Assessing the reproductive contributions of sympatric anadromous and freshwater-resident brook trout

Abstract

The δ13C, δ15N and δ34S isotope values of newly emerged, brook trout Salvelinus fontinalis alevins (free-swimming individuals beginning exogenous feeding) were examined to determine if progeny of anadromous female spawners could be detected and their contributions to reproduction assessed in river systems with mixed migration strategies. Separation of anadromous and freshwater resident and immigrant sources of progeny could be detected primarily using δ13C values before alevins reached a size of 28 mm fork length and c. 20 days after exogenous feeding began. Among 10 populations, the contributions of anadromous females ranged from 0 to 42% of newly emerged alevins. Correlations between anadromous contributions and estimates of total brook trout density and alevin production were unexpectedly negative. © 2005 The Fisheries Society of the British Isles.