Scientists differ on ailment's cause


February 19, 1992|By Frank D. Roylance | Frank D. Roylance,Staff Writer

A Canadian scientist says unseasonably warm winter weather is a possible factor in the mysterious strandings or deaths of more than 300 ailing harbor seals over the past year on beaches from Maine to Virginia.

Other observers say the increased number of strandings -- including two since Dec. 29 in Maryland -- may reflect normal attrition in a population that has boomed in the Northeast since seals came under federal protection in 1972.

Dr. Joseph Geraci, a wildlife biologist and marine mammal expert at the Ontario Veterinary College in Guelph, Ontario, said he and other scientists investigating the strandings haven't pinpointed the cause of the illness that is bringing the animals ashore, dying or too weak to swim.

But Dr. Geraci said he is certain the strandings go well beyond historical "background" levels. "This is by all accounts new to us."

Dr. Geraci, a consultant to the National Aquarium, was in Baltimore last week where he examined the latest arrival, a malnourished harbor seal. The male pup, 7 or 8 months old, was brought to Baltimore Feb. 7. The pup is being tube-fed and treated for lungworms.

Warm weather, like that occurring this winter and last, was linked statistically to a similar rash of seal strandings in 1980 and it's now "something we've been thinking about" to explain the current phenomenon, Dr. Geraci said.

In 1980, he said, at least 500 harbor seals sickened and stranded on Cape Cod, Mass., in an epidemic traced to an influenza virus. But laboratory tests indicated the virus by itself couldn't account for the high number of deaths.

Scientists say that when the air is colder than water temperature, seals normally stay in the water. Mild weather encourages them to "haul out" on coastal beaches. Crowded conditions ashore then may facilitate the spread of airborne viruses, such as influenza.

Federal officials said a similar, but smaller die-off occurred during the unusually mild winter of 1985-1986, and also was blamed on an influenza virus.

Dr. Geraci said the current strandings are centered on Massachusetts. The animals are washing up at three to five times the expected rate, Dr. Geraci said, and "there is no suggestion yet that this has reached its peak."

In the Cape Cod area alone, the New England Aquarium worked with 86 stranded seals in 1991, compared with 42 in 1990. Twenty-four more were brought in just last month.

On Long Island, 39 dead or stranded seals were found in 1991, up from 24 the year before.

Three seal pups suffering from pneumonia, parasites, malnutrition and minor injuries have been brought to the National Aquarium in Baltimore since Dec. 29 after strandings near Virginia Beach, Va., at Ocean City, Md., and on Maryland's Assateague Island -- far south of their traditional range.

One of the pups died, and one was treated and sent to the New England Aquarium to await release. One still is being treated.

Dr. Geraci said examinations of more than 150 seals stranded in New England revealed a variety of ailments, including pneumonia, liver disease and skin lesions.

To Dr. Geraci, that suggests some common underlying cause. "It may be a virus which causes the animals to become debilitated. Thereafter, there are any number of organisms in the sea, lying in wait for a weakened animal," he said.

He discounts theories such as those advanced by Samuel S. Sadove, of the Okeanos Ocean Research Foundation on Long Island, who suspects man-made pollution, especially PCBs, is the culprit. The U.S. Environmental Protection Agency is studying PCB levels in the seals.

"I don't think that's a serious issue," Dr. Geraci said. Although human influences may play some role, in all past cases "we've been able to identify a plausible sequence of events, entirely natural" to explain the events.

Others say the strandings simply may reflect a booming seal population.

P. Michael Payne, of the National Marine Fisheries Service in Silver Spring, said harbor seal populations in New England have grown since state bounties were lifted in the 1960s, and federal protection was extended to seals under the 1972 Marine Mammal Protection Act.

After the 1980 influenza epidemic, seal counters found about 3,500 harbor seals in Massachusetts waters. By 1986, the number had grown to 4,500.

Today, Mr. Payne said, "It wouldn't surprise me to find 6,000 seals south of Maine, more seals than have been counted in this century."

Juvenile seals probably are being pushed south from New England in search of food, and "there is more likelihood you would get an increase in first-year pup mortality," Mr. Payne said.

Three hundred strandings in one year is "a pretty big bump, I have to admit," Mr. Payne said. "But I still think the population is healthy and increasing."

To Greg Early, associate curator for animal care at the New England Aquarium, the situation "doesn't look like an intense, high-mortality event."

Instead, the rising numbers suggest "there are more seals, more widely distributed."

Robert Schoelkopf, director of the Marine Mammal Stranding Center, in Brigantine, N.J., believes population growth and hunger to the north explain both the quadrupled harbor seal strandings in his state and the arrival of northern species.

"Fifteen years ago we saw only harbor seals. Now there are up to five different seals coming in," he said, including gray seals and three arctic species.

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