Spawning Interactions of Hatchery and Naturalized Anadromous Form Rainbow Trout211 'Oncorhynchus mykiss' in a Lake Superior Tributary

摘要

Two strains of rainbow trout Oncorhynchus mykiss are managed in the Minnesota211u001ewaters of Lake Superior. Abundance of the naturalized and self-sustaining 211u001esteelhead strain has declined since a hatchery strain called kamloops was 211u001eintroduced in the 1970s. There are several possible causes for the decline, but 211u001ehybridization of the two strains is suspected of contributing to the steelhead 211u001edecline. Forty-six steelhead and kamloops spawners with strain specific 211u001ehomozygous alleles at the IDH-2 locus were radio tagged and stocked into a 1,200 211u001em study reach to observe movements to spawning areas, observe spawning 211u001einteractions, and to measure juvenile production and survival. Spawners of both 211u001estrains distributed in the reach and most spawners remained in the study reach 211u001elong enough to spawn. Young-of-the-year (YOY) densities were low in the fall when 211u001e44 hybrid and 13 pure strain steelhead YOY were captured. Seven hybrids and six 211u001esteelhead were captured one year later. It was not possible to determine how many 211u001espawning pairs produced the captured hybrids; thus the apparent difference in 211u001eoverwinter survival may have been a parental effect and not a strain effect. We 211u001enow know that viable hybrids can be produced in the wild and that they can 211u001esurvive North Shore stream winters. If appropriate non-lethal genetic markers can 211u001ebe identified, additional work is needed to measure juvenile kamloops and hybrid 211u001esurvival in the wild, the extent of past hybridization, and the practicality of 211u001egenetically rehabilitating the steelhead stock.