Colorado Pikeminnow with a Channel Catfish Lodged in Its Throat in the San Juan River, Utah

Abstract

the decline of the Colorado pikeminnow and other native fish species (McAda, 1983; Pimental et al., 1985). Populations of Colorado pikeminnow remain in the Green, White, Yampa, Colorado, and San Juan rivers (Minckley and Carothers, 1979; Holden and Wick, 1982; Platania et al., 1991; Tyus, 1991; Ryden and Ahlm, 1996). Colorado pikeminnow was listed as endangered by the United States Fish and Wildlife Service in 1974 (Federal Register 39:1175, 1974) and is protected by all states in its historic range (Propst, 1999). Colorado pikeminnow begin to feed on fish at 50 mm total length (TL; Vanicek and Kramer, 1969). Adult Colorado pikeminnow, which can achieve 948 TL in the San Juan River (Ryden and Ahlm, 1996), can take prey 1/3 to 1/2 their body length (Osmundson et al., 1998). Prior to the establishment of nonnative fishes, soft-rayed fishes were the only prey available to Colorado pikeminnow (Holden and Wick, 1982; Pimental et al., 1985). Establishment of nonnative, hardand spiny-rayed fishes, including channel catfish, (Ictalurus punctatus), exposed Colorado pikeminnow to a potential choking hazard which was previously nonexistent. Anecdotal reports of Colorado pikem nnow with channel catfish lodged in their throats (e.g., Vanicek and Kramer, 1969) were undocumented until 1983. McAda (1983) collected an adult Colorado pikeminnow (550 mm TL) from the Green River in 1974 with a channel catfish (120 mm TL) lodged in its throat. Three similar incidents subsequently were reported from the Green River in 1982 and 1983 (Pimental et al., 1985). Our collection of a juvenile Colorado pikeminnow with a channel catfish lodged in its mouth from the San Juan River offers a new perspective on this phenomenon, especially as it relates to recovery efforts for Colorado pikeminnow in the San Juan River. On 1 October 1999, at approximately 1145 h while electrofishing at river kilometer (RK) 138.4, 12.1 km downstream of the bridge at Montezuma Creek, Utah, we collected a subadult Colorado pikeminnow (346 mm TL) with a channel catfish (111 mm TL) firmly lodged in its mouth anterior to the gills. The channel catfish was alive and struggling, with spines extended. The dorsal spine had penetrated the roof of the Colorado pikeminnow's mouth and had entered the right eye socket causing distention and hemorrhagic swelling. Both pectoral spines had penetrated the sides of the Colorado pikeminnow's mouth. The posterior end of the channel catfish, from just anterior to the adipose fin, protruded from the Colorado pikeminnow's mouth. A strip of flesh about 10 mm wide was worn from the body of the channel catfish, where the Colorado pikeminnow's mouth would normally close. We photographed the fishes, then removed the channel catfish from the Colorado pikeminnow's mouth by severing the spines and backing the fish out of the mouth. Both fish were weighed and measured. The channel catfish was removed from the river and the Colorado