PORTLAND – The lobster harvest is down sharply this summer and there are no signs the catch will pick up this fall, according to lobstermen and dealers.

The catch is estimated to be down 25 percent to 40 percent from last year at this time along different parts of the coast.

A strong October could make up for some of the decline, but the slowdown is increasing fears that the state’s 14-year lobster boom may be coming to an end. At the same time, it also coincides with the second straight summer of cool ocean temperatures, suggesting that the lag may be temporary.

Robert Thompson, manager of Spruce Head Fishermen’s Co-op in South Thomaston, estimated the catches among the 60 boats that unload at the co-op to be down 25 percent to 30 percent. He said there are no indications that the lobsters will show up this fall.

“I don’t see it coming,” Thompson said. “They don’t seem to be moving. They’re not feeding.”

In Portland Harbor, lobsterman Peter Pray said that he hauled more than 30 traps Friday before even seeing a lobster. That’s not good because this is generally the time of year when the harvest heats up, increasing from about one legal-sized lobster in each trap to two or three.

“We’ve been waiting for it to kick in all summer, but we just haven’t seen it,” Pray said. “I wouldn’t be surprised if they’re off 40 percent.”

Lobster by far is the most lucrative Maine fishery. The catch last year was valued at $206 million.

Catches averaged about 20 million pounds a year from 1950 to 1990, then jumped as the lobster population exploded. The 2002 catch was a record 62 million pounds, generating sales of $207 million. The state’s catch declined 12 percent last year.

Rick Wahle of the Bigelow Laboratory for Ocean Sciences in West Boothbay Harbor was one of a group of scientists in the late 1990s who warned of a significant decline starting around 2001 or 2002. But he isn’t convinced the population decline is now coming to pass.

“We can’t be sure yet,” he said. “It’s just a matter of time until we know what it’s linked to.”

Many lobstermen blame the lousy spring and summer weather, which didn’t warm up the ocean enough to get lobsters out of their burrows and hiding places.

Measurements of the ocean’s temperature support the theory, said Jim Manning of the National Oceanic and Atmospheric Administration’s Northeast Fisheries Science Center, which mounts gauges on lobster traps all along the New England coast. Despite a long-term warm-up in the ocean, the last two years have been cooler than usual on the ocean floor, he said.

“The deviation from what’s normal has been a few degrees,” Manning said, enough to make a big difference for lobsters. “Every lobsterman I’ve talked to with this project is convinced the temperature plays a big factor in the variations in their catch.”

Steve Train, a Long Island lobsterman, said there’s still enough season left to make up some of this season’s shortfall. Most lobstermen, he added, know how to weather the typical ups and downs of the business.

“You get a bad year or two, people will borrow their way through it if they have to,” he said. “And then, if it doesn’t get better, you hope they didn’t dig too deep.”