9304 - Laserfiche WebLink

Home Browse Search

I I I I I I I I I I I I I I I I I I I Community Structure-- W e found three distinctly different fish communities: the middle portion ofthe river basin, the lower portion, and the side canyons. The native fish community found between Harris Wash and Fence Canyon was remarkably intact. Sampling suggests that speckled dace, roundtail chub, and flannelmouth sucker are still abundant as they were nearly 25 years ago (Holden and Irvine 1975). The maintainance or enhancement of this native fish community is identified as a management objective (Ottenbacker and Hepworth 1999). The roundtail chub is listed as threatened by Utah and the flannelmouth sucker is a state Species of Special Concern. Of the 88 fish collected from the mainstem, 87 (99%) were native. No red shiners or largemouth bass were collected. Our native sample composition was higher than the 65% endemism reported by Holden and Irvine (1975), however, they sampled side canyons. where exotics were quite common. In Holden and Irvine's narrative, they discussed sampling Harris Wash, Steven's Canyon, and Coyote Gulch where they found pools dominated by non- native fishes. They also reported that non-native species dominated (95%) the lower mainstem community as well as the side canyons. We found similar conditions. Non-natives made up 89% of the fish collected in the side canyons and lower sampling sites. Red shiner were quite abundant making up 85% of the fish collected downstream of Fools Canyon. We also collected adult carp (440 mm) and striped bass (600 mm) which undoubtedly migrated upriver from Lake Powell. The native fish community is bracketed, both up- and downstream by exotic fish communities. The river's head waters support 4 species of non-native trout. Side canyon pools throughout the basin have been reported to contain large numbers of red shiner, fathead minnow and green sunfish (Holden and Irvine 1975, McAda et al. 1977). Our survey identified two additional exotics; the yellow bullhead and striped bass, one of which undoubtedly migrated upstream from Lake Powell. Undoubtedly, individuals periodically seed the mainstem during spring and storm runoff. It's not only encouraging, but also interesting that the middle canyon has remained essentially intact during the past 25 years. The resiliency of the endemic fish community between Harris and Fence Canyons must be partially in response to rather harsh, summer conditions where apparently, only natives can survive. The differences in physical habitat types is striking, especially in considering the conditions that fish face through the full range of annual flood and drought cycles. Potential Threats-It appears that during the past 25 years the native/non-native fish community has remained relatively stable. While this is somewhat reassuring, the fish community will always be threatened by human activities that proliferates pollution, further water depletion, and the spread of additional fish species and their parasites and pathogens. Previous reports did not address the possibility that fish are, or can, migrate from Lake Powell. The presence of common occurring largemouth bass, channel catfish, carp, and green sunfish may have resulted of bait bucket introductions or their escape from upstream ponds. However, the absence of largemouth bass and channel catfish from the extensive surveys conducted by McAda et al. (1977) suggests these species may have migrated upstream from the reservoir. 18