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Resource Ecology & Fisheries Management (REFM) Division

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July-Sept 2006
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Resource Ecology & Ecosystem Modeling (REEM) Program

Ecosystem Indicators

figure 1 graph, see caption
Figure 2.  Total catch of all species plotted as color contours by trophic level and year for the Bering Sea, Aleutian Islands, and Gulf of Alaska. The main catches and their approximate trophic levels are labeled on the left side of the graphs.  Note: all scales are different for each ecosystem.
 
 

The Ecosystem Considerations report is a section of the Stock Assessment and Fishery Evaluation document, produced annually by the AFSC for the North Pacific Fishery Management Council. It is utilized to advance our understanding of marine ecosystem dynamics and deliver ecological, oceanographic, and climatic indices to stock assessment scientists and managers. The report includes an ecosystem assessment, updated status and trend indices, and ecosystem-based management indices and information for the Bering Sea (BS), Aleutian Islands (AI) and the Gulf of Alaska (GOA) ecosystems.

Integration of information regarding ecosystem status and trends and the use of models to predict possible future ecosystem states using an indicator approach constitutes the framework of a BS/AI and GOA ecosystem assessment. Annual updates of historical trend and present status of various ecosystem indicators are performed by internal development and update of indicators and communicating with the diverse scientific community that is involved in climate, protected species, sustainable fisheries, and ecosystem research. The purpose of the third section, “Ecosystem-based Management Indices and Information,” is to provide either early signals of direct human effects on ecosystem components that might warrant management intervention or to provide evidence of the efficacy of previous management actions.

The information in the Ecosystem Considerations report is utilized by the NMFS Alaska Regional Office and the Council to evaluate the environmental impacts of various fishery management plan alternatives. The Ecosystem Considerations report was updated in September 2006 and will be updated again in November 2006.

An example of an updated and reanalyzed index is the trophic level of the catch (TL). The trophic level of the catch and the Fishery in Balance (FIB) indices have been monitored in the BS, AI, and GOA ecosystems to determine if fisheries have been “fishing-down” the food web by removing top-level predators and subsequently targeting lower trophic level prey.

The FIB index was developed by Pauly et al. (2000) to ascertain whether trophic level catch trends are a reflection of deliberate choice or of a fishing-down the food web effect. This index declines only when catches do not increase as expected when moving down the food web (i.e., lower trophic levels are more biologically productive), relative to an initial baseline year.

Although there has been a general increase in the amount of catch since the late 1960s in all three areas of Alaska, the trophic level of the catch has been high and relatively stable over the last 25 years. Unlike other regions in which this index has been calculated, such as the Northwest Atlantic, the FIB index and the trophic level of the catch in the EBS, AI, and GOA have been relatively constant and suggest an ecological balance in the catch patterns.

The single metrics of TL or FIB indices, however, may hide details about fishing events. We, therefore, plotted the trophic level of catches in the BS, AI, and GOA contoured by species (Fig. 2). This further examination supports the idea that fishing-down the food web is not occurring in Alaska, and there does not appear to be a serial addition of lower-trophic-level fisheries in the BS or GOA.

In the AI, a decline in the overall trophic level of the catch may have been obscured by episodic fishing events. Catches of Atka mackerel began increasing in the mid-1980s. Pollock catches were relatively high in the 1980s and 1990s, but declined after 1998, at which point cod catches were much higher than they had been prior to 1992. The increase in cod catches may have offset any decrease in the observed trophic level of the catch as would have been expected with the generally increasing trend in Atka mackerel catches and decreasing catches of pollock over time. In general, it appears that fishing events are episodic in the AI and GOA, and pollock dominate catches in the BS.

By Jennifer Boldt


Seabird Interactions

Through coordination and collaboration, the AFSC Seabird Fishery Interactions research addressed several components of its research over the summer. Dr. Ann Edwards’ National Research Council appointment was extended into a third year so that we can further investigate whether a fishery signal can be detected in albatross populations. Several papers are in preparation on work completed to date. Seabird mitigation work for trawl vessels proceeded. One of two contracts with the fishing industry to develop first-generation seabird mitigation gear was completed. The second contract will be finished in the fall. Meanwhile, the Washington Sea Grant Program is working on data collected during experiments in 2005 on the vessels using the gear developed through these contracts, which were funded by the National Cooperative Research Program.

Two analyses relevant to the short-tailed albatross biological opinion are close to completion. Supported by National Seabird Program funding, Stephani Zador, Dr. Julia Parrish, and Dr. Andre Punt, University of Washington, are working on a trawl fleet risk assessment for short-tailed albatross interactions and a threshold analysis for short-tailed albatross incidental takes. A tremendous amount of seabird survey work was completed over the summer months by AFSC staff on groundfish charter vessels and by USFWS staff who joined AFSC cruises.

Finally, Michael Perez of the National Marine Mammal Laboratory analyzed seabird bycatch information provided by groundfish observers and developed estimates of seabird bycatch by fishery and region. Those estimates are being prepared for distribution.

By Shannon Fitzgerald
 

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