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TaDle 1. Number of northern pike sampled by year and river reach in the Yampa River. RIVER REACH YEAR Total Craig Juniper Maybell Lily Yampa No. Park Canyon 1986a - 3 4 - - 7 1987a - 2 6 4 - 12 1988 31 3 29 28 - 91 1989 100 34 23 12 1 175b 1990 78 20 24 18 2 143c 1991 55 15 23 34 1 128 TOTAL 264 77 109 96 4 556 a Fish sampling was for radiotag implantation only. b Includes 5 fish recaptured by anglers; 3 from Elkhead Reservoir, 2 from unreported locations. c Includes 1 fish recaptured by an angler from Elkhead Reservoir. Examination of potential trends in northern pike numbers over years and reaches was considered possible due to the consistency of sampling effort in time and space within well- defmed backwater habitat. As indicated previously, sampling was accomplished primarily in discrete backwater habitats in a stabilized river channel. In the Juniper, Maybell, and Lily Park reaches, backwater habitats were similar in number and location due to the relatively "fIXed" nature of the river channel, lack of numerous secondary channels, and creation of backwater habitat annually at tributary mouths. It was assumed that northern pike captured in these habitats used them due to biological need or preference, and that the proportion of fish using these backwater habitats reflected the species' population abundance in the reach. Each backwater habitat was considered a sampling unit since they were all sampled consistently the same. Therefore at the individual habitat level, sampling effort was assumed to be equal. At the reach level, all backwaters in the Juniper, Maybell, and Lily Park reaches were sampled one or more times per year, and sampling effort differed mostly as a result of the period of time they were available for sampling. Comparison of catch rate estimates for northern pike and other species is presented in the habitat association section of the report. Len2th frequencv distributions Lengths of 542 northern pike collected ranged from 87 to 1118 nun total length and examination of their frequency distribution was possible by years and river reaches. Over the four time periods shown, the length frequency distributions did not demonstrate any notable lateral shifts in size composition of the sample population, but their relative shape did vary 16