Comparing naturally occurring stable isotopes of nitrogen, carbon, and strontium as markers for the rearing locations of Atlantic salmon (Salmo salar)
Abstract
<jats:p> 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 (δ<jats:sup>15</jats:sup>N and δ<jats:sup>13</jats:sup>C in muscle and scales and <jats:sup>87</jats:sup>Sr/<jats:sup>86</jats:sup>Sr 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 δ<jats:sup>13</jats:sup>C varied more than δ<jats:sup>15</jats:sup>N or <jats:sup>87</jats:sup>Sr/<jats:sup>86</jats:sup>Sr. 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 δ<jats:sup>15</jats:sup>N values successfully differentiated fish from tributaries with differences in land use (e.g., agricultural versus forested; ≈ 33% of sites); the δ<jats:sup>13</jats:sup>C 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%). </jats:p>
