Water Temperature Appears to Restrict Distribution of Juvenile Coho Salmon in Redwood Creek, California

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Water Temperature Appears to Restrict Distribution of Juvenile Coho Salmon in Redwood Creek, California

By Mary Ann Madej
July 2006

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Above: Adult coho salmon, held by Mike Sparkman, California Department of Fish and Game. Photograph from the California Department of Fish and Game. [larger version]

Above: Juvenile coho salmon from the Redwood Creek watershed. Photograph from the Redwood National Park collection. [larger version]

Above: The hot reach of Redwood Creek, looking downstream. Few trees shade the river in this area. As the creek flows to the ocean (in the background), it becomes cooler. Photograph from the Redwood National Park collection. [larger version]

Above: Redwood Creek watershed in northern California. [larger version]

The distribution of juvenile coho salmon in Redwood Creek, Calif., appears to be restricted to the lower reach of the river by water temperature, according to a recent publication by U.S. Geological Survey (USGS) and National Park Service (NPS) scientists.

Water temperature is an important physical factor influencing salmonid egg development, juvenile appetite and growth, and fish distribution. Juvenile coho salmon, like most salmonids, require cool water to survive and grow and are susceptible to increased summer water temperatures because they rear in freshwater for at least a year. Historically, coho salmon occurred throughout most of the 108-km-long mainstem of Redwood Creek in Humboldt County, northern coastal California; however, juvenile coho salmon distribution is currently limited to the downstream-most 20 km of Redwood Creek and tributaries entering that reach.

Redwood Creek is currently listed as temperature and sediment impaired (with warmer and muddier water than normal) under the Clean Water Act because of past timber harvest, removal of riparian vegetation, widespread streamside landsliding, and buildup of sediment in the channel. The upstream reach of the creek is beginning to recover from past damage, with an increased frequency of deep pools, extensive shading from alders, a moderate (0.5 percent) channel gradient, and gravel size adequate for spawning; nevertheless, juvenile coho salmon are absent. In the June issue of the Canadian Journal of Fisheries and Aquatic Sciences, USGS scientists Mary Ann Madej, Christopher Currens, and Julie Yee, along with NPS colleagues Vicki Ozaki and David Anderson, hypothesize that elevated stream temperatures in the middle river reach constitute a thermal restriction for juvenile coho rearing. The scientists used 7 years of in-stream temperature monitoring in conjunction with thermal-infrared data collected during a July 2003 helicopter survey to identify warm reaches of Redwood Creek and to compare temperature regimes in coho-bearing river reaches with those in non-coho-bearing reaches. Their report presents detailed discussions of the trends in maximum and minimum stream temperature and the duration of high temperatures along the length of Redwood Creek.

Among the authors' conclusions are the following: Redwood Creek, unlike many rivers reported in the literature, reaches its maximum temperature in the middle basin and becomes cooler farther downstream. Coastal fog and old-growth redwood trees in the riparian zone of the lower basin contribute to the cooling trend there. In the upper part of the creek, the thermal regime has largely recovered from past hot temperatures, and the temperature regime in this non-coho-bearing reach is similar to that in the downstream coho-bearing reach. In the intervening 50-km-long middle reach, however, summer water temperatures remain significantly warmer than the temperatures recommended for coho salmon.

Management implications of the study are as follows:

Although much upslope road-restoration work has been accomplished in the Redwood Creek basin, current riparian conditions along much of the creek are still degraded and do not provide adequate shading (and thus cooler temperatures) for the stream.

The absence of large riparian conifers reduces the availability of inchannel wood to scour pools and provide cover and channel complexity, possibly also contributing to the limited upstream distribution of coho salmon.

Besides efforts to control erosion in this watershed, active riparian restoration may be needed to restore the cool thermal regime along warm stretches of Redwood Creek.

The full reference for the recent paper is:

Madej, M.A., Currens, C., Ozaki, V., Yee, J., and Anderson, D.G., 2006, Assessing possible thermal rearing restrictions for juvenile coho salmon (Oncorhynchus kisutch) through thermal infrared imaging and in-stream monitoring, Redwood Creek, California: Canadian Journal of Fisheries and Aquatic Sciences, v. 63, p. 1384-1396 [URL http://pubs.nrc-cnrc.gc.ca/cgi-bin/rp/rp2_abst_e?cjfas_f06-043_63_ns_nf_cjfas6-06].

Redwood Field Station
U.S. Geological Survey (USGS)

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July 2006

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in this issue:

cover story:
Scientists Study Sources of Nitrogen in Hood Canal

Biologists Count Parasites to Assess Health of Marsh

Researcher Studies Effects of African Dust on Human and Coral Health

Water Temperature Restricts Distribution of Coho Salmon in Redwood Creek

USGS Open House in Menlo Park, CA

Scientists and Educators Support "Watershed Watchers" Program

George Crekos' 30-Year Career Celebrated

Geography Students Speak Out at Science Symposium

Council of Science Editors Annual Meeting

USGS Scientists Receive Coral Reef Task Force Award

National Wetlands Research Center Staff Win Awards for Publications

Visiting Scientist Shares Expertise in Coastal-Evolution Modeling

July 2006 Publications List