Reef Fish at Gray’s Reef Get a Free Lunch: A Study of Fish Behaviors

[Frankie]

Imagine you’re a gag grouper at Gray’s Reef National Marine Sanctuary. You’re hungry and are foraging along the bottom on one of the sanctuary’s scattered protective ledges. This is your favorite habitat because it offers both food and shelter.
Above you in the water column, pelagic predators such as greater amberjack, Spanish mackerel, and great barracuda are circling a big mixed school of juvenile tomtate and cigar minnows. As they swim ever tightening circles around the school, the predatory fish drive the small fish to the bottom so they can more readily eat them.
They also happen to drive the tomtate right in front of you. Lunch is served; all you have to do is grab a mouthful. You, the grouper, have benefited from a form of “facilitative” or “optional” behavior. These are behaviors that produce positive outcomes for at least one or a few individuals, with positive or neutral outcome for others. The only losers in this scenario are the bait fish.
Gray's Reef National Marine Sanctuary Information Page