RESOURCE ECOLOGY & FISHERIES MANAGEMENT
(REFM) DIVISION (cont.)

RESOURCE ECOLOGY AND ECOSYSTEM MODELING PROGRAM:

Fish Stomach Collection and Lab Analysis

Laboratory analysis was performed on 3,063 groundfish stomachs from the eastern Bering Sea and 200 from the Aleutian Islands. No stomachs were collected this quarter.

By Troy Buckley and Mei-Sun Yang.


Ecosystem Considerations for 2004

The Ecosystem Considerations Section for 2004 was completed as part of the Stock Assessment and Fishery Evaluation (SAFE) Reports which are provided to the North Pacific Fishery Management Council (NPFMC). A summary of the first draft of the Ecosystem Considerations section was presented to the NPFMC groundfish plan teams in September and updates/changes to the draft were presented to the plan teams in November. The chapter content and format is very similar to last year, primarily providing information on the status of the environment. The final document is available on the Alaska Fisheries Science Center web site at: http://www.afsc.noaa.gov/refm/stocks/assessments.htm.  A summary of some of the main ecosystem indicators is presented in Table 1 of the document.

New to the Ecosystem Considerations section this year is the addition of status and trend information pertaining to salmon, herring, crabs, and zooplankton. Also new to the chapter is the addition of several community indicators, such as community size spectrum and k-dominance curves, indices of biodiversity, recruitment, and survival. Data gaps still include lower trophic levels, such as phytoplankton, additional zooplankton, and nutrient information.

Stock assessment scientists continued to use indicators from the Ecosystem Considerations section to assess ecosystem factors such as climate, predators, prey, and habitat that might affect a particular stock. Also, information regarding a particular fishery’s catch, bycatch and temporal/spatial distribution was used to consider the possible impacts of that fishery on the ecosystem. We are still in early stages of using this type of information in stock assessments. However, we anticipate the information could be used to modify allowable biological catch recommendations or spatial/distribution of the catch due to ecosystem concerns, or to target further research that would be needed to quantify ecosystem impacts.

Another new addition to the Ecosystem Considerations section is the Ecosystem Assessment. The primary intent of this contribution is to summarize historical climate and fishing effects on the shelf and slope regions of the eastern Bering Sea/Aleutian Islands, and the Gulf of Alaska from an ecosystem perspective and to provide an assessment of the possible future effects of climate and fishing on ecosystem structure and function. This is the first year that this assessment strategy was used and not all of the modeling tools are ready for use in projections. Future development of modeling tools will enable scientists to provide advice on management strategies that are robust to a wide range of future ecosystem states. The assessment could be used to evaluate aggregate effects of groundfish fisheries on ecosystem and habitat and could result in advice regarding changes in aggregate catch levels (OY cap), species mix of the catch, and discard amounts.

By Jennifer Boldt.


Feeding Habits of Demersal Fish

Longitudinal gradients in the feeding habits of Pacific cod, Atka mackerel, pollock and Pacific ocean perch (POP) were assessed from stomach collections during AFSC trawl surveys in the Aleutian Islands and Western Gulf of Alaska region in order to determine the presence of biophysical boundaries. Stomachs were also collected by observers during commercial fishing operations. Samples were taken between 1982 and 1999, and a total of 20,985 stomachs were included in this analysis. The degree of taxonomic resolution varied depending on prey type. Most fish prey were identified to species, if possible, with exception of myctophids which were mostly identified only to family (Myctophidae). Invertebrate prey species were likewise rarely identified to species; euphausiids and copepods were identified to Order. Data were pooled into two-degree longitude areas, from 164^oW to 170^oE. Sample sizes per species, per two-degree block ranged from 11 to 3,588. Diet composition (percent by weight) by two-degree area was calculated for all four species; the major prey items (>approx. 80%) are presented in detail, the remaining approx. 20% is summarized as “other species”.

On average, euphausiids make up 35%-50% of the diets of walleye pollock, Atka mackerel, and POP. However, east of Samalga Pass, the portion of euphausiids consumed ranged from 50% to 90% while west of the pass it generally made up 10%-50% of the diets. Besides a step-decrease in the proportion of euphausiids at Samalga Pass, there was a continuing declining trend in the diets of POP and Atka mackerel from Samalga Pass to the far Aleutian Islands. Copepods and myctophids contributed most to the remaining portion of the diets to the west for POP, Atka mackerel, and pollock. Additionally, these last two species seem to diversify their diet towards the west as well, the portion of “other species” increasing in step fashion. The diet composition of Pacific cod likewise showed a shift from east to west. East of Samalga Pass, pollock predominates as the main prey item; whereas west of the pass, Atka mackerel became an increasingly abundant component. Squid and other fish prevail in the remainder of cod diet west of Samalga Pass, in contrast to east of the pass where their joint contribution is less than 20%.

Other than the shift in diet composition at Samalga Pass, there seemed to be changes in diet occurring further west. Gradients were not necessarily unidirectional all the way to the far Aleutians, which suggests the presence of another biophysical boundary in the west. In the diet of POP, for example, the proportion of myctophids increased substantially west of Buldir Island. The diet of walleye pollock and Atka mackerel likewise showed an increased importance of shrimp, amphipods and polychaetes (not shown; shrimp and polychaetes aggregated within “other species”). And finally, shrimp also increased its importance in the diet of cod sampled west of Buldir. Whereas there is no oceanographical data to confirm this, these changes in diet composition throughout the Aleutians can be viewed as biological evidence of biophysical processes yet undescribed for this region.

By Ivonne Ortiz and Kerim Aydin.

AFSC Quarterly
Research Reports
Oct-Nov-Dec 2003