Taking and Importing Marine Mammals; Taking Marine Mammals Incidental to the Explosive Removal of Offshore Structures in the Gulf of Mexico, 34875-34894 [E8-13898]

Agencies

• DEPARTMENT OF COMMERCE
• National Oceanic and Atmospheric Administration

[Federal Register Volume 73, Number 119 (Thursday, June 19, 2008)]
[Rules and Regulations]
[Pages 34875-34894]
From the Federal Register Online via the Government Printing Office [www.gpo.gov]
[FR Doc No: E8-13898]


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DEPARTMENT OF COMMERCE

National Oceanic and Atmospheric Administration

50 CFR Part 216

[Docket No. 080302357-8703-01; I.D. 030905A]
RIN 0648-AT79


Taking and Importing Marine Mammals; Taking Marine Mammals 
Incidental to the Explosive Removal of Offshore Structures in the Gulf 
of Mexico

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

ACTION: Final rule.

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SUMMARY: NMFS, upon application from the Minerals Management Service 
(MMS), is issuing regulations to govern the unintentional takings of 
small numbers of marine mammals incidental to explosive severance 
activities at offshore oil and gas structures in the Gulf of Mexico 
(GoM). Issuance of regulations, and Letters of Authorization (LOAs) 
under those regulations, governing the unintentional incidental takes 
of marine mammals in connection with particular activities is required 
by the Marine Mammal Protection Act (MMPA) when the Secretary of 
Commerce (Secretary), after notice and opportunity for comment, finds, 
as here, that such takes will have a negligible impact on the affected 
species or stocks of marine mammals and will not have an unmitigable 
adverse impact on their availability for taking for subsistence uses, 
and if the Secretary sets forth the permissible methods of taking and 
other means of effecting the least practicable adverse impact on 
affected marine mammal species or stocks and their habitat, and on the 
availability of such species or stocks for subsistence uses.
    These regulations do not authorize offshore structure removal 
activities as such authorization is not within the jurisdiction of the 
Secretary. Rather, NMFS' regulations together with LOAs authorize the 
unintentional incidental take of marine mammals in connection with this 
activity.

DATES: Effective from July 21, 2008 through July 19, 2013.

ADDRESSES: A copy of the MMS application containing a list of the 
references used in this document may be obtained by writing to Mr. P. 
Michael Payne, Chief Permits, Conservation and Education Division, 
Office of Protected Resources, National Marine Fisheries Service, 1315 
East-West Highway, Silver Spring, MD 20910-3225, by telephoning one of 
the contacts listed under FOR FURTHER INFORMATION CONTACT, or at: 
https://www.nmfs.noaa.gov/pr/permits/incidental.htm.
    Documents cited in this final rule may also be viewed, by 
appointment, during regular business hours (M-F, 8 a.m. until 4:30 
p.m., except Federal holidays) at this address.A copy of MMS' 
Programmatic Environmental Assessment (PEA) is available on-line at: 
https://www.gomr.mms.gov/homepg/regulate/environ/nepa/2005-013.pdf.
    Comments regarding the burden-hour estimate or any other aspect of 
the collection of information requirement contained in this rule should 
be sent to NMFS via the means stated above, and to the Office of 
Information and Regulatory Affairs, Office of Management and Budget 
(OMB), Attention: NOAA Desk Officer, Washington, DC 20503, David_
Rostker@eap.omb.gov.

FOR FURTHER INFORMATION CONTACT: Kenneth Hollingshead, NMFS, at 301-
713-2289, ext 128 or Ken.Hollingshead@noaa.gov.

SUPPLEMENTARY INFORMATION:

Background

    Section 101(a)(5)(A) of the MMPA (16 U.S.C. 1361 et seq.) directs 
the Secretary of Commerce (Secretary) to allow, upon request, the 
incidental, but not intentional taking of small numbers of marine 
mammals by U.S. citizens who engage in a specified activity (other than 
commercial fishing) within a specified geographical region if certain 
findings are made and regulations are issued.
    An authorization will be granted for periods of 5 years or less if 
the Secretary finds that the taking will have a negligible impact on 
the species or stock(s) and will not have an unmitigable adverse impact 
on the availability of the species or stock(s) for taking for 
subsistence uses, and if regulations are prescribed setting forth the 
permissible methods of taking and other means of effecting the least 
practicable adverse impact (i.e., mitigation) the requirements 
pertaining to the monitoring and reporting of such taking.
    NMFS has defined ``negligible impact'' in 50 CFR 216.103 as ``an 
impact resulting from the specified activity that cannot be reasonably 
expected to, and is not reasonably likely to, adversely affect the 
species or stock through effects on annual rates of recruitment or 
survival.''

Summary of Request

    On February 28, 2005, NMFS received an application from MMS (MMS, 
2005a) requesting, on behalf of the offshore oil and gas industry, 
authorization under section 101(a)(5)(A) of the MMPA to take marine 
mammals by harassment incidental to explosive severance activities at 
offshore oil and gas structures in the GoM outer continental shelf 
(OCS). Except for certain categories of activities not pertinent here, 
the MMPA, 16 USC 1362(18)(A), defines ``harassment'' as:

    any act of pursuit, torment, or annoyance which (i) has the 
potential to injure a marine mammal or marine mammal stock in the 
wild [Level A harassment]; or (ii) has the potential to disturb a 
marine mammal or marine mammal stock in the wild by causing 
disruption of behavioral patterns, including, but not limited to, 
migration, breathing, nursing, breeding, feeding, or sheltering 
[Level B harassment].

Description of the Activity

    During exploration, development, and production operations for 
mineral extraction in the GoM OCS, the seafloor around activity areas 
becomes the repository of temporary and permanent equipment and 
structures. In compliance with OCS Lands Act (OCSLA) regulations and 
MMS guidelines, operators are required to remove or ``decommission'' 
seafloor obstructions from their leases within

[[Page 34876]]

one year of lease termination or after a structure has been deemed 
obsolete or unusable. To accomplish these removals, it is necessary to 
(1) mobilize necessary equipment and service vessels, (2) prepare the 
decommissioning targets (e.g., piles, jackets, conductors, bracings, 
wells, pipelines, etc.), (3) sever the target from the seabed and/or 
sever it into manageable components, (4) salvage the severed 
portion(s), and (5) conduct final site-clearance verification work.
    There are two primary methodologies used in the GoM for cutting 
decommissioning targets; nonexplosive and explosive severance. 
Nonexplosive methods include abrasive cutters (sand and abrasive-water 
jets), mechanical cutters (e.g., carbide or rotary), diamond wire 
cutting devices, and cutting facilitated by commercial divers using 
arc/gas torches. Though relatively time-consuming and potentially 
harmful to human health and safety (primarily for diver severances), 
nonexplosive-severance activities have little or no impact on the 
marine environment and would not result in an incidental take of marine 
mammals (MMS, 2005b (the MMS Final PEA)). A description of non-
explosive severing tools and methods can be found in both MMS, 2005a; 
and MMS, 2005b (see ADDRESSES).
    Explosive-severance activities use specialized charges to achieve 
target severance. Severance charges can be deployed on multiple targets 
and detonated nearly simultaneously (i.e., staggered at an interval of 
900 msec), effecting rapid severance. Coupled with safe-handling 
practices, the reduced ``exposure time'' and omission of diver cutting 
also makes explosive severance safer for offshore workers. However, 
since the underwater detonation of cutting charges generates 
potentially damaging pressure waves and acoustic energy, explosive-
severance activities have the potential to result in incidental take of 
nearby marine mammals. For this reason, MMS has requested an incidental 
take authorization governing explosive-severance activities conducted 
under OCSLA structure decommissionings.
    Decommissioning operations conducted under OCSLA authority can 
occur on any day of a given year. Operators often schedule most of 
their decommissionings from June to December (approximately 80 percent) 
to take advantage of the often calm seas and good weather and the time 
period when structure installations tend to decrease.
    Depending upon the target, a complete decommissioning operation may 
span several days or weeks, of which only a few seconds is actually 
attributed to the explosive-severance activity or ``detonation event'' 
for most removal targets (even those with multiple severances) because 
of charge staggering. For complex targets or in instances where the 
initial explosive-severance attempts are unsuccessful, more than one 
detonation event may be necessary per decommissioning operation. Even 
though hours or days may pass to allow for necessary mitigation 
measures and redeployment of new charges, each detonation event would 
similarly last only for a few seconds.
    During the 10-year period from 1994-2003, there were an average of 
156 platform decommissionings per year, with over 60 percent involving 
explosive-severance activities (see Table 4 in MMS, 2005a). In addition 
to historical activity averages, many of the older, nominally-producing 
structures in the mature GoM oil fields are nearing decommissioning 
age; this will result in an increase in removal operations in future 
years. Despite advancements in nonexplosive-severance methods and the 
additional requisite marine protected species mitigation measures, MMS 
expects explosive-severance activities to continue for at least 63 
percent of all platform removals for the foreseeable future. (See 
Appendix A of MMS; Final PEA for additional forecasting information).
    In addition to platform removals, based upon a review of the 
historical trends, industry projections, and recent forecast modeling, 
MMS estimates that between 170 and 273 explosive well-severance 
activities would occur annually over the next 5 years (see Table 7 in 
MMS' MMPA Application).

Comments and Responses

    On April 7, 2006 (71 FR 17790), NMFS published a proposed rule on 
the taking of marine mammals incidental to offshore structure removals. 
During the 30-day public comment period on the proposed rule, comments 
were received from the Marine Mammal Commission (Commission), the Gulf 
Restoration Network (GRN), the American Petroleum Institute and the 
National Ocean Industries Association (API/NOIA), LIS Energy Services 
(LIS), Offshore Operators Committee, DEMEX, Newfield Exploration 
Company, and Explosive Service International. The comments of these 
organizations and the specific recommendations by the Commission are 
addressed next.

Activity Concerns

    Comment 1: The GRN notes that the Government Accounting Office 
(GAO) found that 192 of 570 OCS oil and gas structures were removed by 
non-explosive methods between 1987 and 1992. GRN believes that serious 
consideration of the use of non-explosive removal techniques would 
eliminate potential negative impacts to marine mammal populations and 
should be required before companies are allowed to use explosive 
techniques.
    Response: The use of non-explosive methods for offshore oil-and-gas 
structure removals was fully discussed in MMS' Final PEA and cited 
supporting documentation on this matter. MMS determined that, between 
1994 and 2003, an average of 156 platforms were removed annually. Of 
that total, on average 58 platforms were removed annually by non-
explosive methods (37 percent). While NMFS encourages operators to use 
non-explosive methods whenever feasible and practical, NMFS and MMS 
recognize that the use of nonexplosive methods leads to greater human 
health and safety concerns, primarily because (1) divers are often 
required (for torch/underwater arc cutting), (2) more personnel are 
required to operate cutting equipment (increasing the risk of injury), 
(3) lower success rates require that additional cutting attempts be 
made, and (4) cutters can only sever one target at a time, taking on 
average 30 minutes to several hours for a complete cut. Considering the 
low level of impact on affected marine mammal stocks by this activity 
and the inherent safety risk of using non-explosive methods, NMFS has 
determined that the structure removal operator needs the flexibility to 
determine the best method for a structure-removal operation.
    Comment 2: The GRN states that the GAO found that the costs and 
benefits of these alternative methods of removal had not been 
adequately studied and that the MMS may have encouraged the use of 
explosives as the preferred method of removal.
    Response: In response to a requirement in NMFS' 1995 rulemaking on 
this matter (60 FR 53753, October 17, 1995), MMS contracted for a study 
to be conducted on the operational and socioeconomic impacts of non-
explosive removal of offshore structures. The information in that 
report (Twachtmann Synder and Byrd and Center for Energy Studies, 2003) 
was subsequently incorporated into the MMS PEA. A copy of that report 
is available via written request to NMFS (see ADDRESSES) or on MMS' 
website at: https://www.gomr.mms.gov/PDFs/2004/2004-074.pdf.

[[Page 34877]]

Marine Mammal Impact Concerns

    Comment 3: While the Commission supports NMFS' preliminary 
determinations and supports the various proposed mitigation and 
monitoring activity scenarios, the Commission recommends NMFS clarify 
the apparent discrepancies between the numbers and species of animals 
requested by MMS to be taken by Levels A and B harassment versus the 
numbers and species proposed to be authorized by NMFS in its preamble 
to the proposed rule and in the proposed rule itself. NMFS estimates 
that one bottlenose dolphin would be taken by Level A harassment and up 
to 457 marine mammals of 28 species by Level B harassment. This differs 
from MMS' request for 5 bottlenose dolphins, one Atlantic spotted 
dolphin and one pantropical spotted dolphin by Level A harassment over 
the 5-year period of the proposed regulations and up to 457 marine 
mammals annually of the following species by Level B harassment: 227 
bottlenose dolphins, 65 Atlantic spotted dolphins, 77 pantropical 
spotted dolphins, 27 Clymene dolphins, 12 rough-toothed dolphins, 14 
striped dolphins, 15 melon-headed whales, 10 pilot whales, 5 spinner 
dolphins, 3 Risso's dolphins, and 2 sperm whales.
    Response: NMFS has amended the preamble to this document and the 
regulations to conform with the request of the MMS, which is based on a 
clear analysis for projected incidental harassment takes provided in 
its application.
    Comment 4: The Commission recommends that NMFS evaluate and discuss 
the potential for cumulative indirect effects on marine mammals that 
could result from the disturbance of hazardous substances that 
accumulate around production platforms. Disturbance of sediments during 
decommissioning may release these hazardous substances into the water 
column where they could enter and potentially affect the food chain up 
to top-level predators, including marine mammals.
    Response: The disturbance of sediments during decommissioning 
activities is discussed in the MMS' Final PEA on structure removals. 
The MMS Final PEA notes that resuspension of sediments would be limited 
in both time and space (24 hr for a water column 4 m (13 ft) off the 
bottom and above, and 7-10 days for the water layer contained in the 
first 4 m (13 ft) off the seafloor). Resuspension of sediments would 
extend about 1000 m (3281 ft) away from the structure. The MMS Final 
PEA notes:

    Increased water turbidity and mobilization of sediments 
containing drilling muds and cuttings are both likely due to 
resuspension of bottom sediments following an explosive severance 
activity or structure salvaging. The magnitude and extent of 
sediment resuspension will depend on the hydrographic parameters of 
the area, the location of removal (above or below mud-line), and the 
size and composition of the bottom sediments. The impacts to water 
quality from resuspension of hydrocarbon wastes is expected to be 
temporary and limited to the immediate, localized structure removal 
site. Due to the temporary nature of water quality changes following 
decommissioning activities, no significant impacts to fish, marine 
mammals or sea turtle resources are expected.

    For cumulative impacts, that document states:

    Based on the cumulative impact scenarios and assessments 
presented in the multi-sale EIS's, it is expected that the 
incremental contribution of potential impacts from decommissioning 
activities (i.e., vessel discharges, re-suspended sediments, and 
expended explosive/nonexplosive-severance products) would not result 
in significant cumulative impact on the water quality of the Gulf of 
Mexico OCS.

    Based on the information in the MMS Final PEA, NMFS believes it 
very unlikely that there will be significant cumulative effects from 
resuspension of bottom sediments due to explosive structure removals on 
marine mammals.
    Comment 5: The API/NOIA note that the ``safe'' peak pressure level 
to avoid physical injury recommended by Ketten (1995) is 100 psi (237 
dB re 1 microPa, or about 212 dB re 1 microPa\2\-s). The preamble to 
the proposed rule states that Level A harassment is assumed to occur at 
an energy flux density value of 1.17 in-lb/in\2\ (which is about 205 dB 
re 1 microPa\2\-s). There appears to be a discrepancy in the dB values 
quoted as ``safe'' versus that at which Level A harassment occurs.
    Response: Estimating impacts to marine mammals from underwater 
detonations is difficult due to complexities of the physics of 
explosive sound under water and the limited understanding with respect 
to hearing in marine mammals. Compounding to the difficulty, NMFS 
understands that Ketten (1995) contains air-to-water conversion errors. 
For injury, NMFS uses two criteria: eardrum rupture (i.e., tympanic 
membrane [TM] rupture) and onset of slight lung injury, whichever is 
more conservative. In most cases, TM rupture is more likely at lower 
pressures and is used for this action to indicate the onset of injury. 
The threshold for TM rupture corresponds to a 50 percent rate of 
rupture (i.e., 50 percent of animals exposed to the level are expected 
to suffer TM); this is stated in terms of an energy flux density (EFD) 
value of 1.17 in-lb/in\2\ (approximately 205 dB re 1 Pa\2\-s). This 
recognizes that TM rupture is not necessarily a serious or life-
threatening injury, but is a useful index of possible injury that is 
well-correlated with measures of permanent hearing impairment (e.g., 
Ketten (1998) indicates a 30 percent incidence of permanent threshold 
shift [PTS] at the same threshold). Ketten (1998) also found that peak 
blast overpressures of 1,034 kPa (150 psi) were associated with 50 
percent tympanic membrane rupture. Based on the incidence of eardrum 
rupture in sheep exposed to underwater explosions by Richmond et al. 
(1973), Craig (2001) estimated that 50 percent tympanic membrane 
rupture would occur at an energy flux density of 1.17 in-lb/in\2\ 
(about 205 dB re 1 microPa\2\-s). While this latter criterion is more 
conservative than the 100 psi (237 dB re 1 Pa) derived by Ketten 
(1995), it was used in the WINSTON CHURCHILL ship shock trial Final EIS 
as the criterion for auditory injury, and is used by MMS and NMFS in 
this action based on the CHURCHILL findings (see 66 FR 22450, May 4, 
2001).
    Comment 6: The API/NOIA note that MMS and NMFS are adopting 
``without modification'' NMFS' acoustic criteria (for explosives) 
because they are conservative. To confirm the conservative nature of 
these values, they are contrasted in the same paragraph with much 
higher values reported by Finneran et al. (2003) for experimental 
exposures of a single bottlenose dolphin. This adoption of 
``conservative'' criteria becomes compounded by other conservative 
assumptions used in subsequent discussions.
    Response: NMFS agrees that the dual criteria of a 12-psi peak 
pressure and a received energy greater than 182 dB re 1 microPa\2\-s 
within any 1/3-octave band are conservative. The research mentioned by 
API/NOIA (Finneran et al., 2003) was completed after the Navy released 
the WINSTON CHURCHILL Final EIS and MMS finished modeling the impacts 
from explosives on marine mammals (incorporated into the MMS Draft 
PEA). Therefore, unavailable for use without incurring a significant 
delay by MMS in completing the Final PEA. NMFS intends to utilize any 
new empirical research prior to renewal of these new 5-year 
regulations.
    Comment 7: The API/NOIA notes that NMFS' conservative criteria 
derive from open water detonations of a 10,000 lb charge in open water 
used for the WINSTON CHURCHILL shock trial. ``Conservative'' safety 
zones based on

[[Page 34878]]

the CHURCHILL shock trial and propagation models based on similar 
charge weight and placement assumptions for structure removals, grossly 
overestimates impacts from structure removal activities (which are much 
smaller charges).
    Response: NMFS disagrees. The criteria used to determine the safety 
zones for the WINSTON CHURCHILL shock trial safety zones were the same 
criteria used for the structure removal program; however, the safety 
zones established for each activity were based on their respective 
explosive weight (10,000 lbs (4536 kg) for the CHURCHILL shock trial 
versus less than 500 lbs (227 kg) for this action). In the shock trial 
program, the Navy uses its REFRMS model to estimate zones of impact 
while MMS used the UnderWater Calculator (UWC), which is a verified 
model that predicts the detonation pressure/energy propagation 
resulting from underwater detonations, that is capable of propagation 
modeling for explosives contained within pipes of varying diameters and 
wall thicknesses. The integration of the UWC model with Marine 
Acoustics Inc.'s Acoustic Integration Model (AIM) made it possible to 
perform comprehensive, 3-dimensional modeling of the effects of 
explosive-removal activities on marine mammals. For more information, 
please refer to Chapter 4 of the MMS Final PEA.
    The Navy recently released a new Draft EIS for the shock trial of 
the USS MESA VERDE (for a copy go to https://www.mesaverdeeis.com), 
which contains slightly modified explosives criteria based on 
explosives research completed since the WINSTON CHURCHILL Final EIS was 
released. These new criteria may be used by MMS and NMFS in future 
explosive removal regulations.
    Comment 8: The API/NOIA asks for the source of the criterion for 
Level A harassment definition as tympanic membrane rupture and lung 
hemorrhage in a 27 lb. (12.2 kg) dolphin calf. How did this criteron 
become adopted by NMFS?
    Response: As noted in the MMS Final PEA (page 103-104), the source 
for the calf criterion is Young (1991). Young used the results from 
experimental data on terrestrial animals to develop a computer 
simulation model for determining the region of injury to marine mammals 
subjected to an underwater explosion. For a 50-lb (22.7 kg) explosive 
charge, the model's contour plot indicated that slight injury could 
occur 936 ft (285.3 m) and 1,352 ft (412.1 m) from the explosion in 
open water for an adult and calf bottlenose dolphin, respectively. 
Because the more conservative criterion was for the calf, that was the 
criterion used. This reference was first cited for offshore structure 
removals in API's 1995 application for taking marine mammals incidental 
to this activity.

Proposed Rule Concerns

    Comment 9: DEMEX recommends that sound energy flux and sound 
pressure level (SPL) should be referenced in their common scientific 
format of units (i.e., decibels, dB). For example, Level A harassment 
should be stated as: an energy flux density of above 205 dB re 1 
microPa\2\-sec in any 1/3 octave band and Level B harassment is an EFDL 
(energy flux density level) above 182 dB re 1 microPa\2\-sec in any 1/3 
octave band. Both are unnecessary as SPL is an inherent component of 
the Energy Flux Density. SPLs are an instantaneous reference and do not 
reflect intensity or duration. EFDL values readily give a true 
description of the sound event and potential harm that may be caused.
    Response: NMFS believes that the EFDL concept is unfamiliar to many 
of the reviewers of underwater acoustics authorizations under the MMPA. 
Accordingly, NMFS has provided both SEL and SPL units where possible.
    Comment 10: DEMEX notes that the proposed rule does not have a 
provision to handle emergency situations such as for human safety and 
weather. DEMEX recommends a provision within the rule that would allow 
detonation of an explosive device because of weather or safety to 
personnel, and even leaving the project with explosives still on 
location.
    Response: Leaving the charge unexploded in place is unlikely to 
result in the taking of marine mammals so a provision in NMFS' 
regulations is not necessary. The regulations do not allow for the take 
of marine mammals incidental to use of explosives absent the necessary 
mitigation and monitoring requirements. The industry did not provide 
documentation during the public comment period on the NMFS Notice of 
Receipt on this action or on the MMS PEA substantiating that an 
exception, due to weather or safety, was necessary. Since industry has 
not provided any information on the processes, conditions, or protocols 
by which ``emergency detonation'' should be allowed, NMFS has 
determined that exceptions to required mitigation and monitoring are 
not warranted at this time.
    Comment 11: DEMEX notes that the proposed rule does not have a 
provision for shooting internal strings within oil wells. DEMEX 
believes that small scale shooting of internal strings will not have 
any effect on the environment. However, this particular process is used 
during plugging and abandonment (P&A) activities that are not governed 
by the proposed regulations.
    Response: Since P&A activities related to ``downhole'' casing work 
or perforation guns generally employ very small charges detonated 
several dozen to hundreds of feet below the mudline, NMFS does not 
believe that the activity will have an impact on marine mammals or 
result in incidental take. Therefore, the activities need not be 
governed by these regulations. However, if any P&A activities involve 
the explosive severance of internal strings as it relates to a 
subsequent conductor or well-stub severance, they may occur close 
enough to the mudline and utilize enough explosives to have the 
potential to harm marine mammals. In these cases, MMS' environmental 
review procedures for structure removal permit applications or 
Applications for Permit to Modify (APMs) for P&A work are designed to 
analyze the severance activities and proscribe the appropriate level of 
mitigation measures for marine protected species.
    Comment 12: DEMEX asks who is required to have an LOA? Is it the 
structure operator, the primary removal contractor, the explosives 
contractor, or some combination of these? API/NOIA recommends that as a 
practical matter it would be prudent to require that the person-in-
charge of explosive operations have a copy of the appropriate LOA 
available for inspection on site.
    Response: An LOA should be held by either the company responsible 
for the offshore structure or the contractor hired by the company to 
remove the structure. However, the entity holding the LOA needs to have 
onsite representation to ensure that the requirements of the LOA and 
these regulations are carried out.
    Comment 13: DEMEX notes that Table 2 (in the preamble of the 
proposed rule) for the Small Blasting Category, >10-20 lbs, BML (Below 
Mudline) is a B1 & B2 Scenario which requires a helicopter survey. 
DEMEX believes it would be more of an incentive for explosive shaped 
charges if the helicopter survey was not required.
    Response: The MMS and NMFS protected species scientists determined 
that aerial surveys would be necessary to ensure protection, to the 
maximum extent practicable, of marine mammals and sea turtles for all 
scenarios using explosives greater than 10 lbs (4.5 kg) BML. The impact 
zone for the B1 and B2 Scenarios (10-20 lbs/4.5-9.1 kg) is 373 m (1,224 
ft), an additional 112 m

[[Page 34879]]

(367 ft) beyond the 261 m (856 ft) impact zone projected for charges 
less than 10 lbs. This information was presented to participants at the 
Explosive-Severance Mitigation Workshop hosted by MMS' GoM Region in 
May 2004. MMS incorporated this mitigation measure into its Draft PEA 
and its MMPA application, both of which were released for public review 
and comment. As DEMEX did not raise significant concerns regarding this 
issue at either the 2004 workshop or during the comment periods for the 
Draft PEA, and NMFS' notice of receipt of MMS' application, NMFS does 
not believe a modification at this stage of the action is warranted 
until improved survey techniques are proposed and/or additional 
acoustic data is collected.
    Comment 14: The API/NOIA states that under the proposed 
regulations, many important requirements for individual explosive 
removal activities will be specified in LOAs. This approach offers 
great flexibility in tailoring requirements to conditions unique to 
individual or classes of activities; however, it also underscores the 
need to address concerns discussed previously by the industry.
    Response: Requirements for the mitigation, monitoring and reporting 
the effects of explosive removal of offshore structures are contained 
in the regulations, not in the LOAs. The appropriate mitigation and 
monitoring requirements have been standardized depending upon a number 
of factors. As a result, NMFS does not believe that it is necessary to 
repeat this information in LOAs.
    If an operator desires a variance from the regulations in its LOA 
application, it must provide information in its LOA application (or a 
revision to the original application) supporting that variance and 
analyzing impacts of that change. LOA modifications may require a 30-
day public review and comment period prior to issuance of an LOA. As a 
result, applicants would need to provide sufficient time for this 
review before undertaking the activity.
    Comment 15: The API/NOIA believes that further clarification of the 
phrase ``cooperate with NMFS and any other Federal, state or local 
agency monitoring the impacts of the activity on marine mammals'' is 
needed. Also this requirement should be limited to agencies with 
appropriate regulatory authority and should acknowledge the 
responsibility of the operator for the safety of the operations and 
personnel engaged in or observing such operations.
    Response: This concern has been raised in other regulatory actions 
previously. As a result, NMFS has recently modified the ``cooperation'' 
requirement to clarify that it is limited to Federal, state, or local 
agencies with regulatory authority over the subject activity. It is 
unnecessary for NMFS to make any statements in regard to who is 
responsible for operational safety concerns.

Mitigation and Monitoring Concerns

    Comment 16: The GRN states that the requirement for the use of 
shipboard visual observers is not sufficiently protective of whales. 
Submerged whales are not very visible at the surface. This is 
particularly true of sperm whales, which may dive for up to two hours, 
but routinely dive between 30 and 60 minutes. Under these 
circumstances, the use of visual observers is potentially ineffective 
in avoiding impacts. In order to ensure that impacts to whales, 
particularly sperm whales, are minimized, visual monitoring of an 
impact zone must be coupled with passive acoustic monitoring (PAM) 
systems.
    Response: In addition to shipboard monitoring, aerial monitoring 
and PAM are required in slope waters where sperm whales and several 
other deep-diving marine mammals are more likely to be found than in 
shelf waters. In shelf waters, where bottlenose and spotted dolphins 
predominate, PAM is not a requirement, but aerial monitoring is 
required for all detonations greater than 10 lbs (4.5 kg).
    Comment 17: The API/NOIA and DEMEX note that it is very difficult 
to identify species or to determine ranges and direction to those 
animals by use of passive acoustics. The detection is of no practical 
value for protecting these animals if their proximity to impact zones 
cannot be determined. Therefore, it is premature to require deployment 
of such a developmental tool. The problems associated with its use 
include: (1) inability to determine direction of the marine mammal's 
location, (2) inability to determine distance to the marine mammal, (3) 
passive acoustics only work when the marine mammal is vocalizing, and 
(4) there are no NMFS-approved acoustic monitoring instruments or 
operators.
    Response: Despite the identification, range, and bearing 
limitations, PAM surveys would be able to indicate if a vocalizing 
marine mammal is in the vicinity of the severance activities; 
therefore, used in conjunction with simultaneous surface and aerial 
observations, PAM will assist the observers and focus their attention 
for possible sightings.
    Comment 18: The Commission recommends NMFS encourage the MMS, in 
cooperation with the industry and acoustic consultants, to continue to 
collect on-site data from explosive severance activities for comparison 
with, and verification of, model predictions of the impacts of 
explosive severance activities.
    Response: The MMS has a new acoustic measurement program approved 
through their Technology Assessment & Research (TA&R) Program. 
Information on the project can be found at: https://www.mms.gov/
tarprojects/570.html. The MMS expects to conduct the measurement 
activities during future decommissioning season(s). Data recorded 
during the on site exercises will be used for verification of existing 
models and similitude equations, which will be essential for improving 
future mitigation measures.
    Comment 19: Industry representatives (API/NOIA/DEMEX) state that 
the UWC has not been calibrated against field measurements of acoustic 
and pressure emissions from actual structure removal detonations. Based 
on limited on site data collected by Connor and MMS, it appears that 
the UWC overestimates the distances from detonations at which acoustic 
and peak pressure limits are reached by at least 4 times. Safety zones 
based on the UWC are thus extremely conservative and may have the 
effect of diluting the intensity of the monitoring in the much smaller 
areas where the real impacts could occur. Though NMFS discounts these 
and other in-situ measurements due to imprecise location or 
malfunction, industry feels they represent the best available 
``affirmation'' that the UWC greatly overestimates impact ranges in the 
far field by a factor of three or more. Future field measurements 
should be integrated into the model as they become available.
    Response: The impact ranges developed using the UWC were discussed 
at the 2004 Explosive-Severance Mitigation Workshop and are contained 
in MMS' Final PEA. As detailed in the MMS' PEA, Appendix E (Page E-4), 
MMS utilized in-situ data collected from TAR Project No. 429 to help 
verify that the UWC could be used for incorporating the attenuation 
effects for BML detonations. It also determined that the impact ranges 
projected by the UWC were conservative and would be highly-protective 
for marine mammals and sea turtles when used in survey mitigation 
parameters. NMFS does not agree that monitoring effectiveness will be 
diluted with the establishment of these conservative monitoring zones. 
Monitoring zones range from 261 m (856

[[Page 34880]]

ft) for very small charges up to 1528 m (5012 ft) for large specialty 
charges. With monitoring times for the stationary surface observer(s) 
ranging from 60-180 minutes and for the aerial survey of 30-90 minutes, 
NMFS believes that all impact zones will be adequately monitored prior 
to detonation.
    New measurement activities under TAR Project No. 570 will help 
provide additional data that MMS hopes to use for subsequent 
calibration of the UWC. The in-situ testing will provide additional 
data that MMS hopes to use for subsequent calibration of the UWC. 
However, at the present time, MMS has not been able to secure 
assistance from industry or any volunteered ``targets of opportunity.''
    Comment 20: The API/NOIA note that past efforts to measure 
detonation effects are not considered while criteria derived from the 
CHURCHILL shock trial and results of the UWC are embraced. The 
appearance is that the UWC has been used to apply theoretical 
propagation calculations to the CHURCHILL criteria to produce estimated 
impact zones several times larger than those based on actual 
measurements-in favor of overly conservative impact zones derived from 
theory (UWC) and improper application of the CHURCHILL criteria to 
structure removal detonations. This in turn has led NMFS to attach 
monitoring requirements beyond what is necessary. Additional in-situ 
measurements are needed before models such as the UWC can be treated as 
credible. The commenters state that industry has been willing to 
provide ``targets of opportunity'' for such measurements and will 
doubtless continue to do so.
    Response: Please see response to comment 19.
    Comment 21: API/NOIA note that NMFS proposes to make any future 
take authorization from explosive removal activities contingent on 
additional in-situ measurements of explosive decommissionings. This 
contingency does not make clear which entity (MMS, NMFS, or the 
regulated community) is responsible for conducting such measurements. 
It is also unclear what kinds of measurements are expected, what 
acceptance criteria will be used by NMFS or what purpose they will 
serve.
    Response: See previous responses regarding the TAR program. 
Information on the project can be found on MMS' website (). MMS 
conducted measurement activities during the 2007 decommissioning 
season. Data recorded during the in-situ exercises will be used for 
verification of existing models (including the UWC) and similitude 
equations, which will be essential for improving future mitigation 
measures. Therefore, MMS (the petitioner) is already working to meet 
this requirement.
    Comment 22: The API/NOIA believe that a requirement to use 
helicopters ``running standard low-altitude search patterns'' is 
unclear. Reference to an intended procedure or definition should be 
provided. Is there a specified aerial flight survey ``grid pattern'' 
found in NMFS' observer guidelines?
    Response: NMFS believes that the helicopter grid pattern described 
in the proposed rule and this final rule provide sufficient detail. The 
NMFS observer who will participate in each aerial survey will be able 
to provide more information regarding the grid pattern.
    Comment 23: DEMEX notes that there should be some flexibility in 
the number of observers on a project. The size and scope of the project 
as well as the living-space and other logistical issues should all be 
considered. DEMEX recommends one observer for the surface surveys and 
one observer for the aerial survey. If possible, the surface survey 
observer could join the aerial observer for that portion of the 
observation. LIS recommends observers for all charges over 20 lbs (9.1 
kg).
    Response: The number of observers is based on a number of variables 
such as size of charge, depth of water, etc. A minimum of two observers 
is necessary to provide enough coverage to conduct both the surface 
survey and the aerial monitoring. The minimum number of observers could 
be increased by the NMFS Platform Removal Observer Program (PROP) 
Manager to accomodate the size and scope of larger projects.
    Comment 24: The API/NOIA believe that justification is warranted 
for requiring two teams of observers (3 observers in each team). It is 
also not clear what constitutes a ``team.'' Is it meant to describe two 
groups of three observers (one each for surface, aerial and acoustic 
monitoring)? If so, why, if the observations are only allowed during 
daylight hours in favorable weather, or does one team comprise a 
surface and an aerial observer and the other an acoustic observer? 
These uncertainties should be clarified, consistent with industry's 
position that (passive) acoustic monitoring has not yet been 
demonstrated to be practical for operational applications. As a 
practical matter it is often disruptive, costly and potentially unsafe 
to accommodate unnecessary personnel in a working marine environment.
    Response: NMFS believes that the proposed rule warrants 
clarification on this matter. Generally, two observers will be assigned 
to each operation for detection survey duties. However, because certain 
mitigation scenarios (C2, C4, D2, D4, E2, and E4), which are described 
later in the preamble to this rule, require implementation of an 
acoustics monitoring program, a minimum of three observers for the 
simultaneous surface, aerial, and acoustic surveys will be required. 
There is no requirement for multiple ``teams'' to be deployed.
    In the proposed rule (71 FR 17790, April 10, 2006) and later during 
the Endangered Species Act (ESA) Section 7 consultation, it was 
determined that two NMFS observers would perform marine protected 
species detection surveys for those scenarios taking place in waters 
greater than 200 m (656 ft). For scenarios in waters greater than 200 m 
(656 ft), at least 3 observers are needed for simultaneous surface, 
aerial, and acoustic monitoring. The PROP Manager will determine if 
additional observers are required to compensate for the complexity of 
severance activities or structure configuration. As previously 
discussed, since PAM requirements remain in this Final Rule, operators 
covered by an LOA under this rule will have to work with the NMFS PROP 
Manager to ensure that the logistics for their removal operations can 
accommodate the required number of observers.
    Comment 25: DEMEX asks whether nighttime observations are going to 
be required as they were under the 1995 Biological Opinion (BiOp) and 
Incidental Take Statement (ITS)?
    Response: Those requirements in the 1995 ESA BiOp and ITS were 
determined to be ineffective due to limitations on visibility. 
Therefore, nighttime observations are no longer required.
    Comment 26: Some industry representatives (API/NOIA, DEMEX) believe 
there is too much confusion regarding the definition of daylight and 
dawn which will cause difficulties in the field. Previous rules and 
regulations allowed the detonation 1 hour after dawn. If the proposed 
rule means that the 90-minute surface survey would begin 1 hour after 
dawn, followed by a 30-minute aerial survey, that would mean it would 
be over 3 hours after dawn before explosives could be detonated. DEMEX 
believes it would be much more practical to conduct surface and aerial 
surveys during daylight hours beginning at dawn and concluding at least 
one hour before sunset. (Dawn and sunset conventionally refer to times 
when the upper edge of the disk of the sun is on the horizon, 
considered unobstructed relative to the location of

[[Page 34881]]

interest.) This schedule would allow detonations to occur no later than 
one hour before sunset.
    Response: All pre-detonation surveys will be restricted to daylight 
hours as defined by ``legal sunrise'' to ``legal sunset'' 
(conventionally referred to as the time when the upper edge of the disk 
of the Sun is on the horizon (as determined by the NMFS onboard 
observer)) to ensure that the operator can easily confirm these times. 
Therefore, the time periods for pre-detonation surveys outlined in this 
rule cannot begin until legal sunrise and all detonations must be 
concluded so that post-detonation surveys can be completed by legal 
sunset.
    Comment 27: The API/NOIA believe the statement in the proposed rule 
that ``surface surveys are to be conducted during daylight hours only'' 
is vague.
    Response: See previous response.
    Comment 28: DEMEX asks whether a project can be halted because of 
the unavailability of observers?
    Response: Observers are necessary components of the mitigation 
requirements for lawful incidental take of marine mammals and 
compliance with these regulations and LOAs issued thereunder (as well 
as for sea turtles under the BiOp and ITS). Because the previous ESA 
requirements relating to the 48-hr pre-detonation monitoring have been 
eliminated, the NMFS PROP program manager does not foresee a problem 
related to the availability of personnel. However, if NMFS observers 
are unavailable, a project will be temporarily halted until observers 
are onsite.
    Comment 29: DEMEX notes that the proposed rule requires observers 
to conduct a 90-minute surface survey prior to a severance-charge 
detonation. DEMEX recommends detonation times should be 90 minutes 
after dawn up until 1 hour before sunset.
    Response: As pre-detonation surveys are restricted to daylight 
hours (as defined by ``legal sunrise'' to ``legal sunset''), and as 
vessel surveys may take as long as 150-180 minutes to complete for 
large and specialty charges, the suggestion to limit pre-detonation 
surveys to 90 minutes would not provide an acceptable monitoring period 
for these large charges.
    Comment 30: DEMEX notes that the proposed rule states that: (1) 
detonation operations ``cannot begin until the requisite surface 
monitoring survey has been completed,'' and (2) post-post-detonation 
aerial monitoring surveys must be conducted ``within 2-7 days after 
detonation activities have been concluded.'' DEMEX recommends the 30-
minute aerial survey be done at the same time as the surface monitoring 
to allow blasting to commence 90 minutes after dawn. DEMEX opposes 
having the usable blasting daylight hours become less than they already 
were in the previous regulations.
    Response: Aerial surveys are to commence at the conclusion of the 
surface monitoring because (1) one of the surface observers will have 
to accompany the helicopter pilot and (2) the observation work is to be 
conducted afterward (and not concurrently) to improve the overall 
effectiveness of detection prior to detonation. Reference to ``within 
2-7 days after detonation activities have concluded'' relates to Post-
Post-Detonation Aerial Monitoring Surveys and not the standard Pre-
Detonation Aerial Monitoring Surveys.
    Comment 31: One requirement forbids initiation of aerial surveys 
until the surface monitoring surveys have been completed. If two or 
more observers are available, this appears to be a counterproductive 
restriction. Industry representatives (API/NOIA) recommend amending the 
rule to permit aerial surveys to begin at any time and to conclude no 
earlier than when final clearance to detonate charges is given by the 
observer team. The duration of aerial surveys, of course, would still 
be consistent with the times given in the relevant table.
    Response: See response to comment 30.
    Comment 32: The API/NOIA note that ``post-post-detonation'' aerial 
surveys are to be conducted 2-7 days after the decommissioning charges 
are detonated. In the many years that these surveys have been 
conducted, there has never been a sighting of a dead or injured animal. 
Frequently changing winds and currents make it nearly impossible to 
determine the direction and distance a dead or injured animal may have 
been carried since the detonation occurred. Representatives of the 
industry (API/NOIA, DEMEX and LIS) believe the 2-7 day aerial survey 
should be reconsidered.
    Response: Although there were prior opportunities to raise and 
discuss these concerns (e.g., the 2004 Explosive- Severance Mitigation 
Workshop and the comment period on MMS' Draft PEA), the commenters did 
not raise them before or suggest alternatives. Absent additional 
information, NMFS believes there is merit to continuing the post-post 
detonation monitoring. The fact that these surveys have not detected an 
injured or dead animal does not necessarily mean they are ineffective. 
It could mean the pre-detonation mitigation and monitoring has been 
effective.
    Comment 33: The API/NOIA note that the regulations would require an 
operator to cease an explosive severance activity if a marine mammal or 
sea turtle is found shocked, injured, or dead. The commenters believe 
the intent is to cease detonation of any additional charges, not to 
cease related activity such as supporting, lifting and/or loading 
severed structures for transport. Halting those post-detonation 
operations could lead to unsafe conditions such as losing control of 
the structure or endangering vessels and crew. Although multiple-charge 
operations are normally executed in almost instantaneous sequences of 
detonations, occasionally additional charges may be required to 
complete severing of some structural members. If additional charges are 
required, operations would automatically cease when the operator 
completes activities such as inspection of the structure, preparation 
and placement of charges, repositioning of lifting equipment, etc. 
These activities may take several hours to complete. If this 
interpretation of the requirement is correct, compliance would not 
likely be a problem.
    Response: As noted in the comment, the intent is that only 
explosive detonation and charge deployment work cease, and not the 
other decommissioning activities such as jacket securing, lifting, 
loading, and transport. Direction will be given by NMFS PROP Manager/
representative on resuming any explosive-severance activities after any 
event impacting marine protected species.

ESA Concerns

    Comment 34: The API/NOIA note that the preamble to the proposed 
rule states that the mitigation scenarios developed for this proposed 
rule will also apply to sea turtles (and this thread continues through 
subsequent parts of the preamble). The industry agrees that the 
mitigation measures developed here for marine mammals will provide 
adequate protection for sea turtles. However, will these measures 
supercede existing requirements applicable to turtles?
    Response: On August 28, 2006, NMFS issued a new BiOp for MMS' 
permitting of structure-removal operations on the GoM OCS and for NMFS' 
issuance of LOAs to the industry to take marine mammals by harassment 
incidental to structure removal operations. The 2006 BiOp and Amended 
ITS, which contain measures to protect sea turtles, replace the 
previous 1987 BiOp.

[[Page 34882]]

Description of Habitat and Marine Mammals Affected by the Activity

    Explosive severance activities could occur in all water depths of 
the offshore areas designated by MMS as the GoM Central and Western 
Planning Areas (CPA and WPA) and a portion of the Eastern Planning Area 
(EPA) offered under Lease Sale 181/189 (see Figure 2 or 3 in MMS' MMPA 
Application). Water depths in the areas of the proposed action range 
from 4 to 3,400 m (13-11,155 ft), with the majority of existing 
facilities and wells found within the CPA, concentrated on the upper 
shelf waters (less than 200 m (656 ft) water depth) off of Louisiana. A 
detailed description of the northern GoM area and its associated marine 
mammals can be found in the MMS application and PEA and in a number of 
documents referenced in the application. Detailed information on the 
marine mammals in the GoM can also be found in the NMFS status of 
stocks reports (Waring et al., 2007), which are available for 
downloading or reading at: https://www.nefsc.noaa.gov/nefsc/
publications/tm/tm201/tm201.pdf.
    A total of 28 cetacean species and one species of sirenian (West 
Indian manatee) are known to occur in the GoM. These cetacean species 
are the sperm whale, pygmy sperm whale, dwarf sperm whale, Cuvier's 
beaked whale, Sowerby's beaked whale (extralimital), Gervais' beaked 
whale, Blainville's beaked whale, rough-toothed dolphin, bottlenose 
dolphin, pantropical spotted dolphin, Atlantic spotted dolphin, spinner 
dolphin, Clymene dolphin, striped dolphin, Fraser's dolphin, Risso's 
dolphin, melon-headed whale, pygmy killer whale, false killer whale, 
killer whale, short-finned pilot whale, North Atlantic right whale 
(extralimital), humpback whale (rare), minke whale (rare), Bryde's 
whale, sei whale (rare), fin whale (rare), and the blue whale 
(extralimital).
    A description of the status, distribution, and seasonal 
distribution of the affected species and stocks of marine mammals that 
might be affected by explosive severance activities is provided in MMS' 
MMPA Application).

Potential Impacts to Marine Mammals

    Underwater explosions are the strongest manmade point sources of 
sound in the sea (Richardson et al., 1995). The underwater pressure 
signature of a detonating explosion is composed of an initial shock 
wave, followed by a succession of oscillating bubble pulses (if the 
explosion is deep enough not to vent through the surface) (Richardson 
et al., 1995). The shock wave is a compression wave that expands 
radially out from the detonation point of an explosion. Although the 
wave is initially supersonic, it is quickly reduced to a normal 
acoustic wave. The broadband source levels of charges weighing 0.5-20 
kg (1.1-44 lb) are in the range of 267-280 dB re 1 microPa (at a 
nominal 1-m distance), with dominant frequencies below 50 Hz 
(Richardson et al., 1995; CSA, 2004). The following sections discuss 
the potential impacts of underwater explosions on marine mammals, 
including mortality, injury, hearing effects, and behavioral effects.

Mortality or Injury

    It has been demonstrated that nearby underwater blasts can injure 
or kill marine mammals (Richardson et al., 1995). Injuries from high-
velocity underwater explosions result from two factors: (1) the very 
rapid rise time of the shock wave; and (2) the negative pressure wave 
generated by the collapsing bubble, which is followed by a series of 
decreasing positive and negative pressure pulses (CSA, 2004). The 
extent of injury largely depends on the intensity of the shock wave at 
the receiver (marine mammal) and the size and depth of the animal 
(Yelverton et al., 1973; Craig, 2001).
    The greatest damage occurs at boundaries between tissues of 
different densities because different velocities are imparted that can 
lead to their physical disruption; effects are generally greatest at 
the gas-liquid interface (Landsberg, 2000; CSA, 2004). Gas-containing 
organs, especially the lungs and gastrointestinal tract, are 
susceptible to this type of damage. Lung injuries (including 
lacerations and the rupture of the alveoli and blood vessels) can lead 
to hemorrhage, air embolisms, and breathing difficulties. The lungs and 
other gas-containing organs (nasal sacs, larynx, pharynx, and trachea) 
may also be damaged by compression/expansion caused by oscillations of 
the blast gas bubble (Reidenberg and Laitman, 2003). Intestinal walls 
can bruise or rupture, which may lead to hemorrhage and the release of 
gut contents. Less severe injuries include contusions, slight 
hemorrhaging, and petechia (Yelverton et al., 1973; CSA, 2004). Ears 
are the organs most sensitive to pressure and, therefore, to injury 
(Ketten, 2000; CSA, 2004). Severe damage to the ears can include 
rupture of the tympanic membrane, fracture of the ossicles, cochlear 
damage, hemorrhage, and cerebrospinal fluid leakage into the middle 
ear. By themselves, tympanic membrane rupture and blood in the middle 
ear can result in partial, permanent hearing loss. Permanent hearing 
loss can also occur when the hair cells are damaged by loud noises 
(ranging from single, very loud events to chronic exposure).

Hearing Effects

    Mammalian hearing functions over a wide range of sound intensities, 
or loudness. The sensation of loudness increases approximately as the 
logarithm of sound intensity (Richardson and Malme, 1993). Sound 
intensity is usually expressed in decibels (dB), units for expressing 
the relative intensity of sounds on a logarithmic scale. Because sound 
pressure is easier to measure than intensity and intensity is 
proportional to the square of sound pressure, sound pressure level is 
usually reported in units of decibels relative to a standard reference 
pressure.
    Based on the information presented in Richardson et al. (1995), the 
possible behavioral effects of noise from underwater explosions on 
marine mammals may be categorized as follows:
    1. The noise may be too weak to be heard at the location of the 
animal (i.e., below the local ambient noise level, below the hearing 
threshold of the animal at the relevant frequencies, or both);
    2. The noise may be audible, but not loud enough to elicit an overt 
behavioral reaction;
    3. The noise may elicit behavioral reactions, which may vary from 
subtle effects on respiration or other behaviors (detectable only 
statistically) to active avoidance behavior;
    4. With repeated exposure, habituation (diminishing responsiveness) 
to the noise may occur. Continued disturbance effects are most likely 
with sounds that are highly variable in their characteristics, 
unpredictable in occurrence, and associated with situations perceived 
by the animal as threatening;
    5. Any anthropogenic noise that is strong enough to be heard has 
the potential to reduce (mask) the ability of a marine mammal to hear 
natural sounds at similar frequencies, including calls from 
conspecifics, and underwater environmental sounds such as surf noise.
    6. If mammals remain in an area because it is important for 
feeding, breeding or some other biologically important purpose even 
though there is chronic exposure to noise, it is possible that there 
could be noise-induced physiological stress; this might in turn have 
negative effects on the well-being

[[Page 34883]]

or reproduction of the animals involved; and
    7. Very strong sounds have the potential to cause temporary or 
permanent reduction in hearing sensitivity. In terrestrial mammals, and 
presumably marine mammals, received sound levels must far exceed the 
animal's hearing threshold for there to be any TTS in its hearing 
ability. For transient sounds, the sound level necessary to cause TTS 
is inversely related to the duration of the sound exposure. Received 
sound levels must be even higher for there to be risk of permanent 
hearing impairment. In addition, intense acoustic or explosive events 
may cause trauma to tissues associated with organs vital for hearing, 
sound production, respiration and other functions. This trauma may 
include minor to severe hemorrhage.
Temporary Threshold Shift (TTS)
    The mildest form of hearing impairment, TTS, is defined as the 
temporary elevation of the minimum hearing sensitivity threshold at 
particular frequency(s) (Kryter, 1985; CSA, 2004). TTS may last from 
minutes to days. Although few data exist on the effects of underwater 
sound on marine mammal hearing, in terrestrial mammals, and presumably 
in marine mammals, received levels must exceed an animal's hearing 
threshold (i.e., maximum sensitivity) for TTS to occur (Richardson et 
al., 1995; Kastak et al., 1999; Wartzok and Ketten, 1999).
    Most studies involving marine mammals have measured exposure to 
noise in terms of SPL, measured in dBrms or dBpeak pressure re 1 
microPa. Exposure to underwater sound can also be expressed in terms of 
energy (SEL), or acoustic energy (measured in dB re 1 microPa2-s), 
which, unlike SPL measurements, considers both intensity and duration 
of the sound. If TTS is defined as a measurable threshold shift of 6 dB 
or more (Finneran et al., 2000, 2002), then based on experiments with 
beluga whales and bottlenose dolphins, the onset of TTS is associated 
with an energy level of about 184 dB re 1 microPa2-s (CSA, 2004). 
However, the data are very limited, and Finneran (2003) has noted that 
they should be interpreted with caution.
Permanent Threshold Shift (PTS)
    PTS is a permanent decrease in the functional sensitivity of an 
animal's hearing system at some or all frequencies (CSA, 2004). The 
principal factors involved in determining whether PTS will occur 
include sound impulse duration, peak amplitude, and rise time. The 
criteria are location- and species-specific (Ketten, 1995) and are also 
influenced by the health of the receiver's ear.
    At least in terrestrial animals, it has been demonstrated that the 
received level from a single exposure must be far above the TTS 
threshold for there to be a risk of PTS (Kryter, 1985, Richardson et 
al., 1995; CSA, 2004). Sound signals with sharp rise times (e.g., from 
explosions) produce PTS at lower intensities than do other types of 
sound (Gisner, 1998; CSA, 2004).
    For explosives, Ketten (1995) estimated that greater than 50-
percent PTS would occur at peak pressures of 237-248 dB re 1 microPa 
and that TTS would occur at peak pressures of 211-220 dB re 1 microPa. 
Ketten (1995) recommended a ``safe'' peak pressure level to avoid 
physical injury of 100 psi (237 dB re 1 microPa (peak), or an SEL of 
about 212 dB re 1 microPa\2\-s). Ketten (1998) found that peak blast 
overpressures of 1,034 kPa (150 psi) were associated with 50 percent 
tympanic membrane rupture. Based on the incidence of eardrum rupture in 
sheep exposed to underwater explosions by Richmond et al. (1973), Craig 
(2001) estimated that 50 percent tympanic membrane rupture would occur 
at an energy flux density of 1.17 in-lb/in\2\. This criterion is more 
conservative than the one derived by Ketten (1995) and was used in the 
ship shock EISs as a criterion for injury, and is used by MMS and NMFS 
in this action. PTS is assumed to occur at received levels 30 dB above 
TTS-inducing levels. Studies have shown that injuries at this level 
involve the loss of sensory hair cells (Ahroon et al., 1996; CSA, 
2004).

Behavioral Effects

    Behavioral reactions of marine mammals to sounds such as those 
produced by underwater explosives are difficult to predict. Whether and 
how an animal reacts to a given sound depends on factors such as the 
species, hearing acuity, state of maturity, experience, current 
activity, reproductive state, time of day, and weather.
    Richardson et al. (1995) summarized available information on the 
reported behavioral reactions of marine mammals to underwater 
explosions. Observations following the use of seal bombs as scare 
charges indicate that pinnipeds rapidly habituate to and, in general, 
appear quite tolerant of, noise pulses from explosives. Klima et al. 
(1988) reported that small charges were not consistently effective in 
moving bottlenose dolphins away from blast sites in the GoM. Since 
dolphins may be attracted to the fish killed by such a charge, rather 
than repelled, scare charges are not used in the GoM platform removal 
program (G. Gitschlag, personal communication, in Richardson et al., 
1995).
    There are few data on the reactions of baleen whales to underwater 
explosions. Gray whales were apparently unaffected by 9- to 36-kg (20- 
to 97-lb) charges used for seismic exploration (Fitch and Young, 1948). 
However, Gilmore (1978) felt that similar underwater blasts within a 
few kilometers of the gray whale migration corridor did ``sometimes'' 
interrupt migration.
    Humpback whales have generally not been observed to exhibit 
behavioral reactions (including vocal ones) to explosions, even when 
close enough to suffer injury (hearing or other) (Payne and McVay, 
1971; Ketten et al., 1993; Lien et al., 1993; Ketten, 1995; Todd et 
al., 1996). In Newfoundland, humpbacks displayed no overt reactions 
within about 2 km (1 nm)of 200- to 2,000-kg explosions. Whether 
habituation and/or hearing damage occurred was unknown, but at least 
two whales were injured (and probably killed) (Ketten et al., 1993). 
Other humpback whales in Newfoundland, foraging in an area of explosive 
activity, showed little behavioral reaction to the detonations in terms 
of decreased residency, overall movements, or general behavior, 
although orientation ability appeared t