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Research: Stream Warming Impacts On PNW Salmonids Require Prioritizing Conservation Efforts
Posted on Friday, November 18, 2011 (PST)

According to a newly publish research paper, fisheries and habitat managers in the Pacific Northwest need to be proactive if they want to blunt the likely negative effects on salmon and steelhead of ever-warming streams.


“Continuation of warming trends this century will increasingly stress important regional salmon and trout resources and hamper efforts to recover these species, so comprehensive vulnerability assessments are needed to provide strategic frameworks for prioritizing conservation efforts,” according to “Climate change effects on stream and river temperatures across the northwest U.S. from 1980-2009 and implications for salmonid fishes.”


“Tactical responses are key, but needed conservation projects are likely to greatly exceed available resources, so strategic prioritization schemes are essential. Improving regional monitoring networks and new models capable of accurately downscaling climate change effects on stream thermal regimes and other attributes across broad areas can provide the information necessary to implement such schemes.”


The paper was authored by Daniel Isaak, Sherry Wollrab, Dona Horan and Gwynne. Chandler, all based in Boise at the U.S. Forest Service’s Rocky Mountain Research Station. The researchers are part of Air, Water, and Aquatics Program staff at the Aquatic Sciences Lab.


The research paper was published online Nov. 4 in “Climatic Change, An Interdisciplinary, International Journal Devoted to the Description, Causes and Implications of Climatic Change.”


The article can be found at:


The researchers set out to evaluate how climate change might be affecting temperatures across a broad set of rivers. To do that they assembled 18 available temperature time-series from sites on regulated and unregulated streams in the Northwest to describe historical trends from 1980–2009, and assess thermal consistency between the two stream categories.


The 18 sites used in the assessment encompassed a wide range of stream sizes, elevations, and climatic conditions, but most drained mountainous watersheds and forested landscapes with various land-use histories and limited impacts from urbanization. The 18 river monitoring sites were in Idaho, Montana, Oregon and Washington.


Key findings of the study, according to lead author Isaak, are that: 1) significant warming of the region's rivers and streams has occurred over the past several decades, with the fastest warming occurring during the summer; 2) warming trends on unregulated streams were very consistent across the region whereas those downstream of reservoirs/dams were not, suggesting the latter do not make good climate sentinel sites, 3) very few sites exist with long-term stream/river temperature monitoring data, 4) rates of stream/river temperature changes closely tracked those of air temperatures at nearby climate stations, suggesting air temperature might be a useful surrogate for local stream temperature trends until better monitoring data are available.


“The study is particularly relevant in two regards. First, it documents rates of warming based on historical monitoring data across multiple river/stream sites within a region,” Isaak said.


“Second, the study separates out potentially confounding factors like urbanization or reservoir effects to derive accurate estimates of the background rates of climatically induced warming that are likely affecting all streams.”


“Description and attribution of stream temperature changes are key to understanding how these ecosystems may be affected by climate change, but difficult given the rarity of long-term monitoring data,” the paper says.


“Statistically significant temperature trends were detected across seven sites on unregulated streams during all seasons of the year, with a cooling trend apparent during the spring and warming trends during the summer, fall, and winter,” the paper says.

Those unregulated stream monitoring sites were on the Snake River near Anatone, Wash., the North Fork Clearwater River in Idaho, the Missouri River in Montana and the South Fork Bull Run River, Fir Creek, North Fork Bull Run River and Bull Run River in Oregon.


“The amount of warming more than compensated for spring cooling to cause a net temperature increase, and rates of warming were highest during the summer (raw trend = 0.17°C/decade; reconstructed trend = 0.22°C/decade).


“Air temperature was the dominant factor explaining long-term stream temperature trends (82-94 percent of trends) and inter-annual variability (48-86 percent of variability), except during the summer when discharge accounted for approximately half (52 percent) of the inter-annual variation in stream temperatures.”


The regulated sites are those with stream temperature data measured downstream of reservoirs that could alter thermal trends. Because the Snake River monitoring site is located 160 kilometers downstream of the nearest reservoir it was considered in the unregulated category. Also influencing that decision is the fact that two large unregulated tributaries, the Salmon River and the Grande Ronde River, enter the Snake River and double its size upstream of the Anatone temperature site to further dilute any remaining reservoir effects.


“Although most species have persisted through greater climatic perturbations in past millennia, modern climate change is happening especially rapidly, at the end of an already warm period, and is being imposed on populations that are often already depressed and fragmented from a century of intense human development (McIntosh et al. 2000; Hessburg and Agee 2003),” the paper concludes.


“To minimize the losses of biodiversity that could occur in the next half century, much needs to be learned in a relatively short period of time about changing stream and river thermal regimes and aquatic ecological responses (McCullough et al. 2009).”


“The apparent shift in recent years to cooler PDO conditions across the northwest U.S. may provide a brief respite before a warming trend is resumed that will become increasingly stressful for many salmonid fishes in the northwest U.S. This opportunity should be used to gain important information about stream temperature regimes and develop better tools, knowledge, and prioritization schemes for what may lie ahead.”


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