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Last modified
7/14/2009 5:02:32 PM
Creation date
5/22/2009 5:33:47 PM
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UCREFRP
UCREFRP Catalog Number
8099
Author
American Fisheries Society.
Title
Proceedings of the 21st Annual Meeting, Colorado - Wyoming Chapter, American Fisheries Society.
USFW Year
1986.
USFW - Doc Type
March 5-6, 1986.
Copyright Material
NO
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<br />Wild brown dominated the pre-season trout population at both stations, accounting for 88% of <br />the population numbers and 76% of the biomass at Station 1 and 99% of the numbers and 98% of the <br />biomass at Station 2. Carrying capacities of the two stations differ, primarily due to differences in the <br />size of the stream and the amount of habitat. <br /> <br />Preliminary Habitat Quality Index (HQI) (Binns and Eiserman 1979) scores are 808.2 <br />pounds/acre and 778.3 Habitat Units (HUs) for Station 1 and 358.3 pounds/acre and 348.2 HUs for <br />Station 2 (Dr. Allen Binns, personal communication). <br /> <br />Trout populations declined significantly at Station 1 between April and November 1985. <br />Brown trout decreased by 1,640 fish/mile (28%) and 216.8 pounds/acre (28.3%) from April to <br />November 1985 and rainbow decreased by 361 fish/mile (45.5%) and 134.4 pounds/acre (55.5%). <br />At Station 2 from April to November 1985, there was a significant decrease of 872 brown trout/mile <br />(20.6%) and 190.5 pounds/acre (35.5%) and no decrease in the rainbow trout numbers. All of the <br />reduction in numbers at each station between April and November 1985 were in the fish over six <br />inches. <br /> <br />Brown trout averaged slightly larger at Station 1 than at Station 2 and the majority of the brown <br />collected were between six and 12 inches at both stations (Figure 1). Only one "large" fish was <br />collected during all the sampling, a 24.5 inch, 7.2 pound brown collected at Station 1 in April 1985. <br />Rainbow were larger in size than brown trout at both stations. The general lack of rainbow less than <br />six inches at both stations indicates natural reproduction of rainbow is very low, if present (Figure 2). <br />Rainbow up to 17 inches were collected at Station 1. <br /> <br />Average condition factors varied only slightly between sampling dates at the same station, but <br />indicated that brown and rainbow collected in November 1985 at Station 1 and brown from Station 2 <br />had higher condition factors than in April 1985 or November 1984 (Figures 1 and 2). Brown trout <br />from Stationl generally had higher condition factors than brown from Station 2 (Figure 1). <br /> <br />The number of brown trout less than six inches was proportionately greater at both stations in <br />the November 1985 estimates than on either of the other two sampling dates indicating increased <br />survival of young-of-the-year brown and a strong year class in 1985. At Station 2 in November <br />1985, 56% of the brown trout population was less than six inches. Brown trout less than six inches <br /> <br />also represented a greater proportion of the population at Station 2 than at Station 1 during all the <br />sampling periods. <br /> <br />In order to assess the influence of the 1985 fishing season, population estimates for Stations 1 <br />and 2 were combined and weighted for the section open to fishing. Relative estimates of mortality <br />were then calculated (Table 3). Mortality estimates increased substantially between April and <br />November 1985 due to a 24% reduction in estimated brown trout numbers (32% in biomass) and a <br />43% reduction in rainbow numbers (56% in biomass). The larger decrease in biomass than in <br />numbers is due to the greater proportion of the decrease being in fish over six inches. <br /> <br />The large decrease over the summer of 1985 logically suggests that the first year of open <br />fishing caused the sharp rise in mortality. However, fishing harvest only partially explains these <br />decreases. For the May through August 1985 period, an estimated 333 fishermen fished 719 <br />hours/stream mile on Ranch A. Harvest rates for the season were 0.35 fish/hour for brown and 0.23 <br />fish/hour for rainbow'or 0.53 fish/hour for both species combined. ,Total catch rates (kept and <br />released) were 1.42 brown/hour, 0.53 rainbow/hour and 1.85 fish/hour for both species combined. <br />Seventy five percent (75%) of the brown and 57% of the rain~ow caught were released. <br /> <br />9 <br />
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