Can anglers influence the abundance of native and nonnative salmonids in a stream from the Canadian Rocky Mountains?

The proliferation of normative fishes throughout North America is a major concern for fisheries managers. In this paper, we evaluate the efficacy of selective harvest in reducing normative brook trout Salvelinus fontinalis and restoring native cutthroat trout Oncorhynchus clarki and bull trout S. confluentus populations in a small stream in the Canadian Rocky Mountains. From 1998 through 2000, groups of anglers have been involved in an organized program to selectively harvest brook trout from Quirk Creek, Alberta. Annual population estimates conducted by electrofishing indicate that selective harvest has had little effect on the brook trout population. Bayesian estimates of species catchability (i.e., proportion of vulnerable population caught per unit of angling effort) differed significantly between native and normative species, the catchability of native species being 2.5-fold greater than that for nonnatives. Using population models, we show that the lower catchability of brook trout coupled with their fast growth and early maturity make them resilient to angling exploitation. Higher catchability, slower growth, and later maturity of the native species make them extremely sensitive to overexploitation. Furthermore, the increased angling effort associated with a brook trout suppression program may be accompanied by sufficient incidental mortalities of native species as to prevent their recovery or lead to further declines. We conclude that the use of selective harvest to reduce normative brook trout populations in western North America requires further study before being accepted as an effective method.