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

Abstract

Gizzard shad (Dorosoma cepedianum) is an ecologically important species in many waters of the USA. Their versatile feeding and nutrient-recycling capabilities and importance as prey, combined with their commonly high biomasses, result in widespread ecosystem effects. Despite their importance, few studies have focused on variables that influence their population dynamics, especially in mid-latitude waters. The objectives of this study were to: (1) describe population dynamics including size and age structure, growth, and mortality and (2) determine potential environmental influences on annual variations in growth increments of gizzard shad. Gizzard shad populations were sampled annually in three eutrophic reservoirs in Missouri, over a successive 5-year period. Size and age structure were temporally variable owing to variable year-class strength and differing growth rates. Strong year-classes arose from age-0 cohorts that experienced relatively high overwinter survival. Annual variations in growth increments across all cohorts and reservoirs appeared to be affected by the initial length of fish at the beginning of the growing season and by food availability. Annual mortality estimates ranged from 0.38 to 0.70 for ages 3–7 among the reservoirs. Due to their dynamic nature, effects of these populations on their ecosystems also must be temporally variable and complex. Future studies should focus on the importance of these temporal effects on ecosystem dynamics.

Keywords:

• gizzard shad
• population dynamics
• reservoirs
• growth
• mortality

Acknowledgments

I thank Dean Nicks, Earl Buckner, Jamey Decoske, Mike Colvin, Steffanie Abel, Rachel Wright, Karen Brickey, Bill Mabee, and numerous seasonal employees for their assistance with field and laboratory work. I thank staff from the Limnology Laboratory, University of Missouri, for analyzing nutrient samples. Mike Roell, Mike Siepker, and an anonymous reviewer provided helpful comments on previous drafts of the manuscript. This study was partially funded through Federal Aid in Sport Fish Restoration, Project F-1-R, Study I-38, to the Missouri Department of Conservation.