Native Fishes

With 27 native species, 9 of which are endemic to the Columbia system, the fish native to the Columbia Basin form one of the most distinct freshwater fish faunas in North America (McPhail and Carveth 1994). The endemic fish assemblage housed in the Columbia Basin sets apart the entire freshwater fish fauna of British Columbia from that of the rest of Canada east of the Rocky Mountain Divide.

The amount of biodiversity housed within the unique faunal assemblage of the Columbia Basin is easily underestimated if one merely counts the number of fish species present. A great wealth of selected variability exists below the species level that is often underappreciated by species list-makers. The Columbia system contains unique types of Kokanee, whitefish, sculpins, dace, suckers, sturgeon, Rainbow Trout and Cutthroat Trout. Many of these ecotypes are locally adapted varieties that have become isolated from other reproductive groups by the mountainous terrain and glacial history that is characteristic of the Columbia Basin. Much of the diversity below the species level is represented by phenotypic differences like those of Longnose Suckers (Catostomus catostomus), Umatilla Dace (Rhinichthys umatilla) and Torrent Sculpins (Cottus rhotheus) isolated by waterfalls and other fish-proof barriers. Ecological variation is more pronounced in species like Longnose Dace (Rhinichthys cataractae), Mountain Whitefish (Prosopium williamsoni) and Kokanee (Onchorhynchus nerka).

These and other native, locally adapted fish species display a wide variety of reproductive and foraging behaviours that are dependent on seasonal variations in photoperiod and water flow regimes for continued maintenance over time.

Although large-scale water impoundment is nothing new, the anthropogenic change associated with it, including the introduction of non-native species, has impacted the native fish fauna of the Columbia Basin. Many native riverine fish assemblages in North America have been adversely affected by habitat modifications that are a direct and an indirect result of large-scale water impoundment during the 20th C.

The Columbia River and its tributaries were obvious candidates for flood control and hydro-electric development as western North America became populated through the 20th C. Impoundment of the Columbia River and its tributaries began in 1933 with the construction of the Rock Island dam south of Wenatchee, Washington and a flurry of impoundment construction continued in both the United States and Canada until 1985 when the Revelstoke dam was completed.

The direct effects of anthropogenically induced impoundment on native fish populations are obvious -- fish require water to survive and fare best in natural environments to which they have become locally adapted -- dams impede migration passage, disrupt natural flow regimes, alter water quality and convert complex riverine habitats into slow moving reservoirs (Brett 1957). Currently we find that migratory wild Chinook Salmon (Oncorhynchus tshawytscha) -- a species that historically migrated over 1900 km to spawn in the upper Columbia -- are extirpated from the Canadian portion of the Columbia Basin. Migratory Sockeye Salmon (Oncorhynchus nerka) populations are following the same fate as Columbia Chinook Salmon with populations so dangerously low that only a few individuals survive the long natal return migrations to the Okanagan River below Vaseau Lake.

The indirect effects of impoundment and non-native fish introductions to native fish populations can be complex. The introduction of exotic species (both fish and macroinvertebrates) into impounded waters has visibly altered the native fish communities in the Columbia Basin, and there are some drainages where the numbers of exotic species currently exceed the native fauna.