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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