With Warming Temperatures, Alaska Pollock Are Shifting Northward

In the Bering Sea, fish are finding refuge far from their traditional range. What does this mean for ecosystems and commercial fisheries?

280,000 walruses. That’s how many are estimated to live in the waters surrounding Alaska’s Saint Lawrence Island, in the Bering and Chukchi seas. Compared to the island’s human population of 1,400, walruses outnumber Yup’ik people 200 to 1.

In theory, at least, the region could sustain even more of the marine mammals thanks to a recent influx of additional biomass, including pollock. According to Franz Mueter, a professor of fisheries at the University of Alaska Fairbanks, around 200,000 walruses could sustain themselves for a year on a weight equivalent to the additional fish biomass moving into the Northern Bering Sea from further south. A paper published in Polar Biology in 2018 indicates it’s likely that pollock and other fish populations migrated northward in the summer of 2017, after a warm winter led to reduced sea ice, likely due to climate change.

photo of alaskan pollock
Surveys in the northern Bering Sea indicate that there was a 6,000 percent increase in biomass of Alaska pollock there in 2017 compared to 2010. Photo by George Berninger Jr.

“The blob started in 2014,” Mueter contended during a presentation in 2019, referring to an unusually warm area of water in the Pacific Ocean extending all the way from Alaska down to California. “The first indication[s] in the biology that something was off were the murre die-offs, marine mammal mortalities, algal blooms, [and that] forage fish were lacking.”

While species struggled in the Gulf of Alaska and southern reaches of the Bering Sea due to warming temperatures, they now seem to have found refuge to the north.

In 2010 the National Oceanic and Atmospheric Administration (NOAA) initiated bottom trawl surveys in the northern Bering Sea in response to questions of diminishing winter sea ice coverage in the Arctic. Seven years later when the survey was repeated, Lyle Britt, a fisheries biologist with NOAA who was part of the repeated studies, said that the data indicates a roughly 6,000 percent increase in biomass of walleye pollock (Gadus chalcogrammus) in the region.

“Things like walleye pollock, which makes up the big, big commercial fishery to the south, had moved north,” Britt said.

Alaska pollock, or walleye pollock, are a member of the cod family. The fish can grow up to three feet long, swim along the seafloor, and have a speckled coloring that allows them to blend in with the ocean bottom.

This fish typically prefers temperatures that range from 35.6 to 39.2 degrees Fahrenheit, according to the Alaska Department of Fish and Game. On a recent February day the ocean temperature in the Gulf of Alaska, where the normal pollock habitat range extended, read 41 degrees Fahrenheit from Kodiak Island.

According to NOAA, areas previously considered Arctic marine zones now resemble subarctic ones, both in sea temperature and species assemblage. Essentially there seems to be a shifting, new norm as ecological systems push across latitudinal lines in a northerly direction, inspired by temperature increases due to climate change.

“For something like walleye pollock, from one season to the next to change their distribution by hundreds of miles, that’s no insignificant thing,” Britt said.

And it’s not just pollock that are moving north. Research suggests that terrestrial and other marine species, from yellow cedar trees to market squid, are also pushing northward — an attempt to follow the warmer temperatures they’re accustomed to.

The impacts of this new norm will expand ever further. That’s because walruses in the Bering Sea aren’t the only animals indirectly connected to pollock by the global food chain. Seabirds, like murres, also compete with pollock for food. Marine mammals and other fish directly feed upon them, too.

So do humans: Alaska walleye pollock is what you’re eating when you order a Filet-O-Fish sandwich from McDonald’s. Pollock constitutes one of the world’s largest fisheries. At an estimated rate of 300 million McDonald’s Filet-O-Fish sandwiches sold each year, this equates to more than 22 thousand tons of pollock, or about the weight of one hundred Statues of Liberty.

photo of alaskan pollock
Dan Martin, who operates the “Commodore,” says fishing vessels are now traveling hundreds of miles from Alaska’s Dutch Harbor chasing pollock. Photo by Captain Dan Martin.

While the shift of pollock biomass in a northerly direction was first recognized and published by NOAA research surveys in 2017, Dan Martin, captain and fleet manager of Eveningstar Fisheries, said he personally observed changes in pollock populations about ten years earlier.

“The early beginnings where we started to notice that there were things changing within the pollock biomass or its geographic disbursement was probably somewhere around, I would say, 2006 to 2008,” he said.

Martin currently operates the fishing vessel Commodore. He’s been captain on this boat since 1997, and has been fishing from the Dutch Harbor port, on Unalaska Island, for 37 years.

Fluctuations in ocean temperature, which directly impact sensitive species at the bottom of the food chain, are ultimately responsible for the movement of pollock, Martin says.

“You deal with the smallest organisms first, you know. They’re the most quickly affected by warmer waters,” he explained, “whether that’s the phytoplankton or that’s krill or whatever the food source for the pollock is at the time.”

According to Martin, in order to keep up with human consumption, large fishing vessels are now traveling hundreds of miles, or for a few days, from Dutch Harbor to the northern Bering Sea, chasing pollock. During winter fishing season in the southern Bering Sea, gusts of profound wind swirl snow and throw hail. Brief partings in the clouds, though, enlighten the white-covered volcanic islands forming the Aleutian chain that reaches toward Russia.

According to a report by NOAA in 2014, Alaska’s fishing ports bring in the highest poundage of wild fish caught when compared to all of the 49 other US states. The Bering Sea alone accounts for 30 to 40 percent of the country’s total commercial fishing catch. Over three million pounds of pollock protein was landed in 2014, making the species the most substantial American fishery by volume. The pollock intake is nearly three times the size of the next largest American fishery, the mysterious Atlantic species called menhaden.

A recent paper in the journal Elementa: Science of the Anthropocene, published in 2019, documents a holistic assessment of the Alaska pollock supply chain globally, assessing the industry’s total climate footprint. The study found that while pollock is a fairly fuel-efficient fishery, processing the fish and transporting final fish products — namely battered, breaded and crab-flavored fish sticks — contribute significant emissions through exhaust produced by transoceanic voyages, from the Bering Sea to distant human population centers and McDonald’s restaurants.

Following fish further north into the flux of the Bering Sea, via fishing vessel or processor, means even more emissions. It also means steaming through the feeding grounds of tens of thousands of shearwaters and puffin rafts, past walrus haul-outs, and alongside killer whale pods. Behind the cacophony of sealife, a dark and steep face of land reaches from the ocean. Brown earthy tones stack into cliffs which build ridges that, with time, erode into rubble. Held by a bowl of land, a collection of snow now drips into slender streamlets that feed the warming sea.

Correction: An earlier version of this article incorrectly stated that the population of Saint Lawrence Island is 140,000. It is 1,400.

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