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I in the Maybell reach, 49 northern pike in the Lily Park reach, and 1 in Yampa Canyon. Sizes of northern pike examined ranged from 87 to 1036 mm total length and examination of the length frequency distribution of these fish shows this sample was representative of the sample population size distribution (Figure 11). Also, the size distribution of northern pike containing food in their gut was quite similar to the size distribution of northern pike with empty stomachs. Overall, 63.8 % of the northern pike examined had ingested fish prey. Non-fish food items were found in 7.5 % of the northern pike examined and 36.1 % of the northern pike had no food in the stomach (Figure 12). Twelve species of fish prey ingested by northern pike were identified. In order of abundance, fish prey included redside shiner Richardsonius balteatus, roundtail chub Gila robusta, white sucker Catostomus commersoni, speckled dace Rhinichthys osculus, flannehnouth sucker Catostomus ladpiwds, mottled sculpin Cottus bairdi, bluehead sucker Catostomus discobolus, plains killifish Fundulus zebrinus, fathead minnow Pimephales promelas, common carp Cyprinus carpio, green sunfish Lepomis cyanellus, and sand shiner Notropis stramineus. Northern pike prey composition was dominated by four species; two non- native species comprised 42.3 % of the fish eaten and two native species comprised 13.6 %. By species, redside shiner comprised 33.3 %, roundtail chub comprised 9.5 %, white sucker comprised 9.0 %, and speckled dace comprised 4.1 % of the prey composition. The remaining seven species made up 9.5 % of the prey identified and 34.7 % of the fish prey could not be identified. Only in two instances were two different fish species found together in a northern pike stomach. In the spring months of April through June, 60% of the 160 northern pike stomachs contained food. In the fall months of September through November, 74% of the 31 northern pike stomachs contained food. Other food items identified in northern pike stomachs included Cladocera, Annelida, Insecta, Decapoda, and Anura. In two other studies occurring downstream in the middle Green River below the confluence with the Yampa, Tyus and Beard (1990) found 54.5 % of 58 northern pike stomachs to be empty. Frequency of occurrence of fish species ingested were red shiner Cyprinella lutrensis at 7.3 %, followed by fathead minnow, flannehnouth sucker, and speckled dace. Another eight fish species comprised 13.6 % of the fish prey and 10.6 % could not be identified. Non-fish prey occurred in 2.4% of the northern pike. Overall, nine introduced fish species comprised 25% of northern pike stomach contents and three native species comprised 9%. Crowl et al. (1995) examined 26 northern pike and found stomach contents comprised of 5 % juvenile Colorado squawfish and 72% other cyprinid species, followed by mice, crayfish and sucker species. Seasonal differences were also noted by Crowl et al. with 89 % of the northern pike containing food in the spring and 12.5% in the fall. In studies elsewhere, Rich (1992) observed empty stomachs in 63-74 % of northern pike during the spring and 45-69 % in the fall. Headrick (1985) also noted high percentages of empty stomachs in northern pike. Northern pike feeding was determined to be more intense during spring and fall (Seaburg and Moyle 1964, Weithman and Anderson 1977). Headrick and Carlin (1993) noted condition factors for northern pike in impoundments was highest in the spring and lowest in late summer. They found northern pike would lose weight during the summer and gain again in the fall. DRAFT March 12, 1996 35 1