As divers, we know that the ocean is home to some magnificent spectacles, and over time, some of them have become legend, immortalized by iconic images. One such image is that of thousands of scalloped hammerheads, their distinctive silhouettes tattooed against a rich background of endless blue as they move like shadows across the sun. For many divers, the splendor of schooling hammerheads like these is the holy grail of underwater spectacles, and once, they were not such a rare sight. But the relentless targeting of these sharks by the finning industry has pushed them to the brink of extinction. Listed as Endangered on the IUCN Red List, there are just a handful of places left in the world where divers can still see these magnificent animals in their natural environment. Of these, the most famous is a tiny volcanic island named Cocos, 340 miles off the western coast of Costa Rica. Accessible only by liveaboard charter, Cocos Island is a UNESCO World Heritage site recognized by Jacques Cousteau in 1994 as “the most beautiful island in the world.”
Protected as a marine park since 1978, Cocos is a significant center of biodiversity, both on land and beneath the waves. Its productive waters are home to at least 27 endemic fish species, while impressive shoals of large game fish including tuna and trevally represent a level of productivity seen in few other places on Earth. Cocos is most famous for its sharks, with regular sightings of Galapagos, tiger, silvertip, whitetip, silky and whale sharks awaiting those willing to make the 36-hour boat trip to the island. There is one sight above all others that draws divers here, though — the schooling hammerheads that have come to define the island’s diving. The hammerheads’ tendency to congregate at dive sites such as Baja Alcyone, Dirty Rock and Punta Maria is explained by Cocos’ underwater topography, which creates the perfect conditions for the sharks. The island drops away steeply into deep water, the depths punctured occasionally by dizzying submarine pinnacles. Perennially strong currents keep the visibility clear and help create upwellings of nutrient-rich water around these pinnacles; it’s here that divers can see the hammerheads, not singly or in pairs, but in the thousands.
The hammerheads come to the island’s pinnacles to feed, socialize and visit the cleaning stations at dive sites like Dirty Rock. Because of the strong currents, divers access most of the pinnacles via a shot line to keep them on target. At depths of over 100 feet (30m), the top of the pinnacle ridge is a world bathed in blue. This is frontier diving, in a place so untouched it’s easy to forget that elsewhere in the world fish are disappearing from the oceans and reefs are being destroyed. On days that the hammerheads don’t appear, there are plenty of other sights to see on the pinnacles, from winged squadrons of spotted eagle rays, to a silvered Galapagos shark cruising in the blue or a swirling, pulsating shoal of trevally suspended cloud-like over the reef. When the hammerheads do come out to play, all other distractions fade away until sheer wonderment at the sharks swirling above is all that’s left. When seen from below, the school seems to be made up of sharks upon sharks, endless layers of alien silhouettes filling the blue expanse. It’s that iconic image come to life, and in that moment it is hard to imagine anything more magnificent.
It is important to remember that Cocos Island dive sites are not for the faint-hearted, nor for the inexperienced. Strong currents, plunging depths and the close proximity of many of the world’s largest shark species can make for some intense dives. It is recommended that visitors have at least 25 hours of underwater experience, and due to the depth of most sites, divers must have completed a Deep Diver course in addition to their Open Water at the very least. Hammerheads can be seen year round at the island, although they occur in greater numbers during the Costa Rican wet season, which runs from June to October. The wet season typically coincides with rougher seas and can affect visibility, and yet the hammerheads favor this time of year for the elevated level of nutrients (and therefore prey fish) in the water. It is also possible, however, to see the hammerheads from November to May, when drier weather means calmer seas and better visibility. Whenever you choose to visit Cocos, one thing is for certain: you’ll never forget the thrill of witnessing one of Nature’s greatest spectacles unfold before you.