Un resumen en espan˜ol se incluye detra´s del texto principal de este artı´culo.Abstract -Diets of adults of six important piscivorous fish species, black crappie Pomoxis nigromaculatus, largemouth bass Micropterus salmoides, northern pike Esox lucius, smallmouth bass Micropterus dolomieui, walleye Stizostedion vitreum, and yellow perch Perca flavescens were quantified in Spirit Lake, Iowa, USA from May to October in 1995-1997. Forty-one prey taxa were found in the diets of these species, including 19 species of fish. The most important prey taxa overall were yellow perch, amphipods and dipterans. Diets of northern pike and walleye were dominated by yellow perch. Largemouth bass diets included large percentages of both yellow perch and black bullhead Ameiurus melas. Smallmouth bass diets included large percentages of both yellow perch and crayfish. Black crappie and yellow perch diets were dominated by invertebrates, primarily amphipods and dipterans. There were pronounced differences in diets among species, among size classes within species and over time. Most of the dominant prey taxa we documented in the diets of piscivorous species were in accordance with previous studies, but a few deviated significantly from expectations. Many of the temporal diet changes were asynchronous among piscivorous species and size classes, suggesting different responses to common prey resources over time.

– We assessed temporal dynamics and variation among species and age‐classes in the diets of age 0 and age 1 piscivorous fish species in Spirit Lake, Iowa, USA during 1997 and 1998. Species included walleye Stizostedion vitreum, yellow perch Perca flavescens, smallmouth bass Micropterus dolomieui, largemouth bass Micropterus salmoides, black crappie Pomoxis nigromaculatus and white bass Morone chrysops. Thirty taxa were identified in diets, including 12 species of fish. We found dramatic differences in diets among species, among age‐classes within species and over time. Walleye, largemouth bass, smallmouth bass and white bass were piscivorous at age 0. Black crappie began piscivory at age 1. Yellow perch also began piscivory at age 1, but fish were a very small fraction of age‐1 diets. The primary temporal pattern, seen in several species and age‐classes, was an increase in piscivory from spring to fall. This pattern was due to the lack of small, age‐0 prey fish in spring. Although some patterns were evident, the taxonomic composition of the diets of all species was highly variable over time, making generalizations difficult. A surprising result was the absence of yellow perch in the diet of age‐0 walleye, despite their abundance in Spirit Lake and prominence in diets of age‐1 walleye and other age 1‐piscivores. Age‐0 yellow perch were consistently too large to be eaten by age‐0 piscivores, which preyed primarily on invertebrates and smaller fish such as johnny darters Etheostoma nigrum and age 0 bluegill Lepomis macrochirus. This finding suggests that predator‐prey interactions and resulting population dynamics may be quite different in Spirit Lake than in other systems dominated by walleye and yellow perch.

We assessed the dynamics of the littoral fish assemblage in Spirit Lake, Iowa, and examined potential consequences of these dynamics for availability of prey fish for piscivores. Using beach seines, we quantified the annual, seasonal, and spatial variation in density and biomass of the entire assemblage and of component species over a 4-year period. Potential prey fish availability was inferred from the biomass of the cumulative total fish length groups and sizes of fish eaten by piscivores. Total fish density and biomass averaged 10,024 fish/ha and 276.3 kg/ha, respectively. Density and biomass of total fish varied among years and seasons, but seasonal patterns differed among years. Yellow perch Perca flavescens, bluegill Lepomis macrochirus, walleye Stizostedion vitreum, and common carp Cyprinus carpio were the predominant species overall, but the proportional species composition of both total density and total biomass varied highly. Changes in the fish assemblage resulted in dramatic changes in the potential availability of prey fish over time and with piscivore size. These dynamics could lead to variable growth and condition of resident piscivores as well as to variable success of stocking fingerling piscivores. RightsWorks produced by employees of the U.S. Government as part of their official duties are not copyrighted within the U.S. The content of this document is not copyrighted. Abstract.-We assessed the dynamics of the littoral fish assemblage in Spirit Lake, Iowa, and examined potential consequences of these dynamics for availability of prey fish for piscivores. Using beach seines, we quantified the annual, seasonal, and spatial variation in density and biomass of the entire assemblage and of component species over a 4-year period. Potential prey fish availability was inferred from the biomass of the cumulative total fish length groups and sizes of fish eaten by piscivores. Total fish density and biomass averaged 10,024 fish/ha and 276.3 kg/ha, respectively. Density and biomass of total fish varied among years and seasons, but seasonal patterns differed among years. Yellow perch Perca flavescens, bluegill Lepomis macrochirus, walleye Stizostedion vitreum, and common carp Cyprinus carpio were the predominant species overall, but the proportional species composition of both total density and total biomass varied highly. Changes in the fish assemblage resulted in dramatic changes in the potential availability of prey fish over time and with piscivore size. These dynamics could lead to variable growth and condition of resident piscivores as well as to variable success of stocking fingerling piscivores.