MEPS 359:239-248 (2008)  -  DOI: https://doi.org/10.3354/meps07349

ABSTRACT: Migrations and home range shifts by adult blue cod Parapercis colias provide an important means of dispersal among resident subpopulations within the Doubtful–Thompson Sound complex, a fjord system in southwestern New Zealand. In the present study we used stable isotope analysis (δ¹³C and δ¹⁵N) to investigate regional differences in the carbon sources for, and likely migration patterns among, subpopulations of P. colias. We found consistent differences in δ¹³C and δ¹⁵N of blood and muscle collected from outer coast (mean ± SE: blood, δ¹³C = –18.4 ± 0.2, δ¹⁵N = 11.5 ± 0.2; muscle, δ¹³C = –17.9 ± 0.1, δ¹⁵N = 13.0 ± 0.1) and inner fjord (mean ± SE: blood, δ¹³C = –19.9 ± 0.5, δ¹⁵N = 9.5 ± 0.3; muscle, δ¹³C = –19.3 ± 0.4, δ¹⁵N = 11.6 ± 0.2) locations, likely reflecting long-term (>1 yr) residency. Inner fjord fish had evidence of significant input of recycled carbon from chemoautotrophic bacteria. On the outer coast, δ¹⁵N and δ¹³C reflected a diet likely supported primarily by new production from macroalgae and phytoplankton. To provide information on isotopic turnover rate of blood and muscle we translocated fish from the outer coast to an inner fjord site and measured change in δ¹⁵N and δ¹³C after 160 d. These data showed a depletion of ¹³C and ¹⁵N with shift in habitat and provided a basis for classifying likely migrants (<160 d) to each study site. The conclusion that populations of blue cod within Doubtful Sound are made up of long-term residents with some subsidy from the outer coast has implications for the efficacy of 2 newly established marine reserves in Doubtful Sound and others in Fiordland.

KEY WORDS: Stable isotopes · Metapopulation · Connectivity · Diet · Isotopic turnover · Temperate reef fish