PORTLAND – Lobstermen in the ’90s and early this decade went like gangbusters in August catching Maine’s signature seafood, making it the No. 1 month to catch lobsters.

But lobstermen now get their biggest hauls in the fall, and October has emerged as the top lobster-catching month. Even catches in November, typically a fraction of those in August, have exceeded August’s in two of the past four years.

The shift in the peak season has created angst among lobstermen, especially those who stand to finish in the red without a strong close to the season.

Lobstermen, dealers and scientists say a number of factors combine to make the lobster season’s peak a moving target, from water temperatures and ocean currents to more lobstermen using bigger boats to fish farther offshore.

“It goes in cycles,” said Peter McAleney, owner of New Meadows Lobster. “It’s something we’ve noticed, but there’s not a damn thing we can do about it.”

Old-timers will tell you that the catch, which last year totaled 72.6 million pounds worth nearly $300 million, was stronger in the fall than in the summer in decades past.

They’re right, according to an Associated Press analysis of data from the state Department of Marine Resources. In the 1960s, October was the top lobster-catching month statewide, while September had the largest monthly catches on average in the 1970s and ’80s.

In the 1990s and early this decade, August was the No. 1 month.

But beginning four years ago, the strongest catches started coming later in the year – with October on top the last two years. In 2004 and 2005, even November’s catches were higher than those in August.

With this year’s slow summer season, lobstermen are banking on another strong fall.

Water temperatures in the spring were cold, leading to the slow start, said Jack Merrill, a longtime lobsterman from Little Cranberry Isle.

“It’s returned back to the way it traditionally was,” Merrill said. “We used to have later seasons, and September, October and November were the best months.”

The timing of the season can sometimes hit lobstermen and dealers in the wallet, depending on where they’re located and the supply and demand at the moment.

At the least, the later season generates anxiety.

Many lobstermen place their traps in the water in the spring and wait for the lobsters to come to their traps in search of food. But if the season gets off to a slow start, lobstermen who are running up expenses pin their hopes on stronger catches later in the season, said Dana Rice, a lobster dealer in Gouldsboro.

Longtime lobstermen know that the best catches used to come in the fall and that not every year can be a banner one, he said.

“But the young ones aren’t old enough to remember,” Rice said.

The biggest factor in the timing of the catch is water temperature, scientists say.

In some years, ocean bottom temperatures might get warm in early July, said Carl Wilson, the state lobster biologist with DMR. But in other years, they might not warm up until well into August – resulting in sluggish lobster catches early in the season.

“A 3-degree change in temperature can mean a week to three-week delay in the molt,” Wilson said.

Other variables could help explain why the fall fishery has come on strong in recent years.

The fall catch might be stronger because fishermen have bigger boats nowadays that allow them to pull traps later into the year and farther offshore, where many lobsters migrate in the fall, said Diane Cowan, head of The Lobster Conservancy. Catching lobsters farther offshore could leave fewer lobsters to migrate to nearshore waters the following spring, she said.

Lobstermen have plenty of questions about the recent slow starts to the lobster season.

“They ask me why,” Cowan said. “I tell them I don’t know.”

Lobstermen’s biggest concern this year has been economics – not the timing of the catch.

With costs up for bait, fuel and other expenses, fishermen say they aren’t getting a high enough price for their catch. Scores of lobstermen tied up their boats and refused to pull traps for a few days in August to protest the prices they were getting for their catch.

But the lateness of the peak season can also fit into the economics equation, McAleney said.

Dealers often can get higher prices for lobsters that go to the live market, feeding tourists at restaurants. But in the fall most lobsters go to processors, most of whom are in Canada and usually pay lower prices, he said.