A resident school of bigeye scad, logged on the slate between 09:12 and 09:58. Selar crumenophthalmus, fork length 18 to 22 cm.
Sweep a finger or the cursor through the water to scare the school. Tap open water to drop food.
The school holds off the east wall in a loose ellipse, a few hundred fish spaced about one body length apart. Nobody leads. Each fish matches the speed and heading of the six or seven nearest to it, and that local rule keeps the whole shape together.
Where the wall breaks into boulders the school splits without slowing. The two halves pass either side of each rock and close again behind it within two or three seconds. The turn starts a full body length before the rock, so they read it at a distance with eyes and lateral line.
A hand moved toward them and the school flashed. The turn spreads from the fish nearest the hand faster than any one fish can swim, because each fish reacts to its neighbour turning. Their flanks catch the light in sequence and a band of silver runs through the school. Biologists call this the Trafalgar effect.
A bluefin trevally came through on patrol. The school drew in to a tight ball and kept moving. When it charged, the scad parted around it and rejoined behind its tail. This is the fountain effect, and it keeps the predator arriving at empty water.
Released a pinch of pellet along the buoy line. The nearest fish broke formation first. The rest followed their neighbours in before they could see the food. Ascent at 9 m/min with a three-minute safety stop at 5 m.
Logged on slate 2 by the station dive team. Current 0.3 kn NE. Slate wiped 10:20.