Water Temperature

Importance to Salmonids

Cool water temperatures are required for salmon survival during all life stages. Water temperature is critical for spawning, egg development, the maturation of fry, juvenile growth, distribution, and survival. Temperatures also significantly influence smoltification, adult migration, and the reproductive health of spawning adults. The relationship of water temperature to salmonids is a function of interactions between temperature, available prey, acclimation, presence of thermal refugia, life stage, and species (CDFG 2002). These factors are site-specific and are best understood in the context of the specific streams in which the factors interact to produce sustainable, sublethal, or lethal conditions for salmonids.

photo of riparian trees shading Scott Creek

Riparian canopy cover provides shade to Scott Creek, which helps maintain cooler water temperatures for salmonids.

For example, acutely lethal temperatures for coho salmon (Oncorhynchus kisutch) are 28 – 30+° C (Smith 2003). Sublethal temperatures can reduce or eliminate coho populations by the metabolic effect on food intake, increased dissolved oxygen demands, or the effect on competitive relationships. While coho are poor competitors at higher water temperatures, at lower temperatures, they can outcompete steelhead. Unless food is abundant, mean water temperatures of about 16° C with weekly maximums of up to 19° C are the upper range of temperatures that can sustain coho (Smith 2003). However, in Waddell Creek in very productive pools, coho have been found at higher temperatures (Smith 2003). Steelhead trout (O. mykiss) have a greater ability to withstand high temperatures. As long as food is available, steelhead can withstand means of 20° C with weekly maximums of up to 24° C. When the water is warm, steelhead have been observed to use highly productive riffles to feed in order to meet the increased metabolic demands of the warmer water (Smith 2003).

Water temperature may be affected by a variety of factors including climate, riparian cover, flows, riparian vegetation, geomorphic features, and human impacts. Temperature becomes a limiting factor when it falls outside the ideal range for a particular life stage. Temperature regimes that support or are deleterious to coho and other salmonids vary across their northern Pacific ranges (CDFG 2002). Sustainable thermal regimes for central coast coho and steelhead probably differ from elsewhere in their respective ranges.

Human Impacts

Anthropogenic impacts affecting factors that affect stream temperatures include the clearing of riparian and upslope vegetation, the modification of channel configuration, and the manipulation of stream flow. Although riparian canopy does not reduce temperatures, the shade provided by the vegetative cover over the stream maintains the cooler water temperatures that are so critical to salmonids. The shade from the canopy prevents the sun from heating the water but does not cause a temperature decrease.

References

California Department of Fish and Game (CDFG). 2002. "Chapter VI. Factors Affecting the Ability to Survive and Reproduce. in Status Review of California Coho Salmon North of San Francisco." Report to the California Department of Fish and Game Commission. 79-133 pp. View on-line document.

Smith, J. 2003. "Water Quality Concerns and Central Coast Steelhead and Coho." 2 pp. View on-line document.

Local References

Hatch, C.E., F.T. Andrew, J.S. Revenaugh, J. Constantz, C.R. Ruehl, M. Los Huertos, and C. Shennan. 2002. Time-Series Analysis of Streambed Thermal Records to Model Surface Water - Groundwater Interaction Within a Coastal Watershed. Paper presented at American Geophysical Union, Fall Meeting 2002, Abstract # H61A-0747.

Swolgaard, C. 2001. "Water Quality Monitoring - Chemical Constituents of Streams." California State Parks Inventory, Monitoring, and Assessment Program, Wilder Ranch State Park.

General Reference

Berman, C. 1998. "Summary of Temperature Preference Ranges and Effects for Life States of Seven Species of Salmon and Trout (Appendix A)." US EPA Region 10.