Life history and ecology of the Colorado squawfish (Ptychocheilus lucius) in the upper Colorado River basin
Category: Wildlife Science
Author(s): Karl Seethaler
Author(s): Karl Seethaler
Description: The Colorado squawfish (Ptychocheilus lucius) was once abundant throughout the Colorado River system; it is now an endangered species found in small numbers only in limited portions of the upper basin. The major cause of this decline is attributed to man-made alterations of the river environment. The Endangered Species Act of 1973 was enacted in response to increased public concern for vanishing native wildlife, although the rationale for the preservation of species is not yet universally under stood. Federal and state agencies charged with the management of en dangered species and their environments found that they needed to gather considerable information on such endangered species as the Colorado squawfish. This work constitutes a broad synthesis of current knowledge about the Colorado squawfish: distribution, abundance, habitat requirements, systematics, reproduction, early life development, age and growth, food habits, movement, maturity, diseases and parasites, causes of decline, and the phenomenon of its endangered status. The main objective was to synthesize this knowledge into a single volume to aid in effective man agement decisions. An exhaustive chapter on historical and present distribution of the Colorado squawfish documents every known sighting of this species in all rivers and tributaries in the Colorado River system since 1825. A wide ranging piscivore, this species frequents all habitat types in the river except the cold headwaters, though it was most often found in eddies, backwaters, and deep holes. Field observations were made primarily in Dinosaur National Monument and adjacent areas of the upper Green and Yampa rivers, and at Grand Junction on the Colorado River main stem. Trammel nets, seines, and occasionally electrofishing were used to capture fish. The Colorado squawfish, one of four species of the genus Ptychocheilus, evolved with the Colorado River system. Attesting to its reputation as a food and sport fish, it has locally acquired such names as "salmon," "whitefish," and "pike." In fact, the species is the largest cyprinid in North America, a family which arrived in this con tinent about the time of the Miocene epoch. Although captured from two widely separated geographical localities in the Colorado and Green Rivers, the species apparently consists of a single population. Analysis of electrophoretic and meristic data failed to show any intraspecific differences between fish captured from these two locations. Positive identification of larval and juvenile fish often presents a problem to collectors. Because there is a need for adequate descrip tions of the young, a series of 15 detailed drawings was made using a "camera lucida." These drawings document the development of young Colorado squawfish from egg, various larval stages, and juveniles. Morphometrics and meristics were tabulated for each stage. Age and growth were similar for fish captured in the Yampa-Green Rivers and Colorado River at Grand Junction, Colorado, during 1974-76. Moreover, there was no significant difference between these fish and those from the upper Green River in 1964-66. Colorado squawfish became mature when individuals reached a size of 428-503 mm in total length and an age of 6-8 years. Spawning re quirements were speculated from observations in the field and hatchery, and comparison from related species. Food habits are similarly deduced from observations and the literature. Movement of the Colorado squawfish has been difficult to validate, but seasonal patterns were noted. Two squawfish were tracked briefly with the use of sonic tags. The most common parasite of the Colorado squawfish is the copepod, Lernea sp. Other parasites and diseases include the fungus, Ichthyophthirius sp., the tapeworm Proteocephalus ambloplites, and the protozoa Myxosoma sp. and Myxobolus sp. The decline of the species appears to have resulted from the loss of habitat due to environmental changes in stream flow and biological composition. Dewatering, dams and reservoirs, alteration of stream flow and stream morphology, changes in water quality, and the introduction of exotic species are discussed as being the principal causal factors. While additional studies would be useful to management, the urgency of the situation indicates the need for expeditious efforts at preser vation. Artificial propagation is a very important means of buying time and should be vigorously undertaken for all endangered native species. Public education, in the long run, is probably the most important con sideration. Further water development projects, especially in the upper Green River and its tributaries, should be considered incompatible with the recovery effort.