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P1 ans are to stock -razorback sucker i n a backwater or i nf1 ow area (San Juan Ri ver <br />arm of Lake Powell) in 1997 and 1998. One group of razorback sucker will be <br />released and allowed to escape the backwater, migrate into the main channel <br />voluntarily following stocking, and roam free. Another group of razorback sucker <br />will be stocked and held in a backwater temporarily (3 to 6 days) that has been <br />blocked off with nets to prevent fish from migrating to the river. Therefore, <br />stocked fish will be preconditioned by allowing them to slowly acclimate to the <br />backwater. In time, block-off nets will be removed and fish will ultimately be <br />allowed to migrate from the backwater into the river. Recapturing stocked fish <br />or monitoring their movement with telemetry will be critical to evaluating each <br />group's survival. Additional testing of this hypothesis will be conducted with <br />pond-reared razorback sucker stocked in Lake Mohave (1997 and 1998) and in the <br />lower Green River (1998) in Canyonlands National Park (Personal communication, <br />Gordon Mueller). <br />Reasons for Low Survival <br />We can speculate why survival was low for pond-reared adult razorback <br />sucker stocked in the Upper Colorado and Gunnison rivers. Captive-reared fish <br />that are stocked into the river may not be able to cope with the riverine <br />environment unless they are physically conditioned prior to release (Sanger <br />1993). Pond-reared razorback sucker that had not been accustomed to flow may <br />therefore have not been physiologically or behaviorally adapted for riverine <br />life. Radio-implanted fish were all stocked in no or low-velocity riverine <br />habitats, similar to the pond environment where they had spent their entire life. <br />to allow gradual conditioning to various river currents and velocities. Fish <br />were stocked in early April and should have had ample time to adjust to the <br />increased flow velocities associated with runoff. Inspection at the time of <br />radio-implantation revealed vast amounts of fat in their body cavities, <br />indicating fish were in good condition in spring 1994 prior to being stocked in <br />the river environment. One hypothesis is that food items utilized and possibly <br />preferred by razorback sucker in Etter Pond were not available in the river at <br />the time of stocking or that fish had developed a specific "search image" for <br />preferred food items while in the pond and were not physiologically or <br />behaviorally capable of utilizing riverine organisms, even though food may have <br />been available. <br />The relation of food at the time and location of stocking is also critical <br />to survival. Post-stocking survival is often related to the Match or Mismatch <br />Principle where environmental conditions such as water temperature as well as the <br />quality and quantity of food organisms must match the needs of the fish at time <br />of stocking in river backwaters to realize high survival (Hjort 1914; 1926). In <br />other words, food resources must "match" or be available at the time of or <br />following stocking to increase survival of stocked fish. This is especially <br />critical for larval razorback sucker. However, in both the Upper Colorado and <br />Gunnison River systems, stocked razorback sucker had ample time to utilize food <br />resources in the river since mortality was delayed and occurred over several <br />months following stocking. If stocked fish did not utilize riverine food <br />resources, one reason mortality was delayed is that stocked fish may have had <br />adequate fat reserves to initially sustain them, but were not capable of <br />converting to or learning to utilize natural food items in the river and, <br />16