An Overheating Gulf of Maine Is Now Forcing Wildlife to Adapt—or Move

Rapid warming in the Gulf of Maine is shifting the marine food web, putting already endangered Roseate Terns and their broods at even greater risk. Figuring out how to help these seabirds could point the way for safeguarding other species.

It's lunchtime on Seavey Island, and the thousands of terns on this rugged five-acre outcropping off the New Hampshire coast are none too happy to have company for their meal. Their shrill, kipping call creates an otherworldly din intended to scare away the human intruders. No one but me seems to notice. 

A crew led by Jennifer Seavey, executive director of Shoals Marine Laboratory, blithely inches across precarious, seaweed-covered rocks, weighing and counting tern chicks. I’m sandwiched between them, a procession deliberately ordered to minimize the chance that my newbie feet will accidentally make contact with a precious egg. Exacerbating that likelihood is my comically oversized straw hat. Just shy of a film-set sombrero, its crown is crammed with reams of towels, bandannas, and socks—anything to blunt a sharp beak. 

The birds, however, are undeterred by our defense system. They alternate between relentless assaults on our hats and flights off the island for food. Of the nearly 6,000 adult terns here this summer, most are common, along with 70 pairs of endangered roseates and a single breeding arctic pair. When they return from sea with tiny silver fish in their mouths, plum-size chicks emerge from low-lying vegetation and crevices. They swallow their meal in a single gulp, retreat to their safe havens, and their parents head out  again.

Last summer, at the height of hotter-than-normal temperatures, Seavey and her staff noticed a disturbing trend: Adults were returning to the colony not with the usual small herring or sand lance or hake. Instead, they carried butterfish, a species found in greater abundance much farther south. Seen from above, a juvenile butterfish looks a whole lot like a herring or hake; from the side, though, it’s much wider. For generalists that regurgitate food for their young, like Herring Gulls, that difference doesn’t pose a problem. For tern chicks, it can be deadly. 

“We’d sit there and watch a chick try to swallow the butterfish for several minutes and then eventually just give up,” says Elizabeth Craig, the laboratory’s tern conservation program manager. “The whole island was covered in dead fish and hungry birds.” 

Today the overwhelming majority of Roseate Terns in the northeast nest at just three sites.

Craig and Seavey were especially concerned about young Roseate Terns. The population that breeds in the Northeast, once prolific from Nova Scotia to Virginia, experienced two catastrophic collapses: the first at the hand of the millinery trade at the turn of the century, and again beginning in the late 1930s, when human development and unrestricted predation wiped out many remaining colonies. (Roseate Terns that breed in the Caribbean, Europe, and the Indian Ocean remain healthy.) Today the overwhelming majority of Roseate Terns in the northeast nest at just three sites located in the Long Island Sound and south of Cape Cod—a dangerous predicament for an already beleaguered species. With such a concentrated nesting area, a single predator or disease outbreak could decimate the population. So, too, could a tropical storm, the likes of which will intensify as climate change amplifies and reroutes weather systems. 

That’s why the recovery plan calls for restoring at least six Northeast colonies with more than 200 breeding pairs at each. Seavey is one of five such sites in the Gulf of Maine. 

Restoring roseates to a healthy population—5,000 pairs, up from around 3,200 today—depends upon a complex system of relationships. Roseate Terns rely upon an abundance of the more bellicose Common Terns for protection. Both species have evolved to return each summer just in time to capitalize on a rich supply of a few particular types of fish. Once chicks fledge, terns travel to Cape Cod to fatten up for the roughly 5,000-mile flight to their South American wintering grounds. Remove one step in this cycle, and a colony could collapse. 

“Everything that goes on at this island depends upon synchronicity,” says Seavey. (She should know: The island is named for her eighth great grandfather, who shed these waters for cod four centuries ago.) Hence her concern at the appearance of butterfish in terns’ beaks last year. Researchers reported the phenomenon at colonies of terns and puffins, which also feed their chicks whole fish, throughout the Gulf of Maine. “With shifts in climate resulting in changes in temperature, we expect to see changes in the food web and the distribution of fish,” says Craig. “But we were all alarmed it happened that fast.” 

The ocean absorbs 90 percent of Earth’s excess heat, which is why sea temperatures are rising everywhere. But few places are warming as fast as the Gulf of Maine, a robust cold-water ecosystem that spans from Cape Cod north to Nova Scotia’s Bay of Fundy. Here, changes expected to take decades are materializing in a few years. It’s a little like watching a movie on fast-forward. And in many ways, the star is the Roseate Tern. 

As an apex predator, the roseate offers a view into the intricate happenings beneath the waves. Its success, or failure, reveals a lot about the ecosystem as a whole. And so if scientists like Seavey and Craig can succeed at shepherding terns through the tumult, they may well create an effective model for safeguarding other seabirds across the world’s  oceans.

Last year wasn’t the first time strange species started showing up in the Gulf of Maine. The office of Andrew Pershing, chief scientific officer at the nonprofit Gulf of Maine Research Institute, looks out on one of Portland’s commercial fish piers, where boats bring in halibut, haddock, and cod. In 2012, then one of the hottest years on record there, fishermen returned with reports of unusual creatures in their nets: warm-water dwellers like black sea bass, longfin squid, and blue crabs—mid-Atlantic species, just like butterfish. Meanwhile, beachgoers observed other warmer-water species such as loggerhead turtles and seahorses. 

Puzzled, Pershing and his peers pulled up temperature records and satellite data for the past 40 years. What they discovered surprised even them: The Gulf of Maine wasn’t just warming; it was doing so more than four times faster than the global average, faster than 99 percent of other regions. 

Picture two spinning gears: one in the north Atlantic, one to the south. The northern one spins counterclockwise, pushing water from the Labrador Current south. The southern gear spins clockwise, with the powerful Gulf Stream on the western side bringing warm water into the north Atlantic. The gears overlap near the Gulf of Maine. 

Manmade warming is changing that historical pattern in several ways. Rising ambient temperatures are melting polar ice caps, sending massive amounts of fresh water into the North Atlantic. Fresh water doesn’t sink as quickly, and so stalls the engine that powers the gears. As a result, the point where the gears meet shifts and more warm water flows into the Gulf of Maine. Records bear that out: The average sea temperature there has risen about 3 degrees Fahrenheit over the past 30 years. 

That incremental increase has allowed some species to gain a foothold. Lobsters, for example, prefer temperatures between 54 and 68 degrees Fahrenheit, and the gulf is currently in that sweet spot. While shell disease decimated populations in warmer waters off southern New England, the Gulf of Maine is experiencing an unprecedented boom. Last year Maine harvesters brought in nearly 120 million pounds, about 80 percent of the nation’s total, worth about $485 million. “Just a small amount of warming crossed an important biological threshold for lobster that really helped fuel the explosion,” says Richard Wahle, director of the University of Maine’s Lobster Institute. 

But the boom may be short-lived. To understand why, you have to begin at the base of the food chain and work back up to predators like lobsters and terns. Historically, minuscule organisms called phytoplankton have been in rich supply here, but climate-driven changes are causing their decline. More rainfall, for instance, dilutes ocean salinity. It also increases terrestrial runoff, which darkens the water and limits phytoplankton’s ability to absorb sunlight and thus photosynthesize and grow. 

That, in turn, affects keystone species that consume phytoplankton, most notably the zooplankton Calanus finmarchicus. This copepod lives its life like a tiny oceanic bear: It gorges on phytoplankton much of the year, then hibernates and conserves energy in winter. That strategy makes copepods calorie-dense—Pershing likens them to floating drops of butter—and everything from juvenile lobsters to right whales to herring makes a living off them. 

Without healthy phytoplankton, copepods can’t store up the energy they need. And when water gets too warm, copepods skip their slumber and use up their energy stores, making those that survive less nutritious. Meanwhile, changes in oceanic currents are slowly shifting healthy populations north. 

The well-being of this one species has myriad impacts. Wahle has observed a strong correlation between copepod availability and the health of larval lobsters. Marine mammal experts, meanwhile, believe that copepods’ changing distribution has altered the range of the endangered North Atlantic right whale, forcing more away from traditional feeding grounds off New England into heavily trafficked areas like the Gulf of St. Lawrence (at least three have been struck and killed by ships there this year alone). 

Adult herring also depend upon Calanus, which could at least partly explain why the fish are trending to cooler waters in the northeastern gulf. That, in turn, may be drawing unusual seabirds south, including the Common Murre, which reared chicks in the Gulf of Maine in 2018 after a 27-year hiatus. “It all seems to link back to this one copepod,” says Wahle. 

Video: Chris Linder

Scientists are tracking animals like copepods and how they respond to incrementally warming waters in order to make educated guesses about what’s to come. Complicating that research are marine heat waves that have hit the gulf in recent years. 

If global warming is the constant pressure on an ecosystem, marine heat waves—five-plus-day stretches when temperatures exceed the 90th percentile of historical averages—are best understood as a sudden shock, explains Alistair Hobday, research director for oceans and atmosphere at CSIRO, Australia’s national science agency. “Marine heat waves impact right through the food chain,” he says. “Some species die; other species arrive; diseases occur. So management gets challenged by new things that have not been previously considered or encountered.” 

In 2018, the Gulf of Maine experienced 250 days that qualified as marine heat waves. 

In 2018, the Gulf of Maine experienced 250 days that qualified as marine heat waves, making it one of the hottest years on record. But even it was eclipsed by both 2012 and 2016, which witnessed 360 and 302 marine heat wave days, respectively. 

That statistic floored Pershing. But what really interested him was how the marine ecosystem responded to these changes. “There are a few species that react really fast to these events,” he says. Squid, for instance, can arrive after just a few days or weeks of warm water. Herring, meanwhile, make a hasty departure. “And if you see an impact on herring,” Pershing warns, “that’s going to have an impact throughout the ecosystem.” That’s particularly true for seabirds, as we saw last year. 

Seabird species respond to these changes in ocean temperature differently. Species whose young take to the ocean right away, such as Razorbills, abandoned the waters around their breeding colonies faster than other species, presumably in search of suitable food. Atlantic Puffins, meanwhile, surprised scientists with their resiliency to the temporary food shortage. As sea-surface temperatures rose in early summer, puffin parents slowed down their feedings. When cooler waters, and the fish that occupy them, returned a few weeks later, the adults redoubled meals, feeding their chicks 10 times or more a day. They also extended the time they spent rearing their single chick—in some instances nearly doubling it, from 40 days to 83. Nevertheless, last year’s fledging rate was one of the lowest on record. 

It’s far more challenging for terns to adapt, explains Don Lyons, director of conservation science for Audubon’s Seabird Restoration Program. Audubon manages four islands in the gulf that host Roseate Tern colonies. “They have a pretty hard-wired growth-and-development pattern,” says Lyons. “Terns start out with multiple chicks. If they run into a food shortage, it gets really hard to feed the whole family, and so they really struggle.” To give terns and other seabirds a better chance of finding food, says Lyons, we have to reconsider how we manage our fisheries. 

Herring, for instance, were once so prolific that they formed shoals 30 miles long and five miles deep. Overfishing caused the collapse of the industry in the 1960s and 1970s, which led to stiff quotas. The total fishery catch limit today is about 15,000 metric tons per year, down from over 180,000 metric tons just 15 years ago. That number will drop further next year. Meanwhile, stock assessments conducted by the New England Fisheries Management Council show that the number of baby herring is declining, perhaps in response to copepod declines. 

At the same time, terns’ other preferred staple, the sand lance, faces its own struggles. On Stellwagen Bank off Cape Cod, the survival of eggs and embryos decreases as much as twentyfold when carbon dioxide levels increase in ocean water, suggests a forthcoming study. “Sand lance might be the most CO2-sensitive fish species tested to date,” says Hannes Baumann, senior author and a fisheries biologist at the University of Connecticut. “This means that long-term marine climate conditions are likely to worsen for sand lance.” Baumann says industries related to fracking and construction have expressed interest in mining sand in the lances’ habitat, posing additional threats to the species, which are commercially exploited for fish meal. 

Given the dissipating numbers of these key fish, it’s more important than ever that management of these species takes a truly ecological approach, Baumann, Lyons, and others say. In the past, fish quotas have been set strictly on analysis of historical data. Allowing for seasonal forecasts that include marine heat waves would do a lot to improve management as temperatures rise, argues CSIRO’s Hobday. “It would lead to more-rapid decision making.” 

If ocean warming here has taught us anything, it’s that more-nimble management is necessary, says Mary Beth Tooley. She coordinates government and regulatory affairs for O’Hara Corporation, a herring fishing company, and served on the New England Fishery Management Council until 2017. “Our job is to leave this company in good shape for the next generation,” she says. “We’re not interested in taking the last fish. If you rely long-term on fishing, you’re looking for stability over time.” 

To achieve that ecological sustainability, Hobday says, fisheries need to consider seabirds specifically. It’s an idea first advanced in a 2011 Science paper that argued, when considering a healthy biomass of any fishery, it’s important to leave “one-third for the birds.” 

Environmental legal scholar Alison Rieser agrees. She’s studied the rise and fall of the herring fishery and what it means not only for the fish themselves, but also for the human societies that depend upon them. “It takes a village,” she says. “You need a whole ecosystem to have a productive fishery. You need healthy seabird populations, you need everybody.” 

Seabirds might be able to help. Seavey’s team is using advanced technology, working with the Cornell Lab of Ornithology to DNA test guano in order to better understand the birds’ diet. “Genetic sequencing has become so cheap, it is only now possible to do research of this scale,” says post-doctoral research fellow Gemma Clucas, “and luckily for us, poop is everywhere.” 

As if to prove it, a giant blob of guano lands on Seavey’s arm. “Excellent!” she beams. “More data.” 

Beginning this fall, GPS trackers attached to terns will enable them to chart precisely where they caught the fish that becomes this data point. They’ll sample those waters to gather fish DNA sloughed off a shed scale or even a single cell sample, revealing which fish species are present in the water column. Together, the information will tell them what terns are eating, what’s available to them, and what—if any—preferences they have for particular fish. 

“What if seabirds could help fishermen by acting as indicators of what is to come two or three years out? Then, they really do become allies.”

Seavey says they still don’t know exactly which fish warmer waters will bring or how Roseate Terns will respond to these new additions. That, she says, is one reason why charting the birds’ preferences will help conservationists save these long-flying birds. What’s more, science shows that seabirds are particularly good indicators of forage fish populations. So, while some in the fishing industry may be put off by the idea of setting aside a percentage of their stock for seabirds, Seavey sees it as the start of a mutually beneficial partnership. “We used to think of these organisms as competitors for the same resource,” Seavey says. “But what if we instead considered them as compatible? What if seabirds could help fishermen by acting as indicators of what is to come two or three years out? Then, they really do become allies.” 

We might someday soon look to seabirds like roseates as effective sentinels for letting us know where fish populations are heading. We can in turn help them by making sure they have breeding habitat nearby. 

When Audubon’s Steve Kress began an audacious plan to restore Atlantic Puffins in the Gulf of Maine, he encountered a lot of skepticism from the scientific community, who worried that relocating birds from Canada to Eastern Egg Rock would fail, either because chicks wouldn’t survive long enough to fledge, or they wouldn’t return. Neither scenario proved true. Skeptics also said that any success there would be limited just to that one species. But in 1984, Kress and the Maine Audubon team began successfully restoring both Common and Roseate Terns on Maine’s Seal and Petit Manan Islands. 

In a lot of ways, these two species are uniquely suited for this kind of recovery work. What terns lack in growth flexibility over time, they make up for in a willingness to relocate. “Terns are somewhat unique in that they’ve evolved in areas close to the coast in habitats that are pretty dynamic and constantly changing,” says Lyons. “Because these environments are dynamic and changing, they’ve typically evolved the capacity to move around and find them.” 

The key, he says, is selecting and maintaining optimal habitat for terns. So far, that’s included managing invasive plants to preserve nesting grounds and protecting birds against predators. But for roseates and other sensitive seabirds, in the face of 21st-century climate change, the biggest challenge may be the availability of meals.

Lyons would like to see a chain of islands with appropriate habitat from which the terns can choose and possibly even use to follow their preferred prey fish as they seek out waters that match the temperatures they’ve traditionally preferred.

It’s a manageable vision. Unlike other apex predators like polar bears or wolves, terns are content packing into a small amount of space. Many Gulf of Maine islands have enough elevation to weather sea-level rise there. What most limits their habitat selection, says Lyons, is finding environments that haven’t been completely influenced by humans. 

That’s part of what makes colonies like those on Seavey and nearby Stratton Island so essential. “It’s all about a good network,” says Lyons. “Nodes of the network don’t have to be big. We just need to scatter the nodes across as big a space as possible.” 

As further evidence, he points to reports from Great Gull Island, some 200 miles south. Anecdotal evidence suggests that this season was a particularly tough one for terns there. Here in the Gulf of Maine, colonies seemed to fare well—for now. 

All of the scientists interviewed for this piece agree on one thing: To preserve and expand imperiled populations, we need a new paradigm, one nimble enough to accommodate unexpected temperature spikes caused by marine heat waves as well as the more gradual—but no less inevitable—warming in the Gulf of Maine and beyond. Where we once relied almost entirely on historical data for everything from catch limits to restoration plans, the climate crisis insists we be more forward-looking. We need models and data-driven research to help predict where key species like herring and copepods will be trending (and in what numbers). Rather than studying species in isolation, we need an ecological approach that considers the relationships between fish, seabirds, and marine mammals. And we need to ensure that they all have options in terms of where they live and what they eat. 

That is especially true, says Lyons, for endangered animals like the Roseate Tern. “We can manage habitat. We can attract birds where we can protect them. We know how to do this,” says Lyons. “What we need now is to just commit to doing it.”

This story originally ran in the Fall 2019 issue as “A Moveable Feast.” To receive our print magazine, become a member by making a donation today.​