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Friday, February 22, 2019

Why Do Smallmouth Bass Catch and Release Crayfish?

The interaction between bass and crayfish is something I've been watching for a very long time and now think I understand. Typically, when people view these kinds of videos, they get the wrong impression of what's going on. Most people believe the crayfish is successfully repelling the attack of the hungry bass simply by its posture and extending the claws out in a menacing fashion. What in fact is happening is the bass is choosing not to eat the crayfish. This decision is arrived at by a single factor that has nothing to do with the defensive posturing of crayfish.

Bass are initially attracted visually to the crayfish, and rush in close. The decision to attack is then based solely on the hardness of the shell or exoskeleton. This most certainly can be determined once the crayfish is in the bass's mouth, causing the bass to immediately spit out the crayfish, if the crayfish is in its "hard shell" state. But it seems that bass can also detect this without first mouthing the crayfish. At first I thought they were doing this by visually inspecting the crayfish, but now I think they must be picking up a scent as well. Crayfish that have recently molted have soft shells and are much sought after by bass. Crayfish can't ward off attacks by sticking their claws out defensively when confronted by a bass. Bass laugh at this pathetic attempt. When they're in this soft shell phase, after a recent molt, no amount of claw wagging, or any other posturing is an effective defense.

When there are competing bass nearby, there's no time to evaluate whether the crayfish is soft or not. The main goal here is just to get to the food before your competitor. So in these cases, bass will more or less attack and "ask questions later". Once they have the prey in their mouths safely secured from other bass, they will release it if it turns out to have a hard shell.

Predation on individual crayfish seems to be solely determined by the current state of hardness of the crayfish exoskeleton.

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