ABSTRACT: Comparing naturally occurring stable isotopes of nitrogen, carbon and strontium as markers for juvenile salmon rearing locations

We compared the success of using naturally occurring stable isotopes of N, C, and Sr as markers for the rearing locations of juvenile salmon. We analyzed the isotopic signatures (?15N and ?13C in muscle and scales and 87Sr/86Sr in otoliths) of >200 juvenile Atlantic salmon (Salmo salar) from 12 tributaries of the Connecticut River, USA. Young salmon had distinct N and C signatures 5 weeks after stocking. Signatures were stable over the summer although ?13C varied more than ?15N or 87Sr/86Sr. Scale and muscle signatures were highly correlated, demonstrating the feasibility of nonlethal sampling using fish scales. Some C (but not N) signature from the hatchery was retained in scales of 3-month-old fish, implicating scale annuli as a repository for past C signatures. The ?15N values successfully differentiated fish from tributaries with differences in land use (e.g., agricultural versus forested; ? 33% of sites); the ?13C values differentiated fish from 45% of sites. Based upon a discriminant-function analysis, group membership of individuals was correctly predicted in 44.3% (74 of 167) of cases for which both N and C were analyzed. In combination, N and C isotopes differentiated 73% of study sites, which was close to the success of Sr isotopes in the same system (83%).

Kennedy BP, Nislow KH, Blum J, Chamberlain CP, and Folt CL. Comparing naturally occurring stable isotopes of nitrogen, carbon and strontium as markers for juvenile salmon rearing locations. Canadian Journal of Fisheries and Aquatic Sciences 62(1):48-57, 2005.