WSP01460 - Laserfiche WebLink

Home Browse Search

C) (.'_' -" """ ~ c.o e..:, Figure 3.5 also shows the distribution of the general habitat categories in the study area. Because run habitat dominates the San Juan River, the scale on this figure was adjusted so that rarer habitat categories could be compared. Key habitats for the endangered fishes are fairly well distributed across the study area, except for the section from RM 20.0 to about RM 65.0, which is generally within Reach 2. This canyon- bound area has very few backwaters at any flow. It has relatively high amounts of slackwater and low- velocity habitats at all flows, and it has little inundated vegetation during high flows because of the canyon. The lack of backwater habitat in this section is the likely reason why stocked yay Colorado pikeminnow retention was low in this reach. Key habitats for adult Colorado pikeminnow and razorback sucker included edge pools, pools, eddies, slackwaters, and backwaters. These habitats fit into the low-velocity, slackwater, and backwater habitat categories (Table 3.2). Figure 3.7 shows the amount of pool and eddy habitat at various flow levels. Pool habitat area declined with increased flow, whereas eddy habitat increased with increased flow. Eddies were most available during high-flow periods, and pools were most available during low-flow periods. The two endangered fishes' habitat use followed this same pattern; eddies were used extensively during high- flow periods, and pools and eddies were used at lower-flow periods, suggesting the fish used the type of low-velocity habitat most available at the time. Slackwater habitats did not change with flow (Figure 3.8) (Bliesner and Lamarra 2000). Backwater habitats, used by adult fish during high-flow periods and by yay during late summer and autumn, were generally most abundant at low-flow periods, and varied at medium- and high-flow periods by reach. Reaches I and 2 were similar, as were Reaches 3, 4, and 5, but these two groups of reaches differed from each other (Figures 3.9 and 3.10). This variation in the relationship of the amount of backwater habitat versus flow results from the timing of flushing flows that clean the backwaters and the timing of the habitat mapping runs in relation to storm events and flushing flows (Bliesner and Lamarra 2000). Even though backwater habitat varied with flow and varied with the timing of flushing flows, stocked yay Colorado pikeminnow primarily used backwater habitats and survived well in the San Juan River (Trammel and Archer 2000). This suggests that, even in low abundance, backwater habitat was sufficient for at least the mnnber of stocked fish that survived in the San Juan River. It remains to be seen if this habitat type is sufficient for a larger, self-sustaining population of Colorado pikeminnow. Flooded vegetation was used by stocked razorback sucker during the high-flow period. As shown in Figure 3.7, that is the only time this habitat type is available. Larval and yay razorback sucker habitat use was not determined for the San Juan River. Flooded bottomland habitat, similar to that used by razorback sucker along the Green River, was essentially non- existent along the San Juan River because of its narrow floodplain, steep floodplain gradient, and lack of water-holding floodplain depressions. Inundated vegetation was an available habitat during high-flow periods in the San Juan River, but it disappeared rather quickly as flows receded (Figure 3.5). September 2000 3-21 Program Evaluation Report