Spatial structure and movement of blue cod Parapercis colias in Soubtful Sound, New Zealand, inferred from δ13C and Δ 15N

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. © Inter-Research 2008.