Mysterious Sea Lion Deaths On US Coast

Mysterious Sea Lion Deaths On US Coast

National Marine Fisheries Service and National Ocean Service found that a natural toxin caused by a harmful algal bloom resulted in the death of more than 50 California sea lions in the Monterey area.
California Sea Lion


In just a few days, nearly 80 adult and juvenile California sea lions washed ashore in obvious physical distress along the coast from Santa Cruz to San Luis Obispo. Rescuers from the Marine Mammal Centre in Sausalito sad that these sea lions exhibited vomiting and seizures, which are strong signs of being exposure to a toxin affecting the nervous system.

The mystery of why sea lions have been stranding in droves on US west coast beaches in recent years is one step closer to being solved. A new study suggests that sea lions have been eating fish and crabs laced with the toxic domoic acid from algae, which causes brain damage and chronic seizures impairing the animal’s’ ability to eat, navigate, and generally survive in the ocean.

Harmful algal bloom in a healthy population of animals like the California sea lions may have a significant impact, but if the species is critically endangered, it can be devastating. Scientists are encouraged that information learned from this terrible event will help them to more effectively respond to future sea mammals exposures to biotoxins.

Initially, scientists from the state of California considered 3 possible causes of deaths: infectious disease, pollution or natural biotoxins from harmful algal blooms. High levels of domoic acid were found in anchovies and sardines, a common sea lions diet, which further indicated that these deaths can be linked to a harmful algal bloom. Scientists conducted more blood tissue and other biological tests on these animals and found that stranded California sea lions had microscopic lesions in certain sections of the brain, consistent with seizures in animals and known effects of domoic acid poisoning.

Biotoxin analysis on the sea lions urine and tissues resulted in only 4 confirmed positive tests for domoic acid. But, scientists stressed that the lack of positive findings doesn’t necessarily indicate that these sea lions were exposed to domoic acid. The toxin has left the body very rapidly and is often very hard to detect. Scientists also searched for evidence of human-caused acute infectious disease or chemical pollution, but neither factor was implicated in the event.

The conclusion of scientists were further supported by the fact that some sea lions recovered very fast as a result of emergency medical care as opposed to animals with infectious diseases, which generally take longer time to respond to treatment. Of the sea lions treated at the Marine Mammal Centre, more than 50 animals died, while 19 appear to be fully recovered and 29 are still alive.
California Sea Lion
Historically, the toxic algal bloom would last just about a month, but due to warmer waters from this year’s El Niño weather phenomenon and climate change, this time bloom lasted for months. Persistence and its northward expansion make studying the ‘sub-lethal chronic effects’ of domoic acid on animals highly important. Further investigation of this horrible event will help scientists determine whether future effects on sea mammals can be predicted, and thus determine the most effective ways of responding to these events.