7823 - Laserfiche WebLink

Home Browse Search

species collected in that stratum. Strata F and B contained the largest • number fish species with 20 and 19, respectively (Figure 11), (genus Gila included as one species). Strata C and D contained the lowest number of species with 14 and 13, respectively. Strata E and A were intermediate in numbers of fish and species collected, with 16 and 15 species. The numbers of fish species generally reflects the suitability of environmental conditions in those strata. Strata' C and D, with the fewest species, were dominated by riffles and rapids, stressful condi tions for the existence of fish. Strata F and B, with the largest numbers of fish species, did not contain rapids, but all other habitats were present in them. Strata E and A, which'were intermediate in fish species, did not contain rapids, but differed conspicuously from F and B since riffle habitat were virtually nonexistent (Figure 10). Strata C and D (Figure 10) contained a very diverse assemblage of habitats. However, the stress imposed on fishes by the rapids.in these areas and the short, heterogeneous ordering of the available habitats apparently dominated the response of different fish species and made these areas unsuitable habitat for many. Strata E contained the largest numbers of fish collected, followed by F, B, D, and C. Stratum E also contained a very high number of young fish, probably because of good nursery habitat afforded by backwaters and quiet eddies. Juvenile fish were collected in about the same numbers in all strata. Adult fish were most numerous in strata F, B, and E and less numerous in the canyon areas, C, A, and B. The number of young fish was dominated by red shiners and channel catfish. Adult fish were predominately red shiner, flannelmouth sucker, fathead minnow, channel catfish, and speckled dace. Various gear types differed in their ability to effectively sample different habitat types and tended to select for different species and sizes. Seines were effective in sampling shallow water areas for small fishes while trammel nets, gill nets, and electrofishing were more effective for larger fish in deeper water. Although not as effective in a variety of habitats as the other gear types,. wire traps were used in shallow, boulder substrate areas and where high water velocity dictated that other gear types could not be used. Seines were most effective for red shiner, fathead minnow, green sunfish, speckled dace, redside shiner, and sand shiner as well as small individuals of all the other species. Occasionally these small fishes were collected by electrofishing but not consistently. None of the above species were collected with trammel or gill nets. Although no statis- tical-analysis has been, done, there does not appear to be any difference between catch rates for 1/4-inch mesh seines and 1/8-inch mesh seines. Trammel nets were the most effective gear for large fishes in deep water areas. Electrofishing was more successful in shallow areas, particularly with.rubble or gravel substrate. No gear type was very effective for juveniles of the large species These individuals were generally large enough to avoid capture with • seines, but were not large enough to be captured with trammel nets. These fish were collected most effectively with electrofishing gear. 30