Trawl catch of killer whales brings new scrutiny to federal science behind Alaska take levels

Up to 19 fish-eating resident North Pacific killer whales can be accidentally killed annually by Alaska fishing fleets or other human activity without triggering a federal effort to reduce this toll.

This take number has received renewed scrutiny in the aftermath of a Sept. 21 NOAA Fisheries disclosure that 10 killer whales were incidentally caught this year by Bering Sea trawl vessels. One was released alive.

It represents a NOAA Fisheries determination of the toll that humans can take each year without impacting the optimum population of resident killer whales off Alaska. Some scientists say it is based on an outdated assessment, and is likely too high to protect smaller genetically distinct populations.

“Killer whales are an iconic species,” said Doug DeMaster, who served as director of the federal Alaska Fisheries Science Center from 2001 to 2018. “A reasonable interpretation of the current data is that the current bycatch levels could be adversely affecting a western stock of resident killer whales.”

[10 killer whales caught this year by trawl vessels off Alaska, according to federal fisheries agency]

Some of the catcher-processors that target yellow-fin sole and other bottom-dwelling fish were involved in the 2023 accidental take of killer whales, according to a statement from the Groundfish Forum, an industry group.

Another killer whale did not appear to survive an entanglement this year with longline gear deployed by a federally contracted research boat.

In years past, some killer whales have died in encounters from trawl and other fishing gear off Alaska. The levels this year are much higher than the levels reported in any one year during the 1991 to 2020 period, according to mortality information published by NOAA Fisheries.

Killer whales off Alaska are currently divided into three broad groups: offshore that feed primarily on sharks, transients that focus on smaller marine mammals and the residents that are nourished by fish.

NOAA Fisheries will conduct genetic testing of the dead whales caught in the trawl nets to determine if they are resident killer whales or from the other two groups, according to the statement posted Sept. 21.

These populations are not listed under the federal Endangered Species Act. They do have safeguards under the Marine Mammal Protection Act that calls for NOAA Fisheries to authorize any incidental take of the whales due to commercial fishing or other human activities.

The act calls for “potential biological removal levels” to be established for the resident killer whales. If that number — now set at 19 — is exceeded, NOAA Fisheries would be expected to designate these stocks as strategic and could eventually put together a team of conservation, fishing industry, government and scientific representatives. Their task would be to come up with a plan to reduce the annual deaths.

Since that number has not been exceeded, the resident killer whales are not deemed to be strategic. And, “it is not clear” that a team would be convened, said Julie Fair, a NOAA Fisheries spokesperson, in a statement.

Hannah Myers, a University of Alaska Fairbanks doctoral student who studies killer whales, spent a week observing them aboard a trawler in May as a researcher for the North Gulf Oceanic Society under contract to the Alaska Seafood Cooperative. The roughly two dozen killer whales she saw were feeding on fish, and she believes they were residents.

The 2023 year’s take of killer whales has prompted bottom trawl industry officials to try to come up with changes in fishing gear in an effort to reduce the killer whale deaths.

One vessel skipper experimented this year with a kind of water kite that stretched out in front of part of nearly half the net’s opening, according to John Gauvin, fisheries science director for the Alaska Seafood Cooperative. Gauvin said that the kite did not appear to impede fishing but more study is needed to determine how effective it could be in keeping whales out of the net.

Other options under consideration include a widely spaced rope barrier at the mouth of the net or an excluder device that would lead a whale to an escape portal, according to a research proposal.

As part of that effort, some trawl lines would be coated with an “acoustically reflective” material such as iron oxide or barium sulfate so that whales could more easily detect the nets and hopefully avoid them.

Killer whales, also known as orcas, may live for decades.

The current resident population stock grouping off Alaska notes a minimum of 921 whales in the Gulf of Alaska. It also cites a minimum count of 999 for the Aleutian Islands and Bering Sea, according to a federal stock assessment — revised in June of this year — that reaffirmed that up to 18 resident whales could be taken without impacting the population.

But the document is prefaced by a bold-faced note that says, “genetic information on killer whales in Alaska … indicates the current stock structure needs to be reassessed.”

The case for revising the threshold removal number — known as the “potential biological removal” — was made a decade ago in a study led by Kim Parsons, a National Marine Fisheries Service researcher. That study found strong evidence of genetically distinct subpopulations of the resident killer whales, which have a fish-based diet, as well as different populations of transient killer whales that prey largely on marine mammals.

These findings “highlighted the need to revisit current stock designations,” which are a “critical component for evaluating the impacts of incidental bycatch” in fisheries, according to a 2013 Journal of Heredity article about the study by Parsons and nine other scientists.

The genetic divisions among the resident populations could include a Gulf of Alaska group that reaches to the Kodiak area, and others farther to the west.

A federal move to reclassify them into smaller groups would need a formal reassessment of stock structures that looks more closely at their range, diet and other information. An Alaska scientific review group has repeatedly recommended that a study be done, according to Craig Matkin, a former member of that group who said he quit in frustration when that failed to happen.

“There’s just no excuse for it,” said Matkin, founder and executive director of the North Gulf Oceanic Society.

In a 2022 response to the science review group, the National Marine Fisheries Service stated that the agency did not have the resources to conduct a comprehensive modeling effort.

DeMaster said that Congress does not allocate enough money to comply with all the requirements of the Marine Mammal Protection Act. And during the past decade, other stock reassessments have had a higher priority, including Cook Inlet beluga whales and harbor porpoises in Southeast Alaska.

“Every year there was a triage of what’s the most important,” DeMaster said.

Scientists are hoping to learn more about why the death of killer whales escalated this year.

Myers’ research found whales taking deep dives to swim near the nets while they were catching fish, and also pursuing the nets as they came to the surface.

Researchers say that killer whales pass learned behavior from one to another. So, if feeding around trawl boats is successful, that tactic can spread to more whales.

Could the dire consequences for some whales that were trapped in nets eventually prompt others to be wary of trawlers?

That is uncertain.

“We assume that whales are aware when one gets caught in a trawl and dies,” Parsons said. “But there are a lot of assumptions there. And it’s hard to know how often that would have to happen before they would make that connection.”

Journalist Hal Bernton has covered Alaska fisheries issues extensively. He was a longtime reporter for The Seattle Times, and previously reported for the Anchorage Daily News and The Oregonian. Reach him at hbernton@gmail.com.