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Otters dying west coast { April 30 2003 } Original Source Link: (May no longer be active)
http://www.sfgate.com/cgi-bin/article.cgi?file=/chronicle/archive/2003/04/30/MN211481.DTLhttp://www.sfgate.com/cgi-bin/article.cgi?file=/chronicle/archive/2003/04/30/MN211481.DTL
Otters dying in record numbers
92 have washed up on California coast in past four months
Carl T. Hall, Chronicle Science Writer
Wednesday, April 30, 2003
©2003 San Francisco Chronicle | Feedback
Alarming numbers of California sea otters are washing up dead or sick from Point Conception to Half Moon Bay, biologists said Tuesday, threatening to undermine efforts to save the playful sea mammal from extinction.
In April alone, a record 45 dead or dying otters were recovered -- including one added to the grim total late Tuesday by marine biologists.
The month's count is more than twice the expected number of strandings based on a 10-year average. So far this year, 92 otters -- known as southern sea otters to distinguish them from a separate population in Alaska -- have washed up on California beaches.
That is a record for any January-April period and 25 percent more than the previous high, set in the stormy El Nino year of 1998.
"This is a serious problem," said David Jessup, a senior wildlife veterinarian with the state Department of Fish and Game in Santa Cruz. "We need to be very concerned. Any continuation of this certainly threatens the recovery of the southern sea otter."
No single cause has been identified to explain the deaths. The mortality rate does not appear to be concentrated in very young or very old animals. Nor are males or females disproportionately affected.
A large number of carcasses or sick animals have been picked up in the Monterey Bay area, but biologists said strandings are being seen in disturbing numbers throughout the otters' range.
Marine biologists speculate that something may be adversely affecting the ability of the animals -- listed as a threatened species -- to endure parasites, fight off infectious disease, evade sharks and dodge boat propellers.
Whatever the culprit, the die-off is especially worrisome against a backdrop of annual southern sea otter censuses suggesting that the total population, which climbed slowly over several years, has actually declined in recent years.
The spring 2002 census counted 2,139 sea otters in California, down 10 percent since the recent peak of 2,377 in 1995. This year's otter count begins in May.
Officials at the U.S. Fish and Wildlife Service are considering whether to issue a formal declaration of an "unusual mortality event" to clear the way for extra resources to investigate the problem.
UNPRECEDENTED STRANDINGS
Biologists said it's all they can do to respond to the unprecedented number of strandings. In most cases, it takes a full necropsy and lab analysis to pinpoint the likely cause of death.
Eight sick animals are undergoing rehabilitation at the Monterey Bay Aquarium. Andrew Johnson, manager of the aquarium's sea-otter recovery program,
noted that a record 17 sick animals have been picked up so far this year, compared with the previous high of 12 during the first four months of 1998.
"The numbers have been extraordinary," Johnson said, adding that the problem shows no sign of abating. "We're seeing a range of causes, including some shark bites and a couple hit by boats. It's young animals, it's old animals, but the big concern is that we're seeing high numbers of prime-age animals" dying in their peak reproductive years.
Biologists estimate that the bodies of about 60 percent of the total number of California otters that die each year are picked up when they wash ashore. And they said they are certain the apparent increase in mortality is genuine, because nothing has changed of late to increase the percentage of carcasses recovered.
"The concern is it's affecting the population's health as a whole," said Greg Sanders, sea otter recovery coordinator at the U.S. Fish and Wildlife Service.
Biologists are hoping the problem will stabilize of its own accord, and it would not be the first time such a mystery has evaporated. Several marine- mammal stranding episodes, including a recent spate of gray whale strandings in Northern California, remain puzzles years later. Despite extensive study, scientists ultimately gained little insight into what drove the animals ashore.
SEA OTTERS ONCE UBIQUITOUS
Sea otters, once ubiquitous off the California coast, were hunted to the edge of extermination for their luxuriant fur coats. They were added to the threatened species list in 1977.
After much wrangling and many studies, the Fish and Wildlife Service early this month released a final recovery plan, including a target population of about 3,100 animals. The "optimal sustainable population" is said to be far higher, however: about 8,400 animals.
Now, it seems the numbers are going the wrong direction. Just so far this year, the body count represents about 3.5 to 4 percent of the population.
Biologists said some deaths are being attributed to infections in the gut from the parasitic thornyheaded worm, which burrows through intestinal walls. Other types of microscopic parasites also have been implicated, including a toxoplasma common in house cats and afflicting some AIDS patients.
But experts have no idea what could be causing an increased vulnerability to dangerous microbes among California sea otters this year. There has been some evidence of a food shortage affecting some animals, but that could be caused by foraging problems brought on by some underlying condition slowing animals down.
The equatorial warm-water phenomenon known as El Nino has reappeared this winter, though not with sufficient ferocity to explain the otters' difficulties. Stormy weather indirectly tied to El Nino conditions can increase otter mortality by eliminating some food sources and separating mothers from their pups.
For now, the search continues for any underlying pattern to explain all the deaths.
"We get a lot of answers about what happened to each animal," Jessup said, "but the question is -- does it mean anything for the population?"
E-mail Carl T. Hall at chall@sfchronicle.com.
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