Date of Award:


Document Type:


Degree Name:

Master of Science (MS)


Wildland Resources

Department name when degree awarded

Wildlife Science

Committee Chair(s)

Richard S. Wydoski


Richard S. Wydoski


Donald B. Porcella


Charles W. Fowler


The distribution, abundance and life history were studied for three catostomids -- the razorback sucker (Xyrauchen texanus), the flannel-mouth sucker (Catostomus latipinnis), and the bluehead sucker (Catostomus discobolus) -- all native to the upper Colorado River basin. The razorback sucker has declined in abundance due to man's impact upon the system and it has been recommended that this species be listed as ''threatened" on the U. S. Department of the Interior's list of Threatened or Endangered species [Personal corrmunication, G. C. Kobetich, U. S. Fish and Wildlife Service, Las Vegas, Nevada]. During this investigation, razorback suckers were found in relatively large concentrations at the mouth of the Yampa River and in a flooded gravel pit connected to the Colorado River near Grand Junction, Colorado. Flannelmouth and bluehead suckers were collected in large numbers throughout the study area.

Razorback and flannelmouth suckers spawned in April and May, when water temperatures were between 6 and 15 C. Bluehead suckers spawned later (June and early July) when water temperatures exceeded 15 C. It can be inferred from this study that razorback suckers made a spawning migration, but the data are insufficient to draw any conclusions about the pervasiveness of this phenomenon. There was no evidence that flannelmouth or bluehead suckers made a spawning migration.

Fecundity of razorback suckers was variable and ranged from 24,490 for a fish 529 mm in total length (TL) to 76,576 eggs for a fish 485 mm TL. The youngest razorback sucker that was collected during this study was age IV; all razorback suckers were mature. Flannelmouth suckers first matured at age IV and most fish were mature by age VII. Flannelmouth sucker fecundity ranged from 4,000 eggs (450 mm TL) to 40,000 eggs (500 mm TL). Bluehead suckers produced as few as 4,000 (340 mm TL) and as many as 20,000 eggs (430 mm TL). Bluehead and flannelmouth suckers from the Colorado River produced significantly greater numbers of eggs than fish of equivalent lengths from the Green and Yampa Rivers.

Razorback and flannelrnouth suckers collected in 1974-76 attained a maximum age of nine years. Razorback suckers from the Colorado River were significantly longer than fish of the same age from the Green and Yampa Rivers. Flannelmouth suckers from the Colorado River were significantly heavier than fish of equivalent lengths from the Green and Yampa Rivers. The differences in fecundity and growth rates for fish from the two locations can probably be attributed to differences in temperature between the rivers.