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AbstractSaugeyes, a purposeful hybrid between walleye Stizostedion vitreumand sauger S. canadense, were introduced into 336-ha Richmond Lake, South Dakota, with a management objective of improving the size structure of the population of black crappies Pomoxis nigromaculatus. The objectives of this study were to determine (1) the influence of stocking size on the relative survival of saugeyes, (2) changes in the black crappie population that were potentially associated with the saugeye introduction, and (3) the incidence of black crappies in the diet of saugeyes. Saugeyes were stocked at a total length of 3–4 cm in 1992 and 1993; survival was low. Larger, 14–25-cm saugeyes were stocked annually from 1994 to 1998, and survival was significantly greater. The larger fingerlings were able to survive and establish a population in the face of predation by and competition with black crappies. Black crappie growth rates increased significantly after the saugeye population was established. Before the saugeye introduction program, a 20-cm black crappie typically grew less than 25 mm over a year, but by 1999 this had increased to 70 mm. As a result, black crappie size structure increased significantly. Before the saugeye introduction, few black crappies exceeded 25 cm total length, whereas 25-cm and longer fish were common by 1998 and 1999. Saugeye food habits were monitored seasonally at Richmond Lake during 1998. Saugeyes in all length-groups consumed age-0 black crappies during all sampling periods except in early spring, when age-0 fishes were not yet available. Larger (>20 cm) black crappies were not observed in saugeye stomachs during our study. Thus, the saugeyes in Richmond Lake probably reduced the abundance and intraspecific competition of small black crappies, which resulted in increased growth and improved size structure for crappies. |
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