Atlantic lobster population boom poses a puzzle for marine scientists

Record catches defy warnings of a crash but might not be sustainable

October 24, 1999|By CHICAGO TRIBUNE

WALPOLE, Maine -- The small white buoys bobbing on the bright blue water of the Damariscotta River mark this as a dangerous spot for lobsters.

Tethered to each buoy is a line that reaches down to a lobster pot on the river bottom.

In 1997, the state's 6,500 lobstermen tended 2.6 million traps and hauled in 47 million pounds of lobster, a record that was repeated last year and looks likely to be matched this year.

Along most of the northern Atlantic seaboard, including the maritime provinces of Canada, lobster catches are at all-time highs and have defied biologists' predictions of a crash. At a time when many once-thriving fisheries around the world are in ruins, this continuing largess of the ocean baffles scientists.

The most obvious explanation is the catastrophic collapse in the number of large fish, such as cod, that once preyed on lobster. Overfished for years, the cod population crashed in 1994. But lobsters take seven years to reach minimum legal size. If cod were the only thing responsible for keeping lobsters in check, the lobster catch would not yet have shot up.

"When you have a highly complex ecosystem like we do in the North Atlantic, it is almost impossible to come up with a one-to-one relationship between predator and prey," said Steven Murawksi, a biologist at the National Marine Fisheries Service in Woods Hole, Mass.

Water temperatures have been rising, Murawski notes, and that is probably helping juvenile lobsters survive and grow faster.

But fisheries managers and scientists worry that the record hauls of recent years may be unsustainable. About 95 percent of the lobsters destined to be dinner are juveniles that have not reached reproductive age.

In an effort to forestall a crash, Maine is gradually reducing the maximum number of traps that one person is allowed. At one time, some lobstermen had strings of up to 2,000 traps; but by next year, the maximum will be 800, and some regional management zones have set even lower limits.

For Murawski, who studies the sea, tighter limits on the number of traps or an increase in the minimum lobster size is critically important.

"All the leading indicators that show a population under stress are there," Murawski said. "There's too much at risk to play biological roulette."

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