NOAA Fisheries has confirmed the causes of death or injury for 11 killer whales caught incidentally in fishing gear and a NOAA research survey in Alaska in 2023.
Nine of these 11 whales were caught by Bering Sea/Aleutian Island catcher processor vessels using non-pelagic trawl gear targeting flatfish (e.g., arrowtooth flounder, rex sole). A tenth killer whale was taken by a Bering Sea/Aleutian Islands catcher processor vessel using pelagic trawl gear to target pollock. The eleventh whale was entangled in survey gear during the Alaska Fisheries Science Center’s annual longline survey for sablefish and groundfish.
The number of incidental takes is higher than previous years. However, it is still below the annual level that would pose a risk to the long-term health for any of the three killer whale stocks found in the region where the incidental takes occurred.
Incidental Catch from Non-Pelagic Gear Targeting Flatfish
Nine of these 11 whales were caught by Bering Sea/Aleutian Island catcher processor vessels using non-pelagic trawl gear targeting flatfish. Based on independent fishery observer reports and photographs, we determined that of these nine:
- Six were killed by fishing gear
- Two were already dead when captured
- One was caught in fishing gear and released alive but was seriously injured
NOAA Fisheries scientists determined the cause of death for one of the previously dead whales was a strike from an unknown vessel (not the fishing vessel). Scientists were not able to determine the cause of death for the second whale. However, the body condition indicated that it had been dead for some time before being caught by the fishing vessel. Since it cannot be confirmed that the whale’s death was human-caused, it is considered natural mortality.
The six whales killed and one whale seriously injured by gear will be assigned to Alaska Bering Sea/Aleutian Islands flatfish trawl fishery on the Marine Mammal Protection Act List of Fisheries. This is an annually updated list of commercial fisheries classified based on incidental mortality and serious injury of marine mammals.
Incidental Catch from Pelagic Gear Targeting Pollock
A tenth killer whale was caught by a Bering Sea/Aleutian Islands catcher processor vessel using pelagic trawl gear to target pollock. We determined this whale was not killed by fishing gear, but was dead prior to being caught.
Incidental Catch from Alaska Fisheries Science Center’s Annual Longline Survey for Sablefish and Groundfish
The eleventh whale was taken during the Alaska Fisheries Science Center’s annual longline survey for sablefish and groundfish. The cause of death for this whale was determined to be entanglement in survey gear. This was the first observed killer whale mortality in the 30 year history of this survey.
Incidental Takes Are Below the Allowed Annual Potential Biological Removal Level
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.
We will undertake further analyses to fully assess the impacts of all human-caused mortalities and serious injuries for these stocks of killer whales in 2023. We do this every year for all marine mammal stocks. Scientists will examine additional data such as Marine Mammal Authorization Program self-reports from fishermen and strandings data.
NOAA Fisheries also anticipates releasing a new technical memo, Killer Whale Entanglements in Alaska: Summary Report 1991-2022, in the coming weeks. It includes comprehensive information about reported killer whale entanglement cases in Alaska over the past three decades.
“Given the high level of incidental catches of killer whales in 2023, we knew it was important to move as quickly as possible to better understand whether these incidental takes pose a conservation concern to any of the potentially affected killer whale stocks,” said Robert Foy, director, Alaska Fisheries Science Center. “As a result, we expedited processing and some procedures to complete genetic analysis as samples were received to provide some preliminary information on stock-specific impacts of these mortalities.”
We will continue to work with the industry and our own survey operations teams to explore ways to reduce killer whale interactions.