11th National Stock Assessment Workshop (abstracts)
A Framework for Incorporating Climate Impacts on Pelagic Ocean Habitats Into Stock Assessments Anne B. Hollowed, Angie Greig, Libby Logerwell, and Chris Wilson; AFSC, Seattle, WA
The volume of suitable pelagic ocean habitat can influence the dynamics of recruitment and growth of marine fish. In the case of recruitment, habitat volume influences survival through its role in governing the overlap of predators and prey and through its role in governing competition for limited resources. In the case of juvenile and adult growth, habitat volume influences the probability of spatial overlap between predators and prey. We present a framework for quantifying climate-induced shifts in pelagic ocean habitats and incorporating these shifts into the walleye pollock stock assessment as explanatory variables governing growth and recruitment. In this study acoustic backscatter and oceanographic data collected on the eastside of Kodiak Island from 2001 to 2006 are used to demonstrate the analytical approach. In most years, dominant pelagic fish species are walleye pollock and capelin. These species exhibit niche partitioning in most years and patterns of habitat association are used to identify proxies for essential foraging habitats for capelin and pollock. The volume of suitable habitat for the western central Gulf of Alaska is estimated by applying these habitat definitions using GIS software. The role of habitat volume is compared to time trends in size at age and reproductive success to establish functional relationships between habitat volume and key life-history parameters. These estimates are incorporated into stock assessments to assess the influence of these factors on the resource.
An Independent Estimate of Natural Mortality for Atka Mackerel Using Tagging Data Susanne McDermott, James N. Ianelli, Sandra A. Lowe; AFSC, Seattle, WA
The importance of reliable natural mortality (M) estimates has long been recognized for stock assessments as applied for fisheries advice. M is often confounded with other parameters (e.g., selectivity and catchability), and tagging studies hold promise to avoid these problems. For Atka mackerel, Pleurogrammus monopterygius, assessments in Alaska, M estimates have been derived from life-history parameter correlates. Information outside the assessment is needed to configure appropriate prior distributions of M. Tagging data provide a means to estimate natural mortality independent of fishery or life history data. In this study a model of 3 years of tagging data from two distinct aggregations in the Aleutian Islands is proposed to estimate natural mortality. Preliminary results indicate that tagging data can provide supplemental information to stock assessments. However, more data are needed to validate assumptions from the tagging model (e.g., that the estimates reflect a long-term average for the population or apply only for the time period and areas considered in the study).
