7969 - Laserfiche WebLink

Home Browse Search

1990] HUMPBACK CHUB IN DINOSAUR NATIONAL MONUMENT 263 humpback chub were captured at tempera- tures (ac = 19.5, range = 14.5 -23 C) that approximate optimum egg incubation condi- tions (i.e., 20 C; Marsh 1985}. These tempera- tures are similar to the 14-24 C range noted by Kaeding et al. (1990) but slightly higher than the 11.5-16 C temperatures noted by Valdez and Clemmer (1982), both in the up- per Colorado River. All humpback chub and most roundtail chub in breeding condition were captured in shoreline eddies. Our recapture data indicate that adult humpback chub remain in or near specific eddies for extended periods and that they return to the same eddy during the spawning season in different years (i. e. , they exhibit a fidelity to a specific site). Ten of the 11 recaptures were captured in the same eddy as the initial capture (50% in two different spawning seasons), and 73% were captured in breeding condition at least once. We do not know whether these fishes deposited eggs in these eddies or used such habitats only for staging, resting, or feeding. However, we consider the use of such habitats as part of the breeding requirements of humpback chub in the Yampa River. Shoreline eddy habitats in Yampa Canyon were ephemeral (i, e. , disap- peared with declining summer flows), and it was obvious that the fish moved elsewhere after the spawning period. Our observations of Gila species in pools near Big Joe Rapid in September 1989 suggest that some fish re- main in nearby deep habitats during low-flow periods. Feeding habits of humpback chub are not well known and were unknown in DNM. Cap- ture of some fish in the interfaces between shoreline eddies and adjacent runs suggests that chubs use these areas for feeding on drift. Stomachs of two humpback chub that died in trammel nets contained hymenopterans and plant debris; and gross examination of fecal material taken from live fish indicates exten- sive use of hymenopterans and other terres- trial insects (e.g., Mormon crickets) as food. We observed humpback chub and other fishes (e.g., roundtail chub, common carp) feeding on Mormon crickets at the water surface in eddies. The high numbers of channel catfish in habitats used by humpback chub and round- tail chub and the gross overlap in foods consumed and in feeding habits (Banks 1964, Holden and Stalnaker 1975a, Tyus and Minckley 1988, Tyus and Nikirk 1990) indi- cate apotential for negative interactions be- tween these fishes. Although the incidence of predation by channel catfish on native fishes is unknown, observations of bitelike abrasions on some chubs collected in DNM suggest channel catfish predation because no other piscivorous fish in that system could have caused such damage. Humpback chub re- mains were found in channel catfish stomachs from the Little Colorado River (W. L. Minck- ley, personal communication}, and channel catfish are known to consume fish, fish parts, and eggs in DNM (Tyus and Nikirk 1990). Only a few common carp were captured syn- topically with humpback chub. However, we speculate that their abundance may also have some negative impact on the native fishes, due perhaps to predation on eggs. The humpback chub persists in only a few canyons in the Colorado River basin, and planned water development projects may fur- therjeopardize its survival. The Yampa River in DNM supports all native fishes known to have occurred there, including the endan- gered humpback chub, Colorado squawfish, and razorback sucker (Xyrauchen texanus). Existing flows of the Yampa River inay be singularly responsible for enabling the persis- tence of chubs in the Yampa and Green rivers. Alteration of Yampa River flows could reduce the availability or character of chub spawning habitat and presumably adversely affect their reproduction, aid in further proliferation of introduced competitors and predators, and reduce the quality and quantity of usable habitats. Dinosaur National Monument should be considered a refugium for native fishes, and efforts should be made to protect flows of the Yampa River. ACKNOWLEDGMENTS This study was funded in part by U. S. Fish and Wildlife Service, Bureau of Reclamation, National Park Service, and the Northern Col- orado Water Conservancy District. J. Beard, P. Clevenger, and L. Trinca were among several who assisted with data collection. P. B. Marsh, C. O. Minckley, and W. L. Minckley improved an earlier draft of the manuscript.