first published in Landings, February, 2020
The Gulf of Maine is growing warmer. From 1982 to 2013, the Gulf warmed by an average of 0.05o F. per decade. The rate of that increase in temperature took an upturn in 2004. The Gulf is now warming by an average of 0.04 o F. per year, according to data from the Gulf of Maine Research Institute in Portland. The results of a warmer Gulf of Maine are many, ranging from the introduction of new marine species to alterations in the chemistry of the ocean itself. This montn Landings begins a series that explores some of the changes that Maine fishermen are experiencing as a consequence of alterations in the Gulf’s environment and what may face them in the near future. Fishermen are known for cryptic sayings. After all, they spend a lot of time on the ocean, keep a keen eye on weather patterns, and note the patterns of the seasons in relation to their catches. All that information gets mulled over during long hours behind the wheel, resulting in some pithy observations. Nick Faulkingham fished one fall with Ossie and Sonny Beal out of Jonesport. “I asked Ossie, when do you think things will pick up? He pointed in towards the shore and said, ‘When you see orange in the trees, there will be orange in the traps.’ The ole boy was right!” Another lobsterman in southern Maine recalled that his father always timed the start of the shedder season by the raspberry bushes. When the raspberries were ripe, it was time for the shedders to arrive. As the Gulf of Maine changes, however, these sayings may no longer hold true. A paper entitled “It’s about time: A synthesis of changing phenology in the Gulf of Maine ecosystem,” published last year in the journal Fisheries Oceanography, looked at what is known about changes in the seasonal patterns of the many species that call the Gulf of Maine home. A team of scientists, led by Michelle Staudinger, an ecologist at the Northeast Climate Adaptation Science Center at the University of Massachusetts in Amherst, found only 20 research studies of shifts in seasonal patterns in the Gulf of Maine compared to a multitude of terrestrial reports. Their in-depth review of those studies revealed some of the complex changes that are affecting the entire Gulf food web. Different species use the Gulf of Maine at different times of the year. Elvers arrive in the late winter, alewives in the spring, whales migrate through in the spring and summer and ospreys return in April. These comings and goings are not haphazard but timed to coincide with certain water temperatures and food availability. These species leave their winter homes to come to the Gulf just at the time they most need energy for reproduction and growth. But, as the paper noted, the Gulf of Maine is “experiencing rapid and intense changes in bottom, air, and sea surface temperatures during all seasons, and relative to other global oceans, with the most pronounced warming occurring in recent decades.”
Calanus finmarchicus. Image courtesy of Maine Public.
“The responses to climate change are very species-specific,” explained Staudinger in a recent interview. “There’s wide consensus among experts that the consequences of species shifting in space and time mean changes in the broader ecological relationships in the region.” Take the spring phytoplankton bloom, for instance. Typically, that bloom occurs in April followed by a peak in zooplankton growth. Among those zooplankton are the all-important copepod called Calanus finmarchicus. Calanus finmarchicus basically goes to sleep deep in the Gulf during the winter months, puts on a little weight, and reappears when water temperature rises in the early spring. North Atlantic right whales love Calanus finmarchicus because they are packed with fat. The right whales begin to appear in Cape Cod Bay as early as January, with the number of whales reaching a peak in late spring as they take advantage of the zooplankton blooms. Other migrants to the region in spring include alewives, blueback herring, shad, Atlantic sturgeon and rainbow smelt. Staudinger’s paper notes that the time each species returns is tied to water temperature, river flow and ice breakup in the rivers that flow to the Gulf. Migratory birds such as terns and Atlantic puffins typically return to their summer homes on offshore islands in April or early May. But the timing of these migrations may be altering, leading to what ecologists call a mismatch between a particular species and the food it needs. It’s like someone hearing a far-off bell ring for supper and, upon arriving, finding that the meal has already been served.
Black sea bass is one marine species that has taken advantage of a warming Gulf of Maine. Photo courtesy of New England Boating.com.
Staudinger and her colleagues found average air temperature over New England increased most in the winter months, rising at rates of 0.18°C/decade (1895–2017). In the central Gulf of Maine, on the other hand, the uptick in temperature was most pronounced between July and September, with an increase of about 1.0°C/decade (1982–2014). That additional warmth results in a cascade of impacts. Think about the freshwater flowing from the many rivers that enter the Gulf. On average, there’s been an increase in precipitation throughout the region from 1895 to 2010, according to Staudinger’s paper. That precipitation is coming down as rain, however, not snow. The rain is moving more dissolved organic carbon into the Gulf earlier in the year, with more entering the Gulf in March and April and less in May and June. A 2016 study by William Balch at the Bigelow Laboratory in East Boothbay suggested that the additional dissolved carbon and particulates from increased river flow has, in effect, “muddied the waters” of the Gulf, diminishing the amount of sunlight in its surface waters, sunlight critical to the growth of phytoplankton. And what about those Calanus finmarchicus? Staudinger and colleagues found that the sequence of zooplankton blooms in the Gulf has changed during the past several decades. From 1961 to 2013 the first zooplankton of spring was Calanus finmarchicus, followed by a series of smaller copepod species in the fall and winter months. By the 1990s, the authors note, “the successional pattern broke down, yielding a less regular pattern typical of an ecological disturbance.” “Spring, thermally, is occurring earlier,” Staudinger said. “Calanus has less time to accumulate fat during its overwintering period. That means it has less energy for other species . There’s been a change of when the zooplankton bloom peaks and how big that bloom may be.” Right whales, which once frequented the area around Grand Manan Island, have rarely been seen there in recent years. Instead, the endangered whales congregate in Massachusetts Bay in the spring to snack and then travel north into the Gulf of St. Lawrence, an area where biologists believe dense clumps of copepods can be found. What about fish? The Gulf of Maine has long been renowned for its vast schools of codfish and other pelagic species. Has warming caused any change in the behavior of those species? A 2015 article by Harvey Walsh, a researcher at the Northeast Fisheries Science Center, and colleagues, looked at the distribution of 45 larval and 40 adult fish species along the Northeast Continental Shelf during two periods, 1977-1987 and 1999-2008. The authors found that larval stages of 43% of the species changed distribution and 50% of the adult stages shifted distribution over the same time period. Shifts were predominantly northwards or along the Continental Shelf. “Ecologists refer to this as adaptive change in a climate change context,” Staudinger said. “Are you a generalist or a specialist species? Generalists are those that can move to other sources of food. Some species can respond quickly to changes, such as a shift in timing or range of their prey.” Black sea bass are an example of a flexible species; the fish, once found only below Cape Cod, are now common enough in the Gulf of Maine that Maine enacted rules for a commercial fishery. The question troubling scientists such as Staudinger is what will happen as new species make their homes in the Gulf of Maine and interact with other species that may or may not have the ability to adapt to the new, warmer environment and new predators or prey. “How they deal with each other when they haven’t had to before, especially at the bottom of the food chain, makes us concerned,” she said. These shifts and alterations beneath the waves may be invisible to the eye of the average Mainer but to fishermen, they are all too obvious. The warmth now imbued in the Gulf of Maine has caused alteration in patterns at sea, patterns once thought immutable. How marine species adapt to those changes and how fishermen adapt to them remain crucial questions as yet not fully answered.
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