In the fishing areas in Boston Harbor and off the South Shore, fewer lobstermen are pulling in fewer lobsters in recent years, and those who still fish often need to take second jobs to make ends meet.

At 5 a.m., Kevin Ferent was already sweating as he pulled lobster traps up through green water, fishing off South Boston’s industrial waterfront.

‘‘Terrible,’’ he said, clearing seaweed and crabs from the last trap on the line. ‘‘Four lobsters in 25 traps. That’s very, very slow.’’

Ferent, a 38-year-old Quincy resident, is not alone. In the fishing areas in Boston Harbor and off the South Shore, fewer lobstermen are pulling in fewer lobsters in recent years, and those who still fish often need to take second jobs to make ends meet.

Though statistics are not yet available for 2007, total lobster landings by inshore fishermen in the state fell from 9.8 million pounds in 2000 to 7.1 million in 2006, with most of the drop happening in 2001.

Meanwhile, the overall lobster catch in the Gulf of Maine, which runs from the southern tip of Nova Scotia to Cape Cod and includes

Massachusetts Bay, has held steady at about 75 million pounds a year over the same period.

Ferent and other lobstermen blame human influences in the bay, including the construction in 2002 and 2003 of the HubLine, a 29-mile natural gas pipeline running from Weymouth to the North Shore, and, ironically, the late 1990s cleanup of Boston Harbor. State fishery officials are more circumspect.

‘‘We don’t really know why Massachusetts Bay lobsters are not doing well compared with the rest of the Northeast,’’ said Paul Diodati, the director of the Massachusetts Division of Marine Fisheries. Climate change, construction, shell disease and environmental contamination could all come into play, Diodati said.

One theory is that the HubLine altered lobster distribution by creating a barrier that the bottom-feeding crustaceans decline to cross.

‘‘It’s also possible that the movement of gas through the pipe could create noise vibrations ... and that causes them to move from one area to another,’’ Diodati said.

The cleaning of the bay and the installation of the Deer Island treatment plant could also have played a part in the long-term slump, said Bill Adler, executive director of the Massachusetts Lobstermen’s Association.

‘‘When they cleaned the harbor in the 90s, they cleaned it with chlorine, just like your swimming pool, and everything left,’’ Adler said. ‘‘It’s like a moonscape down there.’’

But Adler said that while lobstermen often blame chlorine contamination for lackluster hauls, the chemical has not been a problem in the harbor since the Deer Island sewage treatment plant came online in 1997.

The Deer Island treatment plant also makes harbor water cleaner, potentially decreasing food availability for lobsters. ‘‘Typically in past years, the exit of a sewer pipe before treatment was a pretty popular fishing spot,’’ Diodati said.

Since lobstermen operate on relatively slim margins - in a good year, operating costs can eat up at least one half of revenue - a bad set of years can drive many out of business.

That’s what happened in the 1990s, Adler said. When the state declared a moratorium on new lobster fishing licenses in 1987, 1,877 lobstermen had the right to drop traps. Currently, only 1,352 inshore licenses remain, and of those, only 902 actually fished for lobster last year.

The stresses of the past 15 years have prompted many lobstermen to get side jobs, Adler said.

‘‘Lobstermen always seem to be getting hurt,’’ Adler said. ‘‘If it isn’t one bullet, then it’s another one.’’

Costs are likely to rise even more if gas prices increase. Each time Ferent leaves the dock to pull traps, he expects to burn $100 worth of fuel, use $250 of bait and pay a deck hand $150. At $5 a pound, he needs to catch 100 lobsters just to recoup his daily expenses - a quota he’s met only 30 days this season.

Moreover, prices are not determined by local markets. While fewer lobster are caught in Massachusetts, prices still stay relatively low in this state because of a steady supply from Maine and Canada.

Ferent, a second-generation lobsterman, took a second job as a Quincy firefighter three years ago to help make ends meet. He said he doesn’t see a bright future in lobstering. But he still sometimes brings his 11-year-old daughter, Krista, aboard his boat to help him mark buoys and band claws.

Krista recalled past years, when the family often dined on lobster at home.

‘‘But not this year,’’ she said, fitted in fishermen’s overalls during a recent lobstering trip. ‘‘We’ve got to save all we can.’’

Lobster facts

Lobsters take four to seven years to grow to legal harvesting size, or about 1.25 pounds. To conserve the resource, lobstermen notch the tail of egg-bearing females and throw them back. A 1-pound female can spawn 8,000 to 12,000 eggs, which are attached to the underside of her tail. Lobsters carry the eggs for about a year until they are released as larvae. For every 50,000 eggs, only two survive to legal size.

Source: Massachusetts Division of Marine Fisheries, the University of Maine