WSPC02460 - Laserfiche WebLink

Home Browse Search

Bliesner and Lamarra (2000) searched portions of the upper half of the San Juan River study area for potential Colorado pikeminnow spawning habitat. They found several potential sites with cobble characteristics (cleanliness and size) similar to the two known spawning sites (RM 131 and RM 132) identified by Miller and Ptacek (2000) and other spawning sites in the Yampa and Colorado rivers. The fairly large Colorado pikeminnow population in the Green and Yampa rivers uses two major spawning areas, suggesting that the San Juan River can supply needed spawning areas for a relatively large population of Colorado pikeminnow, as well as razorback sucker and other native species that need clean cobble spawning bars. Habitat for flannelmouth sucker (all habitats), bluehead sucker (riffles), and speckled dace (riffles) is common and abundant in the San Juan River. Because flannelmouth sucker use a variety of habitats, they are common throughout much ofthe river. Habitat was not limiting for this species; flannelmouth sucker abundance, which is higher in the San Juan River than in other Upper Basin systems (Ryden 2000a), suggested habitat for this species is more abundant in the San Juan River than in other rivers. Bluehead sucker and speckled dace were also abundant. Their key habitat, riffles, was also abundant, especially during low-flow periods (Figure 3.5). Habitat for these two native species was not limiting in the San Juan River. Habitats for roundtail chub (pools and eddies) were rare, but as seen for stocked Colorado pikeminnow and razorback sucker, rareness does not make a habitat limiting for the relatively small populations of these species; the case may be the same for roundtail chub habitat. The endangered fishes used portions of the river that had high habitat richness. Figure 3.11 shows how habitat richness varied throughout the entire 180-mile study area at high flow (June 1994) and low flow (January 1996). This graph was developed from habitat mapping runs made by Bliesner and Lamarra (2000), and it reflects the average richness (number of habitat types) for overlapping 300-meter sections of the river with center points every 150 meters. Average richness by mile was generally less than five habitats per 300-meter reach. Areas selected by Colorado pikeminnow and razorback sucker averaged six to nine habitats, indicating that the fish selected relatively rare sections of the river. To examine the distribution of 300 meter reaches with higher richness, an exceedence evaluation by Geomorphic Reach was performed (Table 3.3). These data indicated that during both high and low flows, Reaches I and 2 have very few 300-meter reaches with more than five habitats, and richness is generally highest in Reach 5, the area containing the Mixer and Colorado pikeminnow spawning areas. Another way to evaluate habitat richness was to look at the number of total habitats (versus total habitat types) within a river reach. Figure 3.12 shows total habitat counts from mapping runs (Bliesner and Lamarra 2000) for the study area at three flow levels. Total habitat count is lowest in Reaches I and 2 (RM 0 to RM 70), and it peaks around RM 130 in the Mixer. In the lower river, habitat count peaked at low flows, whereas in most of the remainder of the river it peaked at medium or high flows. This likely reflects the canyon area in the lower river, which is very habitat poor during high flows but increases in richness as flows recede. Higher values in the upper river result from flooding of areas that create more secondary channels and other habitat features adding to habitat richness. September 2000 3-26 Program Evaluation Report I I I I I I I I I I I I I I I I I I I