7226 - Laserfiche WebLink

Home Browse Search

~5 m t~~ Son l s ~z ~~d ~ ~~-~~ to ~ ~ ~~ SLOW GROWTH OF COLORADO SQUALJFISH IN THE UPPER BASIN AND ITS EFFECT ON RECOVERY Lynn R. Kaeding United States Fish and Wildlife Service Colorado River Fishery Project 529 25-1/2 Road Grand Junction, Colorado 81505 Douglas B. Osmundson Utah Cooperative Fish and Wildlife Research Unit Utah State University Logan, Utah 84321 INTRODUCTION Colorado squawfish (Ptychocheilus lucius) was formerly widespread and abundant in the large rivers and major tributaries of the Colorado River basin (Jordan 1891, Evermann and Rutter 1895, Gilbert and Scofield 1898, Jordan and Evermann 1896). The principal native piscavore of the basin, Colorado squawfish occur today only in upstream regions of former range (Figure 1) and are threatened with extirpation (Seethaler 1978, Holden and Wick 1982, Tyus et al. 1982). For populations of widely distributed species, the high latitude and elevation at such limits of range can result in a relatively short growing season. Fish in' these populations often grow much slower than the potential for the species (cf. Nikolsky 1963, Weatherley 1972). We will show that this effect is especially profound for Colorado squawfish. We then discuss how life at the upstream limits of range affects both the ability of the Colorado squawfish population to increase and our efforts to recover populations of this endangered species in its remaining habitat. GROWTH OF COLORADO SQUAWFISH Earlier workers described growth of Colorado squawfish in the upper basin but gave no indication that they considered it unusually slow (Vanicek and Kramer 1969, Seethaler 1978). However, to us it seemed unusual because it was inconsistent with piscavore evolutionary theory. Piscavores like northern pike (Esox lucius) and largemouth bass (Micropterus salmoides)--in marked contrast with Colorado squawfish--show rapid growth (Figure 2). It is believed such rapid growth evolved as a mechanism to increase survival, allowing piscavores to use a wider variety of smaller prey as well as reducing the period when they themselves are prey -108-