(Quarterly Report for Apr-May-Jun 1998)
by Patricia Livingston and Loh-Lee Low
The Bering Sea is one of the most productive marine ecosystems in the world. As a northern extension of the North Pacific Ocean, it is the third largest semi-enclosed sea on Earth, with a wide eastern continental shelf, which makes up about half its total area. These waters, rich in nutrients, are home to an array of biological resources including at least 450 species of fish, crustaceans, and mollusks, 25 species of marine mammals, and 50 species of seabirds, the largest international aggregation of seabirds in the world. In domestic terms, the Bering Sea is the most productive marine ecosystem off the coast of the United States, currently providing about 56% of the Nation’s total commercial catch of fish and shellfish. Walleye pollock comprise the bulk of the fish landings, and the region’s snow crab fishery is the Nation’s largest crustacean fishery by weight. The Bering Sea also supports 43% of all breeding seabirds in the United States. Further highlighting the significance of the region are several endemic species such as red-legged kittiwakes and whiskered auklets.
Over the past few years, several Federal, state, and academic institutions concerned about environmental changes observed in the Bering Sea have developed science plans that address elements of this rich and productive region. Because the Alaska Fisheries Science Center (AFSC) conducts considerable research on groundfish, marine mammal, and fisheries-oceanography in the Bering Sea, AFSC scientists have played an integral role in virtually all research planning efforts. To promote research coordination and data-sharing among agencies that study the Bering Sea, the National Oceanic and Atmospheric Administration (NOAA), U.S. Department of the Interior (DOI), and Alaska Department of Fish and Game (ADF&G), sponsored the Bering Sea Ecosystem Workshop in Anchorage, Alaska, in December 1997. AFSC scientists Loh-Lee Low and Pat Livingston of the Center’s Resource Ecology and Fisheries Management Division served on the interagency workshop planning committee.
Highlights of the Research Plan
The goal of the Bering Sea Research Plan is to achieve “a productive, ecologically diverse Bering Sea ecosystem that will provide long-term sustained benefits to local communities and the nation.” To attain this goal, the research plan identifies and addresses the most critical fishery management and marine ecosystem information needs. The most pressing management issues concern the possible effects of humans on the ecosystem.
One of the greatest concerns expressed in the research plan involves the potential effects of fishing on endangered or threatened marine mammals, seabirds, and on benthic communities and habitats. Unfortunately, the nature and extent of the effects of fishing are largely unknown. Despite the scarcity of scientific studies on these issues, management has restricted fisheries in many areas and times of year to mitigate the possible effects of fishing on other Bering Sea ecosystem components. Examples include time-area closures due to concerns about benthic habitats in areas important to red king crab or closures due to concerns over forage species near Steller sea lion rookeries. Whether the closures are successful in helping protect Bering Sea resources or whether different measures might be more effective remains unknown. Thus, directed research on the effects of fishing on the Bering Sea ecosystem is necessary for fisheries managers to make better, more informed decisions.
Other issues facing fishery managers relate to ensuring the long-term productivity of Bering Sea resources. A true ecosystem approach to the Bering Sea requires understanding the system as a whole, not just the parts. Decadal scale climate shifts have been linked to changes in ocean productivity and the availability of species for harvest. Climate factors may shift the distribution and abundance of key resources such as walleye pollock to waters outside the U.S. EEZ (exclusive economic zone) where they are subject to a different management regime. A research program that focuses on understanding the effects of climate change on resource production will help us design better management strategies that can accommodate changes in production and ease economic dislocations that might result from such changes.
The buildup of marine pollution poses a potential threat to marine populations and to sustainable subsistence and commercial use of living marine resources of the Bering Sea. An understanding and prediction of the trends in contaminant levels, especially as they relate to long-range transport from other more polluted regions, is necessary to assure the maintenance of a healthy and productive Bering Sea ecosystem.
The above issues and the synthesis of concerns from previous research programs led the Bering Sea Ecosystem Research Plan to two hypothesis-driven areas of investigation: 1) the effects of human activities such as fishing, pollution, and coastal development on the health, production, and composition of the Bering Sea ecosystem; and 2) the effects of climate on individual species and productivity of the Bering Sea. To focus such a research effort, the plan lists five research themes.
Climate Variability And Ocean Processes
Natural climate variability influences the Bering Sea on a range of time scales, from annual to decadal, and longer. The decadal scale is a dominant mode of observed climate variability for the Bering Sea and has the most impact on management concerns about long-term productivity. A major climate change occurred in 1977 when the Bering Sea went from a cold regime to a warm regime, which appears to favor production of walleye pollock, an important commercially exploited resource. It is unclear how much decadal variability is generated in the atmosphere and how much is forced through sea ice, snow cover, and sea surface temperature. Understanding the existing and emerging climate patterns is necessary to understand and predict impacts of climate change on the ecosystem.
Ocean processes may be critical to the dynamics of the Bering Sea ecosystem. The exchange of water between the oceanic and shelf regimes of the Bering Sea may provide as much as 50% of the annual nitrogen needed to support the high productivity on the shelf. The processes which result in the basin-shelf exchange are poorly understood, and their link to changes in atmospheric forcing and North Pacific circulation is also uncertain. Sea ice, the sources and role of iron, wind-driven mixing from storms, and ocean fronts also play important roles requiring investigation in structuring the physical environment of the shelf and the resulting biological production regime.
Individual Species Responses to Perturbations
Our understanding of the status of living marine resources in the Bering Sea ecosystem is largely confined to commercially important fish and invertebrates and marine mammals and seabirds readily observed from land and sea. Even this limited view of the ecosystem reveals that major increases or decreases in population abundance have occurred among groundfishes, forage fishes, salmon, shellfish, marine mammals, and seabirds in the last 30 years. Though causes for changes in population abundance are not well understood, for some individual species large shifts in populations are probably triggered directly by climate, resulting in strong year classes that sustain fisheries or poor year classes that lead to stock declines. For many species, physical climate and oceanographic factors can have direct effects on important population characteristics such as geographic distribution, reproductive success, growth, and recruitment. When combined with periods of low productivity, overfishing can reduce stocks to levels so low that reproductive success may be jeopardized. More information is needed about how individual species respond to their physical environment and how human influences can impact species in changing environmental regimes.
Food Web Dynamics
The dynamic nature of the Bering Sea is affected by species’ responses to climate and the timing and location of nutrient inputs. Changes in phytoplankton production can translate into significant shifts in zooplankton distribution, composition, and production, which are then translated through the food web to higher trophic levels of fish, mammals, and birds. Our understanding of energy flow at low trophic levels in the marine ecosystem has altered due to the development of new techniques for sampling plankton too small to be captured by traditional plankton nets. However, we lack information about the role these very small plankton play in the energy pathways of the Bering Sea ecosystem. We also lack information about nearshore foodwebs that are important nursery areas for fish and invertebrates, the foraging behavior and energy requirements of mammals, birds, and fish outside the summer season, and the trophic roles of relatively abundant species such as jellyfish, ctenophores and benthic predators. The lack of baseline distribution and abundance data on key forage fish species consumed by mammals, birds, and fish such as capelin, eulachon, boreal smelt, and cephalopods limits our understanding of how these forage species influence the observed population changes in marine mammals and seabirds. Understanding the role of fishing activities on the food web and on prey availability to marine mammals and birds is also crucial.
Habitat is critical to fish, invertebrate, marine mammal, and seabird populations and their productivity. Identification of habitat requires sufficient knowledge to evaluate all major phases in the life history of each species of interest. For example, a certain type of habitat may be necessary for spawning, a different type may be necessary for survival of early life stages, and yet another type may be needed for juvenile and adult growth. Furthermore, fishing may directly or indirectly affect habitat and the plants and animals that contribute to that habitat. Whether fishing has detectable short-term and long-term effects depends on gear types used in combination with specific habitat characteristics. Coastal development also can adversely affect important habitats located in estuaries, embayments, and shallow and intertidal waters along open coastlines. Development and fishing activities may disrupt the habitats of marine mammals and birds in many ways. Habitat research will ultimately improve our ability to develop baseline data to assist in planning future coastal development, predict changes in stock status, provide protection of presently adequate habitat, and make improvements to degraded habitat necessary to maintain and improve the health of fish stocks.
In comparison to shallow seas adjacent to more populated and industrialized parts of the world, the Bering Sea tends to have low levels of toxic contaminants. However, levels of contaminants in the Bering Sea have been rising over the last 50 years due to increased human activities such as mining, fishing, and oil exploration. Increased contaminant levels in the Bering Sea also are connected to long-range transport of contaminants through the ocean and atmosphere from other regions. Other sources of pollution such as trash and plastics, as well as exotic species, can also have adverse consequences to native flora and fauna. Cold region ecosystems such as the Bering Sea are more sensitive to the threat of contaminants than warmer regions because the loss and breakdown of these contaminants are retarded in colder areas. Also, animals high in the food web with relatively large amounts of fat tend to have high concentrations of organic contaminants such as pesticides and PCBs. This causes concerns about human health in the region, particularly for Alaska Natives who rely on marine mammals and seabirds as food sources. Quantifying the sources and fates of contaminants and other introductions and the effects of these on the living marine resources and health of communities reliant on these resources is essential.
Characteristics of the Research Effort
Although the Draft Bering Sea Ecosystem Research Plan does not include a complete implementation plan, it summarizes key issues to consider for implementing research. The plan places priority on implementing a research program that will:
This first draft of the Bering Sea Ecosystem Research Plan was completed in April 1998. A second workshop was held in June 1998 in Anchorage to get feedback on the plan from a broader constituency. Center scientists Pat Livingston and Loh-Lee Low were part of the interagency organizing committee for this workshop. Pat Livingston is overseeing the revision of the draft research plan and incorporating into the plan the comments and perspectives presented at this workshop.
Coincident to the development of the research plan, Congress created an Environmental Improvement and Restoration Fund to be administered by a North Pacific Research Board to “conduct research activities on or relating to the fisheries or marine ecosystems in the North Pacific Ocean, Bering Sea, and Arctic Ocean (including any lesser related bodies of water).” The Fund would make available about $5-$10 million annually for research on a continuing basis. The Board is charged with reviewing and recommending research priorities and grant requests for approval by the Secretary of Commerce. The enabling legislation for the Board directs it to avoid duplicating other research activities and to place priority on cooperative research efforts designed to address pressing fishery management or marine ecosystem information needs. The draft Bering Sea Ecosystem Research Plan will serve the North Pacific Research Board (NPRB) in guiding needed research in the Bering Sea. Later, similar science plans will be developed for the North Pacific Ocean and Arctic Ocean. Implementation of the Bering Sea ecosystem research effort will begin when funding is appropriated by Congress.