Title: Productivity of Pollock and Capelin Principal Investigator(s) and Recipient Organization(s)

Project Summary: Our work investigates the potential for competition between juvenile pollock and capelin, which has implications for how ecosystem change can affect capelin and pollock productivity. Competition negatively impacts feeding opportunities, which can in turn impact fish nutritional status, size and subsequent overwinter survival and recruitment. We are conducting an intensive study of the role of hydrography on zooplankton composition, and on the diets of capelin and juvenile walleye pollock in Barnabus Trough, Kodiak Island. In previous years (2000-2004) we have observed a hydrographic front in Barnabus Trough that appears to physically separate capelin and pollock schools, with capelin occurring offshore of the front and pollock occurring inshore. These observed differences in habitat utilization have implications for resource use and competition between pollock and capelin in that region. Work on competition between capelin and pollock is important because it has the potential to elucidate some of the mechanisms by which climate variability influences fish populations. For instance, climatedriven ecosystem variability could influence the physical oceanography off Kodiak Island such that the hydrographic front in Barnabus Trough breaks down, thereby increasing the degree of spatial overlap of the two species. As discussed in the Draft NPRB Science Plan, most assessments of the effect of ecosystem change on fish populations rely on correlations between climate indices and time series of variables such as fish recruitment. However, the processes (such as competition) linking ecosystem change and fish populations remain largely unknown.