When the National Oceanic and Atmospheric Administration announced the first-ever cancellation of the Bering Sea snow crab season in October—and extended the closure of the king crab fishery—explanations were thin. Headlines relayed what the government had gathered: Nearly 11 billion crabs had, effectively, disappeared. The cause remained an open case, albeit with a prime suspect: climate change.

But climate doesn’t tell the whole story. Nautilus interviewed marine scientists, fishermen, former and current government officials, from Alaska to D.C., whose expertise and testimonies indicate there’s another force at play: fishing. Yet like all good mysteries, the story goes even deeper. It begins with a diver and a camera.

It was September 1993 at the bottom of the Gulf of Alaska. As he descended and the seafloor came into view, Braxton Dew witnessed a phenomenon few others had ever seen: a mountain of king crabs. There were some 9,000 of them, towering above his head once he reached the seabed. He checked the depth gauge: 75 feet. He captured a photograph.

CRAB COMMUNITIES: At left, a pod of adult king crabs; at right, a pod sets off to forage. Photo credit: C. Braxton Dew.

Dew would log 943 dives observing the crabs during his 25-year tenure as a marine biologist at NOAA, where he studied their complex social systems, cooperative foraging techniques, and unique podding behavior: when king crabs come together in daytime to rest in spherical or dome-shaped formations before foraging in a herd at night.

In 1996, Dew used the photo to help demonstrate to NOAA administrators that the survey methods they used to estimate adult king crab populations were flawed.1 It was too easy to pull the sampling net through an aggregation and extrapolate that highly localized density to an entire region. If this occurred, the population estimates used by government managers of Alaska’s king crab fishery could be inaccurate.

According to Dew, the evidence he presented caused turmoil inside NOAA. He was transferred from Kodiak to Seattle; underwater crab research conducted by the agency declined sharply. He remained there for 12 years without assignment, waiting to publish his final manuscripts in the NOAA Sea Grant Collection, in which he laid out evidence suggesting that king crab management should better account for factors like social behavior and habitat preference.2 Some of the papers would spend over a decade stalled in review until his former bosses retired in the late 2000s.

It’s possible that if this kind of underwater behavioral research had been sustained, biologists might have a wider base of knowledge from which to build a more comprehensive and unified theory explaining the presumed deaths of billions of snow crabs in two years. Unfortunately, we are left to conjecture.

One billion crabs didn’t simply “disappear.”

Everything must be considered in the context of climate change, which is driving massive shifts in Arctic ecosystems. Yet unlike 1 billion heat wave casualties in the shallow and intertidal zones of the Salish Sea last year, snow crabs live on seafloors in deeper waters, and there are no records of water temperatures high enough to kill crabs directly. While it’s likely that whatever happened to the crabs was catalyzed by climate, the question remains: What was it?

The dominant theory suggested by NOAA scientists is that climate change caused the collapse of the snow crabs’ nursery. As sea ice forms in winter, salt is expelled and cold, dense water sinks to the floor of the Bering continental shelf, forming what oceanographers call the “cold pool.” This is where young snow crabs grow up with abundant food, protected by water that is too cold for many of their predators—until now.

As the planet has heated, sea ice has diminished, reaching record lows in the Bering Sea between 2017 and 2019 and triggering a “dramatic ecosystem transformation.”3 The shrinking cold pool put snow crabs’ backs against the proverbial wall. Where once they were safe, juvenile crabs could be caught by predators like cod penetrating the warming water.

Yet there are problems with this theory. In many years past, cold pool conditions didn’t form in the Eastern Bering Sea, yet snow crabs fared well. And Pacific cod populations, instead of benefitting from new access to prey, have crashed alongside the crabs: Catches fell significantly in the absence of Bering Sea ice and, in the Gulf of Alaska, low numbers prompted the first-ever closing of the cod fishery.

Another possible explanation is that disease has afflicted the crabs. Snow crabs are plagued by a parasitic alga called Hematodinium. Experiments indicate that increasing temperatures may facilitate infections, but severe cases of the disease have spiked and leveled off in years past without population collapse.4 Other explanations include starvation, migration, and even mass cannibalism, although this has only ever been observed in captivity. None are mutually exclusive.

However, fishing impacts have been largely absent from the discussion. Ship-tracking data compiled by Global Fishing Watch shows that vessels in the Eastern Bering Sea took advantage of contracting sea ice, encroaching into previously inaccessible habitat. Geographical data show that the historical winter habitat of snow crabs overlaps with recent vessel movements,5 which in some cases have pushed into the snow crab “hotspot” near St. Matthew Island, a landmass usually locked in ice through winter.

Up until the year of the crash, NOAA’s North Pacific Fisheries Management Council—the appointed body that regulates fishing in the region—ratcheted up catch limits, which nearly tripled from 19 million to 45 million pounds between 2017 and 2020. As quotas rose, crabbers struggled to find the large males they are permitted to keep; in 2020 they discarded roughly as many crabs as they kept, suggesting an unusual age structure and perhaps an excessive catch limit.6

Meanwhile, scores of fishing trawlers seeking shrimp and pollock dragged their nets and cables for hundreds of hours across the sea’s northern floors—and this took place during critical breeding months, when the region’s crabs are concentrated more tightly and females are brooding the next generation in vulnerable eggs against their bodies.

This isn’t the first Bering Sea crab collapse NOAA has portrayed as a mystery.

NOAA reports corroborate concerns suggested by the geospatial data, showing massive spikes in snow crab deaths during the sea ice lows. The fishing mortality rate—encompassing both directed crab catches and “bycatch” by vessels targeting other animals—increased more than fivefold, with bycatch multiplying by a factor of more than 11.

“The fishing industry wants to point the finger at environmental factors, especially climate change,” said Jennifer Jacquet, a professor of environmental studies at New York University. “But we know that even in the face of a shifting climate, direct exploitation remains the largest factor affecting aquatic animals.”

“You would think that fishery managers would want to set more precautionary catch limits to account for climate uncertainty,” John Hocevar, a marine biologist at Greenpeace who has led two submersible expeditions surveying trawler damage in the Bering Sea, wrote in an essay on Greenpeace.org. “They don’t typically do that, but they definitely blame climate change if things go wrong.”

This isn’t the first Bering Sea crab collapse NOAA has portrayed as a mystery. In 1959, Japan established a no-trawl zone protecting the breeding territory of king crabs North of the Aleutian Islands. Catches increased throughout the next 15 years. But in 1976, the United States Magnuson-Stevens Fishery Conservation and Management Act codified the concept of the exclusive economic zone, extending 200 miles from shore—effectively claiming the reserve as U.S. waters. Then, in 1980—in the midst of the Cold War—the U.S. and USSR joined forces to trawl the now-unprotected breeding ground, targeting sole.

In a period of five years, bycatch of king crabs increased by more than 600 percent, with casualties concentrated in reproductive-age females.7 Much of it went unreported, although photographs survive from a NOAA fisheries observer, who captured trawlers dumping nets full of dead, egg-laden female crabs into the sea. Meanwhile, catches for king crabs in the region escalated from 8.8 million in 1975 to 20.8 million in 1980.

Within three years, the population plummeted to single digit proportions. To this day, red king crabs have never recovered in the Bering Sea. The official NOAA report stated, “Declines in abundance are attributed to a combination of high natural mortality and variable year-class strength rather than inadequate management measures,” but never identified the cause of this “drastic increase in natural mortality.”

In 2021, with the help of the nonprofit watchdog Public Employees for Environmental Responsibility, a whistleblower came forward.8 In a complaint filed under the Information Quality Act, he alleged that “managers pushed the natural mortality story because they knew it might divert the focus from overfishing to natural catastrophe.” It was Dew, the exiled crab biologist.

While it’s likely that whatever happened to the crabs was catalyzed by climate, the question remains: What was it?

On the surface, the king crab tragedy rhymes with the recent collapse of the snow crab: Like in the early ’80s, a once-protected habitat was exposed and, after a few years of high crab quotas and spiking trawler bycatch, populations collapsed. And just as with king crab, NOAA officials have described the snow crab crash as a mysterious natural phenomenon.

NOAA scientists don’t think the role of the seafood industry has been downplayed. “The magnitude of bycatch is just not there, in terms of orders of magnitude,” said Mike Litzow, the shellfish assessment program manager at NOAA’s Alaska Fisheries Science Center.

Yet despite requirements for observers on every trawler, official bycatch data is notoriously undercounted. Research published in NOAA’s Fisheries Bulletin underscores the difficulty of quantifying unreported mortality of crabs who are crushed, but not caught.9 In addition, observers tasked with recording bycatch only count it in a specific area, are instructed not to count crabs who are dragged up in pieces, and are often pressured or threatened by boat captains and crew.10

Even considering all these factors, Litzow contends that “bycatch could be a hundred times greater and it still wouldn’t explain the decline.” By his account, the models rule out crabbing impacts as well. “We’ve fished this population for 20 years at these kinds of rates and we’ve never seen anything like this before,” he said. Litzow and his colleagues at NOAA believe the best explanation is a mass starvation event caused by the increased energy demand of warming water on the crabs’ metabolisms.

However, Paul Dayton, a benthic ecologist at the Scripps Institute of Oceanography, points out how the starvation hypothesis does not necessarily absolve the fishing industry. If crabs were indeed struggling to find food, Dayton suggested that the “situation would be made much worse by the very heavy fishing and trawling on the bottom.”

Research by Dew and colleagues on chronic trawling impacts in the Eastern Bering Sea corroborates this idea, demonstrating how trawling activity can impair seafloor food webs for decades.11 “There’s definitely an idea in the science that exploited populations are more vulnerable to climate variability,” Litzow said.

It may be that billions of snow crabs died in the darkness of the deep sea, but Dew offers an additional hypothesis: Many of them never existed. They were figments of an inaccurate survey design that overestimates crab populations, leading to excessive catch quotas and lax bycatch regulations.

The flawed sampling methods Dew tried to warn against in the 1990s are still used today. While snow crabs don’t form proper pods like king crabs do, they still aggregate in large groups and are patchily distributed across the seascape, creating the potential to overestimate crab populations.

In a 2007 Fisheries Research paper, Dew and his wife Roberta Austring, a mathematician, analyzed 22 years of NOAA survey data, demonstrating that while the sampling methods NOAA uses may work fine for fish, they’re more fallible for crabs.12 “Consider that a trawl-haul survey sample covers about 0.01 square nautical miles,” he posited. That trawl is then used to estimate the crab density in a 400 nautical square mile sector on a grid—“an extrapolation of 40,000 times!”

This opens the possibility for inflated population estimates if surveys happen to intersect aggregations of crabs. That may have happened twice with king crabs: their Cold War collapse in the Bering Sea was preceded by a “recruitment pulse”—a cohort of maturing males—that motivated regulators to double catch limits every three years.

Simultaneously, the king crab population on the other side of the Aleutian Islands in the Gulf of Alaska crashed after a reported recruitment pulse between 1979 and 1981 “stimulated Alaskan managers to cheerlead a doubling of the harvest in the near future, thus exposing the entire stock to terminal depletion,” concluded a post-mortem led by fisheries biologists Janet Armstrong and Ray Hilborn of the University of Washington.13 “In 1982 the largest harvest in 14 years was taken from a stock that had reached an unprecedented low level of abundance.”

In strikingly similar form, between 2015 and 2018 NOAA surveys reported a 2,000 percent increase in recruitment of male snow crabs. Bob Foy, head of the North Pacific Fishery Management Council’s crab plan team, called it “one of the largest snow crab recruitment events biologists have ever seen.” In the following years, catch limits were more than doubled. Within five, the fishery was shut down.

“We know that recruitment boom was real,” Litzow responded when asked about the possibility that survey methods had caused crab populations to be overestimated. He cited crab reproductive cycles, improved survey coverage, and the fact that the boom persisted for two consecutive years. But while a pulse did occur, was it truly as large as the models suggested? And should NOAA regulators have raised catch limits when its assessments also suggested that the abundance of harvest-sized males had dropped by half in the decade prior?

“This is a lesson which has been repeated but not learned,” Dew said. Mary Peltola, who directed the Kuskokwim River Inter-Tribal Fish Commission and now serves in U.S. Congress, tweeted, “One billion crabs didn’t simply ‘disappear.’” She cited “mismanagement and factory trawler operations” among likely causes. Erik Velsko, a former advisor to the North Pacific Fisheries Management Council, told Mongabay that NOAA models rely on “too many assumptions” and that the management of the fishery was “archaic.”

Fishermen excoriate conflicts of interest in the council, attributing its failures to limit bycatch14 or expand trawl exclusion zones to the fact that many of its private voting members declare financial interest in heavy industries like trawling and at-sea processing. Several of the council’s high-ranking government officials, including the director who oversaw the recent snow crab crash, have gone on to work for companies with large Bering Sea trawling operations.

Alaskan communities, despite the promising quotas of the final years, have little to show for it now. Crab fishermen and their families invested their lives into an industry as its future crumbled beneath them.

But we’ve lost so much more than that. The great gatherings of crabs across the continental shelf formed a central pillar of once-astonishing Arctic ecosystems, supporting food webs culminating in sharks and whales in multitudes inconceivable in modern times. Dew describes drifting over crab congregations spanning 90,000 acres, comparing them to the world’s most spectacular biological wonders. “Think of the great herds of the plains buffalo, or the almost indescribable abundance of the extinct passenger pigeon,” he said. The magnificent marches of Arctic crabs now take place alongside them, in memory.

Lead image: Kondratuk Aleksei / Shutterstock

References

1. Dew, C.B. Podding behavior of adult king crab and its effect on abundance-estimate precision. In Kruse, G.H., et al. (Eds) Biology and Management of Exploited Crab Populations under Climate Change. Alaska Sea Grant, University of Alaska Fairbanks (2010).

2. Dew, C.B. Historical perspective on habitat essential to Bristol Bay Red King Crab. In Kruse, G.H., et al. (Eds) Biology and Management of Exploited Crab Populations under Climate Change. Alaska Sea Grant, University of Alaska Fairbanks (2010).

3. Fedewa, E.J., Jackson, T.M., Richar, J.I., Gardner, J.L., & Litzow, M.A. Recent shifts in northern Bering Sea snow crab (Chionoecetes opilio) size structure and the potential role of climate-mediated range contraction. Deep Sea Research Part II: Topical Studies in Oceanography 181-182 (2020).

4. Shields, J.D., Taylor, D.M., O’Keefe, P.G., Colbourne, E., & Hynick, E. Epidemiological determinants in outbreaks of bitter crab disease (Hematodinium sp.) in snow crabs Chionoecetes opilio from Conception Bay, Newfoundland, Canada. Diseases of Aquatic Organisms 77, 61-72 (2007).

5. Mills, B.M. An exploration of the spatiotemporal distribution of snow crab (Chionoecetes opilio) in the eastern Bering Sea. Thesis presented to the University of Southern California Dornslife College of Letters, Arts and Sciences (2021).

6. Bernton, H. Into the ice: A crab boat’s quest for snow crab in a Bering Sea upended by climate change. The Seattle Times (2022).

7. Dew, C.B. & McConnaughey, R.A. Did trawling on the brood stock contribute to the collapse of Alaska’s king crab? Ecological Applications 15, 919-941 (2005).

8. Ruch, J. Alaska Red King Crab dethroned by scientific fraud. peer.org (2021).

9. Rose, C.S., Hammond, C.F., Stoner, A.W., Munk, J.E., & Gauvin, J.R. Quantification and reduction or unobserved mortality rates for snow, southern Tanner, and red king crabs (Chionoecetes opilio, C. bairdi, and Paralithodes camtschaticus) after encounters with trawls on the seafloor. Fishing Bulletin 111, 42-53 (2013).

10. Thomson, J. “You’re out there alone”: Whistleblowers say workplace abuse hides true impacts of B.C.’s trawl fishery. The Narwhal (2020).

11. McConnaughey, R.A., Mier, K.L., & Dew, C.B. An examination of chronic trawling effects on soft-bottom benthos of the eastern Bering Sea. ICES Journal of Marine Science 57, 1377-1388 (2000).

12. Dew, C.B. & Austring, R.G. Alaska red king crab: A relatively intractable target in a multispecies trawl survey of the eastern Bering Sea. Fisheries Research 85, 165-173 (2007).

13. Armstrong, J., Armstrong, D., & Hilborn, J. Crustacean resources are vulnerable to serial depletion—the multifaceted decline of crab and shrimp fisheries in the Greater Gulf of Alaska. Reviews in Fish Biology and Fisheries 8, 117-176 (1998).

14.  Social media post alleges orcas caught in Alaska trawler bycatch. thebluealaskan.com (2021).

  • Spencer Roberts

    Posted on November 23, 2022

    Spencer Roberts is a science writer, ecologist, engineer, and musician based in Colorado.

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