Determination of River Herring Natal Origin using Otolith Chemical Markers: Accuracy as a Function of Spatial Scale and Choice of Markers

We investigated the spatial and temporal accuracy of otolith chemistry for distinguishing populations (and subpopulations) of anadromous river herring (Alewife Alosa pseudoharengus and Blueback Herring A. aestivalis ) from New York watersheds. Water chemistry of selected analytes (Sr:Ca, Ba:Ca, 87:86 Sr, and δ 18 O) differed spatially and interannually among sites within the Hudson River as well as between the Hudson River and Long Island estuaries. Otolith chemical markers for juvenile river herring differed significantly among all sampling sites, with combined elemental and isotopic ratios differing significantly between species and between years, although the effect of year did not influence assignments at broad spatial scales (i.e., 10 5 m). Adult river herring collected in the Hudson River were assigned to natal sites using all juvenile otolith markers except δ 18 O, which had methodological problems. Adult Alewives and Blueback Herring were classified to Hudson River populations at 73% and 42%, respectively. Inclusion of δ 18 O in the assignment model likely would have increased the percentage of adults assigned to the Hudson River, as juvenile reclassification accuracies were lower without δ 18 O and oxygen isotopes are strongly correlated with latitude. Otolith chemistry matched our geochemical atlas of water and distinguished among populations and subpopulations at a range of spatial scales. However, rates of reclassification are dependent on the markers included and the geographic distances among groups. Received March 31, 2014; accepted July 16, 2014