Dolphin Population Steady, Initial Study Finds : Environment: More than 96,000 dolphins died after being snared last year in tuna fishing nets. But the population is not threatened with extinction, initial results of a dolphin census show. Environmentalists still disagree.

Despite fears of environmentalists that dolphins will become extinct because they are being trapped and killed in tuna fishing nets, preliminary results of a government-commissioned dolphin census have detected no change in the dolphin population in the eastern Pacific Ocean.

“At this point our best analysis is that these stocks are stable,” Doug DeMaster, chief of the marine mammal division at the Southwest Fisheries Science Center in La Jolla, said. “There is no extinction that we envision.”

The fifth leg of the six-part dolphin census will start this morning when two research ships carrying scientists from the La Jolla center, a division of the National Marine Fisheries Service, leave San Diego harbor for another four-month stint of counting dolphins.

This part of the census comes just three months after major U.S. tuna canners pledged not to buy or sell fish caught using methods that kill or injure dolphins.

Scientists heading the dolphin count said Friday that their results do not mean that dolphins are no longer drying in tuna fishing nets.

Last year, the United States and other countries were responsible for the deaths of more than 96,000 dolphins trapped in nets, according to the National Marine Fisheries Service. This tally, however, was not part of the center’s study.

In fact, the center doesn’t count precise numbers. Instead, it attempts to determine the general size of the dolphin population. The scientists do this by taking small population samples and, through complex statistical calculations, making general observations about the dolphin population as a whole.

Environmentalists who disagree with the center’s findings said a change in the dolphin population isn’t apparent because scientists are only able to study a small sample of the dolphin population.

“Their methodology is flawed. There would literally have to be a 50% increase or decrease to show statistically that there is a change,” said Lesley Scheele, dolphin coordinator for Greenpeace International, in a telephone interview from Florida.

But to some in the tuna industry, the steady, yearly dolphin population counts collected by scientists on four sea excursions, begun in in 1986, are proof the industry’s preventive efforts are working.

“We’re not pleased by the fact that we have mortality, but we are pleased that we’re reducing the levels of mortality,” said Bill Gillis, adviser to the American Tuna Sales Assn. who is based in San Diego. “We feel that record is not recognized.”

The scientists will spend the next four months determining how the dolphin population in the Eastern Tropical Pacific has fared since last year.

This area of the Pacific, a triangular stretch of sea extending from the coast of Washington, south to the central coast of South America and west toward Hawaii, is known for its yellowfin and skipjack tuna, the primary sources for canning.

In these waters, there is a little-understood symbiosis that exists between the dolphin and tuna because the tuna swim underneath dolphins, which are more easily spotted by fisherman.

Scientists on board the two ships, the David Starr Jordan and the McArthur, will spend from sunup until sundown perched behind extra-strength binoculars taking count and keeping careful record of any dolphin schools they see. Dolphin schools usually average about 200 mammals but can be as big as 4,000 dolphins, DeMaster said.

The Jordan will cruise inshore, never wandering more than 400 miles from the beach, in its hunt for the sea mammals, while the McArthur will travel anywhere from 400 miles to 1,200 miles offshore.

During the cruise, the more than 25 scientists aboard the two ships will cover an area the size of the United States in search of the four dolphin species: common, spinner, spotted and striped dolphins.

Because the area is so big and the location of the dolphins so unpredictable, the scientists admit they can’t keep track of every dolphin out there.

“Finding them is more than half the battle,” DeMaster said. “Once you find (a school) you approach it within a half a mile to 3 miles, estimate the number of animals and the species out there.”

The Jordan is equipped with a helicopter so that scientists can photograph the dolphin schools as well as have a bird’s-eye view when they are counting.

“From the air you can see most of the school because the water is extremely clear,” said Tim Gerrodette, chief scientist for the project.

The scientists realize their methods are imprecise. They know dolphins are being killed. However, the scientists contend, the numbers just aren’t significant enough to affect their statistics.

“There is no evidence that the stocks have declined, so the number of (dolphin) taken in the tuna industry has not been so large as to cause a reduction that we can detect statistically,” De Master said.

The six-part study of dolphins was commissioned by Congress under the Marine Mammal Protection Act to keep track of dolphin population trends and to see how their numbers are affected by international tuna fishing, which flourishes in the Eastern Tropical Pacific, De Master said.

The four-month journey for the scientists will be broken up into four legs of 30 days each so the ships can dock to pick up water, food and fuel at ports in Hawaii, Costa Rica, Peru, Guatemala and Mexico, said Gerrodette, who will be traveling on the first leg. Halfway through the cruise, the scientists will switch ships.

The stint at sea costs about $700,000 plus the daily costs of the ships’ crews and maintenance that can run about $10,000 a day per ship, said Izadore Barrett, director of the Southwest Fisheries Center.

In 1992, the Southwest Fisheries Center is due to report to Congress, detailing what it has done and what has been found.

Included in the report will be results from the sea survey, reports on the biology of the area that include information on the dolphins’ reproductive and birth rates, as well as information scientists collect from tuna fishermen.

“We figure with the three prongs, we’ll get a pretty good idea of what’s going on,” Barrett said.

In addition, the scientists will observe sea birds and turtles, take water samples and study different areas of oceanography that include temperature, current and salinity.