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7/14/2009 5:02:31 PM
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5/20/2009 10:09:19 AM
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UCREFRP
UCREFRP Catalog Number
7834
Author
Burdick, B. D. a. R. B. B.
Title
Experimental Stocking Of Adult Razorback Sucker In The Upper Colorado And Gunnison Rivers.
USFW Year
1997.
USFW - Doc Type
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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
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