Laserfiche WebLink
<br />C) <br /><7"> <br />..... <br />co <br /> <br />smothered or simply washed downstream. Although habitat quality studies were not an emphasis during <br />the 7-year research period, several studies were conducted that assessed various components of habitat <br />quality. <br /> <br />t,,) <br /> <br />As noted above, critical components of Colorado pikeminnow spawning bars are cobble size and <br />cleanliness. Bliesner and Lamarra (2000) evaluated Colorado pikeminnow spawning bar characteristics <br />in the Yampa and Colorado rivers and compared those results with the characteristics of23 bars in the San <br />Juan River, including bars where Miller and Ptacek (2000) observed spawning behavior. They found that <br />cobble in many of the San Juan River cobble bars was similar in size and size distribution to cobbles at the <br />Yampa River spawning site (more than half the cobbles were 71 mm or larger), although bars at the <br />Colorado River spawning sites had slightly larger cobble (more than half were 78 mm or larger) (Table <br />3.5). Although it was generally known that the Yampa spawning site had very clean, loose cobbles <br />(O'Brien 1983, Harvey et al. 1993), these characteristic were not quantified. Bliesner and Lamarra (2000) <br />developed a method to measure the depth-to-embeddedness characteristic of San Juan River cobble bars. <br />Figure 3.13 compares cleanliness of21 cobble bars investigated in the San Juan River during 1995 (data <br />from the two [RM 132.0 and RM 131.0] spawning bars identified in 1994 are also included). The two <br />spawning bars had measurements of 13 to 24 cm depth-to-embeddedness. In 1995, several other bars <br />had similar cleanliness, which was similar to depths-to-embeddedness from Yampa River spawning bars. <br />This analysis indicated that the spawning bars selected by Colorado pikeminnow were some of the cleanest <br />bars in the San Juan River and that there were a number of potentially suitable, high-quality bars available. <br /> <br />Table 3.5. <br /> <br />Average cobble size distribution for potential spawning sites in the San Juan, <br />Yampa, and Colorado rivers. Diameters (mm) represent the maximum size <br />cobbles within the designated percentage (Source: Bliesner and Lamarra <br />2000). <br /> <br /> <br />Yampa <br />Colorado <br /> <br />:;: 110 <br />:;: 125 <br /> <br />:;:94 <br />:;: 104 <br /> <br />:;:76 <br />:;:78 <br /> <br />:;:58 <br /><49 <br /> <br />:;:46 <br />:;:38 <br /> <br />Archer and Crowl (2000b) surveyed nursery habitats, primarily backwaters, in the San Juan River <br />and found that deep backwaters (>0.5 meter) were relatively common, but their number declined <br />from August to September every year from 1994 through 1997, although the differences were not <br />statistically significant (Table 3.6). The loss of deep backwaters may be an effect of late summer <br />storm events, which are common in the San Juan Drainage. Bliesner and Lamarra (2000) studied <br />backwater depth and productivity in the San Juan River and how these factors varied with late <br />summer thunderstorm activity. They also made comparisons between San Juan River nursery reaches <br />and those of the Green and Colorado rivers. They found that backwater depths in the San <br /> <br />September 2000 <br /> <br />3-31 <br /> <br />Program Evaluation Report <br />