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<br />LJ24!)S <br /> <br />use of fish toxicants to kill nonnative fishes in certain areas; biological controls by <br />stocking Colorado squawfish; and management of flows to confer advantage on the <br />natives and disadvantage on the nonnatives. <br /> <br />From a technical perspective, a control technique should be selected for its <br />potential to remove the target species from a specific habitat without harming the <br />beneficiary (i.e., endangered) species. The technical considerations, which alone <br />present a formidable challenge, are complicated by sociopolitical (e.g., angler <br />opposition) and economic factors. Predicting the effectiveness of a control technique <br />can be difficult and imprecise. In a recent review of 250 fish control projects in the US, <br />Meronek et al. (1996) found that only 43% met their objectives for controlling fish. The <br />typical project involved mechanical removal of "rough fish" (e.g., minnows, catfish, <br />suckers) from a small impoundment for the purpose of altering community composition <br />in favor of gamefish. The authors also pointed out that a successful outcome of any <br />control measure depended on providing suitable habitat and water quality for those <br />fishes that were intended beneficiaries. <br /> <br />The endangered fishes, which are the presumed beneficiaries of any control <br />project in the UCRB, are residents of the main river channel and complete their life <br />cycle in the river and the adjacent floodplain. The introduced nonnative species, which <br />would be the target of control measures, also occur in the main channel habitat and <br />must be removed. Because many of the non natives do not reproduce in main channel <br />habitats, consideration must also be given to control measures that will eliminate the <br />source of non natives. Control measures for main channel habitats are constrained by <br />the presence of endangered fishes and the physical complexity of the habitat. <br />Chemical control techniques are therefore undesirable for the riverine habitat because <br />it would be virtually impossible to prevent the loss of native endangered fishes, Control <br />techniques which are suitable for use in the main stem, and which minimize the by- <br />catch (incidental capture) problem, are chiefly mechanical, but may also include some <br />flow manipulation options. Because the appropriate control measures are unlikely to <br />be 100% effective, complete eradication of the target species is not a realistic goal <br />where recruitment cannot be prevented. If the target species can restore its population <br />through recruitment, the removal effort must be repeated. Managers must be prepared <br />for a continuing investment in control measures. <br /> <br />The list of mechanical control techniques is extensive, but can be divided <br />generally into the following categories: physical barriers (e.g. screens and nets), <br />structural guidance devices (e.g. racks, louvers, collectors), modification to existing <br />structures (e.g. bypass chutes, sluiceways), behavioral guidance devices (e.g. <br />acoustic, visual, and electric barriers), and physical removal (e.g. traps, pumps)(Bates <br />1993, USOTA 1995). Once the non natives have been removed, they may be <br />transported to another location if it is desirable to retain these individuals for <br />recreational purposes. Because the traditional technologies are relatively well known <br /> <br />21 <br />