PORTLAND — Maine’s commercial fishing catch topped 276 million pounds in 2011, the largest harvest since 2004 and the first time lobstermen caught more than 100 million pounds of the state’s signature seafood in a single year.

The No. 1 species as usual was lobster, with the catch coming in at a record 103.9 million pounds valued at a record $331.4 million, the Department of Marine Resources said.

The harvest of all commercial seafood species was worth $425.8 million to fishermen. That’s down $30 million from 2010, largely due to a decrease in farmed salmon.

Although the overall catch was the highest it’s been in seven years, it’s the lobster numbers that continue to impress. The lobster catch has been on a tear for more than 20 years, growing from less than 30 million pounds in 1990.

The harvest has been particularly strong in eastern Maine. Since 2002, the catch has increased from 7.5 million to 16.6 million pounds in Washington County, and from 16.5 million to 33.5 million pounds in Hancock County.

While the lobster population is strong, officials and fishermen are concerned that the state’s fishing industry is too reliant on a single species and needs more diversification. Last year, lobster accounted for 78 percent of the overall value of the industry.

And lobstermen are feeling the pinch of low prices they’ve been receiving since the global economy tanked in 2008. Fishermen last year got $3.19 a pound on average for their catch, down from $3.31 a pound in 2010 and roughly the same price they were getting a decade ago.

“If you talk to fishermen, while the volume is there, their expenses have done nothing but increase so their margins are declining,” said Carl Wilson, a lobster biologist with the Department of Marine Resources. “And that has a biological impact, because it puts an expectation on the resource that this volume has to support the fishery.”

The top species by value after lobster were soft-shell clams ($15.2 million), herring ($14.2 million), baby eels ($7.7 million) and worms ($7.0 million).

Shrimp landings came in at $6.9 million, while the harvest of haddock, cod and other so-called groundfish was worth $5.8 million.

Pen-raised salmon was the No. 2 seafood in Maine in 2010, valued at more than $76 million. The harvest fell in 2011, when there was only one salmon producer. Final numbers haven’t been released because the information is considered proprietary.