Stable isotope (δ13C and δ18O) and Sr/Ca composition of otoliths as proxies for environmental salinity experienced by an estuarine fish

The ability to identify past patterns of salinity habitat use in coastal fishes is viewed as a critical development in evaluating nursery habitats and their role in population dynamics. The utility of otolith tracers (δ13C, δ18O, and Sr/Ca) as proxies for environmental salinity was tested for the estuarine-dependent juvenile white perch Morone americana. Analysis of water samples revealed a positive relationship between the salinity gradient and δ18O, δ13C, and Sr/Ca values of water in the Patuxent River estuary. Similarly, analysis of otolith material from young-of-the-year white perch (2001, 2004, 2005) revealed a positive relationship between salinity and otolith δ13C, δ18O, and Sr/Ca values. In classifying fish to their known salinity habitat, δ18O and Sr/Ca were moderately accurate tracers (53 to 79% and 75% correct classification, respectively), and δ13C provided near complete discrimination between habitats (93 to 100% correct classification). Further, δ13C exhibited the lowest inter-annual variability and the largest range of response across salinity habitats. Thus, across estuaries, it is expected that resolution and reliability of salinity histories of juvenile white perch will be improved through the application of stable isotopes as tracers of salinity history.