COOL WATER SAVES SALMON

THERMAL REFUGES AND SALMONID SURVIVAL

In most watersheds there are places where fish seek cooler water during periods of low, warm flows. I have seen westslope cutthroat and whitefish lined up in the cool flow of a tributary of the Selway River in Idaho. Spring chinook form a large school at the mouth of a cold creek on the Molalla River. On the Middle Fork John Day River spring chinook are found in a few pools that are influenced by cool ground water flow. Recognizing the value of these thermal refuges, environmental groups are seeking wilderness protection for cold water tributaries of the lower Rogue River to maintain their important ecological benefits for salmonids.

Historically, these thermal refuges have played an important role in salmonid life history, for during the hot days of summer, from July through September, migrating fish such as steelhead, summer chinook, and fall chinook, depend on these cool reaches of stream in order to complete their migration and reduce stress. As the climate changes and warms, these thermal refuges become even more important and should be protected, but they are not. The source of cold water is not protected, and these areas are a favorite among anglers because the fish are concentrated in a relatively tiny area. Even though I have asked the Oregon Department of Fish and Wildlife to protect these areas on the Columbia River, the request has largely fallen on hard times as the agency tries to increase license sales and is reluctant to restrict angling in areas of high conservation value.

This year a team of scientists wrote a letter to the Army Corps of Engineers regarding their research findings about thermal refuges on the Columbia River and made recommendations for their management. In this letter they make the following observations.

“Summertime water temperatures in the lower Columbia River have steadily increased over the last several decades. Annual peak temperatures have exceeded 21 °C (69.8 degrees F) in most recent years and have been as high as 24 °C (75.2 degrees F). The warmest period typically occurs in late July to early September, coincident with late-migrating summer Chinook and sockeye salmon and with substantial portions of the fall Chinook salmon and summer steelhead runs. Water temperatures in the 19-22 °C (66.2 – 71.6 degrees F) range, like those that routinely occur in the Columbia River main stem, are a significant management concern for adult migrants because a large proportion of adults currently experience thermal conditions thought to be stressful. Such temperatures have been associated with behavioral changes and a variety of sub-lethal effects on physiology, disease susceptibility, reproductive development, gamete quality. Based on these and other studies, we assume that temperatures above ~18-19 °C (64.4 – 66.2 degrees F) induce stress in adult migrants and that higher temperatures are associated with stronger negative costs. This issue may become more acute if warmer regional temperatures predicted by climate models come to pass.”

“A series of cool-water refugia are located along the migration corridor at tributary confluences with the main stem rivers. Many of the most-used refugia sites are located between Bonneville and John Day dams in the lower Columbia River, where cool-water tributaries draining the Cascade Range enter reservoirs. These sites are often 2-7 °C cooler than the main stem.”

“The incidence and duration of thermal refugia use differs widely among populations as a function of migration timing and basic life history. In our research, summer steelhead had both the greatest incidence (~70%) and longest duration (up to several weeks or more) of refugia use. Many steelhead also used multiple refugia sites. Extended refugia residence times resulted, at least in part, from the relatively flexible migration timetable for steelhead. Many of the summer-run fish enter the Columbia River study area at the warmest time but have 6-10 months to reach springtime spawning areas. In contrast with steelhead, about 20% of fall Chinook salmon and 15% of summer Chinook salmon were recorded in one or more lower Columbia refugia sites in the radiotelemetry studies.”

“Initiation of thermal refugia use in the lower Columbia River has been associated with main stem water temperatures of about 19 °C for steelhead and between 20 and 21 °C for fall Chinook salmon. The incidence and duration of use for both runs rapidly increased as temperatures rose above 21°C.”

“Presumed benefits of refugia use include reduced metabolic costs, reduced physiological stress, reduced negative temperature effects on maturation and gamete quality, and increased survival. The most obvious direct negative effect is increased harvest risk because fish are spatially and temporally concentrated in refugia, attracting intensive fisheries. We found that Snake River and upper Columbia River steelhead that used refugia in the lower Columbia River were significantly less likely to survive to spawning tributaries, primarily because harvest rates in and near the refugia sites were high. Refugia sites are typically shallow, and intensive human use of the sites presumably can elevate fish stress levels.”

“Overall, it is currently unclear whether refugia are currently ecological traps for adult salmonids, where holding was adaptive under historic conditions but now results in a net mortality cost due to increased mortality factors (e.g., fishing), or whether they primarily provide fitness benefits.”

“As shown in Keefer et al. (2009), the concentration of steelhead in lower Columbia River refugia sites (e.g., at Drano Lake at the Little White Salmon confluence and the Deschutes River mouth) can result in high exploitation rates. Harvest impacts on upriver populations are also possible for Chinook salmon (especially summer and fall runs) and at sites other than those studied by the University of Idaho and NMFS. Harvest management at these sites may become increasingly important, particularly if impacts on threatened populations are significant.”

“The impacts of climate warming are likely to be greater for spring and summer-run salmon than for fall-run populations because spring–summer fish hold in tributaries during summer months, with increased metabolic costs and potential for disease expression. Longer, hotter summers predicted under climate change scenarios would also be expected to differentially affect spring-summer run stocks by increasing metabolic costs of migration. The behavioral flexibility observed in steelhead suggests the potential for greater benefit of thermal refugia use to steelhead than salmon because they can use the sites for extended periods during the warmest time of the year. However, refugia may become relatively more important for salmon under warmer climate conditions, allowing migration in a “stepping-stone” sequence among refugia sites.”

Based on their investigations and research scientists have documented an issue that warrants action by the National Marine Fisheries Service with the authority to protect ESA-listed salmonids and the state fish and wildlife agencies. So far, however, none of these government institutions have recognized the issue or have taken steps to provide improved management of thermal refuges and protection of salmonids.

Source:

Keefer, Matthew, Chris Caudill and Chris Peery. 2010. Temperature regimes during migration and the use of thermal refugia by adult salmon and steelhead in the Columbia River basin. Letter to David Clugston, USACE, May 6, 2010.

Follow this link to read the full letter

http://www.nativefishsociety.org/conservation/wild_population/documents/UI-FWS_thermal_refugia_letter_report_6May10.pdf