Proportions of native and introduced brown trout in adjacent fished and unfished Spanish rivers

Evidence of different degrees of genetic interactions of exogenous hatchery fish with native populations was electrophoretically obtained from collections of brown trout from four heavily fished areas and eight adjacent protected and unfished areas in northeastern Spain. Although some degree of hybridization or introgression was detected in each collection based on fixed differences between hatchery and native fish at the LDH-C* locus and less distinct differences were found at three other loci (sMDH-A2*,IDHP-2*, IDHP-3*), fished populations had significantly lower levels of hatchery genes than protected ones. The greater persistence of native fish in areas that were fished and stocked appeared to reflect a greater susceptibility of hatchery-reared fish to angling. Although it remains uncertain whether this difference is innate or a reflection of hatchery rearing, stocking was ineffective in enhancing the recipient population in the exploited liver. these data suggest that different strategies may be needed for protection of native populations in fished and protected areas and that more intense measures may be required in the latter instance.