Laserfiche WebLink
<br /> h <br /> aut <br />ors report survival rates ofradio-tagged razorback suckers between 40 and 53%. <br /> Twenty-five of the 656 pit-tagged razorback suckers were recaptured during the first <br /> 6 months. The recapture rate ofpit-tagged fish is quite high when considering the large <br /> size of this study area and may indicate that the San Juan River is an excellent choice for <br /> future stocking of razorback suckers. However, since growth rates were low during the <br /> first 6 months following release (mean growth rate = .0105% of total length per % year), <br /> perhaps the aquatic food base available to the razorback sucker in the San Juan River is of <br /> poor quality or made partially unavailable due to competition with other fishes, the threat <br /> of predation, or some other factor. Or perhaps the low growth rates indicate that a <br /> substantial period of time is required for razorback sucker to make the transition from <br /> hatchery to turbid river. <br /> The survivorship of stocked razorback sucker has been increased by releasing relatively <br /> lazge fish (>250 mm) instead of larvae (10 to 20 mm) (Mueller 1995), however, adult <br /> razorback suckers stocked into rivers undertake large movements during the first weeks <br /> of liberation and often suffer high mortality. For example, the releases of adult razorback <br /> sucker made by Ryden and Pfeifer (1995) in the San Juan River, Burdick and Bonar <br /> (1997) in the upper Colorado and Gunnison Rivers, and Day and Modde (1999) in the <br /> Green River have shown that stocked razorback sucker will undertake movements <br /> directed downstream (0 to 80 km) during the first few weeks following their release. This <br /> directed movement downstream accounted for a combined 46 out of 91 (50.5%) <br /> razorback suckers departing the two sites targeted for their introduction. Exceedingly few <br /> suckers (4 of 91) were observed to move upstream from their release points. Downstream <br /> emigration combined with fatalities (27 fish] have contributed in part to the difficulty in <br /> creating and maintaining viable, reproducing populations of razorback suckers in the <br /> habitats deemed to be suitable, as listed in the razorback sucker recovery plan (Tyus <br /> 1998). Researchers have suggested that stocked fish should be "...stocked as far <br /> <br />'~ upstream as possible" (Burdick and Bonar 1997, Ryden and Pfeifer 1996) . This <br />suggestion does have merit considering the propensity of razorback suckers to initially <br /> move downstream from a stocking site, but this technique requires that a great many <br /> individuals be stocked at a far distant location due to the low probability that a particular <br /> fish will survive, move downstream a set distance, and become a resident in a targeted <br /> section of river. <br />This project assessed movements and habitat use of razorback sucker stocked in the <br />Green River, Canyonlands National Park, and tested pre-stocking acclimation as an <br />alternative method to "upstream stocking," as suggested by Burdick and Bonar (1997) <br />and Day and Modde (1999). The study was directed at determining the practicality of <br />reestablishing/augmenting a viable population of razorback sucker into the Green and <br />Colorado Rivers within Canyonlands National Pazk. <br />Two groups of 15 razorback suckers were compared: an acclimated group held in a <br />backwater for ~2 days, and a second group handled identically and placed immediately <br />1 <br />3 <br /> <br />