Research published last month in the journal Marine Mammal Science linked fur seal deaths in the Bering Sea to the same toxins that cause paralytic shellfish poisoning. It marks the first documented case of harmful algal blooms leading to a marine mammal die-off in Alaska.
Last summer, about ten dead fur seals washed up on a beach on St. Paul Island, a small community in the middle of the Bering Sea.
Tribal staff from the Aleut Community of St. Paul Island, the community's tribal government, recovered the fur seals, froze their carcasses and sent tissue samples to a lab that monitors algal blooms nationally.
Lauren Divine, director of the tribe's Ecosystem Conservation Office and co-author of the article, said the results indicated that the seals had been poisoned by saxitoxin — a well-known neurotoxin commonly found in shellfish but previously undocumented in Alaska seal populations.
"This is, in fact, the first documented marine mammal die-off with saxitoxin as the suspected cause, and so that was super important for us to get it out there and get everyone aware of it," Divine said.
Certain algae and plankton naturally produce saxitoxin, which is harmless in small quantities. In large amounts, it shuts down the nervous system, stopping nerve and muscle cells from sending signals. This causes numbness, paralysis and can lead to death by respiratory failure.
"It paralyzes the body. It likely caused them to just suffocate, not even drown, but just stop their lungs from working, stop all of their systems from working," Divine said.
Algae are a natural part of the Bering Sea ecosystem, but warming oceans have disrupted their cycle — causing harmful blooms to appear more frequently and with greater toxicity.
"We're seeing this really just stark warming every year without any type of resetting it back to cold," Divine said. "Seeing toxic algal blooms and toxic phytoplankton as often as we are is something that is really alarming."
Fur seals are an important subsistence food for St. Paul, but so far, there's no sign of risk to the community. That's because people only harvest young males, and those animals haven't shown signs of exposure. The seals affected were mostly females and pups, which feed more actively at sea.
The tribe is monitoring closely. As of now, Divine says the fur seal harvest is safe for the upcoming subsistence season.
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