Deadliest Catch is an award winning documentary series following Alaskan crab boats and their crews as they fish for king crab and Opilio crab. Theirs is a dangerous profession, made so by the waters they fish: a tempest-ridden marginal sea in the very throes of climate change.
Welcome to the Bering Sea.
The Bering Sea
The Bering Sea is a northern extension of the North Pacific Ocean. North of the Aleutian Islands, sandwiched between western Alaska and eastern Russia, it is the world's third-largest semi-enclosed sea. Like other high-latitude marginal seas, much of the Bering Sea freezes during the Arctic winter.
Basic Oceanography
Sea level in the Bering Sea is approximately 0.5 meters higher than the Arctic Ocean, causing a mean northward transport through the Bering Strait up into the Arctic. This northward flow is fed by nutrient rich slope waters of the Bering Slope Current, itself the eastern boundary current of the Bering Sea Gyre. (The Bering Sea Gyre is a large cyclonic current system in the Aleutian Basin). These nutrient rich waters well upwards from depth, shoal over the Bering’s large, shallow, northern shelf, and fuel the region’s seasonal phytoplankton blooms – the foundation of the region’s food web.
Bering Sea Productivity
The Bering Sea’s broad, shallow continental shelf is home to a rich variety of plants and animals. They include:
- The world's most extensive eelgrass beds
- At least 450 species of fish, crustaceans, and mollusks
- 50 species of seabirds
- 25 species of marine mammals
At present, the U.S. Bering Sea fishery constitutes approximately 40% of the U.S. and about 5% of the world harvest of fish and shellfish.
This diversity is not strictly a function of upwelling and summer sunlight, however; the region’s winter ice also plays a role. Within the Bering itself, each winter’s ice cover creates a pool of cold bottom water on the continental shelf. This “cold pool” lingers throughout the summer and supports a specialized seafloor ecosystem, including much of Alaska’s highly profitable crab fisheries.
Bering Sea Fisheries and Climate Change
Fish and shellfish distribution is largely controlled by temperature. Each species prefers a specific temperature range, shunning (if possible) deviation from that range.
Of course, marine ecosystems are very dynamic, with natural warm and cold cycles periodically flip-flopping a region’s dominant species. There are signs, however, that the overall warming underway in the Bering Sea may swamp these natural pendulums.
Warming is happening at such a rapid rate – particularly in the Arctic – that species adapted to ice and Arctic conditions have no recourse but retreat. Bering Sea ice melt is averaging three weeks early, and the cold pool is contracting. Since early 1980’s, the southern edge of the cold pool – which both defines the transition zone between arctic and subarctic communities, and supports the specialized bottom-dwelling ecosystem – has retreated 230 km (143 miles) northward.
The sub-arctic species are following suit. Two decades of data show at least 45 fish species have shifted their centers of distribution north since the early 1980’s.
What Does Climate Change in the Bering Sea Mean?
The challenge with climate change impacting Bering Sea ecosystems is that even as researchers tease out individual effects of the change, they cannot predict the cumulative or synergistic effects on the ecosystems themselves. It is not simply a matter of a northward geographical shift of species, because each species within the ecosystem responds differently, both to the change and to each other.
Predicting – accurately! – the result of these interactions and mutual effects is nothing short of a snarl, and the effort keeps scientists, fishery managers, fishermen, and coastal Alaskans up at night. Recurring cooling periods are possible, of course; but overall, arctic warming is expected to intensify. And environmental disruptions aside, this dramatic a transition may lead to economic and societal upheaval.
Alaskan crab fisheries are especially at risk. The northward retreat of benthic (bottom dwelling) animals, and the apparent sensitivity of some king crab species to sea ice cover suggest that continued warming may disrupt those fisheries even further. The North Pacific Fishery Management Council is working to develop precautionary plans to preserve species and maintain sustainable fishing, but their efforts are slowed by lack of baseline data in northerly waters and the problem's sheer complexity.
Reinvention
Clearly, it is a time of “reinvention” in the Bering Sea: for ecosystems, scientists, managers, coastal communities, and fishermen. Discovery Channel’s programming may need to reinvent as well, with Deadliest Catch morphing into something akin to a high seas version of Survivor.
When Nature bats last, you work with what you are given.
Sources
Alaska Marine Conservation Council. 2009. Impacts of Warming on Fisheries and Marine Life in the Bering Sea May 12, 2009.
Pacific Marine Environmental Labs. 2009. Physical Forcing of Ecosystem Dynamics on the Bering Sea ShelfMay 13, 2009.
Mueter, Franz and Michael Litzow. 2008. Sea Ice Retreat Alters the Biogeography of the Bering Sea Continental Shelf. Ecological Applications, 18(2) pp. 309-320.
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