Maximum Temperature Limits for Chinook, Coho, and Chum Salmon, and Steelhead Trout in the Pacific Northwest

Abstract Wild salmon stocks in the Pacific Northwest are imperiled by a variety of anthropogenic environmental modifications, not the least of which is increasing maximum water temperatures. While many reports have been written on physiological or population-level influences of temperature in terms of the decline of wild salmon, synthesis of these diverse sources is needed for evaluation of numeric temperature criteria and their potential in salmon recovery planning. Various sensitive life stages and biological processes are impacted differently for different salmon species. This article reviews the literature for chinook, coho, chum, and steelhead, which are currently listed in the Columbia River Basin under the Endangered Species Act. Spawning, incubation and early fry development, juvenile rearing and growth, smoltification, and migration are considered. Swimming speed, disease susceptibility, chemical considerations, and lethality are also reviewed. Regional population growth and climate change will exacerbate the difficulties of recovering Northwestern salmon beyond remnant runs. Ethical analysis of the assumptions underlying recovery policy decisions, proposals for regime-based water quality standards, and a systems level vulnerability analysis are components of the recovery planning discussions. Specific numeric maximum temperature criteria that can be integrated into a broader recovery planning process are described for sensitive life stages of three species of Pacific Northwest salmon and steelhead.