Retrospective Determination of Atlantic Croaker Migration through Laser-Beamed Elemental Analysis of Otoliths

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9416579 Jones Year to year variations in the number of fish which survive the first year of life (termed recruitment or yearclass strength) are often sufficient to control the success or failure of the fishery a few years later. Despite the scientific and economic benefits which would result if yearclass strength could be estimated before fish reached a marketable size, recruitment prediction has proved to be an elusive goal. Likely mechanisms contributing to year-to-year variations in the yearclass strength of Atlantic croaker include variations in the location and timing of spawning, the age and date of subsequent advection to the estuarine nursery area, the duration and relative growth rate while in the estuary, and the age and date of migration out of the estuary as an adult. In conjunction with age-structured measures of growth and survival based on otolith daily growth rings, these hypotheses can be testes using a new laser-based elemental analysis technique (LA-ICPMS) to retroactively determine the hatching site and estimate the age and date of subsequent migrations in individual fish. The technique is based on the a cellular nature of the fish otolith (earstone), which forms through the concentric daily additions of mineralized tissue around a central nucleus. Given the fact that the elemental composition of a given daily ring reflects the elemental composition of the otolith at the appropriate daily increment. By corollary, water mass differences at the time and place of hatching will be reflected in elemental composition differences in the otolith nucleus. Previous work confirmed the analytic potential of LA-ICPMS and provided the first demonstration that otolith elemental composition does indeed reflect characteristics of the ambient water. The strength of the current project lies in the refinement of this approach, and its application in a field study using sample sizes well above that of any other study of this type (1200 otoliths). Su ccessful completion of this project has implications not only for recruitment of Atlantic croaker, but for studies of recruitment, stock structure, migration and fisheries management around the world. ***