10 MARINE MAMMALS AND SEA TURTLES - Hebron Project

Hebron Project Comprehensive Study Report
Marine Mammals and Sea Turtles
be minimized, when possible. All other activities expected to affect habitat
quality could also lead to effects on habitat use. The impact of these activities
on the Marine Mammal and Sea Turtle VEC in the Nearshore Study Area are
reviewed in Section 10.5.1.3 (Habitat Use).
Offshore
Geophysical Surveys
In the Offshore, geophysical surveys will include seismic as well as
geohazard surveys. Both seismic and geohazard surveys use airgun arrays, a
key difference is the larger array size used in seismic surveys. The potential
physical/physiological effects of noise from the geohazards equipment
(typically a small airgun array, boomer, side scan sonar, and echosounders)
are of less concern than airgun pulses from 2-D and 3-D surveys given their
relatively lower source levels, emittence in a narrow beam, short duration of
the geohazards program, and that some equipment operates at frequencies
outside the range of marine mammal and sea turtle hearing abilities.
The potential physical/physiological effects of seismic programs on marine
mammals and sea turtles have recently been reviewed for the StatoilHydro‘s
3-D program in Jeanne d‘Arc Basin (LGL 2008a: Section 5.6.4)
Petro-Canada‘s 3-D program in Jeanne d‘Arc Basin (LGL 2007b: Section
5.6.6) and for Husky‘s program in northern Jeanne d‘Arc Basin (LGL 2005b:
Section 6.5.12; Moulton et al. 2006a: Sections 6.1.2 and 6.1.3). Geohazard
surveys are less likely to impact marine mammals and sea turtles as
reviewed in three Environmental Assessments for Jeanne d‘Arc Basin in
2005 (LGL 2005a, 2005b, 2005c, 2005d) and an update to one of the
environmental assessments in 2007 (LGL 2007b).
Temporary or permanent hearing impairment is a possibility when marine
mammals and sea turtles are exposed to very strong sounds. The minimum
sound level necessary to cause permanent hearing impairment is higher, by a
variable and generally unknown amount, than the level that induces
barely-detectable TTS. The level associated with the onset of TTS is often
considered to be a level below which there is no danger of permanent
damage. As discussed earlier, current NMFS policy regarding exposure of
marine mammals to high-level sounds is that cetaceans and pinnipeds should
not be exposed to impulsive sounds exceeding 180 and 190 dB re 1 Pa
(rms), respectively (NMFS 2000a, 2000b). However, those criteria were
established before there was any information about the minimum received
levels of sounds necessary to cause TTS in marine mammals. The 180 dB
criterion for cetaceans is probably quite conservative (i.e., lower than
necessary to avoid auditory injury), at least for delphinids (Southall et al.
2007).
Non-auditory physical effects may also occur in marine mammals exposed to
strong underwater pulsed sound. Possible types of non-auditory physiological
effects or injuries that might (in theory) occur include stress, neurological
effects, bubble formation, resonance effects, and other types of organ or
tissue damage. It is possible that some marine mammal species (i.e., beaked
10-44 June 2010