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During a spike in dangerous paralytic shellfish toxin levels, one scientist warns of impact on Yukon salmon

Climate change could be driving high levels of paralytic toxins in shellfish, like oysters.
Justin Sullivan
Getty Images
Climate change is also making ocean waters more acidic, potentially harming shellfish like oysters.

Over the past few weeks, the Knik Tribe's chief scientist has found very high levels of paralytic shellfish toxin (PST) in samples from mussels and clams in Southern Alaska. The FDA limit for safe consumption of PST is 80 micrograms, but several communities have seen levels many times higher.

  • Chignik Lagoon PST levels peaked in April 2020 at more than 140 times the FDA limit.  
  • In the Aleutian Islands community of Sand Point, mussels peaked in May 2019 at 17,900 micrograms, which is over 223 times the FDA limit. In July of that year, red salmon livers were at 103 micrograms. 
  • Yukon River king salmon livers have also exceeded the FDA limit for PST.

Paralytic shellfish poisoning (PSP) is a potentially fatal illness that comes from eating shellfish that have accumulated PST. Climate-change is warming the ocean, which is driving the spread of harmful algal events. Warming water temperatures, combined with the start of El Niño, exacerbate the algae blooms that cause the toxins to build up in grazers and filter feeders, which is a growing health concern to coastal Alaska communities.

As subsistence users, many coastal Alaskans rely on their local knowledge to determine whether it is safe to consume shellfish. Local knowledge presumes that PSP happens in the summer and can be identified by a red color in the water termed a “red tide.” That is not necessarily true.PSP toxicity can occur during any month of the year and, according to scientists, the algal blooms that cause it are normally colorless.

Knik Tribe Chief Scientist Bruce Wright said that the algal blooms that cause this toxin buildup usually start when water temperatures hit about 41 degrees Fahrenheit.

“And so we’ve been tracking the water temperatures, and then also monitoring blue mussels because blue mussels tend to come up faster than the other bivalves that people like to eat, like butter clams or surf clams,” Wright said.

The Knik Tribe has been involved in sampling, research, and mitigation of harmful algal blooms around the state since the 1970s. Earlier this year, it got federal funding for the sampling, testing, and outreach of PSP information. The tribe is conducting weekly blue mussel sampling at six locations across the state and along more than 800 miles of shoreline. The sampling stretches from the Aleutians all the way to Southeast Alaska, including near Juneau.

“That's a place where, like Sand Point, people have died from eating [PST] contaminated bivalves,” Wright said.

Crabs like these Dungeness can have elevated levels of paralytic shellfish toxins in their guts.

Contaminated crab butter

Some people eat crab viscera, or guts, and Wright said that it’s the hepatopancreas, the organ responsible for filtering impurities from the crab's blood, that causes problems. It’s commonly called crab butter, and lots of people have gotten sick from eating it. Although many find its flavor distinct and delicious, it is recommended not to eat it since many chemical contaminants concentrate in the organ.

“And we have found that, especially (in) Dungeness crab,” Wright said. “One person has died in southeast Alaska from eating Dungeness crab. And I have some data that indicates that not only Dungeness crab, but Tanner crab, snow crab, and king crab can have elevated levels of [PST] in their guts,” Wright said.

Although some people do eat crab butter, most don’t and opt to throw it away. If people do want to eat crab butter, Wright recommends sending samples in for monitoring. Wright said that he has not seen any elevated PST levels in crab meat.

Wright is working with Norton Sound Health Corporation Environmental Coordinator Emma Pate to collect samples from people that are eating king crab in the Norton Sound area. The Norton Sound Health Corporation established a trial series of harmful algal bloom sampling and monitoring program in 2020. Further development continued into 2022. It's intended to be a lifelong, forever program because climate will continue to change and impact the ocean and rivers. And people in Pate’s community and region are very subsistence activity oriented.

“So all the salmon and marine wildlife in our ocean is very important for us for food security. And we're looking for ways to ensure we can monitor the water quality through the base of the food web, which is algae,” Pate said.

In 2022, Pate started collecting samples 2 miles offshore of Nome. She received an Advisory from the research vessel Norseman II R/V on samples in July 2022 that were more than 18 times the normal levels of the toxins which prompted an advisory in Savoonga and Gambell. Pate said that these levels impacted the food web, as it was confirmed by a clam collected 3 miles north of Savoonga that tested over five times the food safety limit.

Not a new threat

“Alaska has a long history with PSP. I mean, the Alaska Native peoples have, you know, they've known about it for millennia,” said state biologist Matthew Forester.

Although the majority of his time is spent working with commercial fishing, Forester does work with other entities and organizations like the Knik Tribe, as well as researchers, research groups, and tribal groups focusing on subsistence harvest safety. Forester said that the state does not dictate the testing or sampling schedule to non-commercial fishermen. He said that they all have a good working relationship and his lab does testing five days a week.

Forester said that it is difficult to predict harmful algal blooms even though scientists are learning a lot through modeling and research. The most important thing he wants people to know is the risk of eating shellfish.

“The only way to ensure that the shellfish people are eating is safe is to test that shellfish," Forester said.

Yukon River salmon strips
Courtesy of ADF&G
Knik Tribe Chief Scientists Bruce Wright has linked high levels of paralytic toxins in fish like sand lance to the decline in Yukon king and chum salmon.

PST could be harming Alaska's fish 

Wright thinks that PST may be impacting fish.

“One of the issues that seems to be of concern is Yukon River king salmon and the juvenile king salmon,” Wright said. “A lot of them move down and spend several years eating in the Aleutian Islands where we have high [PST] levels, and the [PST] is propagating through the food web into forage fish, like sand lance.”

Wright said that he has found dead sand lance on the beaches occasionally in the Aleutian Islands. He has tested both sand lance and herring there and found high levels of PST.

“That's getting in the food web, and that can be taking out the rearing king salmon that spend several years feeding in the Aleutian Islands. That might be one of the factors that are affecting the decline of Yukon king salmon and chum salmon,” Wright said.

“The livers of king salmon, which are a delicacy for some people, are a risk factor for PSP toxicity,” Wright added.

Wright encourages people who are going to eat king salmon livers to throw them in the freezer and send him a sample to better understand the risk of eating that particular food.

The Knik Tribe is testing salmon to try to better understand this, and Wright said that both the Alaska Department of Fish and Game and the U.S. Fish and Wildlife Service sent them a lot of samples last summer.

Water temperatures were cold last year, but if the ocean water temperatures increase, because of El Nino, Wright predicts this year could be different.

Francisco Martínezcuello was the KYUK News Reporting Fellow from November 2022 through January 2024. He is a graduate of UC Berkeley School of Journalism. He is also a veteran of the United States Marine Corps.