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39 In this study the captured fish ranged in length from 444 mm to 620 mm and in weight from 590 g to 1240 g (Table 4). According to information presented by Seethaler (1978), squawfish 400-500 mm in length are 5-8 years old, those 500- 600 mm in length are 9-10 years old and those greater than 600 mm in length are 11 years old or older. Based on this information, those collected in this study were perhaps 8 to 12 years of age. The oldest squawfish collected recently was a 14 year old female. Vanicek and Kramer (1969) captured an 11 year old female 610 mm long, weighing 2268 g. Vanicek and Kramer (1969) documented a steady decrease in fish growth rates in the Green River from 1958 to 1965. They attributed this to the cold water flowing from the recently constructed Flaming Gorge Dam, a condition which is likely to occur in the White River if a dam is built. The sex of the individuals could not be determined by external features or by expressing sex products (Figure 21). Seethaler (1978) reported that all squawfish greater than 503 mm in length were mature, 76% of those between 428- 503 were mature, and all fish less than 428 mm were immature; therefore, those collected in this study should have been mature. Spawning occurs in the rivers of the upper Colorado basin in late July and August when water levels are receding and temperatures increasing (Vanicek and Kramer, 1969). These conditions prevailed during the July sampling trips; therefore, those spec- imenscollected in July should have been ripe. Adult male squawfish can be sexed externally during June, July and August by the presence of nuptial tuber- Iles and/or production of sperm when pressure is applied to the abdominal area. These were not observed on the collected specimens. Adult female squawfish do not develop tubercles, nor do they release eggs when handled (D. Tony, Hatchery Manager, Willow Beach National Fish Hatchery, personal communication). From this information, it can be deduced that the fish captured in late May, June and July were either immature, mature but not ripe, or were females. It is not likely that all were females since the male/female ratio has been