Steadily rising ocean temperatures are forcing fish to abandon their historic territories and move to cooler waters. The result is that fishermen’s livelihoods are being disrupted, as fisheries regulators scramble to incorporate climate change into their planning.

The Cape Cod Canal is a serpentine artificial waterway that winds eight miles from Cape Cod Bay to Buzzards Bay. On warm summer evenings, anglers jostle along its banks casting for striped bass. That’s what 29-year-old Justin Sprague was doing the evening of August 6, 2013, when he caught a fish from the future.

At first, Sprague thought the enormous fish that engulfed his Storm blue herring lure was a shark. But as he battled the behemoth in the gloaming — the fish leaping repeatedly, crashing down in sheets of spray — he realized he’d hooked something far weirder. When the fisherman finally dragged his adversary onto the beach, a small crowd gathered to admire the creature’s metallic body, flared dorsal fin, and rapier-like bill. Sprague had caught a sailfish.

It doesn’t take an ichthyologist to know that sailfish don’t belong in the Cape Cod Canal. Istiophorus albicans favors the tropics and subtropics; it so rarely visits New England that Massachusetts didn’t even have a state record. But strange catches — including cobia and torpedo rays — have become more commonplace. Over the last decade, the Gulf of Maine, the basin that stretches from Cape Cod to Nova Scotia, has warmed faster than nearly every other tract of ocean on earth, as climate change joined forces with a natural oceanographic pattern called the Atlantic Multidecadal Oscillation to increase sea surface temperatures by 3.6 F from 2004 to 2013. The results have been ecological transformation, upheaval in marine fisheries management, and an alarming window onto the warm future of global oceans. Although the Gulf of Maine has faced tumultuous change, it’s far from the only marine ecosystem being turned upside-down. The general — although far from universal — trend, according to a 2013 Nature study, is that fish in hot water flee toward higher latitudes, moving poleward to remain within their preferred temperature ranges. In Portugal, fishermen have caught nearly 20 new species in recent years, many from warmer climes. Chinook salmon are infiltrating Arctic rivers that they rarely, if ever, entered before, even as salmon are imperiled by drought and warming waters in California and Oregon. And in northern Europe, says Steve Simpson, a marine ecologist at the University of Exeter in England, sardines have replaced herring, coldwater-loving cod and haddock are heading north, and bottom-dwelling sole risk being “pushed off a cliff” as suitably cool water temperatures drift away from the continental shelf.



The ocean is warmer today than at any time since record-keeping began in 1880.

“I’m optimistic that we can have sustainable and productive fisheries, but they’re not going to be the fish we used to catch,” Simpson says. “It’s a changing of the guard.”

For decades, the ocean has served as our best defense against climate change, absorbing 90 percent of the atmosphere’s excess heat. But acting as a planetary sponge has taken a toll. Since 1970, global sea surface temperature has increased by around 1 degree F. The ocean is warmer today than at any time since record-keeping began in 1880. As water temperatures have spiked along the U.S. East Coast, the Atlantic’s inhabitants have undergone a dramatic rearrangement. According to an analysis by researchers at Rutgers University, black sea bass, once most abundant off the coast of North Carolina, have shifted two degrees of latitude north, to New Jersey, over the last half-century. Lobsters have all but vanished from Long Island Sound — where rising temperatures have made the crustaceans more susceptible to disease — and, at least for now, proliferated in the Gulf of Maine. Butterfish have supplanted herring in the Gulf, with disastrous consequences for baby puffins, which struggle to swallow the disc-shaped interlopers and starve to death. Even blue crabs, the invertebrate icon of Chesapeake and Delaware bays, have arrived in the Gulf of Maine. A recent study in the journal Progress in Oceanography suggested that continued warming could reduce the range of species from Acadian redfish to thorny skate.



Black sea bass, once abundant in North Carolina, have moved north to New England. NOAA NATIONAL OCEAN SERVICE

Although warming water is the most immediate agent of oceanic chaos, it’s just one front in climate change’s three-pronged assault on marine life. As the ocean absorbs carbon dioxide, it becomes more acidic and less saturated with the calcium carbonate that organisms like corals and pteropods — planktonic snails that support food webs — need to build shells. Fish are far from immune: Ocean acidification may disrupt the development of larval fish and reduce their survival rates, according to a study last year in the journal PLOS One.

Deoxygenation is an even more immediate threat. Scientists have long been acquainted with low-oxygen “dead zones” that form annually in the Gulf of Mexico, the Chesapeake Bay, and other coastal areas where agricultural runoff accumulates. As oceans heat up, those localized hypoxic areas are expected to spread: Not only does warm water hold less dissolved oxygen than cool water, it also tends to divide into layers that don’t readily mix. According to one recent study, the ocean has been losing oxygen since the mid-1980s, likely because rising temperatures have impeded circulation. Lisa Levin, a professor at Scripps Institution of Oceanography, points out that not all creatures are equally fazed: Along the naturally oxygen-poor Pacific Coast, marine life is well evolved to cope. But all animals have their limits. “When oxygen goes way down, it’s effectively habitat loss,” Levin says. “They might move north, they might move upslope into shallower water.” Species that can’t easily relocate, like muck-dwelling invertebrates, may perish. The cruel corollary to deoxygenation is that warmer waters also drive up animals’ metabolic rates, forcing them to use more oxygen to breathe. As Curtis Deutsch, a chemical oceanographer at the University of Washington, puts it, “They need more, at the same time that they have less.” In 2015, Deutsch and co-authors published a study in Science analyzing how the double bind of warm water and deoxygenation would change distributions for common species like cod, rock crab, and eelpout. Deutsch found the creatures would lose 14 to 26 percent of their habitat. “If you’re going to manage for the long-term viability of fisheries, you need to think carefully about the patterns of oxygen loss in the ocean,” Deutsch says.

As stocks shift, many fishermen face a choice: follow the schools northward, or pursue different species.

When climate change and its harmful effects force fish to relocate, entire ecosystems can suffer. That’s what’s happened in the Mediterranean, Australia, and Japan, where tropical grazers like parrotfish, butterflyfish, and rabbitfish have colonized once-temperate ecosystems. As these herbivores expand their range, they graze kelp forests to nubbins, leaving barren wastelands in their wake — a phenomenon known in Japan as isoyake.

Adriana Vergés, a marine ecologist at the University of New South Wales, says that the tropical incursion has created opportunities as well as crises. In the Mediterranean, a cottage fishery has developed around seaweed-munching rabbitfish, while coral has filled the niche vacated by kelp in some Japanese waters. But in other places, the disruption has been catastrophic: Vergés says that the combination of overgrazing and warming water has reduced the extent of kelp by around 60 miles along the coast in Western Australia, depleting valuable species, like abalone and lobster, which take cover beneath seaweed canopies. Vergés fears that kelp and its dependents may be driven south along the Australian coast until they simply run out of near-shore habitat. “Here, species move toward the poles,” she says, “but there comes a point where they can’t move anymore.” While poleward shifts are the rule, exceptions abound. In the Gulf of Maine, many species are drifting southwest instead, seeking cooler spots that form closer to shore. A 2013 Science study analyzed more than 350 groups of marine organisms and found that their movements closely followed local “climate velocity,” the rate and direction of climatic change. More surprising was that those shifts didn’t always track northward — species in the Gulf of Alaska, for instance, moved south in concord with a natural cycle of Pacific cooling. The lesson: The ocean doesn’t warm uniformly, and local conditions drive fish movements as much as broader trends. In the face of rapid turnover, some agencies and fishing communities have begun considering seafood’s future. In 2016, National Oceanic and Atmospheric Administration (NOAA) scientists found that around half the Northeast’s fish and shellfish were highly vulnerable to climate change — particularly species like shad, salmon, and sturgeon, which spend part of their lives in freshwater and must therefore contend with changing conditions in rivers as well as oceans. A parallel NOAA study suggested that ports whose economic fates are hitched to vulnerable species — like New Bedford, Massachusetts, which depends on scallops for around 80 percent of its landings — face particular risk, while towns like Point Judith, Rhode Island, whose fishermen catch the gamut from squid to monkfish to lobster, could fare better. “Ports with fairly diverse fishing portfolios might have an easier time adapting,” says Jon Hare, director of NOAA’s Northeast Fisheries Science Center.

Tropical rabbitfish are now found in the Mediterranean. POOJARATHOD/WIKIMEDIA COMMONS