Turbidity and foraging rate in threespine sticklebacks: the importance of visual and chemical prey cues

In aquatic habitats turbidity can affect the foraging efficiency of visual predators, directly influencing their capacity to detect prey. In a laboratory study we tested the effect of different loads of suspended sediment upon the foraging rates of threespine sticklebacks (Gasterosteus aculeatus). We compared the foraging rates of fish under a series of different turbidity treatments, testing fish originating from four habitats within a single drainage basin that differed in a number of environmental parameters including turbidity. Although we found habitat specific differences in foraging rates, these did not correspond to local turbidity levels. The findings of a follow up experiment revealed habitat-specific variation in boldness, which may be indirecly linked to the observed differences in foraging rate. The main finding of our study was that turbidity alone had no impact upon their prey capture rates, but that high turbidity in combination with saturation with prey odour extract caused prey capture rates to fall significantly. This suggests that olfactory cues can be more important than visual cues in determining foraging performance in this species, potentially influencing how they cope with naturally occurring periods of turbidity, and how they adapt to human-induced eutrophication.