Laserfiche WebLink
<br />0025J2 <br /> <br />Increased exploitation has the potential to cause a major shift in the size <br />distribution of a channel catfish population, especially in locations where growth is slow <br />due to natural conditions. In the Powder River system of Wyoming, effective <br />exploitation virtually eliminated larger channel catfish (Gerhardt and Hubert 1991). The <br />age and growth rates of channel catfish in Wyoming are very similar to that reported for <br />the UCRB (Tyus and Nikirk 1990). <br /> <br />Commercial harvesting of channel catfish in the Missouri River was so effective <br />at removing the larger, and commercially desirable, fish that the fishery had to be <br />closed (Hesse 1994). The response of the fish population to closure of the fishery was <br />dramatic. In six years, the proportion of larger fish (>330 mm TL) increased by 36%, If <br />channel catfish in the UCRB could be exploited to a similar degree, the threat of <br />predation could be greatly minimized. The level of effort is likely to be high and may <br />not be sustainable without a commercial operation. <br /> <br />Fish control technology is an active area of research for public and private <br />entities (e.g., Stone and Webster 1986, EPR11988, Cada and Sale 1993). Entirely <br />new approaches, like guidance systems that rely on fish behavioral responses for <br />redirecting fish movements (Bell 1990), have been developed in recent years. <br />Although a detailed accounting of emerging technology is beyond the scope of this <br />report, it is encouraging that new options are becoming available. <br /> <br />In addition to the use of mechanical techniques for controlling nonnative fishes in <br />the main channels of the UCRB, physicochemical methods also may have merit <br />(Lentsch et al. 1995). Flow regulation helped meet habitat needs of the endangered <br />species, especially the Colorado squawfish in the Green River (Tyus and Haines <br />1991). There is some indication that the timing and duration of instream flows may not <br />only benefit the native fishes, but also place some of the nonnative fishes at a <br />disadvantage. Enhanced flow regimes can shift fish communities to a more diverse <br />fluvial community of native species (e.g" Travnichek et al. 1995). According to Muth <br />and Nesler (1993): "Management of flow regimes to approximate natural hydrographs <br />and periodically provide above-average magnitudes in spring-summer discharges may <br />benefit native fishes and inhibit certain prolific nonnative fishes." <br /> <br />Physicochemical manipulations may also influence the growth and survival of <br />nonnative fishes. For example, increasing turbidity may be disadvantageous to visual <br />predators, thereby advantageous to native prey species (Wootton 1990; Miner and <br />Stein 1996). Also, manipulating water temperature holds potential as a control <br />mechanism for species that are marginal under present conditions (see Tyus and Nikirk <br />1990, Rutherford et al. 1995), <br /> <br />Flow manipulation may be the only available control option for some of the small <br />cyprinid species, such as fathead minnow, red shiner, sand shiner, and redside shiner. <br /> <br />23 <br />