FISHES

J.D. McPhail

INTRODUCTION

This chapter deals with the freshwater fishes of the Canadian Montane Cordilleran Ecozone (MCE). Ecozones are a terrestrial concept based on climate, topography, and plant communities. Although they are useful for cataloging terrestrial biodiversity, ecozones do not coincide with natural biogeographic units in fish. For freshwater fish, the appropriate units are drainage basins. This is because "fish gotta swim" --- they can't fly and they can't walk! Consequently, fish that are saltwater intolerant can only disperse between river systems if there is a drainage connection, and such connections are rare and usually ephemeral. As a result, dispersal in freshwater fishes is slow, and even within the same ecozone environmentally similar adjacent drainage basins typically exhibit some differences in their freshwater fish faunas. Thus, the dominant factors governing species composition in the fish assemblages of the Canadian Montane Cordilleran Ecozone are the pattern and timing of postglacial drainage connections between major river basins. This does not mean that fish are insensitive to climate and topography. On the contrary, water quality, temperature, gradient and biotic interactions strongly influence the distribution of freshwater fish; however, these factors usually organize assemblages within, rather than among, drainage basins.

Seven major river systems originate in the Canadian Montane Cordilleran Ecozone. On the east flank of the Rocky Mountains tributaries of both the North and South Saskatchewan rivers rise in the MCE and flow eastward to eventually drain into Hudson Bay by way of the Nelson River. Other east-flowing rivers also rise on the east flank of the Rocky Mountains in the MCE, but are part of the Mackenzie drainage system and eventually flow into the Arctic Ocean. The major west-flowing rivers rising in the MCE are the Columbia, Fraser, Skeena, Nass, and Stikine rivers. The entire upper Columbia system, and the upper and middle (but not the lower) sections of the Fraser system, fall within this ecozone. In the northwest, however, this ecozone includes only the headwater sections of the upper Skeena, upper Nass, and upper Stikine rivers.