It happened during a dive at Lobster Rock late yesterday afternoon. Bob
Cranston and Michele Hall had gone off to look for a batfish, one of the
ocean's stranger creatures, while Peter Kragh, Lance Milbrand, and I dove on
the sandy flats north of the Rock, hoping to see silvertip sharks. We soon
found them—sleek, beautiful juveniles no more than three feet long.
Pestered by rainbow runners, a silvery fish known to chafe the sides of
sharks, the elusive silvertips came near only when we held as still as
possible. The water was a bit murky, and they never approached closer than
about 15 feet, which lent them an enigmatic mien.
As we were heading back towards Lobster Rock, we were stopped by a
black triggerfish. Also known as black durgon, this fish is a striking blue-
black, with distinctive white lines tracing its tail end at the base of the
dorsal and anal fins. It's a joy to see even a single black triggerfish, but
here there were hundreds, swirling in an underwater tornado right on the
bottom. So dense you couldn't see through it, the swarm was animated by
of movement as six or eight triggerfish at once spun off in tight pursuit of
single one of their kind. Was it males going after a female? Were they
courting, or mating, or doing something entirely different? I didn't know,
I just watched.
I was so entranced by the tornado that it was a few minutes before I
overhead. Then I saw that the tornado of triggerfish was only one part of a
great storm of them. Their hovering black silhouettes filled the sky above
like a plague of aquatic locusts. Spinning around, I could see no end to
At one point they temporarily dispersed, shooting off as one toward the
of the bottom when a school of fast-moving mullet snapper swept through. But
soon they reappeared, and the puzzling ritual continued. With dusk rapidly
approaching, we reluctantly left them.
Back on the boat, there was excited speculation. Kragh thought they
probably mating, which seemed a reasonable enough explanation, though no one
had seen that behavior before. Earlier in the day, the film crew had
a similar black triggerfish swarm at Manuelita. As baffled as we were,
Hall tried to film it, but as soon as he turned the movie lights on the
it broke up. Mark Thurlow told me, "I've never seen anything like it."
The waters around Cocos are full of such surprises. For most divers,
stunning enough just to see sharks on every single dive, as we do, or
of hammerheads. Kragh told me diving in the Red Sea he felt lucky to
a single ray; here you see marbled rays at every turn, occasional spotted
eagle rays, and, if you're lucky, mobula and Pacific manta rays. The sheer
piscine biomass at Cocos Island rivals any place in the world.
But then there are those unexpected surprises. As an inexperienced
least compared to my companions aboard the Undersea Hunter, I enjoyed eye-
openers on every dive. Within minutes of reaching the bottom on my inaugural
dive here three weeks ago, Kragh and I spied a tiger snake eel sliding
sinuously over the sandy seafloor. Every eel I'd ever seen before hid in
crevices. On subsequent dives: a huge, all-yellow grouper, standing out in a
twilit sea like a streetlamp; a shoebox-sized slipper lobster "like a
prehistoric tank" (Mark Conlin); in the final minutes of a dive at Lobster
Rock, a green sea turtle, paddling off into the blue.
Even the Halls have been taken by surprise, which is saying something.
seen everything and filmed it to boot. For them, such surprises have come
in sightings but in unusual behaviors. A green sea turtle is nothing to
but a green sea turtle feeding on a branch of leaves from a rainforest tree
is. (They filmed this unexpected behavior earlier this year.) No one had
seen a mantis shrimp at Cocos Island before the Halls found one near
Bay, nor had anyone ever seen one quite as large (about 14 inches long). But
that's not why they filmed it. They filmed it for its remarkable attack
strategy (see the mantis shrimp video clip). Even the courtship of the
marbled rays was an unplanned bonus. Since the rays
usually court in summer, the Halls had given up on them this late in the
season—and then they went ahead and did it.
Even the second mass ritual that we ran into on yesterday's dive had
surprise for the Halls. After leaving the swarm of triggerfish, the three of
us made our way in the gathering twilight back towards the jumble of
at the base of Lobster Rock. On the way, Kragh surfaced and reboarded the
skiff, which inexplicably motored off, leaving Milbrand and I alone. Happy
have a little more time, I kept swimming. Then I noticed Milbrand pointing:
front of us lay a vast white cloud, suspended in the water column about 20
feet below the surface. What was it? Ahead I saw Cranston, back from his
search for the batfish. I swam towards him, but was soon engulfed in the
Instantly I had that uneasy feeling you get when your plane flies into
cloud and you lose all visibility. I couldn't see my hand in front of my
I had a sudden thought that I might get lost—a ridiculous one since
Milbrand and Cranston were less than 20 feet away. After a minute or so the
cloud began to dissipate, and then there was Cranston, ushering me towards a
darkened reef below.
There, on a twilit ledge, I discovered the source of the mysterious
Hundreds of cream-colored fish with bold vertical stripes teemed above the
ledge. Every half minute or so, a cluster of the fish would start quivering
with apparent excitement and then rocket towards the surface, u-turning
10 or 15 feet and leaving behind a cloud of whiteness. Other clusters,
inspired by the instigators' obvious agitation, performed the same feat
virtually simultaneously. It was synchronized swimming as only nature can do
it. The whole effect, as Michele Hall commented later, was like a burst of
It was convict tangs spawning, I learned later. So-named for the black
that paint their sides like prison stripes, the convict tangs, the Halls
me, congregate on this ledge every evening. During the massive mating
dance that follows, males and females release sperm and eggs together. The
cloud that swallowed me? Millions of potential tangs. For the Halls as for
the spawning of the convict tangs was not in the original script. Like the
tornado of triggerfish, it was an unexpected surprise.
We leave tomorrow night for the mainland, a trip of 30-some hours, so look
for the next and final dispatch on Tuesday, the 20th.