Variation in Freshwater and Estuary Use By Blueback Herring during the First Year of Growth

Understanding the location and duration of habitat use by young fish is critical to management efforts since recruitment to spawning age is vital to population sustainability. Seven spawning runs of Blueback herring in five river systems along the coast of Maine, USA, were the focus of this study. Otolith microchemistry and ambient water concentrations of Ca, Ba, Mn and Sr were used to identify habitat use in the first year by 131 returning adult fish collected in 2010 and 2012. Total area of available habitats ranged from approximately 213 to 6053 ha freshwater and 204 to 3395 ha estuary. Ambient Sr:Ca ratios were correlated with  salinity and were  used as primary indicators of habitat use. Seaward migration was inferred by rapid changes in elemental concentrations in otoliths. Results showed variable individual migration histories with several discrete migratory patterns; some fish migrated into seawater well before the end of the first year, while the majority exhibited longer residency in freshwater/low salinity habitat. Extent of freshwater habitat was positively correlated with freshwater/low salinity residency(r = 0.37, P < 0.001).These results emphasize the importance of maintaining variation in life histories by conserving a variety of habitat types to ensure survival of the species.