Scientists say ocean warming is driving lobsters northward



It’s too early to know what Maine’s 2015 lobster landings will look like, but there’s no doubt that the number will be huge.

In 2014, the last year for which the Department of Marine Resources has figures, Maine’s fishermen landed more than 123 million pounds of lobster — the third year in a row that landings topped 120 pounds — worth a record $457 million.

While last year’s numbers aren’t in, fishermen and dealers talk about a bonanza fishery, and mild weather saw the fishery stay active into December.

In a sense, the landings are unsurprising.

According to a 2015 Atlantic States Fisheries Management Commission stock assessment, the abundance of lobsters in the Gulf of Maine and on Georges Bank showed a meteoric rise starting in 2008 and is now at an all-time high. In southern New England, though, the story is completely different.

From a peak in 1997, the southern New England stock fell swiftly to a point where, by 2004, it was well below what scientists consider the threshold of sustainability. Things leveled off briefly; then the resource began an ongoing plunge again in 2010.

According to last year’s assessment, the Gulf of Maine-Georges Bank stock is not depleted and is not being overfished. The estimated lobster population from 2011 to 2013 was 248 million lobsters, which is well above the abundance threshold — a red flag for fisheries managers — of 66 million lobsters.

In contrast, in the years 2011 to 2013, the southern New England stock was depleted at an estimated 10 million lobsters. The “red flag” abundance level is 24 million lobsters.

Lobster scientists say that the crustaceans that, over the past several years, have brought riches to Maine’s lobster industry thrive best when the water temperatures range between 59 and 64 degrees F.

Water temperature, researchers have found, can have a profound effect on juvenile and adult lobster growth, survival and reproduction — especially in waters with low levels of dissolved oxygen and low salinity.

Those are precisely the factors that scientists believe contributed to the massive die-off of lobsters in Long Island Sound in 1999 and again three years later.

The question facing scientists and fisheries managers is what impact will warming water temperatures have on Maine’s lobster fishery?

Adult lobsters exposed to temperatures above 68 degrees F for several days show symptoms of respiratory stress and compromised immune response, scientists say. Both juvenile and adult lobsters appear to be more sensitive to low dissolved oxygen levels and high temperatures when they prepare to molt.

Studies by Andrew Pershing, chief scientific officer for the Gulf of Maine Research Institute, and other scientists report that the waters of the Gulf of Maine are warming rapidly — reportedly 99 percent faster than anywhere else on Earth.

The rapid warming, the scientist says, is linked to changes in the position of the Gulf Stream and to climate oscillations in the Atlantic and the Pacific that magnify the steady warming caused by global climate change.

Until about a decade ago, according to figures compiled by Pershing and his colleagues, water temperatures in the gulf had risen by about 0.05 degrees per year since 1982. That pretty well mirrored water temperatures around the globe.

Around 2004, temperatures began to increase at about a half-degree per year, a nearly tenfold increase.

In the summer of 2012, a northwesterly shift in the flow of the Gulf Stream caused the water temperature in the Gulf of Maine to spike to record levels.

Some scientists believe that water temperatures in the Gulf of Maine will rise more than 4 degrees by the end of the century.

Late last year, Pershing and his colleagues published a paper linking the decline of the cod population in the Gulf of Maine to the increase in water temperature. How that same increase, and the further increase in water temperature that appears inevitable, may affect the gulf’s lobsters — and Maine’s lobster industry — remains to be seen.

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