9410 - Laserfiche WebLink

Home Browse Search

I I Only 43% of 250 fish control projects were considered to be successful in a comprehensive review by Meronek et al. (1996). Total control of nonnative fishes is impossible in the Upper Colorado River Basin because these fishes are well established with self-sustaining populations (Wiley and Wydoski 1993). However, attempts to remove nonnative fishes should help to increase the numbers of razorback suckers in Upper Basin rivers. Minckley and Meffe (1987) believed that even temporary removal or suppression of nonnative predators or competitors may enhance native fish populations. Although biologists are often intimidated by the inefficient and labor-intensive methods of fish control and possible negative public reaction, there is a necessity to reduce (or eradicate if possible) nonnative fish species because of the magnitude of the problem in certain waters (Temple 1990). Ultimately, the endangered fishes must be able to sustain their populations with the established nonnative fishes in the Upper Basin, if recovery is to be realized. Otherwise, periodic or continuous human intervention will be required to control nonnative, warmwater fishes because compensatory growth and survival of nonnative fishes will allow rapid resiliency (Wiley and Wydoski 1993). I I I I f I l It t Mechanical control methods are most practical for management of nonnative fishes in the Upper Colorado River Basin. Chemical control in the main channels or connected habitats would be undesirable based on numerous accidental fish kills that have occurred in running waters. Chemical control is a viable option for control of nonnative fishes in floodplain ponds and is being implemented to reduce chronic escapement from gravel- pit ponds along the upper Colorado and Gunnison rivers (U.S. Fish and wildlife Service 1998). Biological control generally uses predatory fish species that will consume any suitable fish species including endangered fishes. Increasing the numbers of Colorado squawfish in the Upper Basin would provide some biological control of nonnative fishes. The use of other fish species as predators and the use of pathogens (e.g., a virus specific to channel catfish) are not viable options because of high risk. Partial control using mechanical control methods (e.g., removal with various gear, increased water velocity, increased streamflows, etc.) is the only option that reduces risks but this control method often does not generally remove an adequate proportion of the nonnative fish population and compensatory mechanisms of increased growth and fecundity will allow rapid repopulation (i.e., resiliency) by nonnative fishes (Wiley and Wydoski 1993). Osmundson and Kaeding (1991) suggested that streamflow manipulations might be used to manage nonnative fishes while enhancing native fishes. 'However, Valdez (1990) concluded that regulation of streamflows may not be an effective long-term method to reduce nonnative fishes that are adapted to river environments or with a high reproductive potential. Valdez reported that red shiners were reduced in numbers during a year with high streamflows in Cataract Canyon of the Colorado River but exhibited a high resiliency during the following year with a lower streamflow. Partial control of nonnative fishes should be evaluated in river reaches where experimental floodplain enhancement or restoration is completed to determine the responses of native (including endangered) and nonnative fishes. All habitat enhancement or restoration endeavors and nonnative fish control measures should be implemented concurrently by applying adaptive management (Walters 1986; Walters and Hillborn 1978) that allows actions to be taken even when there is a great deal of uncertainty (Ludwig et al. 1993). t t , ~ t ~ Cover requirements for fish varies by species and life stage that may differ diurnally and seasonally (Gore and Shields 1995). Cover reduction in river ecosystems may reduce fish populations up to 80% (Wesche 1985). Mortality of Age-O razorback suckers may be less in depression ponds with rooted aquatic vegetation that serves as escape cover along the middle Green River (Modde 1997). However, there is no escape cover in gravel- pit ponds without rooted aquatic vegetation along the upper Colorado 35