Migration and habitat use patterns by age 0 striped bass in the Patuxent River estuary, Maryland, USA

Partial migration, the existence of resident and migratory population contingents, is well known for Chesapeake Bay striped bass Morone saxatilis; however, migratory behavior prior to recruitment as juveniles remains unknown.  In this study, we investigated whether resident and migratory contingents occurred during the first year of life as occurs for the congeneric white perch Morone americana.  We collected age 0 juveniles from three salinity regions (<1.0‰, 1.0–14.0‰,  and  >14.0‰) in October 2009.  Samples (n=30) were stratified by region and size class.  Using otolith microanalysis of Sr:Ca (mmol·mol^-1), lifetime profiles of habitat use in freshwater and brackish water were constructed. As previously determined for white perch, ratios <2.00 indicated time spent primarily in freshwater, while those >2.00 indicated time spent primarily in brackish water.  Profiles differed from those previously described for white perch, which displayed distinct fresh and brackish water contingents.  Otolith Sr:Ca profiles indicated that after an initial freshwater larval phase,  all striped bass juveniles migrated to brackish water.  Thereafter a portion reinvaded freshwater habitats prior to capture in October.  This partial behavior suggests that contingent structure may not be established during the first year of life in striped bass as occurs for white perch and other anadromous species.