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Resource Ecology and Ecosystems Modeling Program
Laboratory analysis was performed on 3,198 groundfish stomachs from the eastern Bering Sea and 143 from the Gulf of Alaska. A total of 1,349 stomachs were collected from the Aleutian Islands region and 10,447 from the eastern Bering Sea. Five observers returned 474 stomach samples from the Bering Sea during the quarter.
Sensitivity analysis of the multispecies virtual population analysis model
parameterized for a system of trophically-linked species from the eastern
Results from the individual perturbation parameter analysis also showed that the changes produced by large positive perturbations in the other food parameter were small. The results obtained in this work reinforce the overall conclusion of the robustness of the MSVPA found in previous works. They are also an important step in the validation of the MSVPA and MSFOR models and help in the identification of the parameters requiring further refinement, including the improvement of estimates of annual ration of predators and residual mortality. This model validation is necessary to incorporate multispecies models in ecosystem-based fishery management advice. However, it is also necessary to develop statistical multispecies models able to assess the uncertainty of parameters producing the largest effects in the MSVPA model.
Uncertainty in Trophic
The model was calibrated so that, at the start of the modeled time period, the system was in equilibrium, and the fishing yield on the groundfish species was at maximum sustainable yield (MSY). The model was manipulated by reducing the pinniped population by 50% and allowing the model to reach a new equilibrium over 50 years. The resulting year 50 biomass levels and fisheries catch (assuming constant fishing effort) are shown in Figure 3. As can be seen, the reduction in pinnipeds did indeed increase groundfish biomass and fisheries yield by approximately 10% (bars in Fig. 3). However, a Monte Carlo simulation of the error ranges for these estimates (assuming very low +/-30% error for input diets, +/-10% error for initial biomass and production levels) resulted in the broad 95% confidence intervals shown by the error bars in Figure 3. As can be seen, groundfish biomass and catch were likely to go down or up, and estimates of juvenile groundfish biomass range from explosively upward to crashing.
This result is explained by the fact that the removal of a slow component of the ecosystem (marine mammals) helps its competitors (faster-growing predatory fish of low commercial value) as often as it helps its prey (groundfish). This is true with the smallest realistic levels of input error (equilibrium assumptions, unrealistically small range of error in diets). In other words, trophic cascades are not possible to control across a large marine ecosystem (stock-level) management scale even with extremely precise data; rather, trophic manipulations must be directed and localized in time and place, to avoid causing undesirable and unexpected changes in the system. New models are being prepared to include manipulations involving lower trophic level marine mammals (baleen whales) and are being extended to more detailed models (for example, the eastern Bering Sea model as modeled with 40+ functional groups).
By Pat Livingston.
Economic and Social Sciences Program
Bering Sea/Aleutian Islands Crab Rationalization
The capacity measures computed in the report were constructed using data on catch (in metric tons), participation (in weeks), and vessel characteristics of catcher vessels and catcher- processors that operated in federally managed Alaskan commercial fisheries for 1990 to 2001. Those data were used to estimate fishing capacity, excess capacity, and capacity utilization in 2001 by fleet and species or species group. Fishery utilization was estimated for each fleet and estimates of the number of vessels and mean number of fishing weeks by fleet were reported for 1990-2001.
There are wide ranges of fishing activities, vessel sizes, targeting strategies, and gear configurations in the various federally managed Alaskan fisheries. Generally speaking, however, groups can be established that are likely to share similar technological, economic, and regulatory constraints (TACs, closures, seasonal delineation). In an attempt to establish such groups, vessel characteristics, fishery participation, and processing data (for catcher-processors) were examined. As a result, 12 catcher vessel fleets and 10 catcher-processor fleets were formed. Each of these fleets is comprised of similarly equipped, similarly sized vessels that engage in a common set of fisheries (and, in the case of catcher-processors, produce a similar set of finished products). Such a grouping allows us to present the capacity estimates on a fleet-by-fleet basis, which more clearly elucidates the sources of fishing capacity.
The estimates indicate that current capacity, in terms of total catch of
all species, exceeds actual catch by nearly 40%. However, species-specific
excess-capacity estimates range widely, from 8% to over 300%.
Subsistence Hunting and Fishing Practices
The data indicate a significant shift in contribution of different resource groups to the animal protein diet between 1500 and today, with harvest of marine mammals dropping tremendously (from 92% to less than 1%), and the contemporary diet consisting primarily of fish (50%), shellfish (11%), land mammals (15%), and store-bought meats (24%).
A high diversity of species used by tribal members prior to Euroamerican colonization are still in use today, from halibut and salmon to harbor seals and sea urchins. Several species no longer used, such as wolves and fur seals, can be explained by ecological factors, such as post-colonial extirpation. Other resources no longer used, such as many small birds and small shellfish, represent a general contraction of the subsistence diet breadth following the introduction of commercial foods. As predicted by optimal foraging theory, the resources most likely to be eliminated from the diet are those that rank low in terms of post-encounter caloric return.
Tribal members made use of nearly all available resources in ancient times; additions to the tribes subsistence base in modern times were due primarily to the introduction of exotic species such as the Pacific oyster, and local population growth of other species, such as the California sea lion. Road building and habitat changes in the forests increased access to land-based resources, such as deer and elk. Land-based resources in general (terrestrial mammals and commercial meats) increased from less than 1% of consumed animal protein prior to 1500 to close to 40% today. However, with over 60% of animal protein still stemming from marine resources, Makah tribal members remain oriented, both nutritionally and culturally, toward the ocean environment.
More than 80 interviews were conducted with community members including such diverse representatives as cannery workers, vessel captains, community activists, and elected officials. About 65% of interviews were tape-recorded, which, once transcribed, will allow for textual analysis of data using ethnographic software. These data is being analyzed. Reports on the research will include a profile of each community, which will become part of a larger NMFS social science project to develop profiles and data sets on a wide variety of North Pacific fishing communities.
By Joe Terry and Jennifer Sepez.
Auke Bay Lab