Today, scientists believe that most females reproduce once, if that, and it is rare to catch a lobster that weighs more than three pounds. The result is they seem to be maturing younger, and smaller.
But scientists do not know precisely how long it takes lobsters to reach the reproductive age. Estimates range from five to nine years, with lobsters in the colder north seemingly taking longer and growing slightly larger in the process. As yet, there is no reliable way to tell the age of a lobster.
Another issue, the rate at which lobster larvae develop into harvestable lobsters, "is a black box," Dr. Cobb said. Much is also unknown about lobster migration. "If you are a manager of a fishery you need to know more than we do now," he said.
Finally, he cited the hardiest perennial of fishery problems: the need for cooperation between fishermen and scientists "whose goals don't always mesh."
No one can deny that many people are harvesting lobsters in the Gulf of Maine. Researchers estimate that there are more than three million lobster traps in the waters there. "There is hardly a boat length between buoys" marking lines of traps, said Lewis S. Incze, a senior researcher at the University of Southern Maine. Some people say lobstermen have put so many baited traps in the water that lobstering has turned into a kind of aquaculture, with lobstermen feeding juvenile lobsters that eat the bait but escape their traps.
Scientists also point to a crash of the region's fin fish, in particular its stocks of cod, haddock and hake, which plunged in the 1980's and have not recovered. Without these predators, the theory goes, more young lobsters are surviving. But this explanation leaves some researchers unsatisfied. As they note, the fish virtually disappeared from much of the Gulf of Maine long before the record-breaking catches.
Other researchers point to the strong Asian market for American sea urchin roe. When fishermen began harvesting the spiny invertebrates from the gulf, they removed a major threat to the region's kelp forests, a favored environment for young lobsters.
Still other scientists theorize that lobsters are moving in from offshore to replace those taken in traps. But researchers struggle to model the dynamics of these "meta-populations."
In southern New England the picture is far different, but the uncertainty is, if anything, even larger.
Some of the lobster collapse in the region is due to one-time-only problems, like an oil spill in 1996 that left millions of lobsters dead in Block Island Sound. Also, there are more lobster-eating fin fish, like striped bass, in this region.
There are other problems, however, like the shell disease, a bacterial infection that leaves lobster shells weakened and disfigured. The disease, first detected in Long Island Sound, is well established now as far north as Massachusetts. In Narragansett Bay, about a third of harvested lobsters have areas of gooey weakness on their shells, telltale signs of the disease, said Kathleen M. Castro, a researcher at the University of Rhode Island.
The condition does not appear to be lethal to the lobsters, Dr. Castro said, because "they can molt out of it." And though disfigured lobsters sell for less, they are not harmful to people. Lobsters with shell disease are routinely turned into lobster salad or lobster Newburg. But the disease is setting off alarms among lobster biologists, not necessarily because of its immediate effects but because of what it represents.
They cite Jan Factor's ideas about the lobster crash in Long Island Sound. Dr. Factor, a professor at the State University of New York at Purchase, called it the kind of process that could happen anywhere: ecosystem stress leads to physiological upset that leads to vulnerability to disease and then to population declines.
The specific triggers that set off the lobster crisis in New York - believed to be a period of unusually high temperatures and low oxygen levels in the water - may not occur elsewhere, Dr. Factor said, "but if you think about general categories you can fill in your own environmental threats."
Many scientists believe that is what is happening with shell disease. They say that warmer water stresses lobsters, leaving them more vulnerable to bacteria believed to cause the disease. Dr. Cobb said the water in Narragansett Bay is almost two degrees Celsius warmer now than it was 20 years ago, a huge increase in biological terms.
At least three bacteria have been identified as possible suspects in the shell disease, but research is hampered by the lack of a simple way to assess whether a given lobster is healthy or ailing.
Dr. Factor said researchers had even taken lobsters to veterinarians, hoping that blood tests developed for dogs or cats might reveal some useful information. "Considering the value of the fishery, I am amazed we don't have something simple like that for lobsters," he said.
In both the Gulf of Maine and farther south, fishermen have joined an effort to protect lobster stocks by cutting V-shaped notches into the tails of female lobsters. It is illegal to take a notched lobster and, in theory, this will allow more of them to survive to reproduce. "This one would be on someone's dinner plate," Amanda Wright, who crews for Mr. Ingram on the Blue Moon, said recently as she used a puncher to remove a portion of a lobster's tail, before tossing it into the water.
Mr. Ingram said the widespread cooperation with the notching effort is evidence of the lobstermen's conservation ethic. "We don't want to catch the last lobster, that's for sure," he said.
Dr. Cobb said "anything that contributes to increased egg production in my opinion has to be good." But he said it remained to be demonstrated "that notching contributes strongly to the fishery."
He said he doubted that people would ever fish lobsters into extinction, although "it may come to a point where it doesn't make any sense financially to fish for lobsters."
"There are people poised to start lobster aquaculture when the price of lobster gets high enough," Dr. Cobb continued. "But the Gulf of Maine is not cooperating."
