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Last modified
8/11/2009 11:32:55 AM
Creation date
8/10/2009 12:30:39 PM
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UCREFRP
UCREFRP Catalog Number
7037
Author
Wyoming Game and Fish Department
Title
Fishery Research Report
USFW Year
1978.
USFW - Doc Type
Flaming Gorge Reservoir.
Copyright Material
NO
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DISCUSSION <br />Flaming Gorge Reservoir has been managed as an impoundment <br />consisting of three distinct environments; the canyon, open, and inflow <br />areas. These limnologically and topographically distinct areas support <br />fish populations showing differing growth patterns and divergent food <br />utilization patterns. The amount, volumetrically, of forage fish <br />ingested decreases down-reservoir corresponding to the decrease in <br />numbers of forage fishes demonstrated by gillnetting information. <br />Similarly, greatest use of zooplakton occurred in the open and inflow <br />areas, the location of greatest zooplankton production. It seems <br />apparent then that continued management of the reservoir on a tri- <br />area concept is valid. <br />The dependence on zooplankton demonstrated by our data indicates <br />the importance of the plankton population as a food source; the single <br />most important food can be considered zooplankton. Significant <br />reductions in this food base from whatever cause may have far- <br />reaching effects on the ecology of the reservoir fishery. <br />The use of zooplankton by rainbow and brown trout demonstrates <br />the single area of possible intra-specific competition. Since growth of <br />rainbow and brown trout are comparable it seems apparent that <br />intensive intra-specific competition does not exist. <br />Regarding niche concepts we could not demonstrate that zooplankton <br />taken by rainbow and brown trout originated from the same niche. <br />That the two species of trout may occupy separate but overlapping <br />niches is demonstrated by the use of forage fishes and zooplankton. <br />Significant departure in stomach contents occurred between brown and <br />rainbow when brown were 226 mm and rainbow were 455 <br />mm long; brown trout 226 mm and over included fishes as a <br />significant part of the diet while rainbow did not include fish as a <br />substantial part of the diet until they had reached 455 mm. As has <br />been indicated the single most important food item for all trout in <br />Flaming Gorge Reservoir is zooplankton, an indication of niche <br />overlap. <br />Brown trout in the 251 to 300 mm size range ingested significantly <br />more diptera than rainbow of the same size. That no other significant <br />differences occurred for any of the other food items suggests that <br />partial niche separation as well as behavioral differences occur. <br />The demonstrated cannibalism may have particular significance <br />regarding management with fingerling trout. With an increase in larger, <br />more predatory trout it should be expected that fingerling survival <br />would be reduced. Stocking of larger trout may become necessary. <br />Trout captured from pelagic and littoral habitat were expected to <br />show difinite differences in food utilization. Trout taken from pelagic <br />areas consumed more zooplankton and fish than trout from inshore <br />areas, perhaps, indicative of the availability of these foods in pelagic <br />14
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