Sea Lions, Seizures, and Food Safety: What have Pacific sea lions gotten into and does it pose a risk to humans?

Sea Lions in San Diego © Marshall Masterson 2014Sea Lions in San Diego © Marshall Masterson 2014

By: Thomas Masterson, Editor,


Before the start of the new year, the nation saw a peculiar subject emerge in the headlines: sea lions getting dementia from eating fish. The news described a strange phenomenon involving sea lions getting severe brain damage, amnesia and epilepsy from consuming fish with high levels of domoic acid, a byproduct of the El-Nino related algal blooms. As the news came out, we stopped short of asking ourselves: don’t people eat fish too? Could sea lions be the aquatic version of the canary in the coal mine? After much investigation, a pattern began to emerge suggesting that sea lions are not the only ones in trouble.

While panic makes for a great story, I turned to the California Department of Health to see what public announcements the state had made on domoic acid in the seafood supply. At first glance it seemed as though the state has their eyes on the problem, and I quote:

“The California Department of Public Health is updating its warning to consumers regarding certain seafood caught along the California coastline that may contain high levels of domoic acid. Advisories continue to be in place for:

  • Consumers to avoid eating recreationally and commercially caught Dungeness and Rock crabs caught in waters between the Oregon border and the southern Santa Barbara County line, due to the persistent dangerous levels of domoic acid in these species.

  • Consumers to avoid eating recreationally harvested bivalve shellfish (mussels and clams) from Humboldt or Del Norte counties. The white meat (adductor muscle) of scallops caught in these areas may be consumed; however, the viscera (internal organs) should be discarded.

However, an advisory is no longer in place for bivalve shellfish like mussels and clams or for small finfish like anchovies and sardines caught in the Santa Cruz, Monterey, or Santa Barbara County areas. Recent testing has determined that domoic acid has declined and remained at undetectable levels in samples of these species from these areas.

CDPH is continuing to work with the California Department of Fish and Wildlife, which recently issued emergency regulations closing the recreational and commercial Rock crab fishery and delaying the start of the recreational and commercial Dungeness crab fishery between the Oregon border and the Ventura / Santa Barbara County Line due to dangerous levels of domoic acid found in crabs caught from these areas.

Domoic acid accumulation in seafood is a natural occurrence that is related to a ‘bloom’ of a particular single-celled plant in ocean waters. The conditions that support the growth of this plant are impossible to predict. CDPH will continue its efforts to collect a variety of samples from impacted areas to monitor the level of domoic acid in seafood.

Symptoms of domoic acid poisoning can occur within 30 minutes to 24 hours after eating toxic seafood. In mild cases, symptoms may include vomiting, diarrhea, abdominal cramps, headache and dizziness. These symptoms disappear within several days. In severe cases, the victim may experience trouble breathing, confusion, disorientation, cardiovascular instability, seizures, excessive bronchial secretions, permanent loss of short-term memory (a condition known as Amnesic Shellfish Poisoning), coma or death. There have been no reported illnesses associated with this event.”

The California Health Department’s warning related to the state’s $24 billion seafood industry (source: NOAA) is correct, but stops short of providing the full story. People have been injured in the past by domoic acid from shellfish in the 1980’s and not everyone recovered. The domoic acid poisoning was called “Amnesic Shellfish Poisoning” because a few people lost their short term memory.

Dr. Peter Cook, a researcher who has studied the effects of domoic acid on sea lions, has noted in his work that the sea lions affected by domoic acid had anatomic brain damage. The recent articles about amnesic injuries in sea lions quote from research by Dr. Cook, who was kind enough to provide some perspective to about what we know and don’t know about domoic acid poisoning in sea lions.

Dr. Cook started by clarifying the condition found in the sea lions, “More accurate to say acquired epilepsy. Yes, they end up with hippocampal lesions and disrupted hippocampal connectivity, but the mechanism appears to be nearly identical to temporal lobe epilepsy in humans.”

The original case study of human exposure took place in Canada in the late 1980s. “The big human case, resulting in a number of deaths and long-term anterograde amnesia in some survivors led quickly to uptake of strict regulatory measures, and there haven’t been any big human cases documented since.”

“Domoic acid has been found at high levels in the tissues of a number of marine predators, including birds (Hitchcock’s The Birds is believed to be based on a case of domoic acid poisoning in sea birds). It’s by far best studied in sea lions, who strand when in distress (and who strand with domoic acid poisoning in large numbers).”

Do you think that shellfish are the issue or are fish the issue? Are any food species an issue in particular?  

Dr. Cook: “Domoic acid is a natural byproduct of common algal blooms. Domoic acid gets into the food chain in a few different ways. It gets into fish when fish schools form around the algae and eat the algae, and from there into high-level marine predators like sea lions, dolphins, and sea birds, who exploit large fish schools. Shellfish filter domoic acid out of the water, and it can get from there into otters and humans. Also, domoic acid gets into crabs (likely from feeding on dead tissue of animals who either ate domoic acid-producing algae or filtered the water) and from there into humans, otters, and a number of near-shore pinniped seals.”

Do you think we are looking at an issue of cumulative exposure, or just a single season algal bloom?

Dr. Cook: “Really don’t know! The dose-response stuff is hard to determine in the wild. Domoic acid poisoning has been studied in rats, but toxic effects in rats don’t appear to match up well with what’s observed in sea lions (perhaps due to different hippocampal morphology and connectivity, metabolism, life span, size, who knows?). We do know that most observed cases in sea lions used to be following right on a big toxic algal bloom. Now sea lions come in all year round with chronic symptoms of toxicosis. So it seems a safe bet that something has changed to cause the long-term effects. Whether this is bigger doses from bigger blooms, or more frequent doses remains to be seen.”

Are there any measures of this toxin in the seafood supply now?

Dr. Cook: “Definitely. There’s a huge domoic acid bloom that’s persisted off the West Coast for months now. Many have linked it with “The Blob,” the big body of warm water that’s been off the West Coast this year (likely related to El Nino). Algal blooms seem to do better in warmer water. NOAA has measured domoic acid in tissues of marine animals all the way up to Alaska this year, much farther north than ever before, so we know it’s making its way up the food chain. There have been a number of high profile crab fisheries closed in late fall on the West Coast due to high domoic acid levels in the crab.”

Do you think that what’s affecting the sea lions could be affecting humans who eat fish?

Dr. Cook: “Commercial fish stock are closely tested. However, it’s certainly possible that people fishing for their own food, or catching crab or shellfish for personal consumption are being exposed at worrying levels and with worrying consistency. Lots of folks are working on this right now.”

What question should I have asked (and what’s the answer)?

Dr. Cook: “As I noted above, domoic acid exposure can cause chronic, intractable epilepsy in exposed sea lions. We don’t know the dose size or frequency required to lead to this condition yet. However, this is a big concern. domoic acid-producing blooms have become bigger and more frequent and longer lasting over the last 10-15 years, and the trends appear to be continuing in the same direction. Sea lions are visible sentinels of ocean health, due to their large numbers and tendency to come to shore when in distress. If they’re being affected so severely, it’s likely that other large marine predators who are less accessible for study are also being affected. Without the treatment human epileptics get, these marine animals appear to develop very serious spatial memory deficits, which is potentially problematic for dynamic foragers acting in large, changing ocean environments.”

“Humans are also being exposed, at very low levels from commercial sources (probably safe) and at variable and potentially more dangerous levels if they eat unregulated sea food (e.g., local crab fisherman who fishes for personal consumption, various coastal living people who eat large amounts of unregulated shellfish). Sea lions could serve as a good model for possible effects in humans – they’re long-lived, big-brained mammals exposed naturally over long periods of time. They may serve as a warning for what could start happening in humans.”

In preparing for this article, I found that Dr. Cook studied the effect of disco on a sea lion. That led to my next question:

So it’s definitely the domoic acid and not the disco music that’s messing up sea lion brains? 

Dr. Cook: “Ronan the disco sea lion seems to be doing very well, despite her now three years of bobbing to music in the name of science!”

While conversing with Dr. Cook provided deep and thoughtful answers, it is clear that many questions still remain unanswered and our health departments have shown they can’t protect our sea lions. What have these sea lions gotten into and does it pose a risk to humans?

Peter Cook studies the relationship between brain and behavior in a wide range of animal species, with a particular interest in examining animals in their natural environment. He obtained his PhD at University of California Santa Cruz, where he conducted research into the effects of domoic acid on wild sea lions. He is now a post-doctoral fellow at Emory University, where he splits his time between using functional brain imaging to study decision making and emotion in domestic dogs, and using structural imaging to look at networks in post-mortem brains. He and his colleagues are studying differences in sensory and motor connections across different species, including whales, carnivores, and even marsupials.

Thomas Masterson is Chairman of Medicine at Medstar Southern Maryland Hospital. He serves as Editor at and is the Chief Medical Officer at the American Association of Hospitalist Directors.