Who decides where the school goes?

Hundreds of perch schooled off our pier last week. The problem? They were an inch and a half long, which means nano hooks, water flea bait, very sharp filet knife.

Looking down at that swarm of black-striped fry, moving in unison, I couldn’t help wondering: What holds that school together? Why are they schooled in the first place? And which fish decides where the school goes?

The first thing to appreciate is that these fish don’t “decide” anything. They don’t form the school out of conscious strategic thinking. The behavior is built into their genes; it conveys certain evolutionary advantages that promote survival.

First off, it’s easier for a predator to track down and capture a solitary fish than to eat fish in a school. This seems counter-intuitive, since we’d think attacking a school would amount to the proverbial “shooting fish in a barrel.” However, scientists have found that a school confuses predators. A school moving together, the sides of multiple small fish flashing in sunlight, can appear to a predator as one large fish, discouraging attack. In addition, the sheer numbers of fish in a school disorient predators, making it hard for them to zero in on one individual.

Another advantage to schooling is that more eyes watching means greater ability to find food. Schooling also helps fish conserve energy – in effect they’re able to draft on each other. The principle is the same employed by bicycle racers, one closely following another to reduce wind resistance.

But how does a school of fish move as one? According to an article on the North Carolina Aquariums website, “Each fish maintains an exact spacing from its neighbor. As they swim, they follow the movements of their neighbors and change their course in unison. Vision is the primary sense used to hold their place in a school. Visual markers play a big role – each member of a school follows some key feature of the fish around it, usually a stripe or spot on their bodies, fins or tails. The vibration-detecting lateral line, a row of sensory cells that runs along the sides of the body, also provides information about neighbors’ movements.”

A closer look at the school of perch off our pier showed the individual fish contentedly picking off white specks in the water – likely Daphnia (water fleas) or some other zooplankton. Those of us here on Birch Lake can only hope the schooling behavior helps those perch grow to catchable, edible size. Time will tell.