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Resource Ecology and Ecosystem Modeling Program

Fish Stomach Collection and Lab Analysis

During the fourth quarter of 2009, fisheries observers collected 709 stomach samples from the eastern Bering Sea. In the laboratory, Resource Ecology and Ecosystem Modeling (REEM) Program staff analyzed stomach samples from 6 predator species from the eastern Bering Sea (n = 583), 3 predator species from the Aleutian Islands (n = 29), and 16 predator species from the Gulf of Alaska (n = 1,125). In total, 4,077 records were added to the REEM food habits database.

By Troy Buckley, Geoff Lang, and Mei-Sun Yang

Ecosystem Indicators

map, see caption
Figure 1. Map of eastern Bering Sea area considered when estimating percent area potentially disturbed by trawl fishing gear.

REEM staff completed the Ecosystem Considerations appendix to the stock assessment and fisheries evaluation (SAFE) report to the North Pacific Fishery Management Council (NPFMC) and presented the appendix to the NPFMC Bering Sea/Aleutian Islands and Gulf of Alaska Plan Teams, the Scientific and Statistical Committee, and the Advisory Panel. For this year’s report, updates were made to 40 indicators, and two new contributions were added. One new contribution focused on quantifying the area disturbed by trawl fishing gear in the eastern Bering Sea (Fig. 1). This analysis showed that the maximum total area of seafloor potentially disturbed by trawls varied around 120,000 km2 in the early 1990s and decreased in the late 1990s to approximately 90,000 km2. The area disturbed remained relatively stable in the 2000s with a slight increase in 2007-08.

The second new contribution described the spatial distribution of groundfish stocks in the eastern Bering Sea. The authors demonstrated that both the latitudinal and depth distribution of the demersal community on the eastern Bering Sea shelf have shown clear directional trends over the last three decades, indicating significant distributional shifts to the north and into shallower waters. Although the average distribution shifted slightly south after the very warm years of 2004-05, there was little evidence that recent cold temperatures in 2006-08 have led to a commensurate reversal of the long-term northward shifts.

By Stephani Zador

Ecosystem Modeling

This year REEM staff added information of fish guilds to the Ecosystem Considerations appendix section of the SAFE report to the NPFMC. The status and trends of eastern Bering Sea (EBS) and Gulf of Alaska (GOA) feeding guilds were analyzed by incorporating current stock assessment and survey results within the framework of existing food web models. EBS biomass trends were summed stock assessment model estimates or scaled survey data, where available, for each species within the guild. If neither time series were available, the species was assumed to have a constant biomass equal to the mid-1990s estimated levels.

The GOA ecosystem model was forced by stock assessment model estimates where available for each species within the guild and fit to survey time series, catch data, groundfish diet data, and the mid-1990s mass balance for all other species. Current EBS status (2004-09) mean biomass, catch, and exploitation rates have been within +/- one standard deviation of 1977-2009 levels for all guilds except pelagic foragers (biomass below mean, exploitation rate above mean) and structural epifauna (biomass above mean). Apex predators and pelagic foragers had decreasing trends in biomass, catch, and exploitation rates, while benthic foragers had increasing catch and exploitation rate trends. The apex predator trends were driven largely by a decrease in Pacific cod biomass and catch. The pelagic foragers guild was dominated by walleye pollock (77% of guild biomass in 2009), whose decrease with general declines in other forage species has brought the biomass of this group to overall low levels. Exploitation rate was over one standard deviation above the mean from 2004-07, however the decreased catches in 2008 and 2009 have decreased the pelagic foragers exploitation rate back towards its long-term mean. Increasing trends in benthic forager catch and exploitation rate reflect increased allowable biological catches (ABCs) for flatfish species allowable under the 2.0 million metric ton (t) optimum yield cap with decreased pollock ABCs.

Current GOA mean biomass was more than one standard deviation above 1977-2009 mean levels for apex predators and benthic foragers, and the biomass trend is increasing for benthic foragers. The apex predator guild was driven by the stock assessment-estimated high biomass of arrowtooth flounder, and to a lesser extent for Pacific halibut and Pacific cod, while the benthic forager guild was driven by a stock assessment-estimated increase in flathead sole and survey trends for increasing skates and flatfish. In contrast, pelagic foragers recent mean biomass is nearly one standard deviation below the long-term mean, driven by the stock assessment estimated decline in pollock. Catch for pelagic foragers remains within one standard deviation of the long-term mean, while exploitation rates have trended down. GOA shrimp are above long-term mean biomass, due to a long-term trend, which agrees with trawl survey results.

By Sarah Gaichas and Kerim Aydin

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