Little Spirit Lake,
LITTLE SPIRIT LAKE
Pelham, M. E. (1999). Diet and consumption dynamics of the juvenile piscivorous fish community in Spirit Lake, Iowa.
We assessed spatial, temporal and age-class variation in diets of juvenile age-classes of the major piscivores in Spirit Lake, Iowa in 1997-1998. Piscivore 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). We found major differences in diets among species, and within species among age-classes and over time. Differences in diets of fish collected from littoral and offshore areas were, with few exceptions, negligible. Age 0 yellow perch grew too rapidly to be preyed on by age 0 piscivores, despite high abundance, but represented 56% of age 1 walleye diet. Darter species (primarily johnny darter Etheostoma nigrum, but also Iowa darter Etheostoma exile) were abundant in both littoral and offshore areas and were 49-77% of age 0 bass and walleye diets. Walleye, largemouth bass, smallmouth bass, and white bass were piscivorous as age 0, while black crappie began piscivory at age 1. Yellow perch and age 0 crappie were not piscivorous and consumed primarily zooplankton. Our results suggest that size and temporal abundance of prey fish are important factors in survival and recruitment of piscivores. We also examined variation in total and piscivorous consumption by the juvenile piscivore community in Spirit Lake in 1997-98. Consumption patterns varied considerably seasonally and annually and yellow perch accounted for the majority of juvenile total consumption, while piscivorous consumption was dominated by walleye. Walleye piscivorous consumption consisted primarily of yellow perch for age 1 and darters for age 0 cohorts.
Age 0 yellow perch growth rates were high, apparently preventing predation by age 0 walleye. Darters appear critical to the growth and survival of age 0 walleye cohorts in Spirit Lake; age 0 walleye were more abundant in 1997, but exhibited higher piscivorous consumption and higher growth in 1998 when darters were apparently more abundant. Spirit Lake demonstrates an unusual relationship between walleye and yellow perch where yellow perch is the most abundant prey species, yet contributes little to meet the consumptive demand of age 0 walleye, the dominant age 0 piscivore. A historical decline in walleye abundance and growth in Spirit Lake may reflect intense piscivory coupled with a decline in forage production.