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Executive Summary The Bering Sea, a semi-enclosed northern extension of the North Pacific Ocean, contains a tremendous variety of biological resources, including at least 450 species of fish. cru.~t,q.c~eqn~ _1 ~ Ed ~ ~ ~ · f ~ e and mollusks; ou species or seaboards; and 25 species of marine mammals. The plentiful fish and game of the Bering Sea have supported the lives and livelihoods of people on both the Asian and the North American continents since prehistoric times. As the world's demand for furs and whale oil grew in the eighteenth and nineteenth centuries, exploitation of the Bering Sea's bountiful living resources began on a commercial scale. During the twentieth century, international markets turned to the Bering Sea for its seafood resource. Tor1qv ~qnnr^YimqtPl~' 25 species of fish, crustaceans, and mollusks of the Bering Sea- are considered important commercially. Despite a variety of recent protections for marine mammals, birds, and fish resources afforded by laws of the United States and Russia and a number of international agreements, some species of the Bering Sea and adjacent regions have undergone large and sometimes sudden population fluctuations. For example. Steller sea lions have declined hv an to an Pro a-~ , ~ En _ ~ ~ _ _ ~ ~ _^-a_ ~] _ ~ ~ vie r-~-~11~ ~11~ . . ~ . ~ ~ . . ~ _ northern fur seal pups on the ~nb~lot~ islands (the major Bering Sea rookeries) declined by 50 percent between the 1950s and 1980s. In parts of the Gulf of Alaska, harbor seal populations have dropped by as much as 90 percent since the 1970s. Populations of seabirds such as common murres, thick-billed murres, and red-legged and black-legged kittiwakes have also declined significantly in some areas such as the Pribilof Islands and the eastern Aleutians. Large changes in the abundance of a number of shellfish ,qn(1 fish n~milAtin"~ ^`rPr to" me On years-including some large increases-have t.)~rll - OPT And WPl1 ~ ~ ~~~~~~~~~~~ --- - -amp- Or ~ ~-1 ·~1~ Move rev ~ -~---D ~ DO v by,,,_ ,,_,-~ TV W~11. As a result of concerns about how living resources in the Bering Sea have been and should be managed, the National Research Council (NRC) was asked to assess the current scientific understanding of the Bering Sea. The NRC appointed the Committee on the Bering Sea Ecosystem to study the population dynamics and changes in the marine mammals, birds, and commercially important species in the ecosystem and the probable causes of the chances frank In Knowledge and the research needs to fill the gaps, including opportunities for interagency and . . . 1 ~7 D r
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2 The Bering Sea Ecosystem international cooperation; and as appropriate, alternative management strategies and institutional arrangements.) The committee concludes that a combination of environmental changes and human exploitation of Bering Sea resources is the most likely explanation of recent changes in the Bering Sea ecosystem. CHANGES IN THE BERING SEA ECOSYSTEM Both natural environmental fluctuations and human activities have caused biological changes in the Bering Sea ecosystem. Fish populations and other components of the ecosystem appear to react to many different environmental variables in the atmosphere and ocean. Overall, the committee concludes that cI~mate-driven variability in the Bering Sea ecosystem is significant, occurs at many different time scales, and appears to affect many ecosystem components. It appears that cInnate has caused relatively rapid shifts in the organization of this marine ecosystem most recently in the late 1970s and that changes over periods of decades may have larger effects than those over yearly periods. Human-induced change in the ecosystem is also significant. Fishing and hunting of marine mammals by Aleuts and Eskimos have occurred for hundreds of years at least; intensive exploitation of Bering Sea marine resources by the United States, Russia, Japan, and other nations began in the eighteenth century and increased in the nineteenth and twentieth centuries. Exploitation by indigenous peoples affected the abundance and community structures of marine resources, especially close to shore, and, coupled with natural fluctuations, led to occasional food shortages. The more extensive exploitation of the region's resources by Russia, the United States, Japan, and European nations that began in the eighteenth century led to more severe local food shortages and even starvation among the indigenous peoples. Intensive exploitation of Bering Sea resources continued until the expansion of exclusive economic zones in the 1970s, when overall exploitation rates in U.S. waters began to decline. Intense fishing continued in international waters (e.g., the "donut hole"), but in recent years that has been reduced or eliminated as well. Information on exploitation rates in the western Bering Sea since the dissolution of the Soviet Union in 1991 is very unreliable, but anecdotal information suggests that exploitation rates are unsustainably high, especially near shore. Large-scale, intensive exploitation of whales occurred during the 1950s, 1960s, and early 1970s in many parts of the Bering Sea and Gulf of Alaska. During this period, trawl fisheries severely reduced populations of eastern Bering Sea shelf Catfishes and slope rockfishes. Eastern Bering Sea pollock abundance increased in the late 1960s, perhaps as a result of an increase in the amount of food made available by the reduction in whales and other fishes, and the trawl fisheries switched their primary focus to pollock, where it has remained to the present. As a result of environmental changes and human exploitation of the ecosystem, the eastern Bering Sea fish assemblage probably became pollock-dominated in the late 1960s and ~ A detailed description of the committee's statement of task is in Chapter 1.
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Executive Summary 3 early 1970s, and a similar shift probably occurred in the western Bering Sea as well. In addition, both eastern Bering Sea king crab and herring were reduced significantly, perhaps by fishing, in the 1960s and early 1970s. King crab populations and their fisheries increased in the early 1970s, and then collapsed again in the early 1980s. Several eastern Bering Sea finfish populations grew rapidly in the late 1970s and early 1980s while one Catfish species and a number of forage species appear to have declined significantly. Superimposed on all of this are the changes in Bering Sea and Gulf of Alaska seabird and mammal populations. Fluctuations in seabird populations vary across the region, apparently depending on local environmental and ecological conditions. The pinnipeds (seals, sea lions, and walruses) present a different picture, with more uniform changes. Juvenile and adult female fur seals declined in the Pribilof Islands from the mid-1970s to the early 1980s and then subsequently stabilized. Harbor seals in the Gulf of Alaska declined rapidly in the late 1970s and have remained low. The trend in the number of Steller sea lions is uncertain before the 1970s, but declines were first noted in the eastern Aleutians in the early 1970s and then continued in the central and western Aleutians and western Gulf of Alaska during the 1980s. These declines appear to be related to a lack of adequate food, with juveniles probably affected most severely. CAUSE AND EFFECT IN THE BERING SEA: THE CASCADE HYPOTHESIS The most likely explanation of events over the past few decades in the Bering Sea ecosystem is that a combination of changes in the physical environment acted in concert with human exploitation of predators (whales, other fish) to cause pollock to dominate the ecosystem. The increase of adult pollock and other predatory fishes in the past 20 years might also be responsible for keeping the forage fishes relatively scarce. As a result, some forage fishes that have higher nutritional value than pollock became less available to some marine mammals and birds, leading to their decline. This food shortage might have been exacerbated by fishing for pollock that was concentrated in space and time, which might have removed them from some areas for long enough to cause difficulties to marine mammals and birds, especially juveniles. Although the committee concludes that such a "cascade hypothesis" is the most likely explanation of events over the past 50 years, other explanations of these changes might develop as research progresses. There is no evidence that any human activity other than fishing and whaling has had any significant effect on the Bering Sea ecosystem, although more evidence concerning the effects of various pollutants would be of interest. This scenario does not lead to the conclusion that overfishing of pollock over the past 25 years-often blamed for some of the changes in the Bering Sea-is directly (or even indirectly) responsible for recent declines of mammals and birds. As a result, it is unlikely that reduction of the total rate of exploitation of pollock would halt or reverse the declines in the short term. It is more likely, although by no means certain, that marine mammals and birds have been affected by the distribution in space and time of fishing effort on pollock, and thus that they would be helped by a broader distribution of fishing effort in space and time, especially in areas where they are known to feed.
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4 The Bering Sea Ecosystem It is also hard to predict the effects of protecting other marine mammals. It seems extremely unlikely that the productivity of the Bering Sea ecosystem can sustain current rates of human exploitation as well as the large populations of all marine mammal and bird species that existed before human exploitation especially modern exploitation began. Over the long term, fishing competes to some degree with at least some top-level predators. ~~ ^ ~ ~ ~ ~ . . . ~ ~up Therefore, if the goal of management is to have as many top-level predators as possible (not a common management goal), then it seems that ultimately fishing will have to be reduced. Note that "fishing" includes subsistence, recreational, and various kinds of commercial fishing, all of whose effects need to be dealt with. Finally, it will be difficult for human management to cause a large, complex marine ecosystem to achieve and maintain a desirable balance. Some of the changes that have occurred might be irreversible over normal human tune frames (100 years or less). This difficulty emphasizes the need for an adaptive approach to management and the need for good, long-term data on physical and biological phenomena. r ~-- a___ DIFFICULTIES IN OBTAINING INFORMATION In reviewing data on the Bering Sea, the committee found that data sets are not catalogued in any one place and that there is no way of knowing what organization has what research holdings. Therefore, the committee concludes that a directory of databases relevant to the Bering Sea is needed. Another difficulty was the lack of good information from the former Soviet Union. As a result, the committee concludes that a data rescue and archiving.project should be initiated immediately to preserve physical and biological information on the Bering Sea currently residing in the former Soviet Union, as well as information on resource use and conservation. Many efforts are now underway nationally and internationally to examine the values and usefulness of the traditional knowledge of the region's indigenous peoples. Incorporating their approaches could be of value in furthering our understanding of the history of changes in the region, although the committee concludes that research is needed on how to integrate traditional knowledge into the body of scientific knowledge on the Bering Sea. The above considerations led the committee to the following recommendations. RECOMMENDATIONS Research Recommendations · Adopt a broader ecosystem perspective for both scientific research and management of Bering Sea resources. · Adopt an adaptive or experimental approach to management actions concerning the Bering Sea ecosystem.
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Executive Summary 5 · Conduct research on the structure of the Bering Sea ecosystem, including the nature and causes of the dynamics of pollock populations in the northeastern Pacific and Bering Sea over the past 50 years. Understanding this broad question can be approached by studying a number of specific questions' including: Is the cascade hypothesis a plausible scenario for ecosystem dynamics? What are the short- and long-term effects of commercial fishing on the structure and dynamics of the Bering Sea ecosystem? ecosystem? What are the roles of top-down and bottom-up forcing in the Bering Sea ecosystem? What are the relationships between juvenile pollock and other forage species in the What is the role of ice in structuring the Bering Sea ecosystem? What are the periodicities of ecosystem changes? How do lower trophic levels of the ecosystem interact? What are the structure and functioning of the "green belt"? · Conduct research on how well the management and institutions of the Bering Sea are structured to address problems and provide appropriate management solutions. Management and Institutional Recommendations The committee identified four basic problems that need to be solved to achieve proper management of the Bering Sea ecosystem: the lack of knowledge and inherent limitations on understanding and predictability, incomplete specification of management objectives, lack of appropriate domestic institutional structures through which to make and implement coordinated management decisions on either side of the Bering Sea, and the limited ability to coordinate domestic management with users and management agencies of other nations. The committee recommends the following steps to address these problems: · Improve the coordination of the many institutional structures that make management decisions concerning resource use in the Bering Sea. · Coordinate the philosophy and objectives of laws dealing with management in the Bering Sea ecosystem. · Improve processes and institutions to coordinate the implementation of major federal acts relating to resource use in the ecosystem, and federal-state and international management. · Develop a research program to increase understanding of the Bering Sea ecosystem (keeping international issues and cooperation in mind), to fulfill the research needs identified by the committee to help future policy makers solve both short-term management and longer-term ecological problems.
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6 The Bering Sea Ecosystem Recommendation to Reverse Declines in Marine Mammals and Birds The concentrated fishing for pollock in some places at specific ties probably reduces the availability of food for marine mammals and birds, especially juveniles. Thus one step that might help improve the food supply for and reverse declines in marine mammals and birds would be to distribute fishing over wider areas and over longer periods. This management strategy is unlikely to have any adverse effects. Note that this is a call for broadening the distribution of fishing, not a recommendation to increase total catches; in fact, some areas should probably be closed to fishing to protect specific fish, bird, and mammal populations. This leads to the recommendation below. As with all management actions, this strategy should be followed on an adaptive basis. pOllock. Broaden the distribution of fishing effort in space and time, especially for THE FUTURE The Bering Sea ecosystem, like all ecosystems, has been affected by natural fluctuations since tune immemorial. Like most ecosystems, it has been affected by human activities since prehistoric, but especially within the past 200 years as commercial exploitation developed. Thus, the recent changes that we see today should not be thought of as perturbations of a "pristine" ecosystem, but as part of a pattern of change affected by a complex array of natural and human influences. The complexity of the influences on the ecosystem makes understanding and management difficult, but some things are clear. First, environmental change will continue to occur in the future. Second, significant human exploitation of a single species can affect not only that species but many other species as well. In other words, there are connections among ecosystem components. Finally, the total productivity of the ecosystem has a limit, which means that human use of living resources will affect the ecosystem to some degree. Those three conclusions Imply that unexpected events will continue in the future and that they will be larger as living resources are more heavily exploited. It also follows that actions with respect to single species will have complex consequences that will be hard to Predict. SimnIv changing exploitation rates on a single species pollock, for example is unlikely to have easily predictable effects on other ecosystem components marine mammals, for example. To operate successfully within this complex system, management strategies must be developed based on long-term data on physical and biological phenomena and must be adapted as we learn more about the structure and functioning of the ecosystem. A better understanding of institutional and socioeconomic factors will also be needed. Finding a balance between human uses of the region's many resources and maintaining other desired aspects of the ecosystem, such as high productivity of marine mammals or a particular composition of fish communities, will be an ongoing challenge. r ~--a -a ~--o--o
Representative terms from entire chapter: