NOAA 98-R131

Constituent Contact: Susan A. Weaver 6/29/98

Susan.A.Weaver@noaa.gov

(202) 482-2610

BIOTOXIN IN HARMFUL ALGAL BLOOM RESPONSIBLE FOR THE DEATHS OF SEIZURING SEA LIONS OFF MONTEREY COAST

Biologists from NOAA's National Marine Fisheries Service and National Ocean Service found that a natural biotoxin caused by a harmful algal bloom resulted in the death of more than 50 California sea lions in the Monterey area in May, the Commerce Department's National Oceanic and Atmospheric Administration announced today.

In animals, the harmful biotoxin called domoic acid affects the nervous system, causing seizures and vomiting which can also lead to death. The National Marine Fisheries Service and the National Ocean Service are continuing to track this harmful algal bloom and have detected it in other areas off the California coast. Researchers from the University of California, California state laboratories, Colorado State University and NOAA's Seattle and Charleston laboratories will continue to collect and analyze samples to confirm the presence of domoic acid in water, fish and other marine life.

From May 21-31, nearly 80 adult and juvenile California sea lions washed ashore in obvious physical distress along the coast from San Luis Obispo to Santa Cruz. Rescuers from the Marine Mammal Center in Sausalito noted that the sea lions exhibited seizures and vomiting, which are strong signs of exposure to a toxin affecting the nervous system. Their conclusions were further supported by the fact that some animals recovered quickly as a result of emergency medical care as opposed to animals with infectious diseases, which generally take longer to respond to treatment. Of the animals treated at the Marine Mammal Center, more than 50 died, while 29 are still alive and 19 appear to be fully recovered.

"A harmful algal bloom in a healthy population of animals such as the California sea lion can have a significant impact, but in a critically endangered species, it can be devastating," said Teri Rowles, National Marine Mammal Stranding Coordinator for the fisheries service. "We are encouraged that information learned from this event will help us more effectively respond to future marine mammal exposures to biotoxins."

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

Biotoxin analysis on the sea lions tissues and urine resulted in only four confirmed positive tests for domoic acid. However, scientists stressed that the lack of positive findings does not necessarily indicate that an animal was not exposed to domoic acid. The toxin is cleared from the body very rapidly and is often difficult to detect. Investigators also searched for evidence of human-caused acute chemical pollution and infectious disease, but neither factor was implicated in the event.

"Through strong partnerships between federal and state agencies and university research centers, we were able to detect this event early and initiate a rapid response," said Rowles. "Further investigation of this event will help scientists determine whether future effects on marine mammals can be predicted, and thus determine the most effective means of responding to these events."

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