Resource Ecology & Ecosystem Modeling (REEM) Program
Fish Stomach Collection and Lab Analysis
Laboratory analysis was performed on 2,193 groundfish stomachs from the eastern Bering Sea and on 1,018 groundfish stomachs from the Gulf of Alaska. During this quarter, 2,265 Bering Sea samples and 69 Gulf of Alaska samples were collected by fisheries observers. A total of 9,666 records were added to the groundfish food habits database.
By Troy Buckley, Geoff Lang, and Mei-Sun Yang
Multispecies and Ecosystem Modeling
Food habits data is a key input into the Resource Ecology & Ecosystem Modeling (REEM) Program’s multispecies and ecosystem modeling efforts. These modeling efforts rely on diet composition matrices in order to produce yearly estimates of predation mortality for key species such as walleye pollock. To help discern the relative role of predation on year-class strength, past modeling has used quarter-specific age transition keys to estimate predation on age-0 and age-1 pollock. However, pollock grow rapidly during the summer foraging season, suggesting that quarterly resolution on age-transition may be insufficient for separating out age-specific effects.
An examination of the length frequency of pollock cannibalism (% by fork length of pollock in the stomachs of pollock) shows a clear split between cannibalism on age-0 and age-1 fish during the summer, with the size (fork length) of the split increasing rapidly throughout the growing season as age-0 fish increase as a percentage of pollock diet. Algorithms for including this variable (i.e., split-length by month) in the input data for Multi-Species Virtual Population Analysis (MSVPA) and ecosystem models are currently under active development.
By Kerim Aydin and Jesus Jurado-Molina
Ecosystem Indicators
The Ecosystem Considerations section of the Stock Assessment and Fishery Evaluation (SAFE) was updated again in 2006 and includes an ecosystem assessment, updated status and trend indices, and ecosystem-based management indices and information. The report is made available to the North Pacific Fishery Management Council (NPFMC) and its family (i.e., plan team members, Scientific and Statistical Committee, and Advisory Panel), stock assessment scientists, and the public in the fall of each year. This information is often used in stock assessments and in various reports that are provided to management. A bulleted list of important highlights and recent trends in climate, biology, and fishing impacts is included in a brief executive summary.
New indices included in the report this year include a zooplankton index for the Gulf of Alaska and socioeconomic indicators. A new website has been developed that provides access to the contributions as well as to data time series summarized in the report: http://access.afsc.noaa.gov/reem/ecoweb/index.php.
Major environmental trends this year included the reversion to relatively cold conditions in the Bering Sea during the winter of 2005-06, which resulted in an extensive cold pool in summer 2006. This cold trend, however, was regional in nature, and a continued warming trend with reduced ice extent has been documented through much of the Arctic. Temperature conditions in the Gulf of Alaska were the warmest on record in 2005 (information for 2006 was not available).
A major conclusion from the analysis of various trends is that no apparent adverse effects of fishing on the ecosystems have been documented to date. Concerns about high bycatches of salmon in the Bering Sea pollock fishery remain, however, and these are being addressed by the NPFMC.
By Jennifer Boldt
Ecosystem Assessment
The integration of multispecies and ecosystem modeling results into the SAFE report was substantially expanded in 2006, especially in the ecosystem assessment and Bering Sea walleye pollock ecosystem considerations sections. In particular, forage fish biomass trends from bottom trawl surveys for the last 24 years in the Bering Sea were summed using catchability coefficients (‘q’) calculated from the Bering Sea ecosystem model.
The results show two notable features: first, forage fish seemed to show an “ecosystem response” to decreased pollock biomass in the early 1990s, with the decrease in pollock being followed by an increase in shrimp, capelin, and other forage species. This increase may be due to prey release or alternating climate conditions favoring different suites of species.
More notably in terms of assessing current conditions, forage fish biomass seems to have dropped abruptly after 1998, and the last 7 years (1999-2006) have shown the lowest biomass of nonpollock forage since the time series began. Another trend of note in the Bering Sea has been the increase in arrowtooth flounder in recent years; analysis of this trend, particularly with respect to its impact on pollock, is ongoing.
