Recruitment Energetics and Coastal Assessment

Recruitment Energetics

Arctic cod and isopods from nearshore trawl.

Recruiting fish are those individuals that have successfully navigated the environmental factors that their limit survival to adulthood. In order to identify how well juveniles are navigating those factors, we relate their nutritional status to their developmental state and environmental conditions. The different developmental stages of juvenile fish are associated with different life history demands. The ecological dependencies of larvae differ from those of metamorphosed young-of-the-year. Successful recruitment requires fish to acquire sufficient energy to satisfy the competing life-history demands of development, growth and energy storage. We employ a variety of measures of nutritional status so we can relate each of the different developmental phases to their potential survival. These measures include fish diets, fatty acid, lipid class, and proximate composition, thiamine content and RNA/DNA content.

Coastal Assessment

It is not enough to know how well fish are performing in their environment. We also need to characterize their abundance, distribution and the habitats we find them in. We participate in and conduct surveys aimed at different developmental stages and in different seasons to get this information. Surveys we conduct are focused on nearshore habitats that many fish species use to rear juveniles. We are developing novel techniques for mapping habitat and survey fish distributions in these habitats. This includes use of an autonomous sampler we are developing in conjunction with University partners.

Alaska presents a challenge for coastal assessments due to wide-ranging, regional differences from the Arctic to the Aleutian Islands, Gulf of Alaska, and inside waters of Prince William Sound and southeastern Alaska. Some of these areas are relatively pristine and largely unstudied requiring baseline studies and habitat mapping surveys. Other areas have had a major oil spill like the Exxon Valdez oil spill requiring an understanding of contaminants in the marine environment and long-term monitoring of impacted ecosystems. By combining expertise in recruitment, bioenergetics, and essential fish habitat the Recruitment Energetics & Coastal Assessment Program activities are relevant to agency needs on many levels including an ecosystem approach.

Research

Our research lab applies methods of analytical biochemistry to understand the structure and function of marine food webs. Our studies assess factors underlying energy allocation strategies and nutritional quality of forage species using lipid class and proximate analysis. We employ fatty acid analysis as a means of understanding patterns of energy flow in large marine ecosystems such as the Arctic, Bering Sea and Gulf of Alaska. Our analysis of energy phenology and trophic linkages is aimed at predicting the consequences of climate change on ecosystem functions.

Our work proceeds from the central idea that juvenile fish need to grow rapidly and store energy if they are to survive winter, which is a period of resource depletion. These needs are most acute for those organisms or life stages that depend directly on the annual production cycle particularly at high latitudes. The resulting seasonal flux in energy content of species has a profound influence on their recruitment and nutritional value to their predators. This bioenergetic approach allows us to understand how temperature and forage quality influence the productivity of high latitude marine ecosystems.

Robert Suryan, program manager, Recruitment, Energetics, and Coastal Assessment Program, Auke Bay Laboratories