Escape responses in juvenile Atlantic cod Gadus morhua L.: the effects of turbidity and predator speed.

We examined the effect of turbidity (0.5-14 beam attenuation m-1) and predator attack speed (150 and 296 cm s-1) on escape responses of juvenile cod Gadus morhua in the laboratory. We triggered escape responses using a predator model and measured escape timing, direction and locomotor performance. We also measured responsiveness and estimated the likelihood of fish escaping the `predator attack' (putative escape success, PES). Turbidity affected both PES and the type of escape response used by the fish, but these effects depended on predator speed. PES for the fast predator attack declined from 73% in clear water to 21% in highly turbid water, due to decreased responsiveness and poorly timed escapes. Intermediate turbidity enhanced PES and responsiveness to the slow predator attack. Locomotor performance was reduced by turbidity, whereas predator speed had the opposite effect. Our results suggest that both predator attack speed and turbidity have important roles in determining the vulnerability of fish attacked by piscivorous predators.