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Rising ocean temperatures intensify paralytic shellfish poisoning levels in Southeast Alaska waters

Aug 27, 2019

Blue mussels at Nahku Bay. (Photo by Claire Stremple/KHNS)

Over the past few months, levels of paralytic shellfish poisoning in Southeast Alaskan shellfish have been very high. A coalition of tribal organizations is tracking PSP levels to make sure subsistence users can safely harvest shellfish.

As Reuben Cash walked down to the water at Nahku Bay in Skagway at low tide, the beach was slick and… fragrant.

“That’s the life,” he said, inhaling deeply. “The inter-tidal zone is probably the most productive part of the rain system.”

He reached down and sifted some rocks and algae through his fingers.

“There’s lots of stuff down in this benthic zone. Things that are decomposing, things that are eating, lots of lots of nutrients and biomass,” he said.

The organism that causes paralytic shellfish poisoning or PSP is part of that flourishing life.

A surplus of sunshine and high temperatures can actually put too many nutrients into the system, resulting in an algal bloom. That imbalance is part of a recent spike in PSP levels in shellfish in Southeast Alaska.

“The general rule of thumb: If anything is doing too well, it’s probably causing the problem. The system really likes to be balanced,” he said.

Mussels and clams are filter feeders. So if there’s a toxin in the bloom, it ends up in their flesh. And that’s what we eat. PSP can be fatal at high levels, but just a little bit can cause vomiting, nausea, loss of coordination and other unpleasant symptoms.

The Food and Drug Administration sets the limit for PSP in bivalves at 80 micrograms per 100 grams. Over the last few months, Skagway’s blue mussels have had about 30 times the safe limit. Levels in Haines, Juneau and Ketchikan are even higher.

So Cash is out testing. He’s the Environmental Coordinator for Skagway Traditional Council, one of the fifteen tribal groups that organized into SEATOR: Southeast Alaska Tribal Ocean Research network. They have a special lab for testing shellfish in Sitka.

“The state does PSP testing for commercial shell fisheries. But there really isn’t anything for indigenous consumption. And so this is a way for people that are gathering for subsistence to know whether or not it’s safe,” said Cash. 

Cash is going to test the water for phytoplankton⁠—the organisms that cause PSP.  Back in the lab he’ll look at the samples under a microscope to see if any PSP-producing phytoplankton are among the organisms in the water.

Terns dart overhead as he wades out into the water with a fine mesh net and some testing bottles. If you didn’t know what he was up to, he’d look a little eccentric: waist deep in the cold water, dragging line behind him.

If there’s a lot of phytoplankton, he knows he should send some mussels to the lab in Sitka to be tested. Other than the state’s lab in Anchorage, it’s the only place for Alaskans to get their shellfish tested.

And SEATOR makes that data public.

“I’ve been trying to build models solely based on environmental data in order to predict when and where these blooms are going to happen,” said John Harley, a researcher with the Alaska Coastal Rainforest Center at the University of Alaska Southeast. He uses SEATOR data and any environmental data he can find to build these models. His goal is to predict blooms even in places where people aren’t expecting them. That’s because algal blooms and harmful toxins are starting to show up in new places, like St. Lawrence Island and Norton Sound.

He says this is almost certainly due to rising ocean temperatures.

“Some regions, especially in the Arctic, that don’t have a history of algal toxins or a history of PSP are going to start seeing these occurrences during the summertime,” he said.

Reuben Cash collects a mussel sample from the remains of a sunken ship. (Photo by Claire Stremple/KHNS)

Summertime spikes in PSP levels are common in parts of Southeast. But what has researchers like Harley concerned is the intensity of this spike. The concentration of the PSP toxin was much higher this year than in the past, especially in places like Juneau and Haines. But Harley says the toxin levels are going down now.

Back at the beach, Cash plucks about thirty mussels off the rotting remains of an old, half-submerged shipwreck and cleans them with a wire brush before dropping them in a five gallon bucket.  If he fills the bottom of the bucket with mussels that’s about 100 grams of meat ⁠— a perfect sample size.

“I can’t wait until the levels get back down,” he said. “I’m definitely coming back here to get some. It’s a treasure trove.”

The mussels go the SEATOR lab in Sitka. If the PSP levels are below 80 micrograms per bucket this week, locals will get the green light to harvest them again.