A female lobster laden with eggs is released back into the ocean off Harpswell in this 2009 file photo. Temperatures in the Gulf of Maine in 2017 were the lowest since 2011, but still one of the warmest in the past 30-plus years, according to Gulf of Maine Research Institute. Warming temperatures in the gulf have had a temporary benefit on the survival rate of juvenile lobsters but are expected to adversely affect the gulf’s lobster population as they continue to increase. Credit: Pat Wellenbach | AP

Last year was one the coolest so far this decade for the Gulf of Maine, but the body of water continues its trend toward higher temperatures despite the one-year drop.

In 2017 the average sea surface temperature in the gulf, which typically ranges from just below 40 degrees Fahrenheit in winter to the low 60s in summer, was 50 degrees, according to the Gulf of Maine Research Institute. That’s the lowest average since 2011.

Still, last year’s 12-month average was 1.9 degrees Fahrenheit above normal for the gulf, which is warming faster than 99 percent of the world’s oceans. The temperatures in the gulf in 2017 were cool only relative to how warm it was from 2012, its warmest year on record, through 2016, its second-warmest.

“This is right in line with our long-term warming trend, but it’s cooler than 2016,” said Dr. Andrew Pershing, GMRI’s chief scientific officer.

Last year “was an unusual year in the Gulf of Maine,” Pershing said. “We were warm in the winter, close to average in the spring and summer, and then we had very warm conditions in the fall.”

A trend of increasing temperatures detected in the gulf since the early 1980s is expected to continue. In 2012, the warmest year on record, the gulf was about 3.7 degrees Fahrenheit higher than than the 30-year average from 1982 to 2011. In 2016, the average temperature was about 2.9 degrees above that average.

The gulf, which traditionally has been cooler than the gulf stream waters further offshore, is between Cape Cod to the southwest and Nova Scotia to the northeast.

The drop in temperature in the gulf last year occurred despite 2017 being among the planet’s top three warmest years ever recorded, according to federal officials.

The increasing temperatures in the gulf are noticeably affecting its marine habitat. They have temporarily benefitted the survival of juvenile lobsters, but are expected to adversely affect the gulf’s lobster population as it continues to get warmer.

Warming temperatures in the gulf also have been cited for huge elver harvests in 2012 and 2013 and for the decline of the gulf’s population of cod and shrimp.

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Bill Trotter

A news reporter in coastal Maine for more than 20 years, Bill Trotter writes about how the Atlantic Ocean and the state's iconic coastline help to shape the lives of coastal Maine residents and visitors....