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<br />84 Environmental Enhancement or Water Projects <br />FUTURE ACTIVITIES <br />Future activities are focused on optimizing production <br />of subadult (12 inch) suckers while attempting to use <br />the high degree of genetic diversity represented by the <br />aging population. The grow-out and release of 10,000 <br />subadult razorback suckers is still a realistic goal. <br />Research has provided important insight regarding how <br />best to proceed. Poor survival of smaller hatchery <br />fish has illustrated that even in depleted sportfish <br />populations razorback sucker survival is poor. The <br />temporary barrier will be replaced with a permanent <br />dike in 1994. This dike will allow greater flexibility <br />in optimizing the production of greater numbers of <br />subadult fish. Four other coves isolated from the lake <br />by sand berms were added to the study in 1993. <br />Production from these coves, however, will not be known <br />until removal is completed later this year. <br />Although the on-site collection and use of spawning <br />suckers presents an improvement over hatchery held <br />brood stock, the presence of naturally produced <br />reservoir larvae offers a unique opportunity. Starting <br />in 1994, we plan to collect naturally spawned larvae <br />from the reservoir using light traps rather than <br />collecting spawning adults. Larval suckers will then <br />be stocked into the backwaters. The use of naturally <br />produced sucker larvae, collected at different <br />reservoir sites and throughout the 2 month spawning <br />period, will provide young from a greater parentage <br />than could be produced artificially. This method will <br />provide a more diverse genetic representation of the <br />reservoir population. By intercepting larvae, <br />fostering their survival to a length of 12 inches, and <br />subsequently releasing these fish back into the <br />reservoir, the resulting replacement of razorback <br />suckers is hoped to more closely mimic the genetic <br />traits of the existing population. <br />Monitoring of the adult population will continue during <br />their spawn. These collections and the recovery of <br />tagged, cove-reared suckers will be used to assess <br />survival and future stocking rates. <br />If the program proves successful, we anticipate <br />expansion of the research/management program to other <br />areas of the basin, possibly including other long lived <br />native species such as the bonytail chub (Gila <br />11e), Colorado River squawfish (Ptvchocheilus <br />lucius), and humpback chub (Gila cvoha). This <br />management concept undoubtedly has application for <br />Razorback Sucker Program 85 <br />other relic populations of long-lived endangered fishes <br />elsewhere. <br />We envision a low cost, low maintenance approach using <br />several rearing ponds located along the river to grow <br />native fish. Small rearing ponds could be built along <br />the Colorado River and isolated with gated control <br />structures. Ponds could be fertilized to optimize food <br />production and stocked with native fish from hatchery <br />stocks at levels to optimize growth without the need <br />for feeding. When the fish reached lengths ensuring <br />survival, the gates would then be opened to allow fish <br />to "seed" the river system. The process could be <br />repeated every 2 or 3 years. <br />Another attempt to rear native fish on-site is also <br />being attempted in Lake Havasu, another Colorado River <br />regulatory reservoir farther downstream from Lake <br />Mohave. The effort is being integrated into a habitat <br />improvement program for the reservoir's sport fishery. <br />The active management of long-lived native fishes with <br />other sport fisheries in highly modified habitats <br />appears to be gaining acceptance and support. <br />LITERATURE CITED <br />Horn. M., P.C. Marsh, G. Mueller, and T. Burke. In <br />Press. Predation by Odonate naiads on larval razorback <br />sucker under laboratory conditions. Transactions of <br />the American Fishery Society. <br />Marsh, P. C., and J. L. Brooks. 1989. "Predation by <br />ictalurid catfishes as a deterrent to re-establishment <br />of introduced razorback suckers." The Southwestern <br />Naturalist 34, 188-195. <br />Minckley, W. L., P. C. Marsh, J. E. Brooks, J. E. <br />Johnson, and B. L. Jensen. 1991. Management Toward <br />Recovery of the Razorback Sucker. in Battle Against <br />Extinction, Native Fish Management in the American <br />West. The University of Arizona Press, Tucson & <br />London, pg 303-357. <br />Mueller, G., and G. Hertzog. 1992. Lake Mohave Native <br />Fish Rearing Project. Twelve minute Video. Bureau of <br />Reclamation, Boulder City, NV 89006-1470. <br />Mueller, G., M. Horn, J. Kahl Jr., T. Burke, and P. <br />Marsh. In Press. "The use of larval light traps to <br />capture Razorback Sucker (XVrauchen texanus.) in Lake <br />Mohave, Arizona-Nevada." The Southwestern Naturalist.