Diseased Sea Lions Found on Shore; Outbreak May Raise Shark Danger

Dead and dying sea lions have been washing up along the California coast in unusual numbers this summer, and some marine biologists believe the animals are victims of an epidemic similar to one that killed as many as 7,000 of the mammals in 1984.

The sick sea lions also have raised concerns that increased numbers of great white sharks will be drawn closer to shore to feed on the weakened creatures.

“We have had a tremendous number of (sea lion) strandings and the number is increasing,” said Mary Jane Schramm, a spokeswoman for the California Marine Mammal Center in Marin County.

As of Monday, the center had rescued 44 sea lions suffering from leptospirosis. The cases have been reported as far south as San Luis Obispo and as far north as the Oregon border. So far 27 of the animals have died.

“They usually have excessive thirst, they are very lethargic, and they are often very emaciated,” Schramm said. “The bacteria literally blocks the kidneys and liver and prevents the organs from filtering toxins out of their systems.”

“We are only seeing the tip of the iceberg,” she said, adding that during the 1984 epidemic, the center took in 225 animals between the end of June and December, only to find out afterward that 7% or 8% of the entire sea lion population had died of the disease.

Shark sightings also are increasing, possibly as a result of the outbreak. Earlier this month a surfer was bitten by a shark near Eureka, 300 miles north of San Francisco.

A fisherman reported sighting a 13- to 15-foot shark “ripping a seal to pieces off Duxbury on Saturday,” said park Ranger Robert Del Secco. Duxbury Reef is about 3 miles from Stinson Beach, just north of San Francisco.

A fisherman claimed Wednesday that a 13-foot great white shark jumped out of the water in front of his boat, only 300 yards off Duxbury Reef.

The sightings have been widely reported around the Bay Area and have led to increased shark patrols by National Park Service rangers who administer the Stinson Beach area. Rangers, who had hoped to calm public fear of great whites, took a local camera crew on a patrol Monday--only to see a six-foot shark leap from the water 200 yards from the beach.

“He cleared the water by a good foot and a half, probably went about 5, 6 feet and nosed right back in,” said Del Secco, who was piloting the search boat Monday.

The shark was probably not a great white, the most dangerous species to humans, he said.

Beach Closed in 1984

Stinson Beach was closed for two weeks during the 1984 sea lion epidemic because of sharks feeding close to shore. “If there are sick, slow seals or dead seals in the water, you’ve got an easy meal for a shark,” Del Secco said.

Many experts see leptospirosis as nature’s way of preventing overpopulation in sea lions, and they say that most animal populations carry a disease that recurs periodically.

“There appears to be a population control mechanism whereby leptospirosis seems to thin the herds of seals and sea lions,” said John McCosker, director of the Steinhart Aquarium in San Francisco.

James Lechy, a wildlife biologist with the National Marine Fisheries Service, said one reason for concern is that the known epidemics of 1984 and 1972 were associated with food shortages or other stresses on the population, and no such stress has been identified this year.

However, zoologist Mark Palmer, who studies marine mammals for the Whale Center and the Sierra Club, was less alarmed.

‘Typical Cycle’

“It’s of course tragic, but it’s a fairly typical cycle,” he said. “We think the population is fairly high and possibly growing. The sea lions are packed more densely, so diseases are easier to transmit, there’s more competition for food and rookeries.”

Among the experts who believe it is too early to worry about the outbreak is Sausalito veterinarian Ray Deiter, who runs a group called Coast Watch.

“We didn’t take a look at the California sea lions until 1972, so the data base really isn’t big enough to say this is unusual,” he said, pointing out that northern fur seals have a three- to four-year leptospirosis cycle.

Marine experts say that the California outbreak is not related to an epidemic that has killed about half of the seal population in the North and Baltic seas.

European scientists met in London last week to determine the cause of the epidemic, which has caused thousands of dead seals to wash up on the beaches of Sweden, Denmark, Norway, West Germany and the Netherlands since April. Environmental groups are blaming pollution for the mysterious illness.