THE BOSTON GLOBE 

As the US Environmental Protection Agency prepares to issue conditions for turning on a new 9-mile sewage outfall tunnel this fall that will carry highly treated wastes from Greater Boston into Massachusetts Bay, lobstermen are calling for extensive studies and plans before that.

The lobstermen and environmentalist allies cite what they call evidence that secondary treatment in Lynn Harbor and elsewhere has annihilated lobstering areas.

But Bruce Estrella, the official in charge of tracking lobster harvests for the state Division of Marine Fisheries, and Kari Lavalli, a postdoctoral researcher at the Marine Biological Laboratory in Woods Hole who heads the Maine-based Lobster Conservancy, this week strongly disputed a link between cleaner water and falling lobster catches.

"You have to look at all the available information," Estrella said. "You can't just say, 'We've got cleaner water and a downturn in the lobster resource  -- there's cause and effect.' That's a ludicrous conclusion . . . The strongest evidence that exists is [that] the intense fishing effort" is to blame.

Amid reports of depleted lobstering grounds off Deer Island, Lynn, and Salem  -- areas that now receive much cleaner sewage effluent than they did a decade ago  -- Lavalli said, "A lot of this has to do with overfishing and the fact that over 90 percent of the lobsters they're catching have just molted into legal size to catch and haven't had a chance to breed."

Referring to the aggressive fishing efforts by lobstermen, Lavalli said, "They're shooting themselves in the foot, and yet they don't want to put the blame on themselves. It's a lot more complex than to say this one thing is causing it."

But William Adler, executive director of the Massachusetts Lobstermen's Association, which represents about 1,000 fishing crew members and dealers who handle $50 million worth of lobsters a year, rejected the overfishing argument.

Lobstering areas not far from North Shore bodies of water where he thinks secondary treatment outfalls have harmed the crustaceans continue to be productive, Adler said.

"Lobsters move in and move out. Why don't they move into these areas? Why do they somehow avoid those areas?" Adler said, noting that not only lobsters but crabs and other species have vanished from parts of Lynn Harbor and waters off Deer Island where better-treated sewage effluent now flows.

Because the Massachusetts Water Resources Authority pipe is so huge, likely to produce 300 million gallons a day of effluent, Adler said, that "we're talking about a much bigger area that would die off" if studies show secondary treatment byproducts are in fact harmful.

"We can't take that chance" without having the EPA require better studies first, Adler said. EPA officials plan to issue their outfall pipe license in July, which will require the MWRA to conduct intensive tests of its impacts on fisheries and aquatic life, and are closely reviewing lobstermen's concerns.

Estrella said it is possible there have been "very localized effects" on lobster that once congregated near sewage outfalls to feast on invertebrates and worms that thrived on the much heavier flow of human waste before improved treatment reduced their food source.

But, Estrella said cleaner water is not going to harm lobsters. "Our agency feels that the new outfall and the predicted effluent profile will not present a problem to the coastal lobster resource."

While Adler said many lobstermen find the area around the new outfall location, about 5 miles east of Nahant, a productive area for lobsters, Lavalli said that "we don't have any data about whether lobster larvae are in the water column around the outfall" site to worry about in the first place.

Lavalli said coastal development is the biggest threat to shallow waters where lobsters develop.