Low genetic variability in lake populations of brook trout (Salvelinus fontinalis): A consequence of exploitation?

Abstract

Previous studies have found lower levels ofgenetic variation in lake than streampopulations of brook trout (Salvelinusfontinalis). We test the generality of thisobservation by examining whether brook troutgenetic variation at 10 allozyme loci differedwithin and among 9 pairs of lake and adjacentstream populations. With one exception, wefound that lake populations had lowerheterozygosity than their adjacent streampopulations. Although the lakes in this studyare small and some have had documented fishmortality events, no association was foundbetween lake size characteristics and thedegree of difference in heterozygosity betweenlakes and their adjacent stream populations. There were, however, negative associationsbetween metrics of fishing mortality and thedifference in heterozygosity between lakes andtheir adjacent stream populations. Thegreater the estimated fishing pressure onlake-dwelling trout, the greater the reductionin heterozygosity in those populationsrelative to their adjacent stream populations. We interpret our findings to suggest thatintensive fishing pressure can significantlyreduce genetic variation. Managers shouldtherefore prevent human-induced mortality atany indication of a large natural mortalityevent to allow populations to increase in sizeas rapidly as possible following a decline.