A dramatic increase in the number of dead sea otters found washed up on California beaches this month has wildlife officials puzzled and scrambling for possible reasons.
By Tuesday, 44 sea otters had been found dead from San Francisco to Santa Barbara. During a decade of record-keeping, the previous high for any April was 29, and the high for any month was 34 in July 1996.
“We have been seeing elevated levels of sea otter deaths, but now it’s going off the charts,” said Greg Sanders, sea otter recovery coordinator with the U.S. Fish and Wildlife Service in Ventura. “Right now we are just trying to understand what’s going on.”
State and federal wildlife officials have been stumped for years to explain why so many California sea otters turn up dead, but this year’s death toll has grown so dramatically that they see new urgency in finding answers.
Since Jan. 1, 91 dead sea otters have washed ashore, another record pace, Sanders said. He said many of the animals have died from infectious diseases and parasites, and a few have been fatally injured when struck by boats.
For several years, the southern sea otter population off California has hovered at about 2,150, down from a high of 16,000 before the animal was hunted almost to extinction for its fur. It has been protected by the Endangered Species Act since 1977.
Wildlife experts have estimated that a sustainable sea otter population could be as high as 8,400, and that southern sea otters could be taken off the threatened list if their numbers climb to 3,090.
In contrast, the northern sea otter, also known as the Alaskan sea otter, has always thrived and now numbers about 100,000. Sanders said scientists don’t know why, but conceded that less pollution and lower human population in that area could be part of the answer.
Steve Rebuck, a former abalone fisherman and consultant to the federal government on sea otter survival, said his perspective as a fisherman is that the sea otter habitat is becoming very short on food.
“The sea otters went for sea urchins first, then abalone,” Rebuck said. “In Morro Bay, they have stripped the pilings clean of mussels, and they don’t particularly like mussels.”
Although officials said food availability could be one factor, they dismiss any suggestion that sea otters are starving to death. In fact, they add, their constant diet of shellfish could be part of the problem.
“We are seeing some heart conditions and viral infections,” Sanders said. “Some of that comes from dental problems caused by chewing on hard shells all the time. They get cavities, abscesses and teeth that are broken off. Eventually, the infection spreads and becomes fatal.”
Dave Jessup, senior wildlife veterinarian in Santa Cruz for the state Department of Fish and Game, has autopsied many of the dead otters and agreed with Sanders that starvation is not a cause.
About 25% of the deaths are coming from disease spread by feral cats and from cat litter dumped into sewage systems that ultimately finds its way into the ocean, Jessup said. A worm infestation found in sand crabs, also part of the sea otter diet, is another major cause, he added.
The fight to keep the southern sea otter from extinction has produced a series of controversies with fishermen and experimental programs by wildlife officials over the past two decades.
In the late 1980s, federal officials moved 140 sea otters from the Monterey area to San Nicolas Island 60 miles off the Ventura County coast to set up a reserve population in case of a major oil spill. The deal struck with fishermen angry at the sea otter competition was that any otters that strayed into other areas would be herded back to San Nicolas.
“Some swam back to Monterey and to the other Channel Islands. Others showed up in Mexico and San Diego,” Rebuck said. “The federal government promised to contain them, and they haven’t done it.”
On San Nicolas, there are now 33 otters and five pups, Sanders said. He said the rest of the population is centered more around the Monterey area. Wildlife officials added that sea otters stay relatively close to shore because they cannot forage at depths of more than 100 feet.
A proposal by a panel of scientists earlier this month to the U.S. Fish and Wildlife Service would allow the sea otter population to spread farther south, along the entire California coast, on the theory that there is no realistic way to contain them in any specific area. Fishermen already are fighting that idea.