The Bering Sea, a vast and productive marine ecosystem, has long been known for its valuable crab populations. In recent years, this environment has faced an unprecedented challenge: a dramatic decline in crab numbers. This sudden disappearance has raised significant concerns among scientists, fishing communities, and those who rely on the health of this crucial northern sea.
The Disappearance of Bering Sea Crabs
The decline primarily impacted snow crab and Bristol Bay red king crab populations. Snow crab (Chionoecetes opilio) experienced a catastrophic reduction, with an estimated 11.7 to 12.2 billion crabs disappearing from the eastern Bering Sea between 2018 and 2021. This represented a decline of over 90% in their population.
This led to the unprecedented closure of the snow crab fishery for the 2022-2023 season, marking the first time this lucrative fishery was shut down. The Bristol Bay red king crab fishery also faced closures due to dwindling numbers. These closures highlighted the severity of the population crash, apparent from 2018 onwards during annual surveys.
Investigating the Causes
Scientists identify marine heatwaves as a primary driver behind the crab collapse. The Bering Sea experienced significant warming events in 2018 and 2019, which altered the environment. These warmer waters increased snow crabs’ metabolic rates, requiring more food.
Warmer conditions also reduced their suitable cold-water habitat, concentrating crabs into smaller, denser areas. This combination of increased caloric demand and decreased food availability led to widespread starvation, identified as the immediate cause of mass mortality. This is part of “borealization,” an ecological shift where the Bering Sea transitions to sub-Arctic conditions, less favorable for cold-adapted species.
This ecological shift also brought other environmental changes. The vanishing “cold pool” – a layer of very cold bottom water that acts as a refuge for juvenile crabs – potentially exposed them to more predators. Research also explores the role of diseases like bitter crab disease, which showed increased prevalence in snow crab samples. While overfishing or bycatch were considered, studies largely ruled these out as primary causes, as their estimated mortality was too small to explain the crash.
Consequences of the Collapse
The dramatic decline in Bering Sea crab populations has triggered widespread consequences, impacting both the marine ecosystem and human communities. Ecologically, the disappearance of billions of crabs disrupts the delicate balance of the marine food web. Their loss affects predators and alters the ecosystem’s structure.
The economic repercussions have been substantial for the Alaskan fishing industry. The snow crab fishery alone historically generated an average of $227 million annually. Closures of both snow crab and red king crab fisheries resulted in an estimated $1 billion economic hit, considering ripple effects throughout the seafood supply chain.
This financial devastation deeply affected fishing communities, particularly those in Alaska reliant on crab fisheries. Indigenous communities, such as St. Paul, declared cultural, economic, and social emergencies due to lost income and livelihoods. Fishermen faced job losses and delayed vessel repairs, highlighting the profound social impact of the collapse.
Looking Ahead: Recovery and Management
In response to the severe declines, management measures include continued fishery closures for some crab stocks, though certain fisheries show signs of reopening. Extensive scientific research and monitoring efforts are underway. NOAA Fisheries, in collaboration with other organizations, conducts annual surveys to assess crab abundance, distribution, and health.
Scientists utilize advanced techniques like crab tagging to understand movements and develop ecosystem indicators for early warnings. Despite these efforts, significant challenges and uncertainties remain regarding long-term recovery. While positive signs, such as cooler water temperatures and increased juvenile snow crabs, were observed in 2022, the overall outlook is complex.
The continued trend of borealization and warming ocean temperatures suggests Arctic conditions conducive to snow crab may become increasingly scarce in their traditional grounds. This necessitates adaptive management strategies that respond to a changing climate and include diversification of fishing opportunities to build industry resilience.