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OCR for page 7
1
Introduction
The Bering Sea, a semi-enclosed northern extension of the North Pacific Ocean (Figure
2.2), contains a tremendous variety of biological resources, including many species of marine
mammals, seabirds, fish, and shellfish. The Bering Sea ecosystem includes more than 450
species of fish, crustaceans, and mollusks (about 25 of which are commercially important), more
than 50 species of seabirds, and at least 25 species of marine mammals. The magnitude and
nature of biological productivity in the Bering Sea ecosystem have led to ~,rt~n.~iv~ ll£P of tip
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annals by human sockeyes. indigenous peoples of the region have long used animals from the
Bering Sea as sources of food, clothing, and energy, as well as for a variety of cultural
purposes. In addition, a number of fish, shellfish, and marine mammal species have been used
extensively by the United States and other nations for commercial purposes. Over the past
O~V~1~; LL~a"Ga, ;3Ul11~ i3`UC~l~ Ul 11bll, bllC;llllbil, I~larme mammals, and seabirds in the Bering
Sea and adjacent regions have undergone large and sometimes sudden population fluctuations.
These changes have raised concern about how living resources in the area have been and should
be managed.
Animals from the Bering Sea have been used by the indigenous peoples on both sides of
the Bering Sea as a subsistence resource for thousands of years. Fish, shellfish, marine
mammals, and seabirds from the Bering Sea have been used as a source of food by local
residents along the extensive U.S. and Russian coasts. Marine mammals and seabirds have also
been used for fuel (blubber) and as raw materials for clothing, tools, and other objects (skins,
bones, ivory, feathers). The animals of the Bering Sea ecosystem also play an important role
in the cultural and religious traditions of many indigenous peoples.
Over the last 200 years, the United States, Russia, Canada, and Japan, and in recent
decades Poland, Korea, Taiwan, and China, have also exploited these biological resources
through commercial whaling, sealing, and fishing. Most prominently exploited have been fur
seals, whales, sea otters, salmon, crab, and groundfishes (flatfish, rockf~sh, Pacific cod, walleye
pollock, and Atka mackerel). Although marine mammals are no longer exploited commercially
in the Bering Sea, the fish and shellfish taken amount to between 2 and 5 percent of the world's
fishery production, and 56 percent of U.S. fishery production (U.S. Department of Commerce,
1994).
ret A ~_ ~1_ _11~- ~
7
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8
The Bering Sea Ecosystem
Except for salmon, which have supported a commercial fishery since the turn of the
century, large-scale commercial exploitation of the fish and shellfish of the Bering Sea began
about 1950. In the early years of fishery development, stocks were aggressively fished. By the
late 1960s, a number of rockfish, flatfish, and crab stocks had been significantly reduced by
fishing (Fritz et al., in press; NPFMC, 1993; Wooster, 19921. Over the same period from the
1950s through the early 1970s the substantial populations of large baleen whales and toothed
whales of the Bering Sea, Aleutian Islands, and Gulf of Alaska were nearly eliminated (NMFS,
l991b).
Partly in response to Me threat of overfishing, in 1976 the U.S. Congress passed the
Fisheries Conservation and Management Act, which extended U. S. jurisdiction in coastal waters
out to 200 miles (approximately 320 km) from the U.S. coast. The intent of the act was to
regulate the intensity of fishing, to ensure long-term sustainability of the fish stocks, and within
the constraints imposed by that goal, to maximize fishery yields. This act does not provide for
protection of species that range beyond the 200-mile [unit, the most noteworthy of which are
salmon and walleye pollock. Salmon fisheries in international waters are regulated by
international agreements, whereas pollock fisheries have not been until recently.
TO PROBLEM
Recent declines in populations of some piscivorous (fish-eating) marine mammals and
seabirds in the Bering Sea and adjacent areas have raised concerns and triggered actions
mandated by the United States Endangered Species Act (ESA) and the Marine Mammal
Protection Act. Steller sea lions have declined by 50 to 80 percent and have been listed as
threatened in the area under the Endangered Species Act over the past 15 to 20 years (NMFS,
19921. The production of northern fur seal pups on the Pribilof Islands (the location of the
major Bering Sea rookeries) declined by 50 percent between the 1950s and the 1980s, and the
stock was listed as depleted under the Marine Mammal Protection Act (NMFS, 1993a). In some
areas along the north-central Gulf of Alaska, harbor seal numbers have dropped by as much as
90 percent since the 1970s (Pitcher, 1990~. Bering Sea populations of common murres, thick-
billed murres, and red- and black-legged kittiwakes have also declined significantly in the
Pribilof Islands (Byrd, 1989a).
There are disagreements about the causes and the significance of the declines. The
declines might be due to overfishing of the species on which these marine mammals and seabirds
depend (principally walleye pollock) or to food-web relationships mediated by pollock (Springer,
1992~. Others believe that the declines are due to other factors, including clunate-induced
changes in the physical and biological environment of the North Pacific and Bering Sea,
entanglement of the declining species in marine debris (including abandoned and discarded
fishing nets), shooting by fishermen, pollution, and disease (Alverson, 19921.
,
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Introduction
9
THIS STUI)Y
Because of the questions raised about a number of recent changes in biological
components of the Bering Sea ecosystem, the U.S. Department of State requested that the
National Research Council form a committee to study the available scientific and technical
information on the Bering Sea ecosystem, focusing in particular on factors that influence
variability in populations of marine mammals, seabirds, and fish. The U.S. Coast Guard joined
in financial support because of its role in research, rescue, and law enforcement in polar waters,
particularly the Bering Sea. This report was prepared to assess (1) current scientific
understanding of the Bering Sea ecosystem; (2) gaps in knowledge and the research needs to fill
the gaps, including opportunities for interagency and international cooperation; and, as
appropriate, (3) possible management alternatives or institutional arrangements. The committee
was asked to consider the following topics:
· Environmental factors and ecological relationships that control the Bering Sea
ecosystem, including atmospheric and ocean circulation patterns, biological production pathways,
and energy transfer within the food webs of the region.
~ The life history, distribution, and population dynamics of commercially important
species, with special emphasis on species that migrate through international waters or into the
United States or Russian exclusive economic zones; and the probable causes and effects of their
population fluctuations.
· Estimates of historical population dynamics of marine mammals, seabirds, and
commercially important species of the Bering Sea; and their interrelationships, their current
status, and the factors contributing to their population fluctuations.
The historical records of the commercial fisheries of the Bering Sea.
· The relationship between the biological resources of the Bering Sea and (a)
subsistence cultures and economies of indigenous peoples, (b) commercial fisheries and other
users, and (c) the assemblage of organisms that constitute the biological component of the Bering
Sea ecosystem.
To set the stage for addressing these issues, Chapter 2 presents a general conceptual
framework for understanding marine ecosystems. Chapter 3 then describes the geological,
physical, chemical, and lower trophic level biological attributes of the Bering Sea ecosystem,
and it addresses both the current state of the system and how it has changed over time. Chapter
4 summarizes available data on the invertebrate, fish, bird, and marine mammal species of the
Bering Sea region, including their life cycles, species distribution, and population variability,
if known. Chapter 5 describes the history of Bering Sea fisheries (for fishes and marine
mammals) and their management, including a discussion of coastal communities, cultures, and
economics.
Chapter 6 summarizes the most serious problems and issues affecting the Bering Sea
ecosystem and proposes a hypothesis that is consistent with available data on species abundance
and variability. In a conceptual framework consistent with earlier parts of the report, Chapter
7 then addresses the implications of these data and hypotheses for management policy and
institutional arrangements governing the Bering Sea ecosystem. The most pressing gaps in
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10
The Bering Sea Ecosystem
knowledge and research needs and the commiRee's conclusions and recommendations are
presented in Chapter 8.
Representative terms from entire chapter:
sea ecosystem
