Anadromy and the dispersal of an invasive fish species (Oncorhynchus mykiss) in Eastern Quebec, as revealed by otolith microchemistry

Rainbow trout (Oncorhynchus mykiss) is invading rivers bordering the St. Lawrence Estuary (Quebec, Canada). Some rivers in Eastern Quebec support self-sustaining populations while adult vagrants are frequently captured in rivers where no reproduction has been confirmed. We hypothesised that the development of anadromy has promoted the species dispersal. Otolith Sr:Ca analyses revealed that although all fish captured in the upstream stocking region were freshwater residents, both anadromous and freshwater resident phenotypes were found downstream in Eastern Quebec. The proportion of fish exhibiting the anadromous life cycle increased with the distance from the stocking zone. Eastern Quebec steelhead migrated to sea at the same age but at a larger size than steelhead within their native range. Age at first reproduction was similar to that observed in native populations. The development of the anadromous life cycle enables this species to colonise new rivers following long-distance migrations along the St. Lawrence Estuary corridor. I. Thibault, R. D. Hedger, J. J. Dodson, J.-C. Shiao, Y. Iizuka, W.-N. Tzeng Département de biologie, Québec-Océan, Université Laval, Québec, 1045 Avenue de la Médecine, Québec, Canada G1V 0A6, Norwegian Institute for Nature Research, NO-7485 Trondheim, Norway, Institute of Oceanography, College of Science, National Taiwan University, Taipei, Taiwan 106, ROC, Institute of Earth Sciences, Academia Sinica, 128, Section 2, Academia Road, Nankang, Taipei, Taiwan 115, ROC, Institute of Fisheries Science, College of Life Science, National Taiwan University, Taipei,