Threat-sensitive predator avoidance by slimy sculpins: understanding the importance of visual versus chemical information

The supposition that prey animals assess and behave flexibly in response to different degrees of predation threat is known as the threat-sensitive pre dator avoidance hypothesis. We completed a series of field and laboratory e xperiments to examine whether slimy sculpins (Cottus cognatus) exhibit thre at-sensitive predator avoidance when exposed to sympatric predatory brook t rout (Salvelinus fontinalis). In a field experiment we caged small and larg e trout in similar habitats and found that sculpins avoided areas containin g trout that were large enough to pose a threat to them, but did not avoid areas containing trout that were small and hence not a threat. In a series of laboratory experiments we found that sculpins showed threat-sensitive pr edator avoidance when they could assess the predator visually. However, whe n only chemical cues from the predator were presented, sculpins responded t o the predator regardless of its size. Chemical cues seem to function to wa rn the sculpin that the predator is in the vicinity, but visual cues are ne eded in order to accurately assess the risk posed by the predator.