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Over the past two summers, a pair of remote and treeless volcanic islands in the eastern Bering Sea broadcast signals of climate change danger in the marine ecosystem that feeds Alaska residents and supports much of the state’s economy.

Tribal employees monitoring St. Paul Island’s beaches came across 10 dead but seemingly well-fed northern fur seals in August of 2024, their bodies lying amid piles of dead fish and birds.

Testing revealed that the seals had been killed by an algal toxin that causes paralytic shellfish poisoning. It was the first ever conclusive case of marine mammals killed by saxitoxin, the algal toxin that causes paralytic shellfish poisoning.

The people living on St. Paul, numbering about 400, most of them Unangax, are highly dependent on the marine environment for their food. They are aware of the algal toxins that pose risks of paralytic shellfish poisoning in faraway Southeast Alaska. But seal deaths from algal toxin poisoning on their own island came as a big surprise to local people, said Aaron Lestenkof, who is part of the tribe’s Indigenous Sentinels Network.

“It never occurred to us that it may happen to our marine mammals here,” Lestenkof said. “I guess it was just a matter of time.”

The St. Paul die-off was not a one-time incident. In August of 2025, tribal residents found 21 dead fur seals on a beach at St. George Island, a sister island of St. Paul. Along with the seals were two dead fin whales, a dead sea lion and several dead seabirds.

The events show that deadly levels of algal toxins, once believed to be confined to the warmest waters in the warmest months in southernmost Alaska, are spreading north and into regions and parts of the food web that previously caused no worry for local people.

“This is the scary, ‘I-don’t-know’ moment of this event now happening in consecutive years,” said Mike Williams, one of the National Oceanic and Atmospheric Administration biologists who happened to be on scene at St. George to gather samples and document the event.

St. Paul and St. George, which has about 70 residents, are the only inhabited islands in the four-island Pribilof archipelago. Located about 750 miles west of Anchorage and 300 miles from the mainland, the islands are far from Alaska’s population centers. But the Pribilofs are at the center of a Bering Sea ecosystem so rich with marine life that they are sometimes called the “Galapagos of the North.”

The waters around the islands support some of the nation’s biggest seafood harvests, with vessels catching pollock, cod, halibut, crab and other fish. Millions of migratory seabirds of a dozen species flock each year to nest in the Pribilofs. The Pribilofs are the breeding grounds for two-thirds of the world’s approximately 1 million northern fur seals. Each summer, they gather on the islands’ rocky beaches in noisy congregations to give birth to and nurture their young, molt their fur and rest.

The algal discoveries on the St. Paul and St. George beaches point to a bigger phenomenon in the ecosystem, but how much bigger is yet to be determined.

“The problem is they die at sea. They’re being poisoned at sea, and they can’t even make it back to land, right?” Williams said.  “We don’t know how this may have population consequences because we don’t really have a true estimate of the number of animals that are dying.”

Paralytic shellfish poisoning: a history

Paralytic shellfish poisoning is a long-known hazard in the southern coastal areas of Alaska and other warmer parts of the world. Alaskans still know a spot in Southeast Alaska as Poison Cove, named for the approximately 100 people who died in 1799 after eating tainted mussels. The victims were Native hunters, either Unangan or Alutiiq, who had been brought to the site by Russian colonizers.

Saxitoxin is colorless and odorless. It cannot be cooked out or frozen out of food. Once ingested, there is no antidote. The poison acts within minutes, interfering with signals from the nervous system that enable vital bodily functions. In mild cases, many of which may go unreported, patients feel some numbness and possibly nausea and other symptoms before recovering. In fatal cases, saxitoxin blocks the nervous system’s functions, causing paralysis that suffocates victims.

From 1992 to 2021, 132 people in Alaska were reported sickened with paralytic shellfish poisoning, according to state epidemiologists. Between 1994 and 2020, five people died after eating saxitoxin-tainted food.

Understanding the exact chemical process that leads to paralytic shellfish poisoning took decades of scientific research. Saxitoxin was first identified in 1937 in an Alaska butter clam by a team led by Hermann Sommer at the University of California, San Francisco. They named the toxin for the species of the clam in which it was found: Saxidomus gigantea.

In later decades, researchers purified saxitoxin extracted from host clams and mussels. That led to a covert military operation. During the 1950s, the Central Intelligence Agency made mass purchases of tainted Alaska clams and developed saxitoxin into an alternative to the cyanide capsules that spies would use to kill themselves as a last resort if caught. Francis Gary Powers, the spy plane pilot who was shot down over the Soviet Union in 1960, was carrying a lethal dose of saxitoxin hidden in a modified silver dollar. He did not use it; he was freed in a spy trade in 1962.

The days of saxitoxin as a military tool are over. Now the ominous factor is climate change.

Saxitoxin is produced by a particular algae species, Alexandrium catenella, that blooms in warm conditions. The association of warmth and algal toxin risks was well-known; an old rule of thumb for harvesters was to gather clams only in months with the letter R in their names. An even older guideline was to use the end of herring spawning — an event usually in late spring — as the signal to pause harvests of clams for the season.

There are inescapable facts about the proliferation of Alexandrium and other harmful algae in Alaska: Ocean waters are getting warmer, and staying warmer longer, meaning there are more blooms producing more toxins and creating more exposure risks for marine life and for the people who depend on food from the sea.

Kathi Lefebvre, a NOAA Fisheries research biologist who specializes in algal toxins, ran through the trends during a presentation at January’s Alaska Marine Science Symposium in Anchorage. She showed charts and graphs of reduced sea ice, warming temperatures and Alexandrium blooms even in Arctic waters north of the Bering Strait.

“Do we predict that these blooms will continue to increase and toxins will be increasing in Arctic food webs? Yes, they will,” Lefebvre said in her presentation.

Risks increasing in the Bering Sea and farther north

Eight years before the St. Paul die-off, Lefebvre and her colleagues published a landmark study that documented at least trace amounts of algal toxins in each of the 13 marine mammal species tested, as far north as the Beaufort Sea in the Arctic. Toxins detected included a domoic acid, produced by an algae called Pseudo-nitzschia and the cause of mass die-offs of sea lions, seals and other marine mammals in California. Domoic acid has not yet proved to be a problem in Alaska, but scientists are watching for trends.

A more recent study led by Lefebvre found saxitoxin in feces of bowhead whales swimming in the Arctic.

In 2019, an especially warm year, scientists retrieved clams from the Bering Strait and Chukchi Sea that had levels of saxitoxin well above the threshold for safe consumption by people. That coincided with a large Alexandrium bloom in the region. Three years later, in another warm year, the Northern Bering Sea had one of the largest and densest Alexandrium blooms ever recorded in the nation, indicating more risks for poison-laden clams.

In July of 2024 and July of 2025, a month before each of the Pribilof seal die-offs, large blooms developed around those islands.

Don Anderson, an expert on harmful algal blooms who runs a lab at the Woods Hole Oceanographic Institution in Massachusetts, said there are now two major sources of far-north blooms.

Most of that algae is believed to have been carried north by ocean currents. But climate change has created a possible bigger local source of blooms, he said: germination from massive seed beds that are, by far, the largest and most concentrated ever documented in the world.

The Bering, Chukchi and Beaufort seas used to be dead ends for Alexandrium cysts, the equivalent of seeds. They settled in the sediment after decades and centuries of being washed north, remaining dormant in the cold temperatures.

“We kept having repeated inputs of transported blooms from the south, and that gave us these enormous cyst concentrations that we haven’t seen anywhere else in the world, something we’ve called the sleeping giant,’” Anderson said in a presentation at the marine science symposium in Anchorage.

The warm conditions that enable them to germinate have arrived, albeit sporadically. If temperatures at the seafloor reach a little over 8 degrees Celsius, the cysts can germinate within about 10 days and proliferate during the long daylight hours of Alaska summers, he said.

The new findings have created unease for some Western Alaska residents.

Valerie Tony of Alakanuk, a Yup’ik village near the mouth of the Yukon River, is one of them. At a February workshop on algal toxins held in Anchorage, she asked about the abundant freshwater clams that her people harvest from tundra ponds.

“Does that mean our clams are no good now?” Tony asked. “Any kinds of toxins, we’ve never had to deal with these before.”

The bivalves enjoyed in Alakanuk and other Yukon-Kuskokwim Delta villages are actually mussels colloquially known as Yukon floaters. They should be safe for now, said Thomas Farrugia, coordinator of the Alaska Harmful Algal Bloom Network, a multiagency program.

For St. Paul and St. George residents, food questions are a bit different.

The traditional subsistence diet in the Pribilofs relies little on clams or mussels, wild foods that are the usual sources of the toxins that give people paralytic shellfish poisoning. But residents of St. Paul and St. George rely heavily on the sea for food. That includes fish, like halibut, cod and crab, but also fur seals that are legally hunted in traditional Indigenous harvests.

It is unclear how the fur seals are getting exposed to saxitoxins. Unlike marine mammals considered to be at risk for algal toxins like clam-gobbling walruses and sea otters,  fur seals do not eat bivalves. They do eat squid and schooling fish, including a tiny, slender, silvery fish called sand lance, which is known to absorb large concentrations of saxitoxin.

Luckily for seal hunters, Lestenkof said, the new pattern of Alexandrium blooms seems to be timed to late summer, in between early summer and autumn hunts. But whatever fish the dead seals were eating could be food that the people eat as well.

Sitka a model of testing

About 1,300 miles east of St. Paul, in the rainforest-surrounded coastal town of Sitka, a tribally-operated lab was established in 2016 to help keep locally harvested food safe.

The Sitka Tribe of Alaska Environmental Research Lab is the state’s main algal toxin testing facility for personal harvests. The other main lab in the state, located in Anchorage and operated by the Alaska Department of Environmental Conservation, focuses on commercial harvests.

The Sitka lab accepts any samples brought or sent to it. Mostly, those have been from harvests from Southeast Alaska, though it has tested samples from as far away as Nome.

The lab uses a method called Receptor Binding Assay, a widely used scientific method that measures how well certain chemicals bind to selected materials.

As Environmental Lab Manager Matteo Masotti describes it, the process used in Sitka is intended to parallel what would happen if people ate the tested clams, mussels and other items.

The testing starts with a slurry created once shellfish are delivered. “We blend them up into what we call a shellfish smoothie,” Masotti said. Effective testing generally requires six individuals or 100 grams of tissue, he said.

From there, acid is extracted, “basically simulating the pH of the stomach as if someone was digesting.” Then samples are tested for how well they bind to a swine tissue, a stand-in for a human stomach membrane. Once samples bind, another material is added that converts their chemical radiation into flashes. Those flashes reveal saxitoxin quantities.

It is only one method of testing shellfish. Other labs, such as the state’s Anchorage lab, use different methods, each of which have advantages and disadvantages.

The goal in Sitka is to get results to people within a couple of days, which is not always easy.

“The people out there have to harvest the shellfish, they have to get it to the airport, send it to us – assuming it doesn’t get delayed at the airport and assuming we pick it up immediately, which we try to be really good about,” he said. “We get them, we have to blend them up, we have to extract them, we have to then run them on the test, and then we have to analyze the test. And so we try to give people results in one to two business days after submission. Not always possible, but we do our best.”

There is even a slogan for the process of waiting for test results: “Harvest and Hold.”

In a lot of ways, the Sitka operation is a big success story.

Sienna Reid, a young tribal employee who grew up in Sitka, said the lab’s operations are giving people confidence that their traditional harvests are safe.

She said she has seen no decline in clamming, despite what is now an abundance of information about algal toxins’ presence in the environment. That was not the case in the past, she said. “I remember clam digging growing up. I don’t remember even thinking about algal toxins,” she said.

But for Amos Philemonoff, another young tribal employee who happens to be from St. Paul, information about algal toxins is still off-putting.

When he learned from a St. Paul friend about the 2024 seal paralytic shellfish poisoning deaths, he was taken aback. “I thought that was so weird. I’ve never heard of that before,” he said.

Though he enjoys plenty of wild food, Philemonoff stays away from clams, even though they are widely enjoyed in his adopted home of Sitka. That is specifically because of algal toxins, which he learned about when he was attending Sitka’s Mount Edgecume High School, a boarding school. “It’s kind of scary now, after learning about it in marine biology,” he said. “I kind of stepped away from eating shellfish.”

New challenges in old places

While paralytic shellfish poisoning is a long-recognized hazard in Southeast and Southcentral Alaska, climate change has exacerbated the threat in those regions.

The old guidelines about months with the letter R or timing of herring spawning no longer hold because algal toxins are present beyond the summer.

A significant bloom of Alexandrium was detected last September in Southcentral Alaska’s Kachemak Bay. It was the highest abundance measured since 2016. Blue mussels and butter clams found that month had saxitoxin levels about the safety threshold. The bloom followed a spate of bird and marine mammal die-offs earlier in the summer in the bay, and it did not dissipate until early October.

There are algal toxin  hotspots even in winter. In the far Southeast community of Hydaburg, for example, information from the shellfish data system includes a butter clam found on Dec. 5 with saxitoxin levels more than four times the safety threshold for human consumption. It turns out that some bivalve species, like butter clams, can retain algal toxins in their tissues for several months, and sometimes for more than a year.

Another challenge facing the Sitka lab, also related to warming conditions, is the proliferation of invasive European green crabs in the most southern parts of Southeast Alaska.

The invasive species, known for mowing down eelbeds and devouring native fish, was not seen in Alaska waters until 2022. Last year, the tribal government in Metlakatka, in the far southeast corner of the state, trapped more than 40,000 of them.

To avoid spreading the invasion further, the Sitka lab requires that samples sent from the most southeastern part of the state be frozen for at least 24 hours to kill any green crab larvae that might be attached.

Replicating Sitka success

Compared to other states, Alaska has little safety testing for personal harvest of shellfish. Tribal and science organizations are trying to change that.

The Sitka lab’s services are available free of charge to all personal-use harvesters in the state, but deliveries from remote areas outside of the Southeast Alaska region are logistically difficult.

Locally focused shellfish-screening labs have also been set up on the Kenai Peninsula south of Anchorage: in Seward, at the Native-owned Alutiiq Pride shellfish hatchery, and last summer in Homer at the Kachemak Bay Research Reserve.

An innovative research program led by the Knik Tribe, based in the Matansuka-Susitna Borough near Anchorage, has been tracking the movement of toxins through the food chain. It has gathered samples from various parts of the state, including some from as far away as the Bering Strait. Tests are conducted at the state Department of Environmental Conservation lab.

The Paralytic Shellfish Poisoning Risk Management Project is examining not just clams and mussels but also crabs and finfish, and the program has discovered high levels of saxitoxin in some unexpected places.

Livers and digestive tracts of salmon from the Yukon River and Cook Inlet turned out to have saxitoxin levels above the safety threshold. Hermit crabs from the Kodiak Archipelago and the Alaska Peninsula were found to have saxitoxin levels 15 to 17 times the safety threshold. And a stickleback from Wasilla north of Anchorage was found with a level more than 50 times the safety limit. Sticklebacks are small spiny fish found in different varieties and widely abundant in Alaska in both freshwater and saltwater systems; they are not generally eaten by people, but they are important prey for birds and larger fish.

Funding for the four-year research program, provided by the federal government, ends this year. The Knik Tribe and the Alaska Federation of Natives have urged the state to take up responsibility for funding the program into the future.

No lab in the state tests marine mammals for saxitoxin. Tests of the dead Pribilof northern fur seals were conducted at a lab in Seattle that is part of a West Coast program monitoring toxins in marine mammals.

For residents of St. Paul and St. George — both remote and often fog-bound islands dependent on air service that is spotty, inconsistent and expensive — relying on distant labs for toxin testing has been burdensome.

“I mean, there’s just a million billion things that sometimes are against us to get this information back to the community in a timely manner,” said Chelsea Campbell, marine mammal programs manager for the Aleut Community of St. Paul Island. It can take weeks to get results back to the island, she said.

That is why the tribal government is planning to add algal toxin testing to its on-island science program, Campbell said. The tribe already operates a facility, the Bering Sea Research Center, that tracks things like mercury and microplastics in the ecosystem. It is taking the necessary steps to add algal-toxin testing as early as this summer, as long as equipment arrives and workers are available and trained, she said.

The hope is that in time, the St. Paul lab will serve other remote communities in Western Alaska, from the Aleutians to the Bering Strait. “It’s going to be much easier for Saint George to send us samples than it is to send samples to Seattle, right?” she said.

Such a lab would be a big improvement over status quo in Western Alaska, which is to either take risks or use an old-fashioned screening process that Alex Zaochney, a researcher and tribal council member with the Native Village of Atka, described at the Anchorage workshop on harmful algal blooms.

“I wouldn’t recommend it,” Zaochney said. “Traditionally, we would touch the tip of your tongues on it and wait 20 minutes. If you start to get a tingle, that is not good.”

This article was produced as a project for USC Annenberg’s Center for Health Journalism and Center for Climate Journalism and Communication 2025 Health and Climate Change Reporting Fellowship.

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