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Zion National Park

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Thus far in the study, 4 species of endemic fishes and 2 introduced trout species have been collected, measured for total length, and in some cases, weighed, and then released. Sampling has been accomplished by electroshocking on 6, 7, 8, and 9 July, 1987, at 4 sites on the East and North Forks of the Virgin River, as well as 1 site on the Santa Clara River, and 1 site on Moody Wash near Mogatsu Creek, a tributary of the Santa Clara River. Seining, measuring, and releasing was done on 3, 4, and 20 September, 4 and 10 October, and on 9 and 10 January, 1988, at five sites on the East and North Forks of the Virgin River. Electroshocking was used on 9 January, 1988 at one of the North Fork sites, utilizing a backpack electroshocker unit borrowed from Donna Withers, of the Nevada Department of Wildlife. On 24, 29, and 30 August, fish were surveyed by seining or dip netting at Lytle Ranch, on Beaver Dam Wash, a tributary of the Virgin River, for purposes of determining favorable habitat conditions under a different regime. Electroshocking was determined to be limited in use in the Virgin River system, due to the frequent turbidity of the water, and the depth of the pools. In winter we have not collected substantial numbers of any species, with either electroshocking or seining techniques. It is possible that the fish are located in places unaccessible to our sampling techniques, or possibly they have undertaken significant migration to other locations, most likely towards the warmer waters of lower elevations. Mass mortality can be ruled out due to the fact that all fish species have been observed to reappear in early spring. We need to revise our sampling techniques, and are working on a variety of different procedures to be able to collect fish in winter, or find out where they live. The limitations of the winter habitat may prove to be an important factor in the continued success of the spinedace in the Virgin River in Zion. The borrowed electroshocking equipment seems marginally successful in sampling fishes in the highly conductive water of the Virgin. A more powerful unit needs to be procured. When the water is clear, shocking works well because the fish can be visualized and netted while immobilized by the shocker, but the frequent turbidity of the water would make any fish not surfacing impossible to see and catch, even though it was immobilized.