It seems that shoals of fish are subject to a tension between the tendencies to swim closely to avoid predators and to spread out to get enough oxygen.
(There are examples of eg dolphins blowing bubbles in order somehow to direct a shoal, so maybe the injection of some extra oxygen allows the fish to bunch up more, making them easier to eat).
Today’s invention is an air line from a fishing boat. When a shoal is detected on the sonar, this line would descend into the shoal, aerate it and allow the fish to form a tighter than usual ball…resulting in a higher than normal percentage caught in the vessel’s net.
