In the Galapagos Islands, during certain times of the year, large aggregations of ScallopedHammerheads come together to circle around Darwin Island. Scalloped Hammerheads normallylive in the open ocean, but here at Darwin Island they come close to shore in large numbers. Considering the vast numbers of fish here, it would be logical to assume that the sharkscome to feed. Yet, nobody has ever witnessed the sharks feeding. Instead they just seemto be swim slowly by the reef. What are these sharks up to?I'm hoping to find out. I have come all the way to the Galapagos Islands to investigatethese strange and magnificent sharks. The Galapagos Islands are a remote archipelago 600 miles off the coast of Ecuador in thePacific Ocean. Many incredible animals live here, both above and below the water. It is famous for thelargest fish on Earth—the whale shark—which inhabits these waters. But divers also flockhere to see hammerheads—and lots of them!Hammerheads are most common at the northern island of Darwin, famous for its stone arch. Rolling into the water, my assistant Gator and I head down to the reef to wait for thesharks. Soon a huge school is swimming by my lens. Hammerheads are of course known for their strange, flattened heads. But you have towonder. . . what is that flat head for?Shark biologists put their own heads together to figure it out. At first, they speculatedthat it gave the hammerhead wider stereoscopic vision. But that didn't work: hammerheadeyes face in opposite directions, meaning they can't see in stereo. The wide headprobably has nothing to do with eyesight. So maybe it has to do with the sense of smell. Wider spaced olfactory organs would help thehungry shark sniff out prey more accurately. Well, not really. Although the nostrils and olfactory organs are widely spaced, a groove along the frontof the head effectively connects them together. Therefore, they don't give the hammerheada better sense of directional smell than any other shark. Scientists finally hit upon a graceful reason for the awkward head: It helps the hammerheadturn faster by eliminating the need for large pectoral fins. Some sharks, like white tip reef sharks can rest all day if they want, just gulping waterto ventilate their gills, the shark equivalent of breathing. Hammerheads, on the other hand, cannot accomplish this. Like most pelagic sharks, they mustkeep swimming not only to stay up off the bottom, but to breathe. In an ironic twistof fate, if a hammerhead stops swimming, it will drown. The big flat head is a wing tokeep the hammerhead up off the bottom. Researcher Kanesa Duncan at the University of Hawaii is studying Scalloped hammerheads. She catches the sharks when they are just pups, only a few weeks old, in Kaneohe Bayon Oahu. She uses a hand line and a barbless hook baited with squid to catch the baby hammerheads. By holding the shark upside down, she places it in a kind of trance called Tonic Immobility. Many sharks can be immobilized for handling in this way. Nobody knows why it works, butit makes shark handling a lot easier. She frequently puts the pup back in the water to aerate the gills. Once aboard the boat, she first measures the shark while an assistant records the data. KANESA: PCL is 38. 3. Fork Length: 42. 7. Total length: 56. 5. It's going to be tag number2315. Next she implants a small visual tag with a number on it through the shark's dorsalfin. This does not hurt the shark at all. The fin is almost completely made of cartilage. Next, she weighs the pup. KANESA: 750 on the dot. Finally, Duncan releases the baby hammerhead back into the ocean. Hopefully, she will catchit again in a few months and be able to determine how much it grew. Back at the lab, Duncan has several captive hammerhead pups that she is working with todetermine growth patterns. She wants to learn, among other things, how fast baby Hammerheadsgrow. But I still want to know what they are all doing at Darwin Island in the Galapagos, andI finally get a clue when I see a shark being investigated by a fish. The strong current at Darwin Island allows a hammerhead to swim in place, like a runneron a treadmill, yet hold a fixed position over the reef. King Angelfish make their homes on this reef and they serve as cleaner fish for the sharks. Because the sharks get cuts and scrapes, not to mention parasites, that need cleaning,they come to a cleaning station where a King Angelfish is waiting to clean the wounds andeat the parasites. Everyone gets something out of the deal. . . theangelfish get food and the sharks get cleaned. The sharks never eat their cleaner fish. . . that'sjust considered bad form. A shark looking to be cleaned often swims at an angle, with its white belly showing. This body language tells the angelfish to come on over. Angelfish looking to clean a shark swim up and down in the water to attract the shark'sattention. Often, something seems amiss to the sharkand it rebuffs the fish. The sharks feel vulnerable while they are being cleaned, so they picka cleaning station carefully. If anything doesn't seem right, they move on. But patience pays off and eventually the right shark meets up with the right fish in theright place, and everything goes according to plan. It's love at first bite. Sometimes a really grungy shark needs a whole team of angelfish to complete the task. Darwin Island is one of my favorite places in the whole world to dive, and hammerheadsare one of the most beautiful sharks in the ocean. But alas, the dive must come to anend and we head back to the surface. I'm sad to leave but happy to have learned the secretbehind the mysterious school of hammerheads here in the blue waters of the Galapagos.
