4-02CW271 Supplemental Data - Laserfiche WebLink

Home Browse Search

Methodology For Developing Recommendation -- "Cool Water" Fisheries The Bureau of Land Management (BLM) consulted with the Division of Wildlife (DOW) regarding instream flow recommendations for "cool water" fishery streams in western Colorado. These stream segments have the following characteristics: • • • • • • They are located between 4,000 and 7,500 feet in elevation They are located downstream from headwaters stream segments that are higher in elevation and which support cold - water, salmonid fisheries. Summer water temperatures frequently exceed 18 degrees Celsius, and occasionally exceed 24 degrees Celsius. Lower gradient creates a higher ratio of pool to riffle habitat than in higher elevation, cold water streams. Most the fish biomass is comprised of speckled dace, white sucker, flannelmouth sucker, and bluehead sucker. Other sucker species and mottled sculpin may be present in limited numbers. Salmonids are present in very limited numbers when they use the cool water habitat for refuge from high flow events and icing events. Salmonids may also use the cool water habitat for passage between cold water habitats. For example, when late summer low flows stress the salmonid population, the salmonids may descend to a cool water confluence of two tributaries in order to ascend to the cold water habitat in a parallel tributary with higher flows. The purpose of the consultation was to determine the suitability of using the wetted perimeter, depth, and velocity criteria associated with the R2Cross model for "cool water" fishery recommendations. An initial determination was made that the R2Cross model, which analyzes riffle habitat, is a suitable model for these species. Riffle habitat is important for all of the species listed above for various life stages, and for passage between pool habitats. An assumption was made that if flows through riffles are protected, key pool habitat will be protected by these flow levels as well. A discussion of each of these R2Cross criteria follows: Wetted Perimeter -- DOW and BLM agreed that the 50% wetted perimeter criteria should not be altered for cool -water fisheries. This is considered the "foundation" criteria, because all species must have sufficient quantities of physical habitat to execute all of their life stages, and to have sufficient habitat for feeding. Adopting a criteria of less than 50% wetted perimeter would force undesirable competition among fish species for limited food supplies and reproductive areas, and would reduce the diversity of fish species found in those streams. Depth -- For the species which comprise the majority of fish biomass, BLM and DOW consulted the "Category 2" habitat suitability curves found in Edwards, E. A., H. Li, C. B. Schreck, 1983. Habitat Suitability Index Models for Longnose Dace, United States Department of Interior, Fish & Wildlife Service - FWSOBS- 82/10.33; and in U.S. Fish & Wildlife Service Curve Library - Fort Collins, CO, Item 120, File R. These curves suggested depths ranging from 0.8 to 2.6 feet for