Getting There - Aneel's Travelogue

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Sharks Cocos Island, Costa Rica, Thursday, 16 January 2014 8:06pm

Phew. Back on dry land for the first time in over ten days. I'm pretty sure that's a record for me.

There was some pretty spectacular sea life on many of our dives near Cocos Island (I never actually set foot on the island, though some of our group did a hike there). It's called the "Island of the Sharks" in nature documentaries, and it lives up to its nickname. We saw enough white-tip reef sharks that we stopped noticing them, hundreds of scalloped hammerhead sharks, and a few bigger ones like galapagos sharks and tiger sharks. There were also plenty of close relatives of sharks like marbled rays and spotted eagle rays. A menagerie of random sea life like moray eels, green sea turtles, lobsters, and mushroom-like coral. And lots of fish. Clouds of snappers and goatfish. Cleaning stations full of barber fish.

One of the most impressive dives was a night dive in shallow water frequented by white-tip sharks. During the day, they seem sluggish, lying around on the sandy bottom, or lackadaisically swimming around. At night, they're on the hunt, swimming rapidly, looking for a sleeping fish to eat. They gather so thickly that the bottom of the ocean seems like a writhing mass of glossy sharkskin. And, since the water is only about 20 feet deep at the dive site, they're within an arm's length at many times. They take advantage of divers' lights to home in on prey fish, and once the commotion begins there's a brief frenzy where the nearby sharks try to get a piece of whatever has been caught. Black jacks, large greenish-black fish related to tuna, are also night hunting in the area, but while the sharks seem to rip apart their prey, the jacks tend to gulp it down whole, with a loud chomp.

The white-tips, even when hunting, aren't much of a threat to humans. However, some of their predators are. We had to abort one of our dives because a large galapagos shark (which would normally eat white-tips) started swimming under Chuck. Since they attack from below, this meant that it was time for us to get out of the water. A minute or so after the last diver was back on the dive boat, there was a big splash nearby. Nobody got a good look at it, but it was the right size for a galapagos breaching.

Many of the other dives focused on cleaning stations. Large sea life tends to pick up annoying parasites, and smaller fish have developed a commensual relationship, where they eat the parasites off of the larger fish and aren't eaten. The barber fish do this for many of the large sharks in the area, particularly scalloped hammerheads. If we positioned ourselves correctly, just downstream of a cleaning station, we could watch hammerheads swimming by above and beside us, and the barber fish swimming around them, cleaning.

There's a trade-off in waters like these: big predators like sharks eat smaller fish. And those fish, in turn, eat even smaller fish. And the smallest fish eat plankton, tiny plants and animals that float around, mostly carried by currents. A lot of our dives were cold and kind of murky, through chilly thermoclines full of plankton. Occasionally, something would appear in the hazy distance, perhaps a jack or a tuna... or a shark... or a school of hammerheads... or hundreds of hammerheads, forming something like a wall, swimming through the deep water. It would have been nice to get a really good look (or a good photograph, for that matter) of the hundreds of sharks just a few tens of yards away. But, of course, if the water were clear enough to see them, they wouldn't be there in such numbers, because that would mean insufficient plankton to sustain the food chain.

The fish and sharks are so plentiful at Cocos because it's an isolated island, 300 miles off of the Pacific coast of Costa Rica, which makes it a popular stopover point for fish on their way somewhere, and because it's a protected reserve. It took us about 36 hours of motoring in our ship to get there (happily, I was only a little queasy on the way out, and not at all bothered on the way back).

That remoteness became much more apparent when one of the divers on the other panga (a small boat carried by the ship, which takes the divers out to the dive sites and picks them up after they surface) got a case of decompression sickness. Normally, this would mean an ambulance or helicopter ride to the nearest hyperbaric chamber for recompression treatment. However Cocos Island is too far from the mainland for a rescue helicopter to make it there and back (there being neither a place to land, nor a place to refuel), which meant evacuation by boat. After the diver failed to recover with the treatment on hand (breathing pure oxygen resolves many cases of DCS), the trip was cut short and the ship started back towards the mainland. We rendezvoused with another, faster boat midway and transferred the diver, who was taken back to the mainland for treatment.

The ship then diverted to Caño Island and we did one last day of diving. These dives were generally shallower than the dives at Cocos, and we didn't see nearly as many big creatures. There were some cute nurse sharks sleeping on the seafloor. One had its head under a coral to keep the sun out of its eyes, and the other had its head under the first. We saw some soft coral, including Sea fans and something that made the reef look something like the cherry blossom festival in Japan. There were a lot of garden eels that were unusually bold and allowed us to get fairly close before ducking back into their burrows. Not the spectacular sharks of Cocos, but a fairly relaxed way to round out the trip.

Back on land, our group of six did one last activity together, a boat tour of a crocodile-infested river. There were an impressive variety of birds, and quite a lot of crocodiles. After lunch, we dropped off the others at the airport, and I returned to San Jose.


g-na (Anonymously) Friday, 17 January 2014 5:22pm

Yay, sharks!