Enhancing Percid Stocking Success by Understanding Age-0 Piscivore-Prey Interactions in Reservoirs

Abstract

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...

Contrasting patterns of resource utilization between juvenile estuarine predators: the influence of relative prey size and foraging ability on the ontogeny of piscivory

“…Age-1 striped bass begin their second summer at smaller body sizes in northern US Atlantic coast estuaries compared with systems further south (Rudershausen et al 2005), meaning that the primary forage fish species (e.g., atherinids, clupeids, and engraulids) may quickly grow beyond the most vulnerable sizes. Research in freshwater systems has highlighted the importance of predator-prey body size relationships to the growth and survival of piscivores (Donovan et al 1997;Cyterski and Ney 2005). Our findings suggest that latitudinal variation in diet and growth of juvenile striped bass are also influenced by predator-prey body size relationships, which ultimately determine prey fish availability.…”

Factors related to growth and survival of larval walleyes: implications for recruitment in a southern Great Plains reservoir

“…Conversely, gizzard shad are highly abundant in reservoirs throughout the midwestern US (Cramer and Marzolf, 1970;Noble, 1981) and are often the most important prey species for age-0 walleyes (Momot et al, 1977;Carlander, 1997). Despite the generally positive influence of age-0 gizzard shad on growth of adult piscivores (Carlander, 1997), gizzard shad commonly have negative effects on members of the larval fish community (Dettmers and Stein, 1992;DeVries and Stein, 1992;Stein et al, 1995;Roseman et al, 1996;Donovan et al, 1997).…”

“…When suitable resources are unavailable or when larval walleyes are unable to switch to piscivory, they will continue to feed on zooplankton or macroinvertebrates, resulting in poor growth and recruitment (Colby et al, 1979;Forney, 1980). Donovan et al (1997) found that late spawning and low densities of gizzard shad resulted in poor saugeye (Stizostedion vitreum×S. canadense) survival in Ohio reservoirs.…”

Seasonal Variation in Population Characteristics of Gizzard Shad

“…Since larval and juvenile gizzard shad are often the primary prey for sport fish, their abundance may greatly influence growth of piscivores (Michaletz 1998). Gizzard shad may also enhance recruitment of sport fish by increasing growth rates or functioning as a predatory buffer (Donovan et al 1997); conversely. larval gizzard shad can compete with other age-0 fishes for zooplankton resources which can result in poor recruitment of sport fishes (Dettmers and Stein 1992, DeVries and Stein 1992, Stein et al 1995.…”