General Knowledge
How do sailfish hunt together?
- They herd fish into a ball and take turns
- They chase alone
- They ambush from below
The answer is They herd fish into a ball and take turns. They flash colour to signal whose turn it is, and avoid stabbing each other.
They work a bait ball. A group of sailfish drives a shoal of sardines to the surface, where the fish have nowhere below them to escape to, and then take turns approaching to slash through the mass with the bill - not spearing but striking sideways to stun individuals, which are then picked off.
The taking turns is the remarkable part, because a bill nearly a metre long swung in a crowd is a serious hazard to the other sailfish. As one moves in it flushes bright, its stripes and dorsal sail lighting up blue - a colour change fast enough to be a signal rather than a mood, and the working interpretation is that it announces an attack so the others hold off. Sailfish attacking with the colours suppressed injure each other far more often.
It is not cooperation in the sense of sharing. Each fish is feeding itself, and the group behaviour arises because a bait ball is more productive than a chase and stays available longer if nobody scatters it. What looks like teamwork is a set of individually selfish rules that happen to require signalling - which is a fair description of a good deal of animal cooperation.