Original paper

Are mayfly anti-predator responses to fish odour proportional to risk?

Mc Intosh, Angus R.; Peckarsky, Barbara L.


Adaptive prey behaviour should include responses to predators in proportion to the risk they present. We tested whether two salmonids fishes, the introduced brook trout (Salvelinus fontinalis) and native Colorado River cutthroat trout (Oncorhynchus clarki pleuriticus), presented different predation risks to Baetis bicaudatus mayflies, and whether mayflies used chemical cues to adjust their behaviour in proportion to that risk. In a feeding trial the native cutthroat trout consumed 60% more Baetis than brook trout. To test the antipredator responses of Baetis to fish chemical cues, we added water from holding tanks containing cutthroat, brook trout or goldfish (a non-predator), to microcosms with Baetis larvae. We measured rates of mayfly movement in the water column (drift), which is risky behaviour in the presence of drift-feeding predators. Nocturnal drift was substantially depressed in the presence of cutthroat trout odour, intermediate in microcosms with brook trout odour and relatively high in both goldfish and control treatments. Combined, these results indicate that risky behaviour decreased as predation risk increased. This result implies that Baetis used chemical cues produced by cutthroat trout, and brook trout to adjust their behaviour in proportion to the risk posed by those predators.


chemical cuespredatory fishpredator-prey interactionssalmonidaemayfliesfish odourstream invertebrate drift