Evaluation of mechanical removal of red shiner (Cyprinella lutrensis), survival of stocked woundfin (Plagopterus argentissimus), and results of monitoring

Holden, Paul; Golden, Michael

In May 1999, the Lower Virgin River Recovery Implementation Team began an experimental woundfin (Plagopterus argentissimus) stocking study directed at systematically evaluating stocking efforts in order to better understand mechanisms limiting their success. This report provides the results of red shiner removals, subsequent woundfin stockings, and follow-up monitoring from May 1999 to June 2000, as well as results of a June 2000 population estimate of the remaining stocked woundfin.... EXECUTIVE SUMMARY Nevada Division of Wildlife woundfin stocking experiments in the lower Virgin River from 1993 to 1998 did not result in the establishment of wound fin populations. Heinrich ( 1999) concluded that hatchery-reared fish may not be able to survive in the river, but that large numbers of red shiner may also have been a factor in the lack of survival of stocked woundfin. To further determine if stocked wound fin could be used to re-establish a woundfin population in the Virgin River, additional stocking studies were conducted in 1999. Stockings occurred on May 7 and October 21, 1999, and red shiner removal efforts preceded both stockings. Red shiner removal consisted of sampling an Experimental Reach (between the Mesquite and Bunkerville Diversions) with seines for 3 consecutive days and removal of red shiner and other nonnative fishes just prior to the woundfin stockings. An additional red shiner removal was conducted in early June 2000 to remove red shiner around the spawning time for woundfin. This report discusses the results of the red shiner removals, subsequent monitoring of stocked woundfin, use of an injectable elastomer dye as a marking technique, and results of monitoring three other sites from April 1998 to June 2000. Over 7,800 red shiner were removed from the 5-mile Experimental Reach between the two diversion dams on May 4, 5, and 6, 1999. Approximately I, 700 !-year-old woundfin were stocked into the reach on May 7. Woundfin numbers declined during the summer to relatively low numbers by August. Red shiner numbers increased because of spawning and growth of young during the same period. This experiment suggested that even with lower red shiner numbers, !-year-old woundfin still could not survive in the lower Virgin River. The only positive note was that some reproduction of woundfin did occur during the summer; however, those young also disappeared by the end of the summer.

Evaluation of mechanical removal of red shiner (Cyprinella lutrensis), survival of stocked woundfin (Plagopterus argentissimus), and results of monitoring

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