Home / Blog / Leaving Cocos, and trophic levels in action. Thursday, February 24th 2005

February 24, 2005

Leaving Cocos, and trophic levels in action. Thursday, February 24th 2005

BY: Sandy Mason



We left Cocos. We sailed northeast with the island behind us, gorgeous, streaming water as if it had just lifted itself from the sea. The clouds pile above it.

On the way out we pass another longliner coming iDirty rockn. This is the second we’ve seen since we’ve been at the island. The first had pled engine trouble as an excuse for anchoring in the bay; it’s a common story and there is no way to confirm it. Last night the MarViva patrollers pulled in a six-mile longline that had been set in park waters. Still, this is nothing. The park rangers and MarViva staff say that three years ago, before they began their collective patrols, there were thirty to forty fishing boats in park waters at any given time. I can well believe it. It is impressive to see firsthand the continuous enforcement efforts, patrols that stay out all night through darkness and storms, and the continuous pressure — any gap in the patrolling and the longliners will enter again. The new level of protection around Cocos is both dramatic and tenuous.

But what a difference it makes. Today, before we left, the film crew did a final dive. Juan Pablo reports:

“The site was called ‘Dirty Rock'” — a much-favored target for birds — “and it is a little rocky island without vegetation of any kind. Underwater, the walls of the rock are fairly vertical and drop 55-60 meters. The form or the rock is a kind of pyramidal pinnacle, very steep at the start but which slopes gently toward the bottom.The incredible thing about this dive is that it was a perfect representation of the trophic chain, or the food web, of the marine ecosystem of Cocos Island. You have, at the bottom, at a depth of -50 meters, the big predators — the apex of the pyramid. These are hammerhead sharks, known in the area as “horned” sharks. We saw two or three large ones, patrolling and circling the base of the rock. There was nothing else. The area was stark, just the two or three sharks, circling…

A little bit higher, in the -35-40 meter zone, there were tongues of sand in the rock, almost vertical. Here there was another type of shark — whitetip reef sharks. They were resting. Hammerheads, and most sharks, must move constantly through the water, but whitetip reef sharks are an exception.

At 30 meters: the jacks. Also a large predator. There were small groups of them, and they were large — 60 centimeters or so. At this point we also saw a pair of spotted tropical rays.

Closer to the surface the fish are smaller and there are a greater number. The number of species also increases. In the dark, cavernous fissures in the rock there were bigeyes — soldierfish. Further out were butterflyfish, surgeonfish, parrotfish, and hundreds and hundreds of damselfish.

It was one of the most beautiful dives I have ever done. Both because the conditions were great and because it is so unusual to see this enormous variety of species outside of coral reefs. It’s obvious that the work of MarViva, the government, and FAICO to protect the island have had an effect. All sharks — from hammerheads to rays — are captured in longline fishing. If there were no fishing regulations and no control over the fishing boats, there wouldn’t be this quantity and diversity of species. The entire structure of the system alters when the top predators disappear.

There is a phenomenon that biologists call the “reserve effect,” which consists of the fact that in areas where fishing is well regulated there is an increase in the number of species, in the number of individuals and in their size. Thanks to the work of MarViva, it’s clear that this phenomenon exists in Cocos Island.

As regards Oceana’s work, I am proud — personally and professionally — to be part of this team. In the discipline of enviromental protection and education it’s not easy to find projects of this type and of this scale. It’s a great opportunity, for a marine biologist, to collaborate in an initiative of this size — on a 22-meter boat, twelve people working, each with his or her mission, in some of the best conserved and least accessible areas of the planet.”