Evaluation of Otolith Microchemistry for Identifying Natal Origin of Anadromous River Herring in Connecticut

Abstract

AbstractOver the past two decades, declines in the populations of river herring (alewife Alosa pseudoharengus and blueback herring Alosa aestivalis) have been documented across both species’ ranges. Information concerning the natal origins of spawning adult fish could aid in their restoration but has been unattainable. We investigated the efficacy of otolith microchemistry for identifying the natal environment of alewife and blueback herring in Connecticut. In both 2008 and 2009, water and juvenile and adult fish were sampled from 10 sites across the state. The relationships between water and otolith Sr:Ca ratios differed for alewives and blueback herring, necessitating the development of separate classification models for assigning individuals to capture locations. Reclassification of age‐0 alewives to their site of origin was variable (50–100%) but demonstrated that age‐0 fish could be accurately reclassified to their natal environment at some sites. Discriminant function reclassification rates to site of capture for adult alewives varied greatly (10–85%); the similarity of water chemical signatures among many sites likely contributed to the relatively low rates of assignment to the majority of collection locations. Adult blueback herring reclassification rates were low (15–33%) for three of four collection sites, probably due to overlapping elemental signatures. Blueback herring collected at the fourth site had a distinct signature and a reclassification rate (81%) comparable to that of the highest alewife rate. Changes in Sr:Ca and Ba:Ca ratios across sectioned otoliths suggested a higher degree of movement across salinity boundaries during the first year of life than previously documented for anadromous alewives and blueback herring. Otolith microchemistry may be a useful tool with which to investigate alewife and blueback herring natal homing and life history, but its utility appears to be confined to particular sites with unique signatures or to broader regional assignments of natal origin.Received March 18, 2011; accepted August 23, 2011