Rusty crayfish may not have a nose as such, but they do have an exceptional sense of smell. With a “sniff”, these crustaceans can glean all sorts of information about the world around them.
If rusty crayfish can “smell” a predator, such as largemouth bass, it stands to reason the crayfish will seek to reduce their chances of becoming dinner.
A new study in the Canadian Journal of Zoology found crayfish not only detect the presence of a predator as a threat, but before changing their behaviour they also consider how likely it is that a predator will eat them.
Based at Bowling Green State University, PhD candidate Tyler Wood and Professor Paul Moore fed various sized bass either commercial feed pellets or pellets made from one of three crayfish species—including rusty crayfish.
Over a series of trials in artificial ponds and streams, the researchers monitored the crayfish’s behaviour and the amount of plants they ate in the absence (no predator odours) and presence of a bass; the crayfish and bass were physically separated by a mesh so that the only contact the crayfish would have with the bass was the shared water—and the predator odours carried with it.
Sure enough, the crayfish exposed to bass odours changed their behaviours, but exactly how the crayfish changed depended on how big the bass were and what the bass had eaten.
Crayfish that were larger relative to the size of the bass spent more time eating and less time sheltered than their counterparts who were relatively smaller (or those who weren’t exposed to any predator odours).
The unexpected boldness of relatively larger crayfish was, however, somewhat tempered when the crayfish were exposed to bass fed crayfish-flavoured pellets.