Science / Medicine : Fishing and Pollution Pose Increasing Threat to Dolphins, Porpoises : Sea life: The danger is not as dramatic as the one faced by whales, scientists say. But it is real nonetheless, and has pushed some species to the brink of extinction.
Grass-roots and governmental efforts ended the wholesale slaughter of the Earth’s great whales and saved some species from ignominious extinction for the sake of lamp oil, fertilizer and pet food.
But scientists at a recent symposium here warned that the whales’ compact cousins, porpoises and dolphins, continue to be killed in numbers at least as large as those racked up by the deadliest harpoon-wielding whalers of earlier times.
Extinction, for some species at least, may be only a decade away.
Scientists at the American Cetacean Society conference said some cetaceans--the scientific order of whales, dolphins and porpoises--are vanishing slowly because of people’s growing appetite for fish and the rapid pollution of the seas. And while this scenario is less dramatic than death by harpoon, it nonetheless amounts to extermination, they contend.
“In one sense, we have traded the harpoon for the sewage outfall and the fishing net,” said Scott Kraus of the New England Aquarium in Boston, while describing the danger now facing cetaceans.
“There is great reason to be concerned,” said Robert Brownell of the U.S. Fish and Wildlife Service station in San Simeon, Calif. “For about half the cases where we have enough information to make a judgment (about the possible extinction of a species), things are going to hell in a hand basket.”
Bernd Wursig, a professor in the Marine Mammal Research Program at Texas A&M; University, said 28 species of small cetaceans are in “very real and immediate danger” of extinction, many by the end of the decade.
Fishing is the most dangerous threat for several reasons, scientists postulated in two dozen papers presented over two days. One reason is that humans out-compete cetaceans for food, leaving too few squid, for example, in a traditional breeding ground to support a new generation of juveniles and their parents.
Another is that fishing boats inadvertently snare and suffocate porpoises and dolphins in the huge nets used to sweep oceans clean of tuna and other commercial fishes. Pledges by American tuna boats and canners to abandon fishing methods that kill dolphins has not stopped foreign vessels from taking their place and feeding a growing taste for tuna in other countries, the scientists said.
“The human predator has become an efficient and voracious competitor who threatens domination at all levels of the food web,” warned Charles (Stormy) Mayo of the Center for Coastal Studies in Provincetown, Mass.
A third impact of fishing is even more disturbing, scientists said. It is the increasingly common “targeting” of dolphins and porpoises--netting them on purpose, as a source of relatively inexpensive protein in such impoverished countries as Peru and Sri Lanka.
Tens of thousands are taken for food each year now--a substantial increase in just a few years--and the trend is growing. Several dolphin and porpoise species, such as the beautiful freshwater beiji in China’s Yangtze River and the squat little vaquita in the northern Gulf of California, already are being pushed close to extinction, scientists warned.
As the annual kill climbs--and researchers said spotty statistics indicate that it already is well over 100,000 small cetaceans annually--other species may follow them toward oblivion unless public pressure and the International Whaling Commission are brought to bear on the problem, scientists warned.
Besides the beiji and vaquita, Brownell said that cetacean populations now facing serious problems are the striped dolphin in the Mediterranean Sea, the familiar bottlenose dolphin off South Africa and the harbor porpoise along the east and west coasts of the United States, including California.
“Without immediate and significant intervention, we are going to see the loss of some species, and we are going to see it soon,” Brownell told the other scientists and environmental activists who gathered for the conference.
Such warnings overwhelmed small slivers of good news also presented at the conference, such as an encouraging report that gray whales, the species most often spotted by California whale-watchers, are growing in numbers. Brownell said that in the last three decades the worldwide catch of whales has fallen about 99%, to 669 last year.
Coincidentally, however, incomplete and anecdotal data indicate that the worldwide slaughter of smaller cetaceans has grown dramatically as commercial fishing technologies have evolved and Third World economies have declined.
High seas drift nets, miles-long webs strung across the open ocean to snare whatever is unlucky enough to encounter them, have been used for only about a decade, Brownell said. But their devastating impact on cetaceans, as well as many other species, already is being felt.
Squid drift-net fishers in the Pacific, for example, reported inadvertently killing 19,000 members of one cetacean species last year alone, he said. Drift nets are promoted by economic-development agencies as a cheap and efficient way for poor countries to catch food for themselves.
“There is now evidence that the dolphin population of the eastern tropical Pacific cannot continue to withstand this predation and continue to survive,” Wursig said.
Hundreds more are taken annually by foreign tuna-fishing fleets that snare spotted dolphins in order to catch the yellowfin tuna that inexplicably swim below them. Under public pressure, American tuna boats abandoned this practice, but foreign fleets have eagerly stepped in to succeed them. “Now Mexico has the largest fleets--and the largest (dolphin) kills,” Brownell said.
Mexican fishermen--as well as American farmers and city-dwellers--also are in danger of wiping out the Gulf of California harbor porpoise, a stocky, silver, shovel-nosed cetacean also known as the vaquita, or little cow.
The fate of the vaquita is a microcosm of the danger facing small cetaceans around the world, said Omar Vidal of the Monterrey Institute of Technology and Higher Studies in Mexico. He said vaquitas are imperiled by a combination of fishing, pollution and changing habitat.
Vidal said fishermen inadvertently snare vaquitas while fishing for shark, shrimp or totoaba, another endangered species. Totoaba fishing is illegal, but the species is pursued anyway because an unscrupulous fisherman can cut off a totoaba’s head and pass it off as a corvina, a popular sportfish.
At the same time, vaquitas are being poisoned by DDT and other agricultural chemicals that leach into the Colorado River in the rainy season and are swept into the Gulf of California, he said.
And when the rain is light, he added, drinking water demands by cities, irrigation and hydroelectric dams prevent any river water at all from reaching the gulf, radically changing the region’s ecology by affecting salinity, food types and food availability.
Vidal said he has documented 95 inadvertent deaths just in fishing nets since 1985, and estimates there are 200 to 500 vaquitas left. The true death toll, he said, is probably closer to 30 or 40 a year, or 15% to 20% of the entire population.
Without swift and intensive human intervention, he concluded, the vaquita “is in very serious danger of imminent extinction.”
Andrew Read of the University of Guelph in Ontario, Canada, said that such “incidental” kills are beginning to give way to higher, intentional catches of cetaceans for food, in wealthy Japan as well as such impoverished countries as Sri Lanka.
In Peru, as in other nations with a growing taste for dolphin and porpoise, cetaceans originally were caught by accident in nets set for shark, bonito and other pelagic, or open-ocean, fish. Poverty forced some fishermen to eat their unintended catch, and its popularity grew.
At $1 per kilo, or less than 50 cents a pound, the meat of dusky dolphins, Burmeister porpoises and other cetaceans is cheaper than beef and chicken in that South American country, Read said, and therefore has become “an important protein source for poor Peruvian families.”
Landings at one Peruvian port, Pucasana, were 2,300 dolphins last year, up sharply from 200 just four years earlier, Read said. Extrapolating those figures to the rest of the country, he estimated that Peru alone may be taking as many as 10,000 cetaceans annually for food.
Compounding the problem, he said, is that most of the dolphins are caught in August and September, the prime calving season. Read said fishermen often sell the valuable adult females they catch and bring home their near-full-term fetuses to feed their own families.
“It is unlikely the population can withstand this predation” for long, he added.
Pollution is perhaps the most subtle threat to cetaceans of all sizes, but Mayo of the Center for Coastal Studies cautioned that sewage, oil spills and urban and agricultural runoff are “acting as a catalyst for rapid and unpredictable change” in the oceans.
“Largely for avarice and ignorance, we treat the greatest ecosystem on Earth not as our garden but as our dumping ground,” he said. “We do so on the archaic idea that if we cannot see our wastes on the surface, they are gone forever.”
Ramona Haebler, a research veterinary pathologist at the U.S. Environmental Protection Agency station in Narragansett, R.I., said she is investigating the role pollution might have played in precipitating mass beaching of bottlenose dolphins along the U.S. coast between June, 1987, and May, 1988.
Necropsies showed the proximate cause of death was “overwhelming intrusive infection” of apparently unrelated origin. But she thinks the infections may have spread so rapidly because the dolphins’ immune systems were depressed by chemical contamination. She said the dolphins were tainted by polychlorinated biphenyls, or PCBs, at levels 350 times that in Great Lakes fish, which are very polluted.
PCBs were used to insulate electrical equipment before PCB manufacture was banned; this suspected carcinogen now helps researchers to estimate total pollution in animals. Animal fat readily absorbs PCBs, and when they are found they indicate the presence of a predictable range of other industrial pollutants.
With so many pressures simultaneously bearing on cetaceans, Mayo said that the only hope is for scientists and environmental advocates to make pollution, habitat alteration and the slaughter of small cetaceans as visceral a public issue as was the rapaciousness of whaling.
ENDANGERED CETACEANS
* Harbor porpoise face serious problems off the East and West Coast of U.S. * U.S. tuna boats and canneries have pledged to abandon fishing methods that kill dolphins. * California coastline-Gray whals sightings by whale watchers are growing in numbers. * Gulf of California-Squat little vaquita is close to extinction because of pollution and overfishing. * Peru-Fishermen catch dolphins and porpoises as a sources of relatively inexpensive protein. * Mediterranean sea-striped dolphins face serious problems. * South Africa-Bottlenose dolphins face serious problems. * Eastern Tropical Pacific-Drift nets, which are promoted by economic development agencies, are being used as a cheap and efficient way to catch food for themselves. * China Yangtze River-Freshwater beiji is being stressed close to extinction. * Japan-Intentionally catches cetaceans for food. High Seas Drift Nets * Used as mile-long webs of monofilament fibers strung across the open ocean to snare whatever is in the way. * Mostly used in Eastern Tropical Pacific and other foreign fleets. Abondoned by American tuna boats. * Large amount of fish can be caught which lowers the food intake for whales, porpoises and dolphins. * Used for about a decade with devastating impact on the fist population.
