Researchers Monitor The Effects Of Seismic Survey In Alaska’s Cook Inlet

Manolo preparing to drop sensors in the water
Photo: Brandon Hill
JISAO’s Manolo Castellote and OCR’s Michael Stocker deploy a hydrophone mooring in the lower Cook Inlet to monitor the 400 square mile survey zone.

Hilcorp Alaska LLC recently began a seismic survey in 400-square-miles of federal waters within Cook Inlet near Homer, Alaska. The geological exploration uses airguns onboard the 300-foot Polarcus research/survey vessel to fire high-energy impulses toward the sea floor to generate images of the Earth’s subsurface to determine where oil and gas can be found.

The company’s permit allows the survey from September 1-October 31, 2019. In approving the permit, the federal government has also put in place several mitigation measures to protect marine life in the inlet from near-distance effects, such as, requiring vessel operators to gradually ramp up the airgun volume to allow marine mammals to move away before been harmed; and requiring that independent marine mammal observers be stationed on board the survey vessel to monitor an exclusion zone of 500 meters around the airguns that would force a stop to the activity if marine mammals are sighted.

Noises from the survey can propagate horizontally and be heard hundreds of miles from the vessel, so biologist Manuel Castellote, a researcher with the University of Washington’s Joint Institute for the Study of the Atmosphere and Ocean (JISAO) and affiliated scientist at the NOAA Alaska Fisheries Science Center, together with Michael Stocker, executive director of the non-profit Ocean Conservation Research (OCR), traveled to Alaska to monitor effects of the noise on marine life in the region, specifically whales and zooplankton.

The survey’s airguns send blasts into the water every two to six seconds, amounting to up to 1,800 blasts per hour. The “collateral noise” is already proven to be disruptive to marine mammals, fish, and marine invertebrates, and there is limited evidence to suggest that the impulses may also damage or kill zooplankton, the foundation of the marine food chain. Studies in other regions have shown spatial displacement of whales such as humpback or fin whales as far as 285 km away from the airguns.

Castellote’s team deployed four acoustic moorings equipped with hydrophones, echolocation loggers, and depth sensors around the survey zone. Data will be analyzed to measure sound levels at long distances from the airguns, and quantify any long-range behavioral change in the endangered beluga, humpback, and fin whale populations typically found in this region of Cook Inlet. Presence of other species such as harbor and Dall’s porpoises, minke whales, and killer whales will be explored. The data will also be shared with BOEM scientists to study long-range sound propagation characteristics in this complex environment. The researchers are also sampling plankton near the airguns, in coordination with Hilcorp Alaska LLC, and in collaboration with the NOAA Kasitsna Bay Laboratory and the Kachemak Bay National Estuarine Research Reserve, for possible evidence of impact by the seismic survey.

For more information, contact Castellote at or 206-526-6866.