Estimating Food Consumption by a Heavily Fished Stock of Zooplanktivorous Coregonus lavaretus

Abstract

The food consumption of adult zooplanktivorous Coregonus lavaretus in Lake Constance, Germany, was estimated monthly from May to October 1989 with a bioenergetics model. To achieve fine temporal resolution of lakewide consumption, we scaled the monthly weight increments of fish during the 6-month growing season by the relative weights of the stomach contents of fish sampled around sunset. As a result, the proportion of maximum consumption varied from month to month. When this proportion was held constant, the total consumption estimates were similar but the allocation of consumption to each month differed by up to 30% between the two scenarios. Bythotrephes longimanus was the most important prey item from June to October. The average daily consumption of B. longimanus amounted to 15.4% of the standing stock, while that of daphnids Daphnia spp. and Leptodora kindtii was more than an order of magnitude lower. We conclude that adult C. lavaretus in Lake Constance may control the population dynamics of B. longimanus but not those of other cladocerans.