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speckled dace Rhinichthys osculus, and introduced channel catfish Ictalurus
<br />punctatus and green sunfish Lepomis cvanellus. (Preliminary Abstract)
<br />Report 13- Behavioral interactions between young Colorado squawfish and six
<br />fish species. (Karp and Tyus 1990b)
<br />We evaluated patterns of space use, activity, and agonistic interactions
<br />between young Colorado squawfish Ptvchocheilus lucius, an endangered cyprinid,
<br />and similar-size individuals of native and non-native fishes, including
<br />flannelmouth sucker Catostomus lati~innis, red shiner Notro his lutrensis,
<br />redside shiner Richardsonius balteatus, fathead minnow Pimeahales promelas,
<br />green sunfish Le orris cvanellus, and black bullhead Ameiurus melas, which co-
<br />occur in shoreline riverine habitats. Vertical distribution of Colorado
<br />squawfish was most similar to that of green sunfish and redside shiner. We
<br />detected no overt shifts in vertical space use by Colorado squawfish due to
<br />the presence of non-native fishes. Green sunfish, red shiner, and fathead
<br />minnow initiated more interspecific aggression than Colorado squawfish.
<br />Agonistic behavior in Colorado squawfish and flannelmouth sucker was mostly
<br />intraspecific. Redside shiner and Colorado squawfish were the most active and
<br />widely ranging species, but only red shiner, fathead minnow, and flannelmouth
<br />sucker significantly increased their activity during feedings. Predation by
<br />Colorado squawfish on live fish was slower than that of green sunfish, red
<br />shiner, and redside shiner. Overt physical damage was infrequent, however, the
<br />aggressive nature of the non-natives, in concert with similar activity
<br />schedules, space use patterns, and shared habitat use, suggests that green
<br />sunfish, red shiner, and fathead minnow may adversely affect growth and
<br />survival of age-0 Colorado squawfish. (Abstract)
<br />Report 14- Esox lucius (Esocidae), and Stizostedion vitreum (Percidae) in the
<br />Green River Basin, Colorado and Utah. (Tyus and Beard 1990)
<br />Northern pike, Esox lucius, stocked in the Yampa River in 1977, invaded
<br />the mainstream Green River by 1981, and subsequently increased in range and
<br />abundance. The speed of this invasion is indicated by two recaptured pike that
<br />moved 78 and 110 km, respectively, downstream in about one year. Pike stomachs
<br />(n = 123) were usually empty (54.5%), but some contained fish (43%) and non-
<br />fish items (2.4%). Red shiner, Notropis lutrensis, and fathead minnow,
<br />Pimeuhales promelas, predominated among the 12 fish species eaten. Walleye,
<br />Stizostedion vitreum, presumably introduced to the Green River drainage in the
<br />1960s, was widely distributed but low in abundance. Most of 61 adult walleye
<br />stomachs contained food (60.7%) and of 6 fish species eaten, channel catfish,
<br />Ictalurus punctatus, and fathead minnow were most frequently consumed.
<br />Northern pike and walleye were captured in habitats occupied by endangered
<br />Colorado River fishes, particularly Colorado squawfish, Ptvchocheilus lucius.
<br />Predation on endangered fishes was not detected, but northern pike and walleye
<br />consumed at least three other native fishes. The northern pike may pose a
<br />threat to endangered fishes due to its population expansion, piscivory, and
<br />resource sharing. Diets of northern pike and walleye should be further
<br />evaluated if their abundance increases. (Abstract)
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