Identification of anadromous and nonanadromous adult brook trout and theirprogeny in the Tabusintac River, New Brunswick, by means of multiple-stable-isotope analysis

Multiple-stable-isotope analysis was used to infer anadromous and nonanadro mous origins of adult brook trout Salvelinus fontinalis and maternal migrat ion history of age-0 progeny in the Tabusintac River, New Brunswick. Forty- seven adults collected above head of tide displayed deviations (delta) from standard ratios of C-13/C-12, N-15/N-14, and S-34/S-32 of -30.3 parts per thousand to -16.0 parts per thousand, 7.4 parts per thousand to 16.8 parts per thousand, and 1.5 parts per thousand to 14.1 parts per thousand, respec tively; higher values (positive or less negative) denote relatively greater enrichment in the heavier isotope. Isotopically enriched brook trout exhib ited isotope profiles typical of fish from marine environments, and those t hat were isotopically depleted were considered to be of freshwater origin. Age-0 brook trout from Home Camp Pool, the most downstream freshwater reari ng site sampled, were more enriched (delta(13)C = -24.4 +/- 2.7 parts per t housand (mean +/- SD), delta(15)N = 12.5 +/- 3.1 parts per thousand, and de lta(34)S = 7.4 +/- 1.8 parts per thousand) than those at two other sites, a nd were believed to be progeny of anadromous females. Age-0 brook trout fro m the Bathurst Highway site (delta(13)C = -27.9 +/- 0.6 parts per thousand, delta(15)N = 8.9 +/-: 0.8 parts per thousand, and delta(34)S = 5.8 +/- 0.8 parts per thousand) and the Little Eskedelloc River (delta(13)C = -28.6 +/ - 0.5 parts per thousand, delta(15)N = 8.1 +/- 0.4 parts per thousand and d elta(34)S = 2.9 +/- 0.8 parts per thousand), with less isotopic enrichment, were most likely from nonanadromous parents. Stable-isotope ratios varied with fork length; at Home Camp Pool, this relationship was thought to repre sent an "isotope dilution factor" as recently emerged juveniles assimilated new food from freshwater, grew, and masked the marine signatures of their maternal parents. This study suggests that stable-isotope ratios may be use d to distinguish between sympatric anadromous and nonanadromous adult brook trout and their progeny as long as brook trout are collected before they d ilute their maternal isotope signatures.