Decades ago, sperm whales learned how to raid fishermen’s lines of black cod. Now, an Alaska man is charged with killing one.

A Ketchikan fisherman has pleaded guilty in federal court to killing an endangered sperm whale in a first-of-its-kind case that highlights a long, little known conflict between the giant toothed whales and the fishermen whose sablefish catch they have learned to raid.

In a proposed plea agreement filed May 15, Dugan Daniels agreed to plead guilty to one charge of an illegal taking under the Endangered Species Act, a class A federal misdemeanor.

The charge stems from a March 2020 incident in which Daniels, 54, “knowingly took an endangered species of wildlife” by “having a crewman shoot the whale and trying to ram the whale with the F/V Pacific Bounty” in the Gulf of Alaska about 30 miles west of Yakobi Island, near the community of Pelican in Southeast Alaska, according to court filings in the case.

The case appears to be the first time someone has been criminally charged for taking a sperm whale in Alaska, according to the U.S. Attorney’s Office of Alaska.

Sperm whales can be more than 50 feet long and weigh up to 90,000 pounds. They’ve been listed as an endangered species since 1970.

Decades ago, sperm whales learned to pluck commercial fishermen’s catch from their gear, gaining an easy meal but costing fishermen a day’s work and ruining gear and putting whales at risk of entanglement or injury. Scientists call the phenomenon depredation, and an innovative collaboration between the fishermen and scientists in Alaska has long looked for ways to avoid conflicts.

For the most part, that collaboration has been successful, and fishermen have changed gear types to deter the whales from raiding their catch.

“I am deeply dismayed,” wrote Linda Behnken of the Alaska Longline Fishermen’s Association. “Longliners were proactive about seeking solutions to whale depredation and our organization worked hard to develop deterrents and avoid conflicts. Most eventually switched to pots as the most effective solution.”

“Whale depredation can be frustrating — I understand that— but I cannot comprehend what Mr. Daniels did,” she wrote.

Daniels also will plead guilty to a false labeling charge associated with black cod harvests he said took place legally in federal waters, but actually happened illegally in prohibited state waters. The plea agreement doesn’t discuss Daniels’ motive for illegally taking the whale.

Daniels’ federal public defender said she had no comment on the case.

It’s not clear how the National Oceanic Atmospheric Administration’s law enforcement arm caught wind of the incident, which happened in the open ocean, or why the case was charged more than four years later.

But the plea agreement suggests Daniels wasn’t quiet about it.

In text messages, Daniels “recounted these events — specifically, his crew shooting the sperm whale, his efforts to ram the whale with the vessel and coming within five feet of doing so, and his desire to kill the sperm whale,” according to the plea agreement.

It doesn’t say anything about what Daniels was fishing for on that day in March, or what kind of gear he was using or how he knew — and prosecutors knew — the shot whale died.

Sperm whales are found in every ocean on the planet. They were hunted heavily in the 19th century for a waxy substance produced by their digestive systems.

The 19th century classic “Moby Dick” was about a fisherman driven to madness in pursuit of a sperm whale.

Like humans, sperm whales love sablefish, also known as black cod, a fish prized for its rich, buttery taste.

Alaska fishermen used to harvest black cod in frenzied derby-style openings using longline gear. Then, in the 1990s the derby style opening was changed to a quota system, where fishermen with permits could harvest sablefish over a longer, monthslong commercial fishing season.

That’s when sperm whales started to regard the distinctive sound of longline gear dropping lines as something like a dinner bell.

“They use acoustic cues, sounds like a boat hauling gear. And they’re really deep-diving, capable of going to the bottom of a set,” said Suzie Teerlink, a marine mammal specialist with NOAA.

The whales would pluck an entire set worth of sablefish off longlines. For black cod fishermen, sperm whale depredation became not just an annoyance but a major financial and gear loss.

In 2003, a collaborative research project called SEASWAP was born, looking to understand the relationship between the whales and longline fishermen and to come up with ways to deter conflicts, said Jan Straley, a retired Sitka whale biologist who was a co-founder of the effort.

“The fishermen really drove the study,” said Straley.

In recent years, fishermen started to use a different kind of gear, called a slinky pot, that’s harder for marine mammals to break into than traditional longlines, said Teerlink.

But not impossible: In the Bering Sea and Gulf of Alaska, there have been documented occurrences of sperm whales taking catch even from slinky pots, she said.

Sperm whales are so intelligent, it’s hard to stay one step ahead, Teerlink said.

“They’re really smart and are capable of learning human patterns and taking advantage of ways to get food.”

Daniels is set to appear in federal court on June 6 in Juneau.