Turbidity as cover: do prey use turbid habitats as refuges from predation?
Chiu, Ta-Cheng Scott
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Turbidity has generally been viewed as having detrimental effects on fish; yet, many turbid habitats in the world are also abundant with fish. This phenomenon is often explained as fish enjoying reduced predation pressure in turbid habitats. This represents a trade-off situation where fish should select clear or turbid habitats that provide maximum net benefits. Because turbidity reduces light penetration, both predator and prey visual ranges are reduced, rendering both less efficient foragers. For this reason, I suspected that the benefits of a turbid environment would be greatest in the presence of predators and hypothesized that when predation risk is high, prey should prefer turbid water. Laboratory experiments showed that regardless of predation risk, fathead minnows (Pimephales promelas) preferred feeding in a turbid habitat. The presence of a predator, yellow perch (Perca flavescens) or black bullhead (Ameiurus melas), caused minnows to reduce feeding. There was on interaction between water clarity and predation risk, water clarity and predation risk, thus, appeared to affect the minnows’ habitat selection independently. The predator’s effect on the prey was the same whether in turbid or clear water. Using the prey distributions established in the lab experiment, key parameters and assumptions were identified for a computer model which simulated both prey and predator responses to turbid water and their interactions. The model predicted that prey would always prefer the turbid habitat when one was available. Predators generally used both clear and turbid habitats. Only when its foraging efficiency was reduced significantly did the predator show strong avoidance of turbid water. As the number of predators increased, predators used both clear and turbid habitat more evenly. Turbid environments seem to provide important habitats for small and juvenile fish. It may benefit small fish by reducing predator efficiency or reduce prey energy expenditure.