Distribution of Fishes in Tributaries of the Lower Columbia River

Reimers, Paul; Bond, Carl

Freshwater fishes of the lower 96 miles of the Columbia River include eight families and 29 species, but only three families and seven species are primary. The peripheral family Cottidae reaches great development in the absence of a more extensive primary fauna. Seven of the 12 species of Cottus known from the basin occur in the lower tributaries as the most widespread species. Cottus rhotheus occurred at the most sampling sites, while C. beldingii showed the most restricted distribution. The distributions of C. perplexus and C. gulosus possessed interesting exclusions and overlaps suggesting keen competition. C. confusus was found only in streams with low summer temperatures. Of the seven primary species invading the lower Columbia River, five reach downstream to the influence of salt water. Only Mylocheilus caurinus and Catostomus macrocheilus are known to reside in brackish water. Richardsonius balteatus and Rhinichthys osculus are more typically inland forms as they were generally scarce in the study area, and not found below the Cowlitz River. The relationships of the distributions of fishes in the lower Columbia River and the north coastal streams of Oregon suggests that C. macrocheilus entered the latter area through stream capture of an old Columbia River tributary by the upper Nehalem River. C. rhotheus may have taken advantage of several routes. Why M. caurinus has not reached this area from the Columbia River mouth is difficult to understand. Dispersal routes between the Columbia River and the Puget Sound drainage and coastal drainages of Washington are discussed, but are difficult to assess because of the several possibilities for entry.

Distribution of Fishes in Tributaries of the Lower Columbia River

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