Influence of Abundance and Size of Age-0 Gizzard Shad on Predator Diets, Diet Overlap, and Growth

Abstract

Relationships among age-0 gizzard shad Dorosoma cepedianum and their predators were examined over 5 years (1987)(1988)(1989)(1990)(1991) in Pomme de Terre and Stocklon lakes. Missouri, to determine the influence of gizzard shad abundance and size on diets, diet overlap, and growth of predators. Within years, temporal changes in age-0 gizzard shad size affected predator diets and diet overlap of predators more than abundance. Age-0 gizzard shad were not important as prey until they grew larger than 25 mm total length, even though larval densities were much higher. They were the most common prey for most predators during June through October and diet overlap among predators was usually highest during that period. Lengths of age-0 gizzard shad ingested by predators resembled those available in the reservoirs throughout much of the season except in early summer, when predators ingested larger-than-average individuals, and in the fall, when smaller predators ingested smaller-than-average individuals. Among years, variations in summer production (kg/ha) and mean weight (g) of age-0 gizzard shad were significantly correlated with their importance in most predator diets and with diet overlap among predator species in Stockton Lake but not in Pomme dc Terre Lake, possibly because age-0 gizzard shad were always abundant in Pomme de Terre Lake and annual variation in gizzard shad variables was less in Pomme de Terre than in Stockton Lake. One or both of these gizzard shad variables were usually significant in regression models explaining variation in growth increments of predators. When significant, production of age-0 gizzard shad was positively related to the species' importance in predator diets, to diet overlap among predators, and to predator growth, but mean weight of age-0 gizzard shad was negatively related to those variables. Because mean weight and mean density of age-0 gizzard shad were strongly negatively correlated, predators may have been responding more strongly to prey density than to prey size. Size of age-0 gizzard shad appeared to most strongly influence growth of smaller predators, whereas age-0 gizzard shad production most strongly influenced growth of larger predators. I conclude that changes in age-0 gizzard shad abundance and size can significantly influence predator diets, diet overlap among predators, and predator growth.

Gizzard shad population dynamics in eutrophic Missouri reservoirs with emphasis on environmental influences on their growth

“…They can feed on pelagic phytoplankton, zooplankton, and detritus by pump-filter feeding (Drenner et al 1978(Drenner et al , 1982a and by grazing on bottom sediments Schaus et al 2002). Gizzard shad are also important nutrient recyclers, transporting nutrients associated with benthic substrates into the water column (Vanni et al 2005), and are important prey species for piscivorous fishes (Noble 1981;Storck 1986;Michaletz 1997b). Their versatile feeding and nutrient-recycling capabilities and importance as prey, combined with their commonly high biomasses, result in widespread ecosystem effects (Stein et al 1995;Vanni et al 2005).…”

Seasonal Patterns in White Crappies' Consumption and Growth: Influences of Varying Water Temperatures and Prey Availability

“…Availability of appropriately sized prey fish strongly influences diet composition and in turn the growth rates of crappies (Ellison 1984;Heidinger et al 1985;Muoneke et al 1992;Michaletz 1997b). Like many piscivorous fishes, crappies exhibit ontogenetic diet progressions; upon reaching approximately 150 mm total length (TL), crappies typically transition from a diet of zooplankton and macroinvertebrates to a diet of fish (Ellison 1984;O'Brien et al 1984;Muoneke et al 1992;Michaletz 1997b).…”

Size-dependent vulnerability of juvenile bay anchovy Anchoa mitchilli to bluefish predation: Does large body size always provide a refuge?

“…In freshwater systems, the primary fish prey, such as sunfish Lepomis spp. and gizzard shad Dorosoma cepedianum, can reach size refuges that reduce their vulnerability to piscivores, often with significant effects on predator diets and growth rates (Olson 1996, Donovan et al 1997, Michaletz 1997, Sutton & Ney 2001. The high capture success on large relative prey sizes and strong positive size selection by bluefish predators observed in this study suggest that bay anchovy may never achieve a size refuge from predation.…”