| Summary: | Increasing turbidity in coastal waters of the north Atlantic and adjacent seas has raised concerns about impacts on Atlantic cod (Gadus morhua) using these areas as nurseries. Turbidity limits the visual range of fish and can strongly influence fish behaviour, leading to changes in activity and habitat shifts. Previous experiments have shown that in well-lit environments turbidity does not affect the foraging rate of juvenile cod. Although this was attributed to cod using chemoreception in conjunction with vision to locate prey, foraging rates may also be maintained by increased activity. Higher activity, however, is energetically costly and may offset benefits from increased foraging return. We examined the effects of turbidity on spontaneous activity of juvenile cod in the laboratory. We also measured the activity of juvenile cod with food odour present, to test for effects of turbidity on searching behaviour. Preliminary results indicate that spontaneous activity of juvenile cod increases non-linearly with turbidity. This pattern may represent not only increased searching for prey, but also decreased perceived predator risk. We therefore discuss these results in relation to recent experiments on the effect of turbidity on habitat preference and antipredator behaviour of juvenile cod.
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