Document: JAM-3-26-8

Using individual-based simulations to parameterize large-scale management models.

ANDERSON, J.* and N.BEER

School of Fisheries, University of Washington, Seattle, WA, U.S.A. ¹

Abstract:
The most controversial proposal to recover the endangered Snake River salmon is breaching the four lower dams of the river. In the life cycle models used to evaluate the effects of breaching is the untested assumption that breaching will increase survival over the existing situation in which smolts are barged down river. Although this assumption is untestable without actually breaching, it is generally assumed that smolt survival will increase. In fact, it is possible that survival will decrease, as predators concentrate into the smaller volume of a free-flowing river. To explore this assumption we used an individual-based model (IBM) to study the environmental and behavioral conditions that can increase or decrease smolt survival with breaching. We first modeled smolt migration through the existing 40-km reservoir behind Little Goose Dam on the Lower Snake River. Output from a 2-dimensional hydraulics model was used to define detailed flow fields for both the existing reservoir and a free flowing river. Smolt movement was described by flow and random movements that decrease when smolts are in their preferred depth habitat. Predator movements were random and independent of the flow. Smolt migration was characterized by adjusting their random movement rate to fit observed smolt travel times through the reservoir and the predator-prey dynamics were characterized by adjusting the predator-prey reactive distance to fit the observed smolt survival. The impacts of dam breaching were then explored by using the free-flowing river bathymetry and hydraulics with the smolt migration and predator-prey factors fit for the reservoir. In this manner, we explored the effect of changing the environment without changing the behavior. We then explored how changes in behavior affected smolt survival. It is our hope that this IBM analysis will provide further understanding and a test in kind of the otherwise untested assumption that dam breaching will increase smolt survival.

Keywords: Individual-based modeling, population model, salmon, Snake River, survival, predation

This abstract is being presented at: 11:05 AM in session:
Symposium # 27: Advancing the Individual-Based Modeling Approach: New Tools and Concepts.