10 MARINE MAMMALS AND SEA TURTLES - Hebron Project

Hebron Project Comprehensive Study Report
Marine Mammals and Sea Turtles
209 dB re 1 µPa at 915 m to 221 dB re 1 µPa at 229 m (unspecified measure
type; Klima et al. 1988).
Gitschlag and Herczeg (1994) reported the results from the placement of
observers at offshore sites to monitor and protect sea turtles during explosive
removals of oil and gas structures in the Gulf of Mexico. In 6,500 hours of
monitoring at 106 structures, no injury (or mortality) of sea turtles was
documented.
Results of acoustic modelling (JASCO 2010) for the largest single charge that
is permissible under the DFO 100 kPa overpressure guideline (Wright and
Hopky 1998), indicate that 180 and 190 dB re 1 uPa (rms) sound levels
(un-weighted) occur at 2.7 km and 0.99 km, respectively, from the blast site.
Because the peak in source spectrum occurs at low-frequency, the
application of M-weighting, results in smaller 180 and 190 dB zones for
mid- and high-frequency cetaceans (see Table 9 in JASCO (2010)). Southall
et al. (2007) concluded that PTS might occur if cetaceans and pinnipeds
were exposed to peak pressures exceeding 230 dB re 1 μPa (peak) (or 198
dB re 1 µPa 2 -s) or 218 re 1 μPa (peak) (or 186 dB re 1 µPa 2 -s), respectively.
The corresponding ranges to these sound levels were not estimated during
acoustic modelling but would occur much closer to the sound source than
180 and 190 dB re 1 uPa (rms) sound levels.
Sea turtles are rare within the Nearshore Study Area, particularly at times
other than late summer and early fall. Species most likely to be affected
include those predicted to be common within the Nearshore Study Area,
including humpback whales, possibly minke and pilot whales, and multiple
dolphin species, and are likely to be common during the summer months.
Blasting parameters will be such that they adhere to the DFO guidance
outlined in Guidelines for the Use of Explosives In or Near Canadian
Fisheries Waters (Wright and Hopky 1998). As a minimum, proposed
guidelines (Wright 2002) indicate that detonations cannot knowingly occur
within 500 m of any marine mammal, “or alternately, there must be no visual
contact by an observer using 7x35 power binoculars”.
A monitoring protocol for marine mammals will be established by EMCP prior
to the start of construction activities. This protocol will be developed in
consultation with DFO and may include the following parameters:
Prior to blasting, a blast impact assessment will be undertaken to
determine appropriate marine mammal and sea turtle exclusion zones
and ensure that a 100 kPa charge is not exceeded
The sound levels in the water column will be evaluated to determine a
safety zone for marine mammals
The feasibility of using a bubble curtain to reduce sound levels will also be
investigated
Received sound levels of 180 dB dB re 1 μPa (rms) for cetaceans and
sea turtles, and 190 dB re 1 μPa (rms) for phocids, modelled as 2.7 and
0.99 km for a 100 kPa charge, respectively, will be used as a guide for
these zones
10-42 June 2010