Though young‐of‐year (YOY) saugeyes (Stizostedion vitreum × S. canadense) are routinely stocked in spring to create and maintain percid fisheries, their growth and survival to fall vary greatly among Ohio reservoirs, as well as among years within a reservoir. To understand the relative importance of size‐dependent and size‐independent mechanisms during ontogeny that underlie variable stocking success of saugeye, we quantified the role of stocking date and prey density (zooplankton and ichthyoplankton, i.e., larval gizzard shad [Dorosoma cepedianum]) in field enclosure, pond, and reservoir experiments. In 1‐m3 enclosures, ichthyoplankton density (0, 5, 10, or 20 larval gizzard shad/m3) did not influence time to switch to piscivory by saugeye (all switched in <12 h); saugeye in enclosures with ichthyoplankton, regardless of density, grew faster than those without ichthyoplankton. In 0.4‐ha ponds, saugeye growth and survival did not differ between ponds with zooplankton plus macrobenthic prey and ponds with those prey plus small ichthyoplankton (<10 mm). In reservoir experiments, we evaluated how time in reservoirs, zooplankton density, and peak density (as well as date) of ichthyoplankton influenced saugeye growth and survival during 1991–1994 (N = 31 reservoir‐years). In 1993, we attempted to bracket the ichthyoplankton peak in five Ohio reservoirs by stocking two genetically identifiable cohorts of saugeye 2 wk apart in spring. For all reservoirs, those saugeye stocked before the ichthyoplankton peak grew larger than those stocked after the ichthyoplankton peak by 1 October. In 1994, we hypothesized that saugeye might overexploit local populations of ichthyoplankton when stocked at a single site. We paired 10 reservoirs (N = 5 pairs) with one reservoir of each pair scatter‐stocked (i.e., saugeye numbers equally divided among five sites) and the second point stocked (i.e., at a single site). Stocking method did not influence saugeye survival; late gizzard shad spawning, coupled with low larval densities, yielded poor saugeye survival in 1994. However, YOY saugeye were considerably larger in fall 1994 than in fall 1993, when gizzard shad appeared earlier and produced more larvae. Zooplankton density at stocking influenced neither growth nor survival. Increased time in reservoirs increased fall size but did not influence survival. Although saugeye growth and survival during their first year were unrelated, both measures of stocking success critically depended on gizzard shad availability. Across all years, saugeyes stocked before ichthyoplankton peaks were large (as a result of their ability to consume fast‐growing gizzard shad through summer), but survived poorly to fall (perhaps owing to early, high predatory mortality). Conversely, saugeyes stocked after ichthyoplankton peaks were small in fall (for they were unable to exploit large gizzard shad) but survived better (perhaps because gizzard shad provided a predatory buffer). By manipulating stock date relative to ichthyoplankton peaks, fisheries managers can eithe...

Abstract. In the limnetic zones of small, highly productive reservoirs, young-of-year (YOY) gizzard shad (Dorosoma cepedianum) or threadfin shad (D. petenense) (henceforth, shad) often attain high densities during spring. Environmental factors facilitating early growth and survival of shad plus potential interspecific competition for zooplankton may reduce growth and survival of YOY bluegill (Lepomis macrochirus), another common species in reservoirs. We hypothesized that fewer YOY bluegill moving from the limnetic zone to the littoral zone in late spring probably slows or prevents the ontogenetic switch to piscivory by YOY largemouth bass (Micropterus salmoides), reducing their oversummer growth, overwinter survival, and hence recruitment to their second year. To determine whether shad and bluegill abundances indeed vary inversely in reservoirs, we quantified densities of YOY shad and bluegill in four reservoirs across several years (1987)(1988)(1989)(1990)(1991)(1992)(1993)(1994); N ϭ 22 reservoir-years). To assess how YOY bluegill abundance influenced the ontogenetic dietary switch to fish by largemouth bass, we conducted experiments with differing levels of realism and control (4-m 2 littoral cages, 4.5-m 2 outdoor pools, and 0.33-m 2 laboratory aquaria).In reservoirs, peak YOY bluegill density declined weakly in the limnetic zone but strongly in the littoral zone when peak limnetic YOY Dorosoma spp. exceeded 10 individuals/m 3 . In pools and aquaria, largemouth bass grew more rapidly at Ն3 than at zero bluegill per largemouth bass. Using known temperatures and largemouth bass growth in a bioenergetics model, we discovered that YOY largemouth bass in pools and aquaria ate Յ65% of their maximum daily consumption potential (in grams of wet mass) at Ն6 bluegill per largemouth bass. In cages, largemouth bass consumed only 40% of their maximum and grew less at bluegill abundances similar to those in pools and aquaria, probably because dense vegetation and depletion of bluegill inhibited predatory success. In reservoirs with abundant shad, reduced littoral bluegill density likely compromises first-year growth and recruitment of largemouth bass. However, variable abiotic and biotic factors may modify YOY bluegill abundance and hence invalidate our predictions for largemouth bass recruitment success. To better predict fish community structure and develop management actions for reservoir ecosystems, multi-scale experimentation should be combined with wholesystem manipulations (e.g., via adaptive management) to bound these variable interactions.

Abstract. In the limnetic zones of small, highly productive reservoirs, young-of-year (YOY) gizzard shad (Dorosoma cepedianum) or threadfin shad (D. petenense) (henceforth, shad) often attain high densities during spring. Environmental factors facilitating early growth and survival of shad plus potential interspecific competition for zooplankton may reduce growth and survival of YOY bluegill (Lepomis macrochirus), another common species in reservoirs. We hypothesized that fewer YOY bluegill moving from the limnetic zone to the littoral zone in late spring probably slows or prevents the ontogenetic switch to piscivory by YOY largemouth bass (Micropterus salmoides), reducing their oversummer growth, overwinter survival, and hence recruitment to their second year. To determine whether shad and bluegill abundances indeed vary inversely in reservoirs, we quantified densities of YOY shad and bluegill in four reservoirs across several years (1987)(1988)(1989)(1990)(1991)(1992)(1993)(1994); N ϭ 22 reservoir-years). To assess how YOY bluegill abundance influenced the ontogenetic dietary switch to fish by largemouth bass, we conducted experiments with differing levels of realism and control (4-m 2 littoral cages, 4.5-m 2 outdoor pools, and 0.33-m 2 laboratory aquaria).In reservoirs, peak YOY bluegill density declined weakly in the limnetic zone but strongly in the littoral zone when peak limnetic YOY Dorosoma spp. exceeded 10 individuals/m 3 . In pools and aquaria, largemouth bass grew more rapidly at Ն3 than at zero bluegill per largemouth bass. Using known temperatures and largemouth bass growth in a bioenergetics model, we discovered that YOY largemouth bass in pools and aquaria ate Յ65% of their maximum daily consumption potential (in grams of wet mass) at Ն6 bluegill per largemouth bass. In cages, largemouth bass consumed only 40% of their maximum and grew less at bluegill abundances similar to those in pools and aquaria, probably because dense vegetation and depletion of bluegill inhibited predatory success. In reservoirs with abundant shad, reduced littoral bluegill density likely compromises first-year growth and recruitment of largemouth bass. However, variable abiotic and biotic factors may modify YOY bluegill abundance and hence invalidate our predictions for largemouth bass recruitment success. To better predict fish community structure and develop management actions for reservoir ecosystems, multi-scale experimentation should be combined with wholesystem manipulations (e.g., via adaptive management) to bound these variable interactions.

Abstract. Though young-of-year (YOY) saugeyes (Stizostedion vitreum ϫ S. canadense) are routinely stocked in spring to create and maintain percid fisheries, their growth and survival to fall vary greatly among Ohio reservoirs, as well as among years within a reservoir. To understand the relative importance of size-dependent and size-independent mechanisms during ontogeny that underlie variable stocking success of saugeye, we quantified the role of stocking date and prey density (zooplankton and ichthyoplankton, i.e., larval gizzard shad [Dorosoma cepedianum]) in field enclosure, pond, and reservoir experiments. In 1-m 3 enclosures, ichthyoplankton density (0, 5, 10, or 20 larval gizzard shad/ m 3 ) did not influence time to switch to piscivory by saugeye (all switched in Ͻ12 h); saugeye in enclosures with ichthyoplankton, regardless of density, grew faster than those without ichthyoplankton. In 0.4-ha ponds, saugeye growth and survival did not differ between ponds with zooplankton plus macrobenthic prey and ponds with those prey plus small ichthyoplankton (Ͻ10 mm).In reservoir experiments, we evaluated how time in reservoirs, zooplankton density, and peak density (as well as date) of ichthyoplankton influenced saugeye growth and survival during 1991-1994 (N ϭ 31 reservoir-years). In 1993, we attempted to bracket the ichthyoplankton peak in five Ohio reservoirs by stocking two genetically identifiable cohorts of saugeye 2 wk apart in spring. For all reservoirs, those saugeye stocked before the ichthyoplankton peak grew larger than those stocked after the ichthyoplankton peak by 1 October. In 1994, we hypothesized that saugeye might overexploit local populations of ichthyoplankton when stocked at a single site. We paired 10 reservoirs (N ϭ 5 pairs) with one reservoir of each pair scatter-stocked (i.e., saugeye numbers equally divided among five sites) and the second point stocked (i.e., at a single site). Stocking method did not influence saugeye survival; late gizzard shad spawning, coupled with low larval densities, yielded poor saugeye survival in 1994. However, YOY saugeye were considerably larger in fall 1994 than in fall 1993, when gizzard shad appeared earlier and produced more larvae. Zooplankton density at stocking influenced neither growth nor survival. Increased time in reservoirs increased fall size but did not influence survival. Although saugeye growth and survival during their first year were unrelated, both measures of stocking success critically depended on gizzard shad availability. Across all years, saugeyes stocked before ichthyoplankton peaks were large (as a result of their ability to consume fast-growing gizzard shad through summer), but survived poorly to fall (perhaps owing to early, high predatory mortality). Conversely, saugeyes stocked after ichthyoplankton peaks were small in fall (for they were unable to exploit large gizzard shad) but survived better (perhaps because gizzard shad provided a predatory buffer). By manipulating stock date relative to ichthyoplankton peaks, fisheries man...