Foraging Behavior of Benthic Fish as an Indicator of Ecosystem State in Shallow Lakes

Abstract

In this paper we propose that the foraging behavior of benthic fish can be used to assess the current state of shallow lake ecosystems. Shallow lakes may display shifts between clear and turbid states, where sediment resuspension by benthivores foraging on benthic invertebrates contributes to maintaining the turbid state. We suggest that the giving-up density (GUD) of benthic fish foraging in experimental patches may provide useful information for managing shallow lake ecosystems. The rate of sediment resuspension by fish is a function of the abundance of both benthic fish and benthic invertebrates. Based on the empirical relationship between foraging behavior, habitat quality, and long-term growth prospects, and between habitat quality and rate of sediment resuspension, we conclude that systems should be more resistant to switches from a clear to a turbid state when (i) benthos biomass, maximum benthivore size, and giving up density are high, (ii) benthivore biomass is low, (iii) a low fraction of benthivore population is above the maximum benthivore size predicted from giving up density, and when relative predation cost is high, estimated as the difference in GUD between risky and safe habitats. Although a first step, the methods introduced here should serve to facilitate predicting the probability of switching between ecosystem states, as well as to identify suitable abatement strategies for preventing such shifts.

Keywords:

• shallow lake
• benthivorous fish
• Abramis brama
• resuspension
• patch use behavior