Assessing contributions of cold-water refuges to reproductive migration corridor conditions for adult Chinook Salmon and steelhead trout in the Columbia River, USA

Diadromous fish populations face multiple challenges along their migratory routes. These challenges include unfavorable water quality, harvest, and barriers to longitudinal and lateral connectivity. Interactions among factors influencing migration success make it challenging to assess management options for improving conditions for migratory fishes along riverine migration corridors. We describe a migration corridor simulation model which integrates complex individual behavior, responds to variable habitat conditions over large areas, and is able to link migration corridor conditions to fish fitness outcomes. Our model, developed within HexSim, is built around a mechanistic behavioral decision tree that drives individual interactions of fish with their spatially-explicit simulated environment. Outcomes of the migration corridor simulation model include passage time, energy use, and survival. Outcomes can be used to evaluate trade-offs of behavioral thermoregulation on fish fitness, or test alternative scenarios of refuge availability, connectivity, or barrier permeability. To demonstrate the potential utility of the simulation model, we describe the sequence of model events and basic model mechanisms. Then, we describe an application of the simulation model to a case study of salmon and steelhead adults in the Columbia River, USA, migration corridor.

Impact/Purpose

Many rivers and streams in the USA used by migratory fishes are impaired under the Clean Water Act as a result of high summer water temperatures. Adverse effects of warm waters include impacts to fish populations that may already be stressed by habitat alteration, disease, predation, and fishing pressures. Much effort is being expended to improve conditions for fish, and methods are needed to project anticipated benefits of water temperature improvements, or costs of impairments. This presentation will describe an approach being applied by the EPA to link changes in water temperatures, including the spatial arrangement and connectivity of cold-water refuges, to fish population responses.

Citation

Snyder, M., N. Schumaker, J. Dunham, M. Keefer, P. Leinenbach, A. Brookes, J. Palmer, D. Keenan, J. Wu, AND Joe Ebersole. Assessing contributions of cold-water refuges to reproductive migration corridor conditions for adult Chinook Salmon and steelhead trout in the Columbia River, USA. International Society for Ecohydrology, virtual, Virtual, November 24, 2020.