Merit Johnson, '25
In the year under scrutiny, the snow crab fishery in Alaska faced an unprecedented closure – an event of historical significance. The prevailing belief among catchers was that overfishing had been the main driver of the snow crab population's decline. However, experts cautioned that the term "overfished" is a technical designation triggering conservation measures, and it fails to comprehensively elucidate the underlying causes of the collapse.
The revelations from the study were profound, pointing to an unexpected shift in the challenges faced by fishery scientists. Historically, the primary concern had been overfishing, and extensive management efforts had been directed towards mitigating this issue. However, the study brought into focus a new, formidable adversary: climate change. It had disrupted existing plans, models, and management systems.
To unravel the mystery behind the vanishing snow crabs starting in 2020, scientists conducted a thorough analysis. They categorized the potential causes into two main groups: the snow crabs either relocated or perished.
Exhaustive investigations stretched from the Bering Sea's northern reaches to the waters bordering Russia and even to deeper ocean levels. Ultimately, the researchers deduced that it was unlikely the crabs had migrated, thus emphasizing the significance of the mortality event.
The focal point of this crisis, they determined, was rooted in warmer temperatures and population density, which were closely linked to higher mortality rates among mature crabs.
The mortality event, upon closer scrutiny, revealed a grim explanation: the crabs had gone hungry. Snow crabs are a cold-water species, predominantly inhabiting regions with water temperatures below 2 degrees Celsius, although they can tolerate temperatures up to 12 degrees Celsius. The intrusion of warmer ocean water wreaked havoc on the crabs' metabolism and escalated their caloric requirements.
In the initial year of a two-year marine heatwave in the region, the crabs' energy requirements from food could have surged up to fourfold when compared to the previous year. However, the heatwave had disrupted much of the Bering Sea's food web, making it increasingly challenging for snow crabs to forage for sustenance and meet their escalating caloric demands. Starvation was the likely cause of their demise, with predatory fish like Pacific cod seizing the opportunity to feed in the warmer waters.
A key factor that allowed other species, notably Pacific cod, to exploit this dire situation was the absence of the typical temperature barrier in the ocean. This barrier usually prevented Pacific cod from venturing into the extremely cold habitat of the snow crabs. Yet, during the heatwave, Pacific cod accessed these unusually warm waters, further depleting the crab population.
The heatwave's impact was substantial. It induced a significant period of starvation among the snow crabs, and other species took advantage of this ecological upheaval. Once the heatwave abated, some semblance of normalcy returned, though the snow crabs faced a formidable recovery journey, even in more conventional conditions.
Temperatures in the Arctic have been rising four times faster than the global average, with climate change driving the rapid loss of sea ice in the Arctic, particularly in Alaska's Bering Sea. The years 2018 and 2019 witnessed an extraordinary anomaly in sea ice coverage, plummeting to a mere 4% of the historical levels. The long-term prognosis for ice coverage remains uncertain.
The crisis befalling Alaska's snow crabs underscores the accelerating impact of the climate crisis on livelihoods. While this event was anticipated to some extent, the swiftness of its occurrence caught scientists by surprise. Snow crab populations are expected to migrate northward as the ice recedes, and in the eastern Bering Sea, their presence is anticipated to diminish significantly. This transformation serves as a stark reminder of the urgency to address the mounting challenges of climate change.