Use of a net rate of energy intake model to examine differences in juvenile steelhead (Oncorhynchus mykiss) densities and the energetic implications of restoration.

摘要

Foraging models that weigh the energetic costs and benefits of habitat occupancy have been used to explain position choice among drift-feeding fishes, especially salmonids. In addition to position choice, recent research suggests foraging model predictions indicate habitat quality. While foraging models have often been applied at spatial scales ranging from a single pool to a single stream reach, their broader simultaneous application across streams and basins remains rare. This thesis attempts to advance understanding of foraging modeling with the objectives i) to investigate a foraging model's ability to predict fish density in the context of simultaneous, multi-reach model application, and ii) to investigate energetic implications of physical habitat change for the purposes of restoration design and monitoring.;To address objective i, we collected requisite data in 22 sites from the John Day River and Asotin Creek watersheds in Oregon and Washington, respectively. We modeled hydraulics, drift concentrations, foraging, swimming costs, carrying capacity, and fish density. We compared predicted and observed fish densities in our study sites to find that linear regression between observed and predicted density was significant (R2 = 0.61, p < 0.001). We also found that the combination of assuming uniform drift density and simulating small fish territories in the model exerted strong influence over predicted carrying capacities, with carrying capacity predictions increasing exponentially with increased spatial concentration of simulated foraging locations. Thus, the assumption of territory size is influential in estimating reach abundance.;To address objective ii, we collected data to support foraging modeling both before and after restoration in the South Fork of Asotin Creek in the Asotin Creek watershed. First, we compared foraging predictions based on the ''before'' data set with predictions based on simulated restoration in an attempt to evaluate and better understand the restoration design. Second, we compared foraging predictions based on the ''before'' and ''after'' data sets as part of an effort to monitor and understand restoration outcome. Results from the simulated and actual restorations showed similar patterns. While restoration structures provided energetic benefits to fish even though only six months had passed between our ''before'' and ''after'' data sets, the observed changes were not as large as the simulated changes. This study demonstrates one way foraging models might be used to help investigate restoration designs with respect to their intended outcomes. In addition, this work also identified mechanisms by which observed geomorphic changes might influence fish.