PORTLAND — If you think this has been a hot summer on land, scientists say that the Gulf of Maine is suffering a heat wave and that could be bad news for fish populations and the fishing industry.
The Gulf of Maine is one of the fastest-warming ocean ecosystems on the planet, according to scientists at the Gulf of Maine Research Institute (GMRI). In a study released last week, those scientists highlighted just how serious the situation is.
Over the last 30 years, the researchers said, the gulf warmed at the rate of 0.06 degrees Centigrade (0.11 degrees Fahrenheit) per year. That is more than three times the global average.
Over the past 15 years, this region has warmed at a rate more than seven times the global average.
Measured over either period, the Gulf of Maine warmed faster than 99 percent of the global ocean.
This year has been especially warm. Scientists at GMRI report that on Aug. 8, the gulf officially experienced its second warmest day since climate data has been recorded. On that day, the average sea surface temperature in the Gulf of Maine, measured by satellites operated by the National Oceanic and Atmospheric Administration and the National Aeronautics and Space Administration reached 20.52 degrees Centigrade (68.93 degrees Fahrenheit). This is only 0.03 degrees Centigrade (0.05 degrees Fahrenheit) shy of the record set in 2012.
“The fact that we keep having major events in the Gulf of Maine is both surprising and unsurprising,” GMRI Chief Scientist Andrew Pershing said on Friday. “What’s surprising is how fast it came on. What’s unsurprising is that it’s happening year, after year, after year.”
This year, the Gulf of Maine enjoyed a fairly normal spring. Despite that, the current Gulf of Maine heat wave started on July 20 and has lasted more than a month.
“The main thing is how intense it is and that it came on really quickly,” Pershing said.
“We’ve set 10 daily temperature records this summer, after setting 18 this winter,” Pershing said. “We’ve had to add new colors to our temperature illustrations to reflect just how warm the Gulf of Maine has been this year.”
So far, Pershing said, scientists don’t have a good handle on what impacts the warming waters will have on the ecosystem, though they have some ideas.
As waters have warmed over the past several years, lobster fishing in the Gulf of Maine has boomed, while lobsters have just about disappeared from the even warmer waters of Southern New England. In Maine, landings are lower in the southern part of the state and have increased farther Downeast.
“There’s been a shift from southern Maine to the area around Stonington for the center of the fishery,” Pershing said.
What remains to be seen is whether that shift will continue. Scientists won’t know until they see the results of studies by University of Maine professor Rick Wahle on the rate of settlement of lobster larvae, which take some seven years to reach legal fishable size.
“The impact is not on the adult lobsters, but possibly on settlement,” Pershing said.
In the meantime, there is clear evidence that the ecosystem is changing,
Gulf of Maine fishermen are seeing large numbers of species such as squid and butterfish that have historically been found further south — in southern New England waters and off the Mid-Atlantic states.
Scientists are also trying to determine whether the tiny copepods that are the primary source of food for endangered right whales are moving out of the Bay of Fundy — to which the whales have been notably infrequent visitors this year — into cooler Canadian waters.
Although the concept of a marine heat wave has only recently been defined, the Gulf of Maine is already pushing its boundaries.
In 2012, only six days fell below the 90th temperature percentile. In every year since, the gulf has experienced more than 150 of these heat wave-level days. In every year since 2010, the gulf experienced more than 80 such days.
This year, the Gulf of Maine has already seen 180 days above the 90th percentile, and is now entering the fall season, which has been especially prone to heat waves.
GMRI scientists have an explanation for why the Gulf of Maine is warming so rapidly.
The Gulf of Maine sits in a unique corner of the ocean where currents bringing cold waters from the Arctic and Canada meet warm waters coming from the south. A slight change in these currents can mean a big difference in temperatures, and this region is experiencing significant changes.
Global warming is causing the glaciers in Greenland to melt. As this relatively fresh water pours into the North Atlantic, it disrupts the entire pattern of water circulation in the North Atlantic basin, pushing more warm water into the Gulf of Maine. The same thing is happening in the Barents Sea, north of Norway, another region that has been very warm this year.
“This year really brings home the connection between Atlantic circulation and the temperatures in the Gulf of Maine,” says Pershing. “The satellite images from this year show a persistent mushroom-shaped blob of very warm water at the mouth of the Northeast Channel — a deep gully that leads into the Gulf of Maine. Essentially, shifting ocean currents are functioning like a hot water tap that dumps directly into the Gulf of Maine.”