Habitat variation and invasive species as factors influencing the distribution of native fishes in the lower Fraser River Valley, British Columbia, with an emphasis on brassy minnow (Hybognathus hankinsoni)

Abstract

Brassy minnow (Hybognathus hankinsoni Hubbs, 1929) have disjunct distributions in western Canada, making them a species of conservation concern. We assessed changes in the distribution of invasive species as factors influencing the distribution of brassy minnow and other native species by comparing historical and current distributions in the lower Fraser River in British Columbia. We tested effects of physical habitat parameters on local distributions of brassy minnow and for evidence of negative interactions between brassy minnow and invasive brown bullhead (Ameiurus nebulosus (Lesueur, 1819)). Comparison of contemporary and historical (1956 and 1959) fish distributions indicated significant declines in native cypriniform (minnows and suckers) species, including brassy minnow, but no change in the number of invasive species, although there was some faunal turnover. Logistic regression suggested that conductivity, turbidity, and water temperature were important predictors of brassy minnow presence. Appearances of adult-sized brown bullhead at one site corresponded with reduced abundance of native fishes. In growth experiments with brassy minnow, brown bullhead, and redside shiner (Richardsonius balteatus (Richardson, 1836)), brassy minnow exhibited mass loss and mortalities, suggesting that they were poor competitors. Our results contribute to a better understanding of abiotic and biotic factors affecting distribution and persistence of brassy minnow.