Trophic Linkage between Stream Centrarchids and Their Crayfish Prey

Energetic links between smallmouth bass (Micropterus dolomieu) and rock bass (Ambloplites rupestris) and their crayfish foods were examined in an Ozark stream. A trophic level energy budget was developed by enumerating food habits for different age (size) fish, estimating annual production for both fish and crayfish, and using laboratory- and literature-derived bioenergetic and gross efficiency data. Both fishes began life feeding on small invertebrates (mayflies and chironomids) but within 3 mo switched to a diet of mainly crayfish and Cyprinidae. Total annual production of smallmouth bass was 0.262 g dry weight∙m−2∙yr−1 (6344 J) and rock bass 0.148 g∙m−2∙yr−1 (3607 J). Total annual production of crayfish was 4.15 g dry weight∙m−2∙yr−1 (55 736 J) for Orconectes luteus and 5.05 g∙m−2∙yr−1 (62 394 J) for O. punctimanus. Only about half of the crayfish production was available to fish, due to size-selective predation and behavioral traits of the prey. A predator–prey model suggested that nearly one third of total crayfish production during their vulnerable period was lost to centrarchids, and that half of the existing biomass was consumed. Fish are probably the major cause of mortality in crayfish and undoubtedly influence crayfish population dynamics and energy flow through the river system.