7166 - Laserfiche WebLink

Home Browse Search

riffles for species such as fathead minnow and sand shiner and absence of any centrarchidae. The general upstream increase in number of species/ stratum was due to the appearance of exotic species in samples. Inter- estingly, the stratum with the largest number of species (65% exotic) contained the only major manmade modification in the entire study area, the Juniper Mountain diversion dam. Habitat diversity in these upper strata is low, consisting mainly of a relatively deep medium-fast channel with few backwaters, riffles, or eddies. There are no pools in Stratum 7 and few shallow, sandy runs and side channels in Strata 6 and 8. These , strata compose a transition zone between the lower canyons and upper reaches of the Yampa. Gear types differed in their sampling effectiveness in different habitats and for different species and size of individuals. Seines were most effective in shallow water areas for small fishes while trammel nets and electrofishing were most effective for large fishes in deeper water. Electrofishing was also effective in very swift, shallow water. The standardized stations incorporated all of these gear, and catches between stations are generally comparable for evaluating the.number of species for different seasonal periods. Catch per effort for each gear type provided an excellent way to compare the occurrence of species by habitat types and seasons. Seines were the most effective gear for collecting all cyprinids except adult chubs and adult Colorado squawfish. Adults for any large species (e.g. flannelmouth and bluehead sucker, channel catfish) were rarely captured with seines. Conversely, smaller cyprinids were never collected with trammel nets and rarely with electrofishing gear. Trammel nets were most effective in capturing adult Colorado squawfish, humpback chub, flannelmouth sucker, and roundtail chub in deep pools or eddies where water depth exceeded approximately 6 ft. In shallower areas, electrofishing was the most effective gear type for adults of all the larger species. Juveniles of larger species were captured most effectively by electrofishing. These individuals were large enough to generally avoid capture with seines, but were not large enough to be effectively collected in trammel nets. When captured in trammel nets; juvenile chub, flannel- mouth sucker, bluehead sucker, channel catfish, carp, and white sucker were invariably in the 1 in nets. The number of juveniles captured for all species was noticeably lower than young or adults in all strata except Strata 3 and 4 on the Yampa. Because of the above mentioned sampling bias for juveniles, caution should be used when comparing catch numbers and ratio for juveniles. Green River Speckled dace was the most abundant native species collected in all four strata in the Green River study area (Table 6). Numbers of blue- head sucker and flannelmouth sucker were similar in Strata 2, 3, and 4 but bluehead sucker was almost twice as numerous as flannelmouth sucker in Stratum 1. Roundtail chub was rare in Strata 1 and 2, but relatively common in Strata 3 and 4. Mottled sculpin was collected in all 4 strata but was rare, always comprising less than 1% of total catch. 42