Bering Sea Breakout Session

Discussion Leaders: Alan Springer and James Overland
Participants: Vera Alexander, Hal Batchelder, Paul Bentzen, Ned Cokelet, Dan Costa, Tina Willie Echeveriia, Robert Francis, George Hunt, Evelyn Lessard, Patricia Livingston, Richard Merrick, Kate Myers, Jeff Napp, Thomas Powell, James Schumacher, Gary Sharp, Phyllis Stabeno, Gordon Swartzman, Vidar Wespestad, Anne York

Introduction

The Bering Sea shelf is possibly the most productive of the northern high latitude seas. The foundation is a greenbelt of primary productivity in excess of 200 gC m^-2 yr^-1 extending over the outer 200 km of the shelf. This region supports some of the worlds largest stocks of fish. For example the biomass of the walleye pollock stock is estimated to be approximately 10 million metric tons. Likewise, the largest runs of salmon in the U.S. is the Bristol Bay sockeye run. The region has historically supported large populations of marine mammals and seabirds. The benthos of the Bering Shelf is also productive, supporting large populations of King crab, flatfish and a variety of infauna.

The Bering Sea is an appropriate region in which to study the potential effects of climate change on carrying capacity. There is a rich background of long term monitoring studies of northern fur seal and marine birds at the Pribilof Islands; fisheries catches for numerous species in the eastern Bering Sea; and process studies of the determinants of production and the linkage of production to interannual variation in weather patterns (PROBES and ISHTAR). These studies provide a basis for developing additional process oriented studies for extrapolating the effects of short term changes in weather to longer term climate changes.

The SE Bering Sea has the following characteristics:

The boundary of the arctic and maritime air masses occurs here; small climate shifts might provide major differences in wind intensity, ice extent and cloudiness.
It has a broad, shallow shelf. Tidal and wind mixing create three domains based on stratification with strong frontal boundaries between domains.
There is weak or no advection on the shelf. However, there is interaction of shelf waters with the deep basin of the Bering Sea and perhaps also with the Gulf of Alaska through the Aleutian Chain.
Primary and secondary production is tied to mixed layer dynamics, which are primarily controlled by storm frequency and the extent and timing of ice cover.
Upper trophic level productivity is high, and top down controls have a strong influence on the species mix of the system. Of particular interest is the cannibalistic character of walleye pollock.
Timing of spring bloom relative to storm tracks determine whether energy input is to the benthic or pelagic communities. If the spring bloom occurs when the ice is present, the primary production sinks out of the pelagic zone due to inhibition of grazing at low temperatures (Cooney and Coyle, 1982).

Breakout Discussions

First order understanding of the Bering Sea has been obtained by previous repeated surveys and process oriented studies (e.g., PROBES, Bering Sea FOCI). What is needed now is to quantify the causality between the magnitude of environmental change and the response of the system. The natural variability of the system is large so that it may be possible to find historical analogs of climate change. The primary question is how does climate variability modulate the high productivity of the Bering Sea? Specifically, storm tracks and extent of seasonal ice edge are known to vary on a 7-15 yr cycle, will a climate shift in storm tracks alter the distribution of energy between the pelagic and benthic components of the SE Bering Sea shelf ecosystem? The following research issues have been noted qualitatively. What is required is quantified answers to the following questions.

What is the pelagic biogeography of the Bering Sea?
Where in the Bering Sea do significant processes occur?
What is the importance of production over the shelf, shelf edge, and basin of the Bering Sea to biomass yield at higher trophic levels?
Are all habitats equally susceptible to climate change?
Is the magnitude of variability proportional to habitat importance? i.e., primary or secondary productivity of a given habitat might vary dramatically in response to climate change but it might be irrelevant to most higher trophic levels.
What is the relation of the range of storm activity to the annual production budget and food web dynamics in the mixed layer?
What is the contribution of the sea ice melt-back bloom to total annual production?
How does the nature (e.g. timing and magnitude) of the spring bloom affect total primary production and the partition of energy between pelagic and benthic ecosystem components? Specifically, does an early bloom lead to high benthic production and a late bloom lead to high pelagic production?
Will climate change alter habitat/domain volumes and how will this influence recruitment?
What are the similarities and differences between the Bering Sea and Southern Ocean shelf sea-ice and pelagic sea-ice communities?

Activities

We recommend activities in the areas of retrospective, modeling, process studies and monitoring. An initial approach should be to identify key species in the production and transfer of energy in the ecosystem, identify species sensitive to change in production at lower trophic levels, and develop studies around those species.

Retrospective Studies

Examine sediment cores from anoxic basins for evidence of decadal and secular fluctuations in the abundance of marine fishes.
Determine the summer distributions of marine fish relative to environmental variables such as fronts, ice cover during the previous winter, lagged wind and water temperature.
Examine growth rates of marine fish relative to environmental variables and summer distributions.
Examine marine mammal growth patterns and isotope ratios to estimate level of trophic feeding coupled with variations in food availability.

Modeling/Ecosystem Interaction Studies

Construct a physical model for the shelf and basin incorporating historical records of storm tracks and intensity to predict the interannual range of nutrient dynamics and primary production.
Construct a multispecies virtual population analysis (MSVPA) of the eastern Bering Sea including commercially important fish, and other predators such as mammals and birds to determine if stable predator selectivity estimates are obtained.
Construct a spatially explicit trophodynamic model of the eastern Bering Sea that includes upper trophic level predators, primary and secondary production, and linkages to physical processes.

Process Oriented Studies

Determine food chain lengths and trophic relationships using isotope, pigment, and dietary approaches.
Determine the role of jellyfish, other carnivorous zooplankton, squid, and myctophids in the pelagic food web.
Determine predator selectivity and switching parameters (particularly adult pollock as predator) by sampling predators in prey patches containing different proportions of zooplankton and juvenile pollock. Quantitatively assess zooplankton (including euphausiids) and juvenile pollock in these patches.
Determine the contribution of sub-stocks to pollock recruitment by assessing the location and density of spawning sub-stocks and tracking the fate (location and survival) of spawning products of each sub-stock and determine how climate affects variability in both spawning locations and fate of spawning products.

Monitoring/Lower Trophic Level Response

Determine seasonal and interannual variability in floristics, primary production, and carbon sedimentation rates at key index sites in shelf and basin domains of the eastern Bering Sea.
Determine seasonal and interannual variability in abundance and production of key species of herbivorous and carnivorous zooplankton in the shelf and basin domains of the eastern Bering Sea.
Determine interannual variability in infaunal benthos abundance and location at key index sites in the inner, middle, and outer shelf regimes of the eastern Bering Sea.

Monitoring/Higher Trophic Level Response

Determine interannual and seasonal variability in juvenile pollock abundance, location, vertical distribution and diet throughout the eastern Bering Sea, especially in relation to ice dynamics.
Determine interannual variability in other forage fish abundance, location, and diet.
Conduct predator food habits and energetics survey to determine seasonal variation in juvenile pollock, other forage fish, squid and zooplankton utilization by higher trophic level predators.
Determine interannual variability in the abundance and spatial distribution of spawning pollock.
Conduct summer near-shore midwater surveys of the Bering Sea coast to determine abundance and location of capelin and herring.
Conduct seasonal surveys of forage fish abundance and location relative to upper trophic level predators.
Determine the role of gelatinous zooplankton in mediating the effects of climate change through competition for food with high trophic level species.
Measure foraging effort, behavior and energetics of key species of mammal and birds as index of change in predator effort. Examine differences in onshore versus offshore foraging effort in fur seals.
Compare eastern and western Bering Sea ecosystems. The Eastern Bering Sea is a shelf based system, productivity coupled with extent of sea-ice edge. It is a low advection region. The Western Bering Sea is a high advection system, deep water environment. Both regions have many of the same species and would provide an interesting comparison as to where and how these species make a living in such different oceanographic regions.