Unless you harvest it yourself, crab meat is a pricey delicacy. With a single king crab leg fetching nearly $80 and limbs of other crustacean species not far behind, they’ve always been a treat few can afford. But recently, prices have hiked up another notch due to concurrent population crashes of multiple species in the Bering Sea. The collapses have left entire crab-fishing fleets moored to shore and processors scrambling to find new seafood sources.
One collapse is the widely-reported disappearance of 11 billion snow crabs in the Bering Sea in 2021. At the time, the crash was initially thought to be due to overfishing. New research, however, reveals that scientists may have misinterpreted the initial data. To understand why, it’s necessary to look back at the years leading up to the crash.
Based on annual surveys conducted by the National Oceanic and Atmospheric Administration (NOAA), which manages crab harvest in conjunction with the state of Alaska, total snow crab abundance was at an all-time high in 2018. Then, in 2019, the overall population decreased by 60%. The total number of males (the primary target of the fishery) actually increased, however, leading to a harvest quota increase in 2020.
NOAA didn’t conduct a survey that year due to COVID, but when they resumed in 2021, they found a near-total population collapse–almost 11 billion crabs shy of 2018 numbers. Naturally, overfishing was the primary suspect. But now, after several years without a population rebound, researchers are pointing fingers at another culprit: warming oceans.
The Bering Sea experienced thermal heatwaves in 2016, 2018, and 2019, similar to the “Blob” in the Gulf of Alaska, but a little further north. Marine heatwaves are caused by a combination of unusually warm weather patterns in conjunction with water currents and wind. Their dynamics are similar to atmospheric heatwaves (a week of 100-degree weather in Colorado, for example), with one key difference: water holds heat much longer than air, meaning once the hot weather dissipates, the water stays warm for weeks or months afterward.
It often takes several years to see population and ecosystem shifts after significant environmental events, and in the Bering Sea, we are just now seeing the compounding effects of the heatwaves. Those shifts start with a change in phytoplankton production (small, photosynthetic organisms on the bottom of the food chain), then trickle up to crustaceans, fish, and larger fauna like whales and seabirds. Warmer water also increases the metabolic demands (hunger) of organisms, meaning more competition for a limited amount of food.
In addition to the impacts of warm water on the food chain, it also has a physically detrimental effect on juvenile crab development. In the Bering Sea, immature snow crabs concentrate in colder, shallow waters, and research suggests that 2°C is the critical water-temperature threshold for the development of immature snow crabs. Warmer conditions between 2017 and 2020 kept temperatures hovering around that threshold, leading to low juvenile snow crab survival. In conjunction with heavy fishing pressure in 2020, it was a perfect storm for a population collapse.
In terms of the bigger picture, it’s possible that snow crabs may never reach their former abundance in the Bering Sea. “As you warm Arctic ecosystems, those systems become prone to a state change, where Arctic taxa such as snow crab become replaced by subarctic taxa that are better able to tolerate ice-free and warm conditions,” Mike Litzow, director of the NOAA Fisheries Kodiak Laboratory told the Alaska Beacon. It’s a phenomenon known as “borealization,” which describes the northern creep of boreal, or subarctic, ecosystems–both aquatic and terrestrial.
What we’re seeing in crab populations is just a microcosm of a much larger shift in ecosystems at northern latitudes. And while the impact to most people is limited to higher prices at the grocery store, it’s important to look at the issue holistically. Being connected to your food and where it comes from means learning about the biology of whatever it is you’re eating and being inquisitive when things go awry. Follow food chains back to their bases, and the paths lead to a bigger-picture understanding of what’s happening. In this case, deep on the ocean floor in the North Pacific.