Washington Post Staff Writer

After seven weeks of dead and dying bottlenose dolphins washing up on beaches from New Jersey to the Carolinas, a lull apparently has set in, researchers say.

Three weeks ago investigators in Virginia Beach were responding to half a dozen dolphin strandings each day. Now they can count the death toll for this week on the fingers of one hand and they're not sure why.

Researchers cautioned that although the number of stranded dolphins has dropped significantly this week, it doesn't necessarily mean an end of the dolphin deaths.

"I would like to say that it's run its course, whatever that course might be," said Robert Schoelkopf of the Marine Mammal Stranding Center in Brigantine, N.J.

But beyond an understanding of the last leg of the blight's course -- the dolphins' succumbing to a general bacterial infection -- few conclusions have been reached, least of all that the worst is over. Why the animals have become vulnerable to common and generally innocuous marine bacteria remains unknown.

Joseph R. Geraci, a marine pathologist heading the Virginia Beach team, offered two possible explanations for the lessening of the dolphin strandings. "The winds have been westerly," Geraci said, "and that would tend to keep any carcass drifting off shore. The other possible explanation is that the condition might have reached its peak, and either because there are fewer animals or because there is less disease, there is a decrease in the number of dolphins that we've been able to recover."

Dolphins generally migrate south this time of year. Last Friday eight dolphins were reported stranded off the coast of the Carolinas, four in each state. Until then, strandings appeared to have been confined to the mid-Atlantic states and concentrated in New Jersey and Virginia.

"Those seem to have been flukes because we haven't had any recent reports," James Mead, curator of marine mammals at the Smithsonian Institution and one of the Virginia Beach researchers, said of the Carolina sightings. But Mead added that when the Virginia situation started up, the pattern of mortality began with reports of several strandings followed by four or five days of inactivity. "I hope it isn't moving south," he said, "but I would want to wait about 10 days before I could be sure."

Schoelkopf said that the more northerly strandings seem to have hit a pattern of every other day. "We had one on the 18th {of August}, one on the 19th, another on the 21st, the 23rd, then the 25th, so we're due for another today."

Until this year, the summer of 1985 held the record for bottlenose strandings in New Jersey: A total of five. Now, according to Schoelkopf, the state's death toll is up to 75, climbing in the last 10 days at a much slower rate.

Yesterday, Mead, who surveyed part of the Atlantic coast by air, reported that he found "very few" bottlenose dolphins: "One dolphin carcass floating {off shore} in the whole trip" and "surprisingly few live dolphins."

"It may be that the live dolphins have gone someplace else or it may be that live dolphins have been converted into dead dolphins," Mead said.

But on both counts -- the sighting of few live dolphins and only one dolphin carcass -- Mead cautioned against premature conclusions. "There are several situations I would like to be familiar with before I pronounced a definitive ruling on this," he said.