7785

• UCREFRP Catalog Number: 7785
• Author: Thompson, J. M.
• Title: The Role of Size, Condition, and Lipid Content in the Overwinter Survival of Age-0 Colorado Squawfish.
• USFW Year: 1989.
• USFW - Doc Type: Colorado State University,
• Copyright Material: NO

I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I

INTRODUCTION

The endangered Colorado squawfish, Ptvchocheilus
lucius, is a large piscivorous cyprinid native to the
Colorado River Basin. Once abundant throughout the basin,
the species is now limited to the northern portion of its
historical range (Figure 1). The major causes of its
decline are generally attributed to the combined effects of
dam construction, introduction of non-native species, and
poor land use practices (Miller 1961; Minckley and Deacon
1968; Molles 1980; Behnke and Benson 1983; Carlson and Muth
1989). The small size of age-O Colorado squawfish entering
winter might be an important factor affecting recruitment to
the adult stock (Kaeding and Osmundson 1988).
In populations of temperate-zone fishes near the
northern limit of their range, the overwinter mortality of
age-O fish is often high (Oliver et ale 1979; Shuter and
Post 1989). This mortality may result from hypothermia,
predation, displacement by flooding, inadequate lipid
reserves leading to subsequent starvation, and physical
damage from anchor ice and frazil ice (Seelbach 1987). The
growing season shortens and the winter period lengthens as
one moves from south to north in the northern temperate