Small mountain watersheds provide critical habitat for fish. Habitat quality is dictated by environmental conditions including water temperature, dissolved oxygen, and nutrient availability. All of these conditions are sensitively adjusted to the hydrologic regime. In the semiarid mountains of the intermountain west, stream hydrology and consequently fish habitat, are directly related to the timing and magnitude of mountain snowmelt. The mountain snowpack is changing [Mote et al., 2005]. Although the total amount of precipitation that a watershed receives in a year may not be changing, the proportion that falls as snow is diminishing, and the snow that accumulates on the ground is melting earlier leading to lower summer flows and potentially late-season stream cessation[Luce and Holden, 2009].
The Dry Creek Experimental Watershed (DCEW) has served as a hydrometeorological research testbed in the semiarid rain-snow transition zone since 1999 (earth.boisestate.edu/drycreek). The mission of the DCEW is to provide temporally continuous and spatially distributed hydrometeorological and geographical data from point to watershed scales for researchers and educators. Long-term monitoring and short-term research campaigns have focused on a wide range of topics on the interactions among climate, landforms, ecology, and hydrology.
Dry Creek hosts a native, genetically pure population of Columbia River redband trout, which is a subspecies of rainbow trout native to high desert streams of the western US, east of the Cascades [Richins, 2014]. The American Fisheries Society, United States Forest Service, and Bureau of Land Management recognize Columbia River redband trout as a species of “special concern” http://www.westernnativetrout.org/redband-trout). An attempt to list the species under the Endangered Species Act failed due to a lack of information—as Columbia River redband trout is the least studied of Idaho’s salmonids. Thus, there is a pressing need to document population genetic status (i.e., “purity”) and determine the adaptive basis for this trout’s unique ability to survive in harsh (extreme fluctuations in flow, high temperature, and low dissolved oxygen) desert streams [Thurow et al., 1997].
The redband trout in Dry Creek are isolated from the mainstem Boise River due to regular downstream summer drying of the channel and channel barriers (artificial waterfall). Richins [2014] tagged approximately 500 fish in Dry Creek and have collected genetic samples from the population over the past 3 years. These data provide insight on redband trout distribution, movement patterns, as well as fine-scale population genetic and family structure.
Dry Creek is fed by high elevation springs that most throughout the year most years. In very dry summers such as was observed in 2013 and 2014, Dry Creek contracts upwards, retreating towards its spring sources. In 2013, redband trout migrated upstream as Dry Creek contracted, but the ability of the species to disperse was limited by mountain topography, channel structure, and man-made barriers. Thus, habitat was greatly reduced and fish suffered high mortality, leading to a population reduction and loss of genetic diversity. Individuals which suffered the highest mortality were found in isolated pool habitats with extremely low levels of dissolved oxygen. Survivors established themselves in flowing upstream reaches [Richins, 2014].
References
Luce, C. H., and Z. A. Holden (2009), Declining annual streamflow distributions in the Pacific Northwest United States, 1948–2006, Geophysical Research Letters, 36(16), L16401.
Mote, P. W., A. F. Hamlet, M. P. Clark, and D. P. Lettenmaier (2005), Declining mountain snowpack in western North America.
Richins, S. (2014), Ecology of Columbia River Redband Trout, Oncorhynchus mykiss gairdneri, in Dry Creek, Idaho (Lower Boise River Drainage), 74 pp, College of Idaho.
Thurow, R. F., D. C. Lee, and B. E. Rieman (1997), Distribution and status of seven native salmonids in the interior Columbia River basin and portions of the Klamath River and Great basins, North American Journal of Fisheries Management, 17(4), 1094-1110.
