Determination of river herring natal origin by otolith microchemical markers

Young-of-year (YOY) river herring (i.e., alewives, Alosa pseudoharengus, and blueback herring, A. aestivalis) and water samples were collected from multiple sites (17 water sampling sites and 8 fish collection sites) throughout the Hudson River and Long Island watersheds on multiple dates from July through September 2009. Fish were measured and the sagittal otoliths were removed for aging and microchemical analysis. Concentrations of Ca, Mg, Mn, Pb, Ba, Rb, Sr, δ¹⁸O, and δ²H were determined for the water samples. All fish were measured to compare size ranges among sampling locations and dates. Preliminary findings show good separation of water chemistries from Long Island, the Hudson River mainstem, and its major tributaries including the Mohawk River, where blueback herring spawn and rear. This suggests that it will be possible to separate origins within these water bodies, using otolith chemistries that should reflect water chemistry. Finally, YOY alewives from Long Island watersheds were markedly larger than YOY Alosa spp. from the Hudson River watershed, due either to earlier spawning, higher growth rates, or both factors. The results of aging as well as otolith microchemical analyses will also be presented.