It's a pretty common sight, but an absolutely spectacular one as well. They say they do it to dislodge parasites, but no one knows for sure. I prefer to think they do it just for the sheer joy of it.

But I've never seen them schooling like this around here. I've always thought they were solitary fish. The stingrays do school here, and the bullnose rays, in summer. I used to sail upwind of the sand flats, then run down to leeward with the centerboard and rudder kicked up, into water just deep enough to float the boat. You could really sneak up on them like that, and they would swim together by the thousands, just inches above the the sand in the crystal clear water until they sensed the boat right on top of them. Then they would scatter away from us in all directions, like a silent explosion of sand. I suspect they school this way in their season for some reproductive reason, although they don't need to, they fertilize their eggs internally so they don't need to release milt and roe in the water like other schooling fish do.

Its just another mystery.