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figure 1, see caption
Figure 1.  Pollock diets at different lengths, in nine different regions of the eastern Bering Sea.  The marine regions shown in the right panel were drawn using GIS layers for multiple data seabirds, zooplankton, currents, etc.  Column plots in each region show the number of stomachs available for different lengths of pollock.  The panel on the left show the proportion in diet of a given prey for pollock at different lengths.  Data is represented by circles, red lines represent model estimates.  Click image to enlarge.

The Bering Sea Integrated Ecosystem Research Program (BSIERP) is part of the Bering Sea Project, a multi-year partnership between the National Science Foundation and the North Pacific Research Board. The Bering Sea Project is a collection of 35 distinct but linked proposals that study climate, oceanography, zooplankton, fish, seabirds, marine mammals, fisheries, Native Alaskan communities and management.

Every year, more than a hundred scientists from the Bering Sea Project get together to share and synthesize results of their ongoing research. As the project is in its last year, the March meeting in 2012 was the last of the Principal Investigator (PI) meetings, focusing on modeling results, applications and validation.

As part of the modeling effort, a vertically integrated model couples five distinct modules: climate, oceanography, nutrient-zooplankton, fish, and fisheries. The fish module called FEAST (Forage / Euphausiid Abundance in Space and Time) is fully coupled with the nutrient-zooplankton and fisheries components and will run both in hindcast and forecast mode.

FEAST is a bioenergetics model that includes 12 fish species linked to 5 zooplankton groups and 20 fisheries specified by sector, gear, and target species. Species include walleye pollock, Pacific cod, arrowtooth flounder, salmon, capelin, herring, eulachon, sandlance and myctophids, squids, shrimp and epifauna; these have a two-way interaction with five groups from the nutrient-phytoplankton-zooplankton (NPZ) module: small/large copepods, oceanic/shelf euphausiids and benthos.

Temperature and advection estimates from the physical oceanography portion (ROMS) are used in the fish bioenergetics, movement and reproduction components. The hindcast is compared both to time series and spatial patterns obtained from historical field data, stock assessments, and fishing effort data.

For this last BSIERP PI meeting, Kerim Aydin and Ivonne Ortiz showed a comparison of data versus model outputs, highlighting the model's ability to capture prey switching, species distribution based on temperature and prey availability, interannual differences between cold and warm years, and preferred temperature ranges for walleye pollock, Pacific cod, and arrowtooth flounder.

A large part of the parameter estimation for FEAST was based on the extensive food habits database supported by the program since 1982.

Figure 1 (above) shows diets for pollock at different lengths, which are at the core of the FEAST model.

figure 2, see caption
Figure 2.  Fish distribution as predicted by FEAST for July 2008.  Left panel shows total age 1+ biomass of pollock, right panel shows total age 1+ arrowtooth flounder biomass.  Click image to enlarge.

Figure 2 shows model distributions for pollock, cod, and arrowtooth for July 2008. Fish movement and growth is estimated the same way for all three species, with species-specific bioenergetics and prey preferences dictating the movement and growth of each species.

FEAST will be used as the model representing the real world in the Management Strategy Evaluation project part of BSIERP.

At the meeting Liz Moffitt, Kerim Aydin, Ivonne Ortiz, Andre Punt, Anne Hollowed, and Gordon Kruse met to discuss the preliminary results of developing multi-species harvest control rules. This step is key in using multi-species assessment models for fisheries management, both in general and for the Management Strategy Evaluation project of BSIERP. Many good points were brought up by the group in terms of priorities in moving forward. This work is ongoing and includes the work of Kirstin Holsman, who was not able to travel to the meeting.

By Ivonne Ortiz, Liz Moffitt and Kerim Aydin

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