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EXPLOITATION OF LAKE TROUT IN FLAMING GORGE RESERVOIR MARVIN W. WENGERT, JR. WYOMING GAME AND FISHDEPARThffiNT GREEN RIVER, WYOMING 82935 ABSTRACT Since 1981, the exploitation of lake trout (Salvelinus narnaycush) from Flaming Gorge Reservoir has become a major concern of fisheries managers from Utah and Wyoming. Harvest of lake trout was greatest from 1979 through 1981, but harvest declined in 1982. Fishing pressure for lake trout has been increasing yearly. In response to the concerns of possible overfishing, a lake trout exploitation study was initiated in 1981. The study was also conducted during 1982 and 1985. Lake trout were captured, tagged with $5.00 reward tags and released. The rate of exploitation was dependent upon the voluntary return of the tags. First year exploitation rates were 4.3% for the fall 1981 and 9.9% for the spring 1982 tagged fish. The rate of exploitation for the spring tagged 1985 fish is 13.3% with 2.5 months remaining in the ftrst year period. The report describes the methods used to capture and tag lake trout, the tags employed, the data taken from captured lake trout and how tag returns were handled. The report also describes the length frequency of tagged lake trout, movement in the reservoir, survival of tagged ftsh and gives a population estimate based on the 1982 harvest and tag return data. INTRODUCTION Flaming Gorge Reservoir, located in southwest Wyoming and northeast Utah, was created by impoundment of the Green River in November 1962. When filled to capacity, the reservoir is 91 miles long, has a maximum surface area of 42,000 acres and a mean depth of 111 feet. Maximum depth near the dam is 440 feet. Flaming Gorge Reservoir had been cooperatively managed and studied by the Wyoming Game and Fish Department and the Utah Division of Wildlife Resources since its impoundment. The reservoir has been divided into three areas for study purposes. These are the Inflow, Open Hills and Canyon areas. The Inflow area consists of the northern 39 miles of the resevoir and can be described as eutrophic in character. It is highly influenced by the inflow of the Black's Fork and Green River. The Open Hills extends 28 miles to the south where the reservoir enters the Flaming Gorge. The Open Hills is a transition zone between the eutrophic water of the Inflow area and oligotrophic waters of the Canyon. This area is characterized by gently sloping shorelines, rolling sagebrush hillsides, moderate depths (ranging to just over 200 feet) and extensive littoral bay areas. The Canyon extends 24 miles from the mouth of the Flaming Gorge to the dam near Dutch John, Utah. The Canyon is characterized by steep rock walls, deep waters and limited littoral areas. Lake trout (Salvelinus namaycush) became established in Flaming Gorge Reservoir through downstream drift from the Finger Lakes of the upper Green River. Natural reproduction has maintained and is responsible for the increasing lake trout fishery in Flaming Gorge. Lake trout were first reported in the creel as early as 1971, but were not reported in significant numbers until 1975. By 1977, a trophy lake trout fishery had been established. 15