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1 Common carp were notably less vulnerable to northern pike predation. Common carp at 380 mm in length were vulnerable to only 51 % of the northern pike population and potential northern pike predators started at 570 mm in length or larger (Figure 18). Forty-eight percent of the common carp population appeared invulnerable to predation by northern pike of any size. Based on the length frequency distribution of common carp and the northern pike prey size cap, 49% of the common carp population are vulnerable to northern pike predation (Figure 16). The percentages of vulnerability to northern pike predation based on body area are summarized in Figure 19. Bluehead sucker appear to be the most vulnerable to northern pike predation, followed by roundtail chub, flannelmouth sucker, white sucker, common carp, and Colorado squawfish. Using the maximum prey size index, bluehead sucker and roundtail chub appear wholly vulnerable as populations to northern pike predation, followed in decreasing degree of vulnerability by white sucker, tlannelmouth sucker, common carp, and Colorado squawfish. In comparison with fish prey composition results, the ingestion of roundtail chub and white sucker support this estimated vulnerability, while bluehead sucker and tlannelmouth sucker are notably less frequent in the northern pike diet, despite the apparent physical vulnerability . In the Crowl et al. (1995) study, the juvenile Colorado squawfish consumed were 45-54 mm TL and were 7.5-10.8% the length of the northern pike predators. Rich (1992) found prey size to range from 5-57% of northern pike size in an Idaho lake system and averaged 19-31 % over several areas. He found prey length to be positively correlated to northern pike length, and the slope of the regression of prey to northern pike length was near 38 % . Movements Northern pike movements were investigated through the use of radio telemetry and mark- and-recapture of Floy-tagged fish. A total of 37 northern pike were implanted with radio transmitters (radiotagged) during the study period (Appendix A, Table A-6). Seven fish were radiotagged in October 1986, seven were tagged in August, September, October 1987, 11 fish were tagged in August and October 1988, 3 fish were tagged in May and June 1989, and 9 fish were tagged in 1989. These fish ranged in length and weight from 548 mm and 1000 gm to 1003 mm and 6225 gm. Only within the initial group of radiotagged fish were two fish under the 600 mm length criterion. All radiotagged northern pike were released at the point of capture. Ten northern pike were tagged and released in the Craig reach, 8 fish were tagged and released in the Juniper reach, 13 fish were tagged and released in the Maybell reach, and 6 northern pike were tagged and released in the Lily Park reach. A total of 165 relocation contacts resulted from these radiotagged fish. One hundred sixty-three (163) contacts were subsequently used from 34 of the radiotagged northern pike to assess net movements of northern pike (Appendix A, Table A-7). Only three northern pike (Nos. 2, 163, and 901), all tagged and released in the Juniper reach, were never relocated. Based on determinations that two transmitters may have been expelled, 2 relocation data points were omitted. Net movement by individual fish between contacts ranged 54 l