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7/14/2009 5:02:32 PM
Creation date
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UCREFRP
UCREFRP Catalog Number
8096
Author
American Fisheries Society.
Title
Proceedings of the 19th Annual Meeting, Colorado - Wyoming Chapter, American Fisheries Society.
USFW Year
1984.
USFW - Doc Type
March 7-8, 1984.
Copyright Material
NO
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DLSCUSSION <br />The dependence of rainbow trout on zooplankton has often been demon- <br />- strated in the literature (Barton and Bidgood 1980, Galbraith 1967). In <br />Flaming Gorge Reservoir, zooplankton represented a significant portion of the <br />rainbow trout diet between 1963 and 1969 (Varley 1979, Wiley and Marley _ <br />1978). In 1981 zooplankton were the primary food item of rainbow trout up <br />to 400 mm in length (Schmidt et al. 1981). <br />Along with the intensive stocking of rainbow trout in Flaming Gorge <br />Reservoir from 1963 to the present, there have been increases in the abund- <br />ance of other zooplanktophagic fishes. From 1962 through 1981, 1.2 million <br />kokanee salmon, Oncorhynchus nerka, were planted (Schmidt et al. 1981). <br />Utah chub, Gila atraria, have greatly increased in abundance since impoundment <br />(Varley and Livesay 1976, Wiley and Varley 1978, Schmidt et al. 1981). <br />The white sucker, Catostomus commersoni, has also become established in the <br />reservoir. <br />It has been demonstrated that size-selective predation by fish stocks can <br />alter the composition and density of zooplankton communities (Wright et al. <br />1983, Mills and Schiavone 1982). Changes in the zooplankton community can <br />include a decrease in abundance, a shift to smaller forms, and a decrease in <br />mean size of large species. Comparison of zooplankton stocks in Flaming Gorge <br />Reservoir for 1965-66 and 1983 suggests that these changes are occurring. <br />Reduction in large sized zooplankton due to size-selective predation may <br />mean a lack of suitable-sized zooplankton for rainbow trout (Anderson 1980, <br />Galbraith 1975). It appears that this is the situation in Flaming Gorge <br />Reservoir where a sufficient population of suitable-size zooplankton is not <br />available for maintenance of a good rainbow trout fishery. <br />An additional complicating factor in Flaming Gorge Reservoir is an ex- <br />panding lake trout, Salvelinus namaycush, population. Recent evaluation of <br />lake trout diet in Flaming Gorge Reservoir indicates that predation on <br />recently stocked rainbow trout may be quite heavy (personal communication, <br />Thomas Pettengill, Utah Division of Wildlife Resources, Dutch John, Utah). <br />ACKNOWLEDGMENTS <br />We are grateful to Dave Dufek, Bill Wingert and Ed Berry of the Wyoming <br />Game and Fish Department and Tom Pettengill and Steve Brayton of the Utah <br />Division of Wildlife Resources for their valuable assistance during the 1983 <br />field season including equipment, lodging, and field aid. Base funding for <br />this research was provided by the [Jyoming Game and Fish Department with <br />supplemental funding contributed by the U.S. Department of the Interior, <br />Bureau of Reclamation, and the Utah Division of Wildlife Resources. <br />17 <br />
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