Age Determination Manual of the Alaska Fisheries Science Center Age and Growth Program
At the NOAA Fisheries Alaska Fisheries Science Center (AFSC), fish age data, including catch-at-age data collected from commercial fisheries and population age compositions estimated from scientific bottom trawl surveys, are used to develop age-structured stock assessment models. These models evaluate the overall health of fish populations and guide fishery managers in setting sustainable catch limits.
Age data can provide considerable insight into fish population dynamics. Age determination is particularly important for marine fishes because they are often difficult to census at every life cycle stage. The Age and Growth Program at the Alaska Fisheries Science Center is tasked with providing age data in order to improve the basic understanding of the ecology and fisheries dynamics of Alaskan fish species. The primary focus of the Age and Growth Program is to estimate ages from otoliths and other calcified structures for age-structured modeling of commercially exploited stocks; however, the program has recently expanded its interests to include numerous studies on topics ranging from age estimate validation to the growth and lifehistory of non-target species. Because so many applications rely upon age data and particularly upon assurances as to their accuracy and precision, the Age and Growth Program has developed this practical guide to document the age determination of key groundfish species from Alaskan waters. The main objective of this manual is to describe techniques specific to the age determination of commercially and ecologically important species studied by the Age and Growth Program. The manual also provides general background information on otolith morphology, dissection, and preparation, as well as descriptions of methods used to measure precision and accuracy of age estimates. This manual is intended not only as a reference for age readers at the AFSC and other laboratories, but also to give insight into the quality of age estimates to scientists who routinely use such data.