Alien Trout in British Columbia

No one complains about having ring-necked pheasants or California quail around, and few mind seeing introduced Rocky Mountain Bighorn Sheep in the range of native California Bighorn Sheep, but sometimes the introduction of exotic species has unintended consequences. They can prey on, compete with or parasitize native species; contaminate their genome by hybridizing; and spread diseases to which native species have no immunity. Ecological catastrophes due to invasive aliens are legendary: Indian mongoose (Herpestes auropunctatus), rats (Rattus spp.) and cane toads (Bufo marinus) in Hawaii, European rabbits (Oryctolagus cuniculus) in Argentina and Australia, and so on. Of the 18 exotic fish province-wide, 16 (37% of all fish species) occur in the Columbia River basin. This is a higher proportion of introduced species than in any other river system in British Columbia. They include eastern brook trout (Salvelinus fontinalis), brown trout (Salmo trutta), lake trout (Salvelinus namaycush), broad whitefish (Coregonus nasus), carp (Cyprinus carpio), goldfish (Carassius auratus), tench (Tinca tinca), brown catfish (bullhead: Ictalurus nebulosus), black catfish (bullhead: Ictalurus melas), pumpkin seed (Lepomis gibbosus), black crappie (Pomoxis nigromaculatus), largemouth bass (Micropterus salmoides), smallmouth bass (Micropterus dolomieui), yellow perch (Perca flavescens) and walleye (Stizostedion vitreum). Most introductions in British Columbia have been accidental, but a distressingly high number were purposeful. For example, the introductions of Gerrard rainbow trout into upper Arrow Lake has combined with the exotic mysids and nutrient starvation as well as migration blockage to virtually (possibly completely) exterminate the yellowfin rainbow. Eastern brook trout have invaded and displaced native trout, including the endangered westslope cutthroat trout. Widespread stocking of non-native stocks of rainbow trout has displaced no one knows how many native rainbow trout stocks, and has polluted the westslope cutthroat trout genome by introgressive hybridization. At best, exotic species change biological communities and endangers native species. At worst, they can endanger whole ecosystems.