Eating shellfish you’ve harvested yourself is risky - and can be deadly

In Southeast Alaska this summer, researchers have seen extremely high levels of toxins in mussels and clams plucked from beaches, prompting state health officials last week to warn that harvesting and eating shellfish is risky, sometimes even deadly.

The warning is a familiar one. State health officials regularly caution Alaskans that it’s unsafe to eat shellfish they’ve collected themselves because they may contain toxins that can lead to a disease called paralytic shellfish poisoning.

What’s different in recent years: “We’re seeing warmer water and we’re seeing an increased frequency of (harmful algal) blooms,” said Ginny Eckert, associate director for research at Alaska Sea Grant, a statewide program headquartered at the University of Alaska Fairbanks. The blooms of toxic algae are linked to paralytic shellfish poisoning.

By Wednesday, the Alaska Department of Health and Social Services had not yet received reports of anyone sickened by paralytic shellfish poisoning. Many times the disease goes unreported because symptoms are mild, said Joe McLaughlin, epidemiologist with the Alaska Department of Health and Social Services. But if enough of the toxin is ingested, it can kill you, he said.

“The state of Alaska does not recommend that people engage in recreational or subsistence harvesting because of the potential seriousness of this disease,” McLaughlin said.

While commercial operations are required to have their products tested for toxins, the state doesn’t have a program to test beaches where shellfish are harvested recreationally.

Shellfish that can contain the toxins include clams, mussels, oysters, geoducks, cockles and crab viscera, known as crab butter.


So far this year, elevated levels of the harmful toxins have been found in shellfish foraged from Southeast Alaska to the Gulf of Alaska, the Aleutian Islands and Kodiak Island, McLaughlin said. In some cases, the levels soared above the federal safety standard.

For instance, a blue mussel from a Juneau beach collected June 18 had toxin levels 55 times higher than what’s safe for eating, said Kari Lanphier, environmental lab manager at the Sitka Tribe of Alaska, a member of the Southeast Alaska Tribal Ocean Research network.

A butter clam from that beach had levels more than 30 times above the safety standard, and a mussel from Ketchikan had levels more than 15 times higher, she said.

High levels of toxin have also been found in cockles and littleneck clams, she said.

In the research network’s three years in operation, Lamphier said, “we have not seen levels like this before. … We’ve also never seen so many communities be so far above the regulatory limit.”

The culprit: Toxic algae. The algae lies dormant in sediment on the ocean floor, awaiting the right conditions to grow, Eckert said. That generally means sunshine and calm waters at 50 to 55 degrees.

Sometimes the waters in Southeast Alaska are too cold or it’s too stormy to foster toxic blooms. But in recent warmer years, the waters have hit the temperature zone more often, Eckert said.

“We're reaching that critical threshold in more years than we are in the past, so there is a link between warming and frequency of blooms,” Eckert said.

To eat, shellfish filter water through their systems, extracting food such as algae. Toxic algae can accumulate in shellfish tissues. Shellfish are resistant to the toxins but can pass them on to humans and animals who eat them, inducing paralytic shellfish poisoning.

The toxins are impossible to detect without testing, and they cannot be cooked out, McLaughlin said.

“These toxins are colorless, odorless and tasteless,” he said.

Symptoms of paralytic shellfish poisoning may appear within minutes or a couple hours of eating toxic shellfish. Early warning signs include tingling of the lips and tongue. That may progress to tingling of the fingers and toes, loss of muscle control and difficulty breathing. At its worst, if the concentration of the toxin is high enough, the poisoning may lead to paralyzed muscles of the chest and abdomen, resulting in death in hours, McLaughlin said. There is no antidote.

“Some of these toxins are 1,000 times more potent than cyanide, and toxin levels contained in a single shellfish can be fatal to humans,” according to the Alaska Division of Public Health.

Since 1993, four people have died from paralytic shellfish poisoning in Alaska, and there have been at least 120 cases of people sickened by it, according to reports received by the state health department.

Anyone who chooses to consume shellfish that weren’t commercially harvested should not eat alone, McLaughlin said. If symptoms arise, seek medical attention immediately, he said.

Suspected cases of paralytic shellfish poisoning should also be reported to the state Section of Epidemiology at 907-269-8000 or, after business hours, 1-800-478-0084.

Tegan Hanlon

Tegan Hanlon was a reporter for the Anchorage Daily News between 2013 and 2019. She now reports for Alaska Public Media.