Bering Sea, Aleutian Islands - Key Species
Walleye pollock (Theragra chalcogramma)
Walleye pollock are broadly distributed throughout the North Pacific with the largest concentrations found in the Eastern Bering Sea. They feed mostly on zooplankton such as euphausiids and copepods, but also on fish and other crustaceans and are therefore one of the most important prey species in the system . They represent over 40% of the global whitefish production and they are considered to be a relatively fast growing and short-lived species that currently represents a major biological component of the Bering Sea ecosystem. Since the advent of the U.S. EEZ in 1977 the annual average Eastern Bering Sea pollock catch has been 1.2 million tonnes and has ranged from 0.9 million tonnes in 1987 to nearly 1.5 million tonnes in recent years. Stock biomass has ranged from a low of 4-5 million tonnes to highs of 10-12 million tonnes. Since 1988, only U.S. vessels have been operating in this fishery. By 1991, the current National Marine Fisheries Service observer program for north Pacific groundfish-fisheries was in place. Significant quantities of pollock are discarded and observed length frequency observations indicated that discards include both large and small pollock. Since then the BSAI pollock fishery has been restricted to protect Steller sea lions and to reduce the bycatch of salmon . BSAI pollock is certified as sustainable by the Marine Stewardship Council.
Pacific ocean perch (Sebastes alutus)
Pacific ocean perch (POP) inhabit the outer continental shelf and upper slope regions of the North Pacific Ocean and Bering Sea and feed mainly on euphausiids and calanoid copepods . POP, and four other associated species of rockfish (northern rockfish, S. polyspinis; rougheye rockfish, S. aleutianus; shortraker rockfish, S. borealis; and sharpchin rockfish, S. zacentrus) were managed as a complex in the two distinct areas from 1979 to 1990. Known as the POP complex, these five species were managed as a single entity with a single TAC (total allowable catch). In 1991, the North Pacific Fishery Management Council separated POP from the other red rockfish in order to provide protection from possible overfishing. Of the five species in the former POP complex, POP has historically been the most abundant rockfish in this region and has contributed most to the commercial rockfish catch. Since 2001, POP in the Bering Sea-Aleutian Islands area have been assessed and managed as a single stock because of the uncertainty that the EBS POP represent a discrete stock . During the 1960s the Japanese and Soviet fisheries supported a major trawl fishery for POP, with peak catches of 47,000 tonnes in EBS in 1961 and 109,100 tonnes in the Aleutians in 1965, after which the catches declined dramatically to the lowest levels in the mid 1980s. In 1990 the domestic fishery recorded the highest POP catch since 1977.
Atka mackerel (Pleurogrammus monopterygius)
Atka mackerel are distributed throughout the Aleutian Islands, north to the Pribilof Islands in the eastern Bering Sea with their centre of abundance being in the Aleutian Islands . They are a schooling species with a patchy distribution . Males aggregate around the nests they build in rock crevices and among stones of the Sequam Pass and among the island passes from Attu Island to Umnak Pass, at depths ranging from 15-32 meters . They are also a key forage species in the system feeding mostly on calanoid copepods and jellyfish . Annual catches of Atka mackerel increased during the 1970s and from 1970-1979 and were landed exclusively by the distant water fleets of the U.S.S.R., Japan and the Republic of Korea. U.S. joint venture fisheries began in 1980 and dominated the landings from 1982 through 1988. Since 1990, all landings have been made by U.S. fishermen. Total landings declined from 1980-1983 due to changes in target species and allocations to various nations rather than changes in stock abundance. From 1985-1987, Atka mackerel catches were some of the highest on record, averaging 34,000 metric tonnes annually. Beginning in 1992, TACs increased steadily in response to evidence of a large exploitable biomass, particularly in the central and western Aleutian Islands.
Arrowtooth Flounder (Atheresthes stomias)
Arrowtooth flounder and Kamchatka flounder (A. evermanni) are very similar in appearance and are not usually distinguished in the commercial catches. They are also not consistently separated in trawl survey catches and are combined in the stock assessments. Arrowtooth flounder ranges into the Aleutian Islands where their abundance is lower than in the eastern Bering Sea. The resource in the EBS and the Aleutians are managed as a single stock. Arrowtooth flounder was also managed with Greenland turbot as a species complex until 1985 because of similarities in their life history characteristics, distribution and exploitation but management diverged in 1986. Greenland turbot were the target species of the fisheries whereas arrowtooth flounder were caught as bycatch and are still mostly discarded as they do not have a perceived commercial value . Substantial amounts of arrowtooth flounder are discarded by the trawl and longline target fisheries with the largest discards occurring in the Pacific cod fishery and the various flatfish fisheries . Arrowtooth flounder begin to recruit to the continental slope at about age 4 and they occur from central California to the Bering Sea, in waters from about 20m to 800m, with the highest abundances between 100m to 300m . Arrowtooth flounder are a main predator of pollock, herring and capelin.
Greenland halibut (Turbot) (Reinhardtuis hippoglossoides)
Greenland turbot juveniles spend the first 3 or 4 years of their lives on the continental shelf and then move to the continental slope and are absent in the Aleutian Islands regions. Prior to 1985, Greenland turbot and arrowtooth flounder were managed together. Since then, the Council has recognized the need for separate management quotas given large differences in the market value between these species and the distinct abundance trends for these two species. Discard levels of Greenland turbot have typically been highest in the sablefish fisheries while Pacific cod fisheries and the Greenland turbot directed fishery also have contributed substantially to the discard levels . Greenland halibut feed on finfish and squid although benthic crustaceans and molluscs are also found in their diets (Fishbase).
Pacific halibut (Hippoglossus stenolepis)
Pacific halibut is one of the largest teleost species. It is managed by the International Pacific Halibut Commission, IPHC, which has collected detailed fishing records of the halibut fishery since the early days of the fishery in 1931, with the Bering Sea fishery being reported on since 1964 . Pacific halibut feed largely on fish, with walleye Pollock being the most important species and 20% of the diet also consisting of invertebrates such as Tanner crabs .
Yellowfin sole (Limanda aspera)
The yellowfin sole is one of the most abundant flatfish species in the eastern Bering Sea (EBS) and is the target of the largest flatfish fishery in the United States. They inhabit the EBS shelf and abundance in the Aleutian Islands region is negligible. Adults exhibit a benthic lifestyle and occupy separate winter, spawning and summertime feeding distributions on the eastern Bering Sea shelf. A directed fishery typically occurs from spring through December with bottom trawls. The fishery started in 1954 and the stock was overexploited by foreign fisheries in 1959-62 when catches averaged 404,000 tonnes annually. By 1972-77 the yield had declined to 50,700 tonnes and led to the discontinuation of the U.S.S.R. fishery. During the 1980s, there was also a major transition in the characteristics of the fishery from a foreign fishery to one dominated by U.S. boats and joint ventures.
Pacific cod (Gadus macrocephalus)
Pacific cod is a transoceanic species, occurring at depths from shoreline to 500 m. It is distributed widely over the eastern Bering Sea and the Aleutian Islands area and the resource in these two areas (BSAI) is managed as a single unit. During the early 1960s, a Japanese longline fishery harvested BSAI Pacific cod for the frozen fish market. Beginning in 1964, the Japanese trawl fishery for walleye pollock expanded and cod became an important bycatch species and an occasional target species when high concentrations were detected during pollock operations. By 1977 foreign catches of Pacific cod had consistently been in the 30,000-70,000 t range for a full decade. In 1981, a U.S. domestic trawl fishery and several joint venture fisheries began operations in the BSAI. The foreign and joint venture sectors dominated catches through 1988, but by 1989 the domestic sector was dominant and by 1991 the foreign and joint venture sectors had been displaced entirely. Presently, the Pacific cod stock is exploited by a multiple-gear fishery, including trawl, longline, pot, and jig components . Pacific cod feed both in the water column and in benthic areas, and therefore have a varied diet including commercially important fish such as walleye pollock and crustaceans such as tanner crabs and shrimps . BSAI cod caught by freezer longline fisheries are under assessment by the Marine Stewardship Council (MCS).
Pacific herring (Clupea pallasii pallasii)
Herring have been reported since 1929 throughout the North and South Alaskan Peninsula and in Akutan, Unalaska, and Adak Islands of the Aleutian Islands. A herring food and bait fishery occurred in the vicinity of Unalaska from 1929 to 1938 and in 1945. The early fishery consisted of gillnet and purse seine harvests. From 1946 to 1980 there was no commercial harvest of herring. However, the food and bait fishery were given permits from the 1980s for both purse seine and gill nets at various times . The main area of herring concentrations in the Bering Sea and Aleutian Islands is in the Togiak District of Bristol Bay where abundance peaked in the early 1980s with approximately 2.5 billion fish when herring from the 1977 and 1978 year classes recruited into the fishery as age-4 fish in 1981 and 1982. Temporal trends in Togiak herring abundance show that total abundance in much of the 1980s was above the 1978 - 2003 average . Pacific herring recruitment trends are highly variable, with large year classes occurring occasionally at regular intervals of approximately every 9-10 years and these events drive the population. Environmental conditions may be the critical factor that influences strength of herring recruitment and closer examination of trends in sea surface temperature, air temperature, and Bering Sea ice cover specific to the Bristol Bay area may find a specific correlate for Togiak herring recruitment.
Eulachon (Thaleichthys pacificus)
Eulachon is an energy rich non-commercial forage species that concentrates in shallow waters along river margins during spawning. The spawning aggregations of eulachon provide important seasonal food resources for mammalian and avian predators . They are anadromous smelts (Osmeridae) that spawn in mainland glacial rivers from California to Alaska . Fritz et al. showed that the biomass of eulachon in the eastern Bering Sea decreased by an order or magnitude from 1980-81 to 1985 although the Bering Sea Interagency Working Group suggested that eulachon has been common all years.
Crabs
There are various crab stocks in the BSAI area including the Bristol Bay red king crab (Paralithodes camtschaticus), St. Matthew Island blue king crab (P. platypus), Eastern Aleutian Island golden king crab (Lithodes aequisipinus), Bering Sea Tanner crabs (Chionoecetes bairdi), deepwater grooved Tanner crabs (C. tanneri), triangular Tanner crabs (C. angulatus) and snow crabs (C. opilio). Currently, all BSAI king, Tanner and snow crabs are managed by the Federal government along with the State harvest strategy . Annual trawl surveys are conducted to determine the abundance, sex, size and maturity of the crab stocks. Only males of at or above minimum legal size are harvested and recruitment is largely driven by environmental factors and not by density-dependent responses . Single sex harvest has been in effect since the late 1940s to protect mature females for sufficient recruit production and specific fishing seasons are set to avoid harvesting crab during mating and molting periods . Crabs are currently at low levels, and all Bering Sea stocks are considered overfished.
Steller sea lion (Eumetopias jubatus)
Steller sea lions range from the Channel Islands off southern California around the Pacific Rim to northern Japan, but most of the world population breeds between the central Gulf of Alaska and the western Aleutians . Sea lions mate, give birth and care for their pups at rookery sites, and rest and moult at haulout sites. Most of the haulout and rookery sites are on remote and exposed rocks and islands, and are generally believed to be in close proximity to food resources . Sea lions may feed close to shore or travel more than 150 km out to sea to feed. They prey on capelin, sand lance, pollock, herring, cod, salmon, flatfishes, sculpins, squid and octopus . Stellers in the BSAI region have declined from around 80,000 individuals in the mid 1970s to lows of approximately 20,000 by 2000. Reasons for the decline include predation by killer whales, competition with flatfish, fishing and changes in ocean productivity.
Northern fur seal (Callorhinus ursinus)
The northern fur seal is found throughout the North Pacific Ocean and migrates to the Bering Sea to feed . The Pribilof population of northern fur seals is believed to have numbered 3 million animals in 1867, but due to excessive harvesting the population was down to between 200,000 and 300,000 seals by 1910 . A moratorium on seal harvest increased the population to around 1.5 million animals during the 1940s, but there has been a long-term downward trend in the size of the population since the mid 1950s . The population has failed to recover since the mid 1980s, possibly due to high juvenile mortality, one of the reasons possibly being the large fisheries for their prey species . In the Eastern Bering Sea they feed on walleye pollock, capelin, herring and squid, and throughout their range fish was the main food source, with squid being important in oceanic areas.