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II'< ~ r ~, J;; ,.,. ~ ~ ~. r It. .~, i?'" ...Ai 1t. ~ ;' " Most razorbacks from the Green River did not appear to be old or in poor condition as reported by other locations (Minckley 1983, Valdez et ale 1982). Although age validation has not been completed for razorbacks to our knowledge, an inspection of vertebrae from one 500 mm Green River specimen indicated the fish was about 12 years old. This is in sharp contrast to the ages proposed for lower basin razorbacks (30 years or more) by Minckley (1983). Based on the same slow growth rates observed from our recaptured fish (less than 5 mm per year) and from Minckley (1983), the estimated ages appear to be consistent with the range in lengths. All of the preceding suggests that Green River razorbacks are younger fish than found elsewhere, perhaps indica- tive of more successful recruitment. Spawning of the razorback sucker in the Green River Basin has been evidenced by collections of ripe fish by other investigators (McAda and Wydoski 1980, Holden and Crist 1981, Tyus et al. 1982). More collections of ripe adult and larval razorbacks in areas of apparentlY suitable spawning habitat during spring runoff confirm successful reproduction of the razorback in this basin. Reproduction of the razorback in the Green River is similar to some observations made in lower basin lakes: razorback spawned there at 14 to 16 C in shallow water over gravelly substrates, and congregated near inflowing rivers (Minckley 1983). Bulkley and Pimental (1983) found that hatchery-reared razorback preferred a temperature of 23 to 25 C. This study indicates that razorback spawned at a temperature of 15 to 16 C in 1984, suggesting that they spawn early in the spring each year at a much lower temperature than they prefer during the remainder of the year. Recaptures of razorback indicate that some fish migrate to specific locations for spawning. Such migrations have long been observed, as recently summarized by Minckley (1983), but are not well understood. population abundance estimates must take such migrations into account, since movements to areas that are easier to sample during the spring migration period can significantly inflate them. ACKNOWLEDGMENTS The information presented was obtained from U.S. Fish and Wildlife Service studies funded, in part, by the Bureau of Reclamation, Fish and Wildlife Service, and National Park Service. J.J. Krakker, R.M. McNatt, B.D. Burdick, and C.W. McAda were principles among the many Fish and Wildlife Service employees who aided in gathering the data. The States of Colorado and Utah provided logistical support. 201 -