6012 - Laserfiche WebLink

Home Browse Search

critical to some phase of their life cycle. In order to meet these objectives and limit bias, a systematic sampling program was developed with a randomized start. This ensured the equal pursuit of these fishes across the full spectrum of habitats throughout the study area and permitted interpretation of results independent of bias. Sampling program design and detailed methods of acquiring data are detailed in Appendix A. Other field investigations addressed specific facets of the target fish's life histories and environmental needs. These were directed at describing spawning areas, migratory behavior, prevalence of disease, tolerances to natural and artificial chemical compounds, interspecific competition, speciation, and striped bass predation. Many difficulties were encountered in studying the fish fauna of this large river system because of large areas encompassed, large flows encountered and inaccessability of certain reaches. Water turbitity further complicated the study by precluding any possibility of directly observing various aspects of these fishes behavior or location, therefore, all hypotheses ventured had to be extrapolations from fish captures using a variety of devices; some active, others passive. One solution that was adopted to help resolve this problem was to directly observe northern squawfish which inhabits streams of much greater clarity in the Columbia River Basin. The Idaho Cooperative Fishery Unit was enlisted to conduct those in situ behavioral studies of the northern squawfish as a surrogate to the Colorado squawfish. Program objectives also included areas of investigation that could be dealt with only in a laboratory setting. These included such areas as swimming stamina, temperature tolerance and preferences, total dissolved solids tolerance and preferences, and bioassay tests for potentially toxic trace elements. These investigations were contracted to the Utah and Idaho Cooperative Fishery Units at Logan, Utah and Moscow, Idaho. A third area of investigation included in the study program was the culture of these species both to fulfill the need for laboratory specimens and to advance cultural technologies for them. These activities were centered at the Willow Beach National Fish Hatchery with satelite programs at the Utah State Fisheries Experiment Station and Dexter National Fish Hatchery. These programs dealt with the use of hormones to induce spawning, incubation of eggs and rearing of fry and older fish. A fourth area of study that received some attention was the issue of taxonomic classification of the three endemic Gila species. The appropriate taxonomic designation of these fish has been clouded by much variability between specimens and hybridi2ation. A review of the meristic characteristics of these fish by our field staff and seveFal noted taxonomists was undertaken along with a cytogenetic karyotyp`~'of ~- the various Gila spp. by a scientist at Utah State University.