Bering Sea ecosystem

• Category: Marine and Oceanic Biomes
• Geographic Location: Northern Hemisphere
• Summary: A shallow, productive oceanic ecosystem in the sub-Arctic North Pacific, the Bering Sea is a very important fishing ground for finfish (such as cod, haddock, and pollock) and invertebrates (mostly crabs).

The Bering Sea is located in the northernmost part of the Pacific Ocean, joining the Pacific Ocean with the Arctic Ocean by way of the Bering Strait that spans the gap between easternmost Asia and westernmost North America. This Large Marine Ecosystem (LME), a designation made by the US National Oceanic and Atmospheric Administration (NOAA), encompasses in its western areas the deepwater Aleutian Basin, with depths well in excess of 10,000 feet (3,048 meters), as well as a large area of shallow, broad continental shelf in the east, where depths seldom exceed 200 feet (60 meters). The rapid change in bathymetry (depths) between these two regions brings cold, nutrient-rich bottom water onto the shallow shelf and supports a vast food web.

The Bering Sea is host to a rich and diverse assemblage of marine life, with a large variety of marine mammals, fish, invertebrates, and seabirds living within its bounds. The region also supports very large and productive fisheries for groundfish, salmon, and crabs. Many of these species were severely overfished with the onset of mechanized fishing in the second half of the twentieth century. However, improved international treaties and domestic management plans implemented in the 1980s and 1990s contributed to stabilization of these high-value fisheries into the twenty-first century. Plans such as the Fishery Management Plan (FMP) that governs groundfish fisheries of the Bering Sea and Aleutian Islands and the Magnuson-Stevens Fishery Conservation and Management Act set regulations and protect the integrity of the ecosystem and marine life in the Bering Sea and Aleutian Islands while still allowing commercial fishing practices to occur.

The borders of the Bering Sea are defined by mainland Alaska to the east, the Kamchatka Peninsula of Russia to the west, Alaska's Aleutian Island chain to the south, and the Bering Strait, which separates the Bering Sea from the Arctic Ocean, to the north. The sea's total area is roughly 849,425 square miles (2.2 million square kilometers). Its borders lie mostly within the 200-mile (322-kilometer) Exclusive Economic Zone (EEZ) of either the United States (in the eastern Bering Sea) or Russia (in the western Bering Sea), largely because of the large number of islands dotting the continental shelf and the Aleutian chain, each of which commands a 200-mile (322-kilometer) EEZ radius. A small area of international waters in the center is commonly referred to as the “doughnut hole.”

Oceanography and Marine Life

The physical oceanography of this region is particularly important. Sharp changes in depth from the Aleutian Basin to the North American continental shelf create localized upwelling events, which bring nutrient-rich bottom water to the surface and generate strong currents throughout the shelf portion of the system. Strong winds and frequent storms create hazardous conditions for seagoing vessels, with waves frequently exceeding 30 feet (10 meters) and winds often exceeding 50 miles per hour (80 kilometers per hour), but also create a great deal of mixing of deep ocean nutrients into the well-lit surface layer. These conditions are ideal for phytoplankton growth—the tiny marine plants that are the basis of the Bering Sea food web. Seawater stratification from freshwater formation along the edge of the ice front, which advances and retreats seasonally, also creates areas of high primary productivity.

This productivity supports a range of marine life from varied pelagic (surface-layer-dwelling) and demersal (near-bottom-dwelling) fish species, to large populations of benthic (bottom-dwelling) invertebrates such as crabs, which are scavengers that feed on the large flux of organic matter raining down from the richly productive waters above. The western Bering Sea has the largest population of gadoid (cod-like) fishes in the world; the eastern Bering Sea is home to an array of fish species from cod and haddock to flatfish (flounder, sole, and halibut), to pelagic species like salmon. The system also supports an abundance of marine-mammal species, ranging from seals, walruses, and toothed whales (which feed on the abundant fish stocks) to baleen whales (which feed on krill), as well as pelagic invertebrates.

Coastal regions of the Bering Sea also support large populations (up to 20 million individuals) of predatory fish-eating birds, such as puffins, albatross, kittiwakes, and eagles. Polar bears, too, prey along these shores. In all, more than fifteen mammal, thirty bird, and four hundred fish species call the Bering Sea home—almost as many fish species as can be found in the Caribbean Sea.

Fisheries and Challenges

With the onset of industrialized fishing in the post–World War II era, large mechanized fishing fleets from various nations (mainly from the United States, Russia, Canada, China, and Japan) rapidly increased fishing practices in the Bering Sea. A broad range of techniques and target species are employed in this fishery, although the principal fisheries are groundfish (cod, haddock, pollock, and halibut), salmon, and crabs (king, tanner, bairdi, and opilio). Of these species, the most valuable and most overexploited is the red king crab, the population of which was reduced to less than 10 percent of historical levels by the mid-1980s. By 2024, the red crab population was still far below levels from the late 1970s, and recovery to those levels is unlikely in the twenty-first century without favorable environmental conditions. Scientists believe that the population decline was caused by two years of low sea ice cover and warmer ocean temperatures due to climate change from 2020-2022.

Early management efforts by the National Marine Fisheries Service were predominantly based on single-species catches, setting size limits and total allowable catches. In large part, these measures created a derby-type fishery, in which large numbers of entrants fished target species extremely heavily for a very short time. In some cases, the season for red king crab was as short as four days. This situation created additional unnecessary environmental pressure. It also endangered fishing crews, put excessive pressure on the canning industry, and reduced the total value of the catch by flooding the market.

In the twenty-first century, management efforts shifted to a system dominated by individual transferable quotas (ITQs), in which each entrant to the fishery is assigned a specific percentage of the total quota and can fish that quota over a longer period. This management strategy worked very well in this system, improving the biomass of fisheries species and the total value of the catch while dramatically reducing the fatality rate among fishermen. The system also dramatically reduced the number of entrants into the fishery, however, creating some contention due to the high unemployment rates among local fishers.

Although the Bering Sea is in many respects a “poster child” example of the effectiveness of ITQ fisheries, it is not without major environmental concerns. Availability of food in this system is highly correlated to temperature, with cold years being more favorable for high production than warm ones. Climate change presents a particular concern to the Bering Sea system for this reason, and also because the specialized physical oceanographic features of the system prevent species from simply moving north to remain in their preferred temperature range.

Some scientists estimate that primary productivity in this system dropped by 30 to 40 percent by 2017. Scientisits have shown that high-energy phytoplankton species (diatoms) are being outcompeted by lower-energy species (coccolithophores) during warm years, which results in less energy moving up the food chain. Loss of sea ice is also problematic to species such as polar bears, which hunt along the ice edge. Scientists note that the warmest winters on record occurred in 2018 and 2019, while 2020 was not as warm. The rise in temperature and melting sea ice has hurt commercial fishing in the area. Since the ecosystem's food webs are negatively affected by the temperature changes, the fishing industry is also impacted. For example, warming waters affect the timing of spring phytoplankton blooms, which feed zooplankton and other small creatures that are important for young fish, birds, and marine mammals to feed on. Additionally, warming and loss of sea ice changed fish distributions, with fish migrating further northward and adjusting their migration patterns due to new climate patterns. The water temperature greatly affects crabs and salmon, who rely on the cold water to thrive. For salmon specifically, warming waters decrease areas that provide salmon with their ideal temperature ranges, which could reduce salmon survival rates.

Another concern of note is the disappearance of the "cold pool," an area in the Bering Sea that has served as a barrier that protects cold-water species, such as the snow crab and Arctic cod, from species that can live in warmer waters, such as the walleye pollock. While the warmer-water fish are thriving in the area, some cold-water species have begun to disappear. For example, in 2019 there was a recorded mass die-off of the seabird species called the short-tailed shearwater. While scientists think the species likely died from conditions related to warmer temperatures, other possibilities include the northward migration of warm-water fish competing with shearwaters for food in the northern Bering Sea or increased toxins from harmful algal blooms associated with elevated water temperatures. Scientists continue to study the ecological effects of global warming in the Bering Sea area. Each year, the National Oceanic and Atmospheric Administration (NOAA) collects a Bottom Trawl Survey to collect data on " the distribution and abundance of crab, groundfish, and other bottom-dwelling species in the Aleutian Islands, Bering Sea, and Gulf of Alaska. These data are used for ecosystem monitoring and to aid in the management of commercially important species in Alaska." NOAA has been collecting data annually since 1982, excluding 2020.

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