and 
establish itself in other extant populations.

Population Modeling: Geographic Spread of Disease vs. Disease 
Resistance

    VanBlaricom et al. (2007) calculated the probability of extinction 
with time using a simple formula that accounts for the main threat that 
black abalone faces, withering syndrome. The probability of extinction 
is considered as a function of two parameters (R=the probability that 
the northward spread of withering syndrome will cease very soon and 
S=the probability that resistance will emerge very soon on a large 
spatial scale in the host), using the logic that if withering syndrome 
alone results in a high enough risk of extinction in a short time 
(i.e., 30 years-the expected life span of black abalone), then that may 
suffice to evaluate whether the species is in danger of extinction 
currently or in the foreseeable future.
    Assuming R and S are independent, the overall probability of 
functional extinction (i.e., the reproductive potential of isolated 
survivors is zero and no viable populations remain) in 30 years based 
on the SRT members' best professional judgment was 95.7 percent. The 
collective view of the SRT is that the risk is at a level where 
functional extinction without active management has a very high 
likelihood of occurring. This probability should not be interpreted as 
a prediction of the demise of the last individual black abalone within 
30 years.

Summary of Factors Affecting the Species

    According to Section 4 of the ESA, the Secretary of Commerce 
determines whether a species is threatened or endangered because of any 
(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 man-made factors affecting its 
continued existence. We examined these factors for their historic, 
current, and/or potential impact on black abalone and considered them, 
along with current species distribution and abundance, to help 
determine the species' present vulnerability to extinction.
Present or Threatened Destruction, Modification, or Curtailment of its 
Habitat or Range
     Most of the threats that result in substrate destruction, such as 
coastal development, recreational access, cable repairs, nearshore 
military operations and benthic community shifts, occur infrequently, 
have a narrow geographic scope, or have uncertain or indirect effects 
on black abalone. Some exceptions may exist in the cases of 
sedimentation and sea level rise in that these threats have the 
potential to produce more widespread impacts, but the certainty that 
these factors will affect black abalone is low. For example, sea level 
rise may result in loss of suitable habitat in a preferred depth range 
because of increased erosion, turbidity, and siltation, but we 
currently lack information to determine whether these habitat changes 
will be important factors for further decline.
    Suboptimal water temperatures are likely to have contributed to the 
decline of black abalone and pose a serious threat to the ability of 
the species to persist because elevated water temperatures are 
correlated with accelerated rates of withering syndrome transmission 
and disease-induced mortality. Water temperatures can become elevated 
because of anthropogenic sources of thermal effluent and long-and 
short-term climate change (e.g., global climate change and El Nino - 
Southern Oscillation). For example, discharge from the Diablo Canyon 
nuclear power plant in San Luis Obispo County, California and recent El 
Nino - Southern Oscillation oceanographic events in the Pacific Ocean 
have produced short-term periods of ocean warming and are associated 
with increased rates of mortality due to withering syndrome over 
relatively small spatial scales. Although there is no explicitly 
documented causal link between the existence of withering syndrome and 
global climate change, patterns observed over the past 3 decades 
suggest that progression of ocean warming associated with large-scale 
climate change may facilitate further and more prolonged vulnerability 
of black abalone to effects of withering syndrome.
    Finally, we view the severity, geographic scope, and level of 
certainty that black abalone are affected by reduced food quality and 
quantity as being relatively low compared to other factors. Davis et 
al. (1992) posited that a key consequence of kelp forest ecosystem 
disruption, due to a variety of reasons such as El Nino events, was 
reduced food supply for black abalone. Although reductions in kelp 
abundance occurred in the early 1980s, subsequent studies (e.g., 
Friedman et al., 1997) have suggested that reduced food supply probably 
did not trigger the mass mortalities caused by withering syndrome. Kelp 
abundances had recovered from El Nino effects in southern California by 
the time withering syndrome was first observed in 1985, and the 
abundant black abalone populations at San Nicolas Island showed no 
response in density to the 1982-1984 El Nino disturbances, despite 
dramatic reductions in kelp abundance near the Island (VanBlaricom, 
1993). Thus, this factor has likely not played an important role in the 
overall decline of the species, and, unless new information surfaces, 
this factor is not believed to pose a significant threat in the future.
Overutilization for Commercial, Recreational, Scientific or Educational 
Purposes
    Throughout most of the species' range, local densities are below 
the critical threshold density required for successful spawning and 
recruitment. This predicament has occurred because of mass mortalities 
due to withering syndrome (see Disease or Predation below) and 
overutilization for

[[Page 1993]]

commercial and recreational purposes (i.e., prior to the fishery 
closure in 1993). Data from abalone fisheries in California and Baja 
California, Mexico, indicate a decline in landings of at least 93 
percent during the 1990s. These reductions, however, may not be 
indicative of declines due only to fishing activities because mass 
mortalities caused by withering syndrome had begun in many locations at 
approximately the same time. Rogers-Bennett et al. (2002) estimate that 
the California abalone fisheries may have contributed up to 99 percent 
of the reduction in black abalone abundance in the United States (see 
Abundance section above). Thus, the estimated take of 3.5 million black 
abalone during commercial and recreational abalone fishing likely 
contributed to the decline of local densities. This threat no longer 
exists in California because the black abalone fisheries were closed in 
1993. The limited information we have from Mexico makes it difficult to 
ascertain the relative importance of fishing to overall species 
decline.
Disease or Predation
    Withering syndrome in black abalone is caused by a Rickettsia-like 
prokaryotic organism, Candidatus Xenohaliotis californiensis' (Gardner 
et al., 1995; Friedman et al., 1997; Friedman et al., 2000; Friedman et 
al., 2002). Candidatus Xenohaliotis californiensis (hereafter ``abalone 
rickettsia'') occurs in epithelial cells of the gastrointestinal tract. 
Infected symptomatic animals are unable to transfer digested food 
materials from the gut lumen into the epithelial cells and beyond, 
resulting in malnutrition, dramatic loss of tissue mass, and eventual 
death. Physiological manifestations of withering syndrome include 
reduced food intake and oxygen consumption, and increased ammonia 
excretion (Kismohandaka et al., 1993). The same pathogen is known to 
cause symptoms of withering syndrome in red abalone, and mortality rate 
is positively associated with water temperature in both red and black 
abalone (Moore et al., 2000a, b; Vilchis et al., 2005). Andree et al. 
(2000) have developed a rapid DNA-based test for the pathogen that 
causes withering syndrome, allowing detection of infections prior to 
onset of clinical symptoms in both black and red abalone. Moore et al. 
(2001) have developed a histological method for rapid quantification of 
the intensity of infections by the pathogen that causes withering 
syndrome.
    In wild animals symptomatic for withering syndrome, weakness 
resulting from the disease may cause the individual to lose the 
typically secure grip on the rocky substratum in response to wave 
impacts, allowing attack by predators or scavengers before the 
individual succumbs to the disease itself. Transfer of pathogens from 
animal to animal is fecal to oral on a local scale, and is therefore 
likely facilitated by aggregation of abalone in natural habitats. 
Transmission pathways on large spatial scales are entirely unknown at 
present. The pathogen for withering syndrome is now reported to be 
endemic to all the coastal marine waters of central (Friedman and 
Finley, 2003) and southern California (Moore et al., 2002) south of San 
Francisco. Information from Isla de Cedros and Islas San Benito, Baja 
California, Mexico, on pink (Haliotis corrugata Wood, 1828; termed 
``yellow'' in Mexico) and green (termed ``blue'' in Mexico) abalone 
indicated the presence of abalone symptomatic for withering syndrome, 
and the presence of abalone rickettsia in tissue samples, for both 
species (Tinajero et al., 2002). Recent data indicate the presence of 
abalone rickettsia in farmed and wild green ormer (Haliotis 
tuberculata) symptomatic for withering syndrome at a number of 
locations in the coastal marine waters of western Europe (Balseiro et 
al., 2006).
    Evidence of effects of withering syndrome on black abalone was 
first noticed along the south shore of Santa Cruz Island in 1985, when 
a fisherman noticed a large number of dying black abalone and empty 
shells (Lafferty and Kuris, 1993). The primary symptoms of disease 
noted at the time included pedal atrophy and a diminished ability to 
maintain a grip on rocky substrata. Haaker et al. (1992) and Richards 
and Davis (1993) described the first observations of mass mortalities 
of black abalone in previously monitored populations on the island 
shores of Channel Islands National Park in 1986, and broadened the list 
of recognized symptoms to include epipodial and mantle discoloration, 
and lack of response to tactile stimulation. Haaker et al. (1992) were 
the first authors to apply the term ``withering syndrome'' to the suite 
of symptoms and consequent mass mortalities observed in the field. 
Between 1985 and 1992, mass mortalities occurred at San Miguel, Santa 
Rosa, Anacapa, Santa Barbara, and San Clemente Islands, in all cases 
with symptoms indicating withering syndrome (Davis et al., 1992; Haaker 
et al., 1992; Lafferty and Kuris, 1993; Richards and Davis, 1993). 
Evidence of withering syndrome was first seen at San Nicolas Island in 
spring 1992 (VanBlaricom et al., 1993) and was followed by widespread 
mass mortalities at the Island in the middle 1990s (Tissot, 2007). The 
delayed appearance of withering syndrome at San Nicolas Island, as 
compared to the other southern California Islands, remains unexplained 
but may have reflected patterns of dispersal by disease propagules. To 
our knowledge, no effort has been made to assess effects of withering 
syndrome at Santa Catalina Island, though the Island historically 
supported black abalone populations.
    The first reported occurrence of significant numbers of black 
abalone with symptoms of withering syndrome on the California mainland 
was in San Luis Obispo County in 1988 (Steinbeck et al., 1992). 
Afflicted animals were found primarily within Diablo Cove, which 
receives warmed effluent seawater from the cooling system of a nearby 
nuclear power plant. A mass mortality of black abalone occurred at the 
site between 1988 and 1989, with mortality rates correlating well to 
local patterns of sea temperature elevation associated with power plant 
effluent.
    Since the mid-1990s withering syndrome has appeared sequentially in 
progressively more northward populations of black abalone on the 
mainland California coast (Altstatt et al., 1996; Raimondi et al., 
2002; Miner et al., 2006). The most recent observations available 
suggest that significant mortalities of black abalone associated with 
withering syndrome have occurred at least as far north as Pt. Piedras 
Blancas in northern San Luis Obispo County near San Simeon. Surveys for 
the microorganism responsible for withering syndrome have found 
positive results as far north as San Francisco (Finley and Friedman, 
2000; Friedman and Finley, 2003).
    In the vast majority of cases where long-term monitoring data are 
available, the appearance of animals symptomatic for withering syndrome 
in a population lead inevitably to rapid and dramatic declines in 
population size, most often in excess of 90 percent (Tissot, 2007). The 
pattern has been documented for black abalone populations throughout 
the range in California. Reports indicate similar trends for black 
abalone populations in Mexico. As noted earlier, the exceptions are at 
San Miguel Island, where rates of decline at some long-term study sites 
have been atypically slow, and at one location each on Santa Cruz and 
San Nicolas islands. At Santa Cruz Island, a recruitment event in 2004 
at Willows Anchorage produced an increase in local densities that 
persisted at least until this writing. At San Nicolas Island, black 
abalone numbers

[[Page 1994]]

at study site 8 (as described by VanBlaricom, 1993) have increased and 
experienced recruitment each year since reaching a low point in 2001 
due to withering syndrome, except for a small decline between surveys 
in 2006 and 2007. The pattern at this site can be plausibly interpreted 
as a possible result of genetically-based disease resistance on a local 
scale. These observations are exceptions that suggest the potential for 
resilience and recovery in populations reduced dramatically by 
withering syndrome. However, Tissot's (2007) litany of negative impacts 
of withering syndrome in multiple locations across the entire range of 
the species, coupled with evidence of increasing geographic scope of 
impact, argues to the contrary. The preponderance of evidence indicates 
that withering syndrome continues to damage the size and sustainability 
of black abalone populations on a large scale, with little plausible 
basis for any predictions of reversal.
    Prior to the appearance of withering syndrome there was little 
evidence of significant diseases in black abalone (Haaker et al., 
1992). There is now substantial concern among scientists and marine 
resource managers about the emergence of virulent diseases in marine 
organisms on a global scale, in association with ocean warming in 
recent decades (e.g., Harvell et al., 1999; Harvell et al., 2002). 
Recent surveys of the literature suggest that the frequency of 
reporting of new diseases has increased for several major marine taxa, 
including mollusks (e.g., Ward and Lafferty, 2004). The appearance of 
withering syndrome is consistent with the reported pattern. As 
described above, mortality rates associated with withering syndrome 
often correlate to positive anomalies in sea surface temperature. 
Nevertheless, there is no explicitly documented causal link between the 
existence of withering syndrome and global climate change.
    We conclude that withering syndrome has been and continues to be 
the primary threat contributing to the decline of black abalone. The 
disease has caused mass mortality and near extirpation of populations 
throughout most of the species' range, and the disease continues to 
spread to populations in Monterey County and to the north. The rate at 
which the disease is spreading northward will likely be exacerbated by 
suboptimal (i.e., warmer) water temperatures that may result due to a 
variety of factors.
    Abalone face non-anthropogenic predatory pressure from a number of 
consumer species such as gastropods, octopuses, lobsters, sea stars, 
fishes and sea otters (Ault, 1985; Estes and VanBlaricom, 1985; 
Shepherd and Breen, 1992). At San Nicolas Island, VanBlaricom 
(unpublished observations) has observed directed predation on black 
abalone in rocky intertidal habitats by the ochre star Pisaster 
ochraceus [Brandt, 1835]), the octopus Octopus bimaculatus (Verrill, 
1883), a large cottid fish, the cabezon (Scorpaenichthys marmoratus 
Girard, 1854), and a shorebird, the black oystercatcher Haematopus 
bachmani Audubon, 1838. In addition, VanBlaricom (unpublished 
observations) has observed ingestion of small black abalone by three 
taxa normally viewed as herbivores: the lined shore crab Pachygrapsus 
crassipes (Randall, 1839); the purple sea urchin Strongylocentrotus 
purpuratus (Stimpson, 1857); and the turban snails Tegula spp.
    Despite the large number of identified predators on abalone, we are 
aware of no studies that estimate mortality rates of black abalone in 
association with the predator species that have been identified. While 
the effects of sea otter predation on red abalone are well documented, 
there are few data available to evaluate relationships of sea otters 
with other species of abalone in California. Given that black abalone 
overlap in habitat use, size distributions, and ecological attributes 
with red abalone is limited, the relationship between sea otters and 
black abalone is uncertain. Sea otters are known to feed on black 
abalone, but the quantitative ecological strength of the interaction 
has not been directly investigated and remains poorly known.
    Black abalone have been exposed to varying predation pressure 
through time, and this pressure is likely to continue. However, in the 
past, black abalone populations were much more robust and able to 
absorb losses due to predation without compromising viability. Now that 
the few remaining populations are smaller, more isolated, and still 
declining throughout the range, predation may pose risk to the future 
survival of the species. In addition, non-anthropogenic predation could 
limit the effectiveness of future recovery efforts by interacting with 
other limiting factors.
Inadequate Regulatory Mechanisms
    There is evidence suggesting that aquaculture operations have 
provided a pathway for the spread of withering syndrome, and, unless 
the industry is carefully regulated in the future, may continue to do 
so. Past State and Federal regulations were not adequate to prevent the 
spread of the disease within and outside the United States through 
importation of infected animals from one aquaculture facility to 
another and outplanting of infected animals from aquaculture facilities 
to the wild. It is through the latter pathway that abalone rickettsia 
may have been introduced to two healthy populations of black abalone 
north of San Francisco (Friedman and Finley, 2003), placing those 
populations at higher risk of extinction.
    Recent state regulations to carefully monitor the health of abalone 
at aquaculture facilities and control the importation/exportation of 
abalone between facilities will likely reduce the threat that the 
aquaculture industry poses in the future. Currently, the state monitors 
aquaculture facilities for introduced organisms and disease on a 
regular basis. There is also a restriction on out-planting of abalone 
from facilities which have not met certification standards. If new 
state regulations to carefully monitor aquaculture facilities are 
effective, the future threat that they pose to black abalone will be 
limited. In fact, aquaculture may emerge as being an important, and 
possibly the only effective recovery tool, for restoring black abalone 
populations through captive propagation and enhancement efforts.
    Purposeful illegal harvest, typically termed poaching, has been a 
source of mortality for black abalone throughout their range since the 
establishment of harvesting regulations by the State of California. The 
chronic virtual absence of black abalone populations from highly 
accessible intertidal habitats near human population centers in 
California during the twentieth century can plausibly be viewed as 
evidence for the importance of poaching as a source of abalone 
mortality.
    Since the closure of the California black abalone fishery in 1993, 
a number of black abalone poaching cases along the California mainland 
coast, particularly in the northern portion of the black abalone's 
geographic range, have been documented by the California Department of 
Fish and Game (CDFG) from 1993-2003 (Taniguchi, unpublished data). Some 
of these cases resulted in well-publicized arrests and trials of black 
abalone poachers. These events often involved removals of tens to 
hundreds of abalone, across al