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4. Size and Number of Fish to Stock Ideally, three different size groups (4-, 8-, and 12-inch) will be stocked in this experiment. The smallest group is the smallest fish that can be safely PIT tagged; the largest group reflects the biggest fish that is expected to be produced in one year. The different size classes will allow an assessment of whether survival is related to fish size. If the size groups overlap, two size groups will be stocked. A standard ratio will be used to divide fish into size groups equally among family lots based on the assumption that small fish will exhibit higher mortality. To produce three size groups for stocking, a 75:20:5 ratio will be applied; for two size groups,.a 75:25 ratio will be applied. Because of the expected variability in survival these ratios may vary by up to 10%. These ratios allocate captive-reared fish based on the expectation of survival. Smaller fish are not expected to survive as well as larger fish and will be more difficult to collect during the monitoring effort. The ratios represent reasonable estimates of survival and can be adjusted for future stockings based on the results of the field experiment. The number of fish to be placed into different rearing units will be based on this ratio. Initially, we will probably not be able to adhere closely to the three size classes and numbers proposed above because fish and rearing facilities are limited. Although the plan calls for a total of 26,000 fish to be stocked in 1996, only about 1,140 YOY razorback suckers from the 1995 year class are currently available. Because of expected mortality and holding some of these fish for future brood stock, less than 1,000 fish will be available for stocking in 1996. Large numbers of young fish will probably not be produced until the 1994 and 1995 year classes reach adulthood. More fish will be available for spawning and therefore more young will be produced. Additional facilities are being developed and will be available in the near future. The increased space will give more flexibility and allow us to break up the year classes and rear them in different locations or under different conditions to allow differential growth. The different size classes could also be produced by holding some fish longer and stocking them later in the year. Table 1 summarizes the numbers, sizes, and locations of razorback sucker proposed for stocking in 1996 through 2000. A power analysis will be performed on the number of fish released and recaptured in the first years of stocking to determine if stocking rates should be increased in subsequent years. 5. Location of Release Suitable habitat appears to be available in the floodplain reach of the Gunnison River from Austin, Colorado to Roubideau Creek and also in the Upper Colorado River from Rifle to Debeque, Colorado. These areas are among the last places where razorback suckers have been collected in recent years. The two stream reaches also appear suitable for re- introduction of razorback sucker because of the absence or low densities of nonnative piscivorous fishes. For example, channel catfish (Ictalurus punctatus) are absent both in the Gunnison River upstream of the Redlands Diversion Dam (Burdick 1995) and in the Colorado River