Three studies being presented this weekend at the Orca Recovery Conference at the University of Washington suggest the whale-watching boats have helped cause the decline of an orca population in the San Juan Islands.

"Based on the information we are releasing today, the primary cause of orca death appears to be boats," Mark Anderson, founder of the Orca Relief Citizens' Alliance, said Saturday.

The alliance, a nonprofit organization based in Friday Harbor, commissioned the studies.

One suggests that noise from whale-watching boats is muddying orcas' echolocation signals, which makes it more difficult for them to hunt for fish.

Another study indicates that orcas are swimming faster and breathing more quickly than they were in the mid-1980s, a sign the animals are stressed out.

The third study shows that survival rates have declined most significantly for males, especially older ones.

There has been no independent peer review of the studies, which are not expected to be published until sometime next year, Anderson said.

"This is a work in progress. There's much more to do," he said. "It's a little as if there's been a crime, and pictures have been taken, and we're watching those pictures develop."

Operators of whale-watching boats say they're already taking steps to ease their impact on orcas, such as shutting motors off within a mile of the whales.

"We want to do the right things, but you have to do them for scientifically valid reasons," said Michael Bennett, who runs the Mosquito Fleet, a whale-watching boat out of Everett.

Others who operate whale-watching boats agreed that the three studies must be thoroughly reviewed by other scientists.

"I think obviously every perceived threat must be addressed," said Anna Hall, a University of British Columbia student pursuing her master's degree in marine mammal research. She also works on board a whale-watching boat off Victoria.

Guidelines recently set by the National Marine Fisheries Service specify that boats should stay at least 100 yards away from orcas and slow to 5 knots within 400 yards.

The population of southern resident killer whales off Washington state and British Columbia has dropped from 98 in 1995 to 78 last year, a 20 percent decline.

At the same time, the number of whale-watching boats has increased - from 42 in 1994 to 82 last year.

"If you're a whale lover, as the boat operators themselves are, would you spend 75 bucks to go out there if you knew that what you were doing might be killing the whales?" Anderson asked.

Marc Pakenham, community adviser for Fisheries and Oceans Canada, said the average number of whale-watching boats spotted near orcas is much lower: 18.

Pakenham suggested several changes that could ease the stress whale-watching boats cause orcas: establishing a permit process that would require operators to control the length of their trips, limiting the number of boats allowed in a given area or creating sanctuaries where whale-watching boats are not permitted.

"What we have to do is establish some rules of engagement for their habitat," Pakenham said.

Authors of the three studies were UW Professor David Bain; Birgit Kriete, executive director of the Orca Relief Citizens' Alliance; and Glenn VanBlaricom, an associate professor in the UW's School of Aquatic and Fishery Sciences.

Other threats to orcas include oil spills, pollution from industrial toxins and dwindling Northwest fish stocks.

"They tend to starve," Anderson said, "and as they starve, they draw down their blubber, where all those toxins are, and they get poisoned in the process."

Conservationists are asking the government to list the southern resident orcas as endangered under the federal Endangered Species Act. Biologists with the fisheries service are reviewing the request, which was submitted more than a year ago.

Founded in 1997, Orca Relief Citizens' Alliance describes its mission as learning more about what's causing the decline in the orca population.

The three-day orca recovery conference ends Sunday.