SOUTH BRISTOL, Maine — The Gulf of Maine’s lobster population, which has boomed even as climate change and overfishing have hurt other commercial species, could suffer if water temperatures keep rising, according to a University of Maine study.
The study suggests that, as the Gulf of Maine continues to grow warmer, the state’s $495 million lobster industry — by far the most valuable commercial fishery in Maine — could face the same kind of population decline that has affected urchins, scallops, groundfish and shrimp. Overfishing greatly reduced harvests for many of these species, but warming waters have been identified as an impediment to recovery.
The new lobster study, conducted by UMaine’s Darling Marine Center and by Bigelow Laboratory for Ocean Sciences, indicates that larvae reared in 66-degree water had a distinctly higher mortality rate than those cultivated in the water 5 degrees cooler, the temperature now typical in the western Gulf of Maine. Water temperatures in the western Gulf of Maine are expected to rise 5 degrees by 2100.
The study looked only at larval lobsters, which spend all their time floating, and not at juveniles or older lobsters that live on the ocean floor.
Larvae raised at 66 degrees “developed twice as fast as they did in the current temperature of 61 degrees Fahrenheit, and they had noticeably lower survival [rates],” said Jesica Waller, a graduate student at Darling Marine Center. “Really only a handful made it to the last larval stage.”
Waller was the lead author of the research study, published this month in the ICES Journal of Marine Science.
Waller said that the survival rate for larval lobster is fairly low, regardless of the temperature of their water. For the experiment, researchers raised 1,500 larval lobsters in water maintained at 66 degrees and another 1,500 at 61 degrees. The larvae in the warmer water had a survival rate of 0.8 percent, while those in the cooler water had a survival rate of 1.6 percent — twice as high.
Rick Wahle, a UMaine professor and co-author of the scientific paper, said that the study was aimed at anticipating changes Maine’s most valuable fishery will face.
“Last year, Maine harvested nearly half a billion dollars in lobsters,” Wahle said. “With lobsters now comprising 80 percent of the state’s overall fishery value [of $616 million], Maine’s coastal economy is perilously dependent on this single fishery. We only need to look at the die-offs south of Cape Cod to see how climate change is having an impact.”
South of the Gulf of Maine, which historically has been colder than the current of water that flows eastward off the southern New England coast, once-robust lobster fisheries have shrunk significantly. Shell disease, which is believed to weaken lobsters, is more prevalent in that region. Other possible factors in the decline of the southern New England lobster population include higher levels of pesticide use, ocean acidification and other types of runoff from shore.
Bob Bayer, head of the UMaine Lobster Institute, did not dispute the findings of the study, but he said there other indicators among the many complex factors that affect lobsters’ survival that suggest increased water temperatures may be beneficial.
Lobsters, which cannibalize each other, are most vulnerable to predation when they are floating, he said. Warmer water encourages faster growth in larval lobsters, he added, which shortens the time they spend floating and helps them sink sooner in life to the bottom.
“Mortality from predation could actually be reduced” by warming waters, Bayer said.
Bayer added that although the warming of the Gulf of Maine is a cause for concern, the impact of that change “doesn’t look like doom and gloom to me.”