Understanding Juvenile River Herring Movements with Otolith Microchemistry

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 7 fish collection sites) throughout the Hudson River and Long Island watersheds on multiple dates from July through October 2009. Aqueous concentrations of Ca, Mn, Ba, Sr, Pb, and Rb, and δ¹⁸O, δ²H, and ^87:86Sr isotopic ratios 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 it is possible to separate origins within these water bodies, using otolith chemistries that should reflect water chemistry. Sagittal otoliths were removed, daily ages determined, and analyzed for the same suite of elements and isotopes as water samples. Fish are assigned by multivariate methods to different nursery habitats within the Hudson River and Long Island estuaries. Within Long Island, some juveniles make forays into marine environments and then return inland; these behaviors are documented by changes in elements associated with movement among salinity gradients.