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1 <br />$830. All fish were removed in 71 of the 86 treated ponds. Of the 71 ponds 54 were re- <br />sampled to identify re-invasion by nonnative fish. Sixty-five percent of the 54 ponds had <br />reinvaded. Additionally, movement of some, but not all, larval fish through screens was <br />confirmed. <br />This study, as well as others, has demonstrated that re-invasion by nonnative <br />fish has readily occurred in most waters that have been treated using mechanical or <br />chemical control techniques. However, re invasion of largemouth bass was a notable <br />pp. exception. This fish species was present in 28 of the 54 re-sampled ponds prior to <br />treatment but it had re-invaded only two of the 54 ponds following treatment. Similarly, <br />minor success was observed in the 12 (22%) of the 54 re-sampled ponds that had not <br />re-invaded at the time they were re-sampled. Limited success was also observed with <br />regard to fish screens. Though some nonnative fish larvae passed through screen <br />apertures as small as 0.5mm, other larvae were impinged and did not pass through <br />some screens. <br />Evidence of reduction in abundance of nonnative fishes in existing riverine <br />nursery habitats as a result of nonnative fish control in floodplain ponds on a river-reach <br />scale is nonexistent. Research conducted in the rivers within the study area under other <br />investigations suggests no reach-wide depletive effect was observed. <br /> Recommendations discussed in this report include the following: <br /> 1. Determine the sources of problematic nonnative fishes. <br /> 2. Evaluate potential biological control of nonnative fish with native listed/non-listed fish <br />in a floodplain pond environment. <br /> 3. Evaluate shearing wedgewire screens with apertures < 0.5mm to determine if larval <br /> fish pass through this type of screen. <br /> 4. Examine the potential of controlling the movement of nonnative fish from floodplain <br /> ponds into critical habitat by screening return flow irrigation water. <br /> 5. Continue KE efforts to inform the public and private aquaculturists of the existence <br /> of and changes to the CDOW Nonnative Fish Stocking (NNFS) regulation. <br /> 6. Review current NNFS regulation and make changes where necessary. <br /> <br />t <br /> <br />