RONKONKOMA, N.Y. – Another die-off of lobsters apparently occurred across the breadth of Long Island Sound this fall, rocking an industry still staggering from a much more serious biological collapse two years ago.

Just as they had in 1999, lobstermen began to pull dead lobsters from their traps last month, said Carl LoBue, a marine biologist with the New York State Department of Environmental Conservation.

“The numbers were not as high as in 1999, but we think that’s because there are so many fewer lobsters in the sound now,” LoBue said.

As LoBue and other presenters said at Thursday’s Long Island Sound Lobster Health Symposium, attended by more than 150 people at a Ronkonkoma hotel, scientists are as baffled by the latest die-off as they remain about the 1999 catastrophe that led to federal officials declaring a fisheries disaster.

Meanwhile, lobstermen once again expressed deep-seated frustration at what they consider the slow pace of research even as they have watched fellow fishermen sell their boats and leave the industry during the past two years.

“It doesn’t seem we really know anything more than we did,” said John German of Mount Sinai, president of the Long Island Sound Lobstermen’s Association. “The lobstermen were going to boycott this thing, but it’s a miserable day out, so no one’s out fishing, and here we are.”

There has been progress in the research, however, even if officials acknowledge it does not amount to a dramatic breakthrough.

For one thing, the parasitic paramoeba first identified in sick lobsters in 1999 is still out there. Biologists found the microscopic organism in samples of lobster taken from the sound in 2000 and in 2001, said Richard French, a University of Connecticut researcher.