The genetic effect of stocking and population structure of brook trout (Salvelinus fontinalis) in the Beef River
The management of trout populations in streams often includes stocking hatchery-reared fish to supplement natural reproduction. Due to artificial selective pressures, hatchery populations may vary genetically from wild fish. In the relatively stable hatchery environment, the conditions are conducive to rapid genetic shifts which may be preserved for future use in the form of brood stock. The hypothesis of this study is that stocking has an impact upon the genetic makeup of the wild populations of trout. By examining commonly accepted genetic traits in the hatchery trout and different subpopulations of wild trout, an assessment was made concerning the impact of stocking upon the genetics of the wild trout. Trout were collected from seven stream sections in the North and South Fork of the Beef River and from the St. Croix State Fish Hatchery. Whole eye and liver samples were analyzed for six enzymes using starch gel electrophoresis. Genetic polymorphism was seen in four of the six enzyme systems examined. Distinct genetic divergence between stream sections identified local populations of trout within the North and South Fork of the Beef River. Differences in natural selective pressures, associated with location between and within the drainage basin, may account for the genetic variation in the wild trout. Homogeneity between stream sections stocked for 22 years and stream sections stocked for 3 years may be due to the effects of migration. The St. Croix Hatchery fish represent a genetically distinct population in comparison to the genetics of the wild trout. No interbreeding between hatchery trout and wild trout was evident, but a behavioral/ecological interaction may account for the genetic divergence in heavily stocked stream sections. The interaction was identified by an increase in heterozygous individuals in heavily stocked stream sections. The increase in heterozygotes was not in excess of Hardy-Weinburg equilibrium, but indicated a trend in heterozygosity. The possibility exists of managing trout on a stream section to stream section basis. Stream improvement. particularly in stream sections designated as stocking sections, would decrease migration by increasing the environmental heterogeneity. Evidence for genetic divergence between the St. Croix Hatchery trout and the wild trout signifies a need for the preservation of native gene pools in the Beef River.
Fish stocking -- Wisconsin -- Beef River
Beef River (Wis.)