Fishes on Fellowship: Bumphead spawning

Last Tuesday, a few days before the new moon, I went on another spawning dive, this time for bumphead parrotfish (Bolbometopon muricatum). Researcher Paul Collins picked me up at 4:45am and we joined the rest of the bleary-eyed but enthusiastic group for a dark and rainy ride out to the aggregation site near Ulong Channel. Weaker currents at the new moon and fewer big sharks meant that this dive was less of an adrenaline rush than the snapper spawning, but it was still spectacular to see thousands and thousands of huge fish assembling for this monthly spawning event.

Paul jumped in first to check the progress of the aggregation. He invited the rest of the group in as droves of bumpheads started heading purposefully toward the spawning site.

As they started milling around in the sand, we stayed well above them to avoid disturbing them. Paul compared this stage of the aggregation process to so many cockroaches congregating in a dark kitchen.

As with the snapper, spawning begins as a female darts toward the surface and several males follow, releasing a cloud of gametes.

Visibility was shot within a few minutes; it was best not to think about it too much.

Males assume this white-faced, banded mating coloration only during spawning.

Paul and his colleague Richard Barnden have been studying these spawning events for several years, and although there's still much that's poorly understood, Paul has some theories about how spawning patterns change over the fishes' life histories. "For bumpheads, older terminal phase males tend to have a harem mating structure with maybe ten females, and follow a separate spawning schedule," Paul explained to me after the dive. "We think what we're seeing here is more like a rave."