Since 1980, the North Atlantic Right Whale (Eubalaena glacialis) population has experienced a rapid decline, mainly due to fishing gear entanglements and collisions with shipping vessels. Prior to 1980 the whaling industry also took its toll on the whales; the North Atlantic Right Whale (NARW) population size is now estimated to be 300-350 individuals and faces a serious threat of extinction. The Wind Energy Areas (WEAs) planned in the Atlantic by the Department of Interior will coincide with stretches of the NARW north-south migratory from the Gulf of Maine to the coasts of Georgia/Florida where the animals breed. Offshore wind installation may exacerbate the threats to the NARWs, with the sound from pile driving and the presence of the installation vessels altering the behavior of the whales and potentially causing them harm. Pile-driving activities that support offshore wind installations can reach sound impact level intensities as high as 261 dB re 1 µPa close to the installation; these levels can cause hearing effects such as a PTS (permanent threshold shift) close to the wind farms or TTS (temporary threshold shift) further away. Underwater sound propagation plays a crucial role for marine mammals, allowing them to communicate, navigate, hunt for prey, and find mates.
Researchers at Pacific Northwest National Laboratory (PNNL) calculated the distribution of sound to which a NARW might be exposed as a result of cumulative pile-strikes for a wind turbine installation. Using a Monte Carlo simulation and a behavioral model that takes into account the whales’ typical trajectory, rate and direction of travel, PNNL researchers showed that a NARW approaching within a few hundred meters of active pile driving may be exposed to sufficient sound to induce PTS. There is sufficient overlap between the migratory routes of the whales and the WEAs for this encounter to be of concern. Closer examination of the specific overlap in time and space between NARWs and pile driving activities is needed, and specific mitigation measures must be developed. Some of the most promising mitigation measures being tested in Europe include the use of specialized jackets and bubble curtains to disrupt the acoustic signal from pile driving; and alternative pile driving procedures including slow hammer starts and careful timing of piling operations to avoid close passage of NARWs. Each of these mitigation measures requires improved monitoring of the presence of NARWs using a mix of marine mammal observers, passive and active acoustic instruments.