Laserfiche WebLink
1 <br />' period other reseazchers found abundant Colorado squawfish larvae co-occurring with red shiners <br />' in backwaters of the Green River (Haines and Tyus 1990, Tyus and Haines 1991). Red shiners <br />were often the most abundant species collected in those backwaters and regularly attained <br />' densities greater than 5 individuals/m2 of backwater Haines and T 1990. At these densities <br />( y~ ) <br />' even relatively low predation rates can have a substantial impact on survival' and recruitment of <br />' Colorado squawfish larvae. Thus, red shiner was considered to be the most important predator <br />for inclusion in the IBM. <br />' The mechanistic model focused primarily on the interacting effects of temperature- <br />' dependent Colorado squawfish growth and size-dependent rest shiner predation (Figure 3). <br />Temperature directly influences growth of fish and as a consequence, indirectly influences <br />' developmental changes in swimming speed, foraging ability, predator avoidance, and the length <br />' of time larvae aze susceptible to predation (Weatherly and Gill 1987; Miller et al. 1988). Bestgen <br />' (1996) showed that water temperatures ranging from 18 to 30°C strongly affected growth rates of <br />Colorado squawfish. Thermal regimes in the regulated Green River vary substantially with <br />' dischazge patterns and weather conditions (Bestgen 1997). Therefore water temperature may be <br />' an important factor regulating recruitment processes of Colorado squawfish. <br />' Red Shiner Size Distributions and Density <br />' The potential for predation by red shiners on Colorado squawfish larvae depends on red <br />' shiner size and density throughout the season. Estimates of red shiner densities and size <br />distributions were based on field collections from the Green River, Utah (Haines and Tyus 1990; <br />' K. Bestgen, unpublished data). In eazly June the red shiner population was dominated by age-1 <br />~ . <br /> <br />