Study Finds Bottom-Trawl Fishing Gear Responsible For Some Alaska Orca Deaths

USFWS Alaska photo

From the Alaska Beacon, a National Oceanographic and Atmospheric Administration study found that some Alaska killer whale deaths were due to the mammals getting caught in bottom-trawl fishing gear. Here’s more on the findings:

Of the nine killer whales that were found ensnared in bottom-trawling gear, six were killed by those entanglements but two others were already dead before they were netted, the investigation found. The other whale was seriously injured by the gear entanglement but escaped alive, the agency said.

In addition to the nine whales found in bottom-trawl gear, there were two other cases of dead killer whales found entangled in other types of fishing gear.

The bottom-trawling gear that entangled the nine whales, also called orcas, was from vessels in what is known as the Amendment 80 fleet – roughly 20 large ships that both catch and process fish. These catcher-processors use trawl nets that sweep the seafloor to harvest Atka mackerel, yellowfin sole, rock sole and other flatfish species. They do not harvest pollock, the species that makes up the biggest volume of harvested Alaska seafood.

In the other two cases, one dead killer whale was found in trawl gear used by a vessel harvesting pollock, the agency said. That whale was determined to have been dead before it became entangled.

From NOAA’s report:

Observers were able to collect biological samples from 8 of the 11 whales and determined that these whales were from the Eastern North Pacific Alaska Resident killer whale stock. All eight were females. 

Scientists were not able to determine the stock for the remaining three whales. There were no tissue samples obtained and either photos were not collected or were not useful for stock identification. Three stocks of killer whales have overlapping geographic ranges in the areas where these interactions occurred: Eastern North Pacific Alaska Resident killer whale stock, Gulf of Alaska, Aleutian Islands, and Bering Sea Transient stock, and Eastern North Pacific Offshore stock.

Under the Marine Mammal Protection Act, a Potential Biological Removal estimate determines the maximum number of animals, not including natural mortalities, that may be removed from a marine mammal stock per year while allowing the stock to reach or maintain its optimum sustainable population. For the Eastern North Pacific Alaska Resident killer whale stock, that number is 19 whales per year. For the Gulf of Alaska, Aleutian Islands, and Bering Sea Transient stock, it is 5.9 whales per year. For the Eastern North Pacific Offshore stock, it is 2.8 whales per year.

While the number of human-caused mortalities and serious injuries is higher this year, it is still below this annual level.