Porpoise deaths puzzle scientists

Record number washed ashore along East Coast

April 28, 1999|By Heather Dewar | Heather Dewar,SUN STAFF

Marine scientists are mystified by an apparent spate of deaths among harbor porpoises, with the gregarious mammals' carcasses turning up in record numbers along East Coast beaches, including Maryland's.

Through mid-April, at least 162 of the small, coast-hugging porpoises were washed ashore, dead or dying, between their wintering spots in North Carolina and their summer grounds in Maine. The number of reported deaths is more than triple last year's 51, and well above the previous record of 103 harbor porpoise deaths reported in 1977. Almost all the deaths have been discovered since early last month, experts said.

"This is an extraordinary event. We've never seen anything like it," said Stephen J. Jordan, director of Maryland's Sarbanes Cooperative Oxford Research Laboratory. "This is more strandings in a month than we'd normally see in a year."

Marine mammal experts with the National Marine Fisheries Service, the Smithsonian Institution, Duke University and a half-dozen other institutions will convene an experts' summit in early June to try to unravel the mystery.

"The investigation is ongoing and we don't have any conclusions as yet," said Terry Rowles, coordinator of the marine mammal health and stranding response program for the National Marine Fisheries Service.

Through April 20, 19 dead harbor porpoises were found in Maryland waters, said Susan Knowles of the Oxford Research Laboratory. They were found on the Atlantic Coast, mostly near Assateague Island, she said. No carcasses have been found in Maryland since then, and the coastwide tally has declined sharply in the past week, triggering hopes that the deaths are nearing an end.

`Difficult to determine'

"A lot of the animals are coming in very decomposed, so the cause of death is difficult to determine," said Rowles. "Some of the animals come in obviously sick, because their blubber layers are so thin."

In some cases, she said, the animals' deaths were caused by entanglement in fishing gear. "A very small percentage of them had actual net marks," she said.

In Maryland, about half the porpoise carcasses "had some signs of net marks," Jordan said.

An estimated 2,000 harbor porpoises drown each year along the Atlantic Coast after becoming entangled in fishing nets, in spite of an observer program intended to minimize the number of porpoises and other marine animals killed as part of the commercial fishing "bycatch."

`We have no idea'

The government-paid observers are able to monitor 5 percent to 10 percent of the commercial fishing fleet, said National Marine Fisheries Service biologist Victoria Cornish. "Ninety percent of what's going on out there, we have no idea," she said.

The observers resuscitate porpoises and other netted animals when they can and, when they cannot, tag the animals' bodies and dispose of them at sea, Cornish said.

The tally of dead harbor porpoises does not include tagged animals, NMFS biologists said.

Threatened species

Harbor porpoises, the smallest members of the dolphin family, are listed as a threatened species and are protected by federal law. They are at risk during their annual spring migration and during encounters with commercial fishing nets, biologists said.

The creatures frequently turn up in small bays and harbors, making a soft puffing sound as they surface for air, alone or in pods of up to 10. Most of the East Coast population winters in the Carolinas, where the young are born in spring. Soon afterward, the animals begin a northward migration to their summer haunts, which stretch from Maine to Canada's Bay of Fundy.

The greatest number of deaths, 51, was reported in North Carolina. Farther along the migration route, in Virginia, 25 dead or dying porpoises have been found. Another 43 deaths have been reported in Massachusetts, along with scattered cases in other coastal states. Scientists aren't sure if the porpoises are dying in greater numbers than in past years -- it could be more people are looking for them and more carcasses are being reported, Rowles said.

Commercial fishing

It is also possible that many of the deaths are due to commercial fishing encounters that were unobserved and unreported, Cornish said. The NMFS biologist said she does not know of changes in commercial fishing practices that could account for the sudden upswing in deaths reported this year.

In New England, where marine mammal deaths associated with commercial fishing are most common, fishermen have recently been required to attach "pingers" -- small underwater devices that send alarms porpoises can hear -- to their nets. The pingers are not required in the mid-Atlantic states, Cornish said, nor are observers used in Maryland waters.

Since January, fishermen in the mid-Atlantic region are required to use heavier mesh in their nets because marine mammals should be able to spot and avoid the heavy mesh more easily.

To determine the cause of the harbor porpoise deaths, "we have stepped up our monitoring all along the coast," Rowles said. Veterinarians are taking tissue samples, which will be analyzed for pollutants and toxins, from many of the animals.

When the results are complete, experts from the coastal states will meet in Washington to pool information "and hopefully come up with an answer," Rowles said.

Pub Date: 4/28/99

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