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1 3.5 Northern Pike Removal 3. S.1 Translocation of Northern Pike From Critical Habitat in the Yampa River (Project No. 98; CDOW, Larval Fish Laboratory/Colorado State University) Northern pike were translocated from the Yampa River during 1999-2001. The purpose of the translocation was to reduce risk of predation and competition of northern pike on endangered Colorado pikeminnow. The objectives of the project were to (1) remove by translocation northern pike from the Yampa River to Rio Blanco Reservoir (a small reservoir in the White River drainage in northwestern Colorado), and (2) determine the effectiveness of removal through length-frequency analysis and catch-per-unit-effort data. Northern pike were first introduced into the Yampa River drainage in 1977 when 700 fish were stocked by the Colorado Division of Wildlife into Elkhead Reservoir, an impoundment on Elkhead Creek which is a tributary of the Yampa River just upstream of Craig, Colorado (Figure 10). The first northern pike were reported in the Yarnpa River in 1979, and guiding services for anglers began in the 1980's (Figure 11). Elkhead Reservoir was drawn down in 1993 and again in 1999, resulting in additional releases of fish into the Yampa River. Northern pike were illegally released into Stagecoach Reservoir in about 1994, an impoundment on the Yampa River upstream of Steamboat Springs, Colorado. Northern pike were captured during four sampling occasions, each 11 days long. Sampling was conducted during spring runoff when, adults were congregated to spawn in or near backwater habitats. Shoreline electrofishing, block and shock, and fyke nets were used to capture fish (Table 5). Shoreline electrofishing with one or two boats covered approximately 75 miles of shoreline. A combination of electrofishing and trammel nets (i.e., block and shock) was used to capture fish in backwaters, and fyke nets were set overnight in backwater habitats. Although greater numbers of northern pike were captured in backwaters in the first three trips of 2000 (Figure 12), approximately half of all fish were captured in backwaters (52%) and about half were captured in the main channel (48%). In 2001, 70% of the northern pike were captured in the main channel and 30% were captured in backwaters: The majority of northern pike and the majority of Colorado pikeminnow were captured with electrofishing (Figure 13). A total of 784 northern pike were removed and translocated during 1999 2001, and 246 Colorado pikeminnow were captured and released (Table 5). The ratio of northern pike to Colorado pikeminnow ranged from 1.9:1.0 to 5.3:1.0, for an overall average of 3.2:1.0. A notable change in the range of ratios occurred in the three sample sites between 1988-1991 (1:1-4:1) and 1999-2000 (6:1-11:1). (Figure 14). Ratios for only two sites during 2001 were 2:1 and 3:1, These data are inconclusive as to the trend of either species. Length-frequency analysis of northern pike captured in 2000 and 2001 (Figure 15) showed a shift to a higher mode in 2001; i.e., fish captured in 2001 were larger than those captured in 2000. 27 ~~ 1 r- J 1 1 1 1