The other day I was under the sea, slowly rising up along the sheer rock pinnacle known as Bajo del Diablo, an offshore dive site in Caño Island Biological Preserve, 22 kilometers west of the OsaPeninsula’s DrakeBay, on the southern Pacific coast.
The ocean waters were stacked like oil and vinegar in a bottle of salad dressing: clear, warm water near the surface and cool, green water sloshing below. As I neared the rock tip of the seamount, seven meters below the surface, I expected things to get brighter as I swam out of the green and into the clear, warm surface waters. But things went dark.
I looked up as a monstrous shape blocked the diffuse sunlight. Above me swam the biggest fish in the sea: a whale shark, and a rather large one.
The whale shark got its name from the fact that it grows as big as a whale. But the whale shark is a fish,with gills and a vertical tail, not an air-breathing, horizontal-tailed sea mammal.
Like most sharks, a whale shark is not even slightly dangerous to people. Like the great whales, whale sharks have evolved big mouths for gulping down large quantities of little fish and shrimp-like animals.
Also like the great whales, whale sharks have no sharp teeth for attacking. I suppose a serious gumming is possible, though unlikely, as these strange creatures are timid and delicate. Here, they do not seem very coordinated; they swim slow and can usually be readily approached and touched.
Since most divers know all this, they often swim right over and touch them. Whale sharks seem to enjoy having their skin stroked and sometimes even to expect it. Skin grooming is probably why whale sharks come to Bajo del Diablo; like many other kinds of large fish, they show up at the seamount to let small fish feast on skin parasites.
Some days there is a long queue of big fish waiting to be serviced by the small, colorful fish that live among corals growing on the rock. Bajo del Diablo’s reef inhabitants swarm around the visitors, eating the tiny fish and small crustaceans that live on the skin of the big visiting fish. Divers call this phenomenon a “cleaning station.”
Whale sharks need to be cleaned of their parasites, and that’s why it’s better to not touch these huge beasts at all, unless you want to pick up a few parasites yourself. Also, if you do not touch the whale shark, it is far more likely to stay around, sometimes slowly circling for hours. Sadly, many people grab whale sharks or try to ride them by holding onto a fin. This makes the biggest of all sharks swim away, usually in about a minute.
Whale sharks spend the better part of their existence in the open sea, making most of their lives still a mystery for humans.
Since we see both big and small whale sharks here in the Southern Zone, there may be an unknown, rare birthing area near by. Unlike most fishes but similar to other large sharks, whale sharks are thought to give birth to live young, but so far no one knows.
Scientists do know that whale sharks (Rhincodon typus) seem to live in precarious numbers. They are rare. Few places in the world have reliable whale shark sightings year after year. Costa Rica, as usual with things natural, is blessed.
Scientists and naturalists say that whale sharks are not growing as big as the 18 meters and more they used to, much like the great whales are no longer found as big as once reported. The biggest great whales were slaughtered for their blubber, but no one knows what is happening to the biggest whale sharks – though some have suggested climate change as the culprit.
More than the usual number of whale shark sightings seem to have been reported in the last few months around CañoIsland, perhaps as a result of the cooler, nutrientrich waters lying along the bottom of Costa Rica’s Pacific lately.