|
 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.
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." |
