Development of net energy intake models for drift-feeding juvenile coho salmon and steelhead

Abstract

We developed models to predict the effect of water velocity on prey capture rates and on optimal foraging velocities of two sympatric juvenile salmonids, coho salmon and steelhead. Mean fish size was 80 mm, the size of age I+ coho and steelhead during their second summer in Southeast Alaska streams, when size overlap suggests that competition might be strongest. We used experimentally determined prey capture probabilities to estimate the effect of water velocity on gross energy intake rates, and we modeled prey capture costs using experimental data for search and handling times and published models of swimming costs. We used the difference between gross energy intake and prey capture costs to predict velocities at which each species maximized net energy intake rate. Predicted prey capture rates for both species declined from~75 to 30-40 prey/h with a velocity increase from 0.30 to 0.60 m·s −1 . We found little difference between coho and steelhead in predicted optimum foraging velocities (0.29 m·s −1 for coho and 0.30 m·s −1 for steelhead). Although prey capture ability appears to be more important than are prey capture costs in determining optimum foraging velocities, capture costs may be important for models that predict fish growth. Because coho are assumed to pay a greater swimming cost due to a less hydrodynamic body form, we also modeled 10 and 25% increases in hydrodynamic drag to assess the effect of increased prey capture costs. This reduced optimum velocity by 0 and 0.01 m•s −1 , respectively. Habitat segregation among equal-sized coho and steelhead does not appear to be related to the effects of water velocity on their respective foraging abilities.

Competitive release modifies the impacts of hydrologic alteration for a partially migratory stream predator

“…; Piccolo et al. ). Additionally, reduced recruitment or increased crowding alters density and intraspecific interactions (Keeley ; McKinney et al.…”

Prey abundance, channel structure and the allometry of growth rate potential for juvenile trout

“…This function greatly reduced modelled energy intake, which is otherwise over‐estimated by a factor of two or more if fish are assumed to consume all prey within their reactive distance (Hughes et al. 2003; Piccolo, Hughes & Bryant 2008a,b). Grossman et al.…”

Predator–prey systems in streams and rivers

“…This approach is similar to an equation for the functional response of a stationary predator to a mobile prey discussed by Holling (1961, p. 167). We further assume that there is no handling time and that the capture success, as well as the detection distance, are constant (but see Hughes and Dill 1990;O'Brien and Showalter 1993;Piccolo et al 2007). The dynamic equations for the prey and predators, respectively, are…”