Behavioral Interactions between Young Colorado Squawfish and Six Fish Species

Abstract

We evaluated patterns of space use, activity, and agonistic interactions between young Ptychocheilus lucius, an endangered cyprinid, and similar-size individuals of native and non-native fishes (i.e., Catostomus latipinnis, Notropis lutrensis, Richardsonius balteatus, Pimephales promelas, Lepomis cyanellus, and Ameiurus melas), which co-occur in shoreline riverine habitats. Vertical distribution of P. lucius was most similar to that of L. cyanellus and R. balteatus. We detected no overt shifts in vertical space use by P. lucius due to the presence of non-native fishes. Lepomis cyanellus, N. lutrensis, and Pimephales promelas initiated more interspecific aggression than Ptychocheilus lucius. Agonistic behavior in P. lucius and C. latipinnis was mostly intraspecific. Richardsonius balteatus and P. lucius were the most active and widely ranging species, but only N. lutrensis, Pimephales promelas, and C. latipinnis significantly increased their activity during feedings. Predation by Ptychocheilus lucius on live fish was slower than that of L. cyanellus, N. lutrensis, and R. balteatus. Overt physical damage was infrequent, however, the aggressive nature of the non-natives, in concert with similar activity schedules, space use patterns, and shared habitat use, suggests that L. cyanellus, N. lutrensis, and Pimephales promelas may adversely affect growth and survival of age-0 Ptychocheilus lucius. THE native fish fauna of the Colorado River