Monday, September 19, 2011

Whale Sharks: Nat Geo documents unusual feeding behavior

Whale sharks - the largest fish on the planet. For many of us who dip below the surface of the sea, either with snorkels or scuba, catching a glimpse of any large marine animal is always a powerful and memorable experience. It almost seems surreal; something so large gliding past you like a zeppelin in a liquid sky.

That feeling is heightened when the leviathan in question is a whale shark. Not that you are concerned about becoming prey to the whale shark - these animals are filter feeders like baleen whales - but it's a shark all the same. Throughout the world there are several "hot spots" for finding small congregations of whale sharks, but it's not always guaranteed. Many divers can tell you of their experiences being skunked, and then learning about the sharks that appeared the day after they departed.

For underwater photographer Michael Aw, luck was on his side while taking pictures for National Geographic. Not only did he find whale sharks off the northern shores of Papua, Indonesia, but he was able to document an unusual behavior. The whale sharks had come across a reliable food source, that of the baitfish caught by local fishermen. With hundreds of small fish corralled into fishing nets, the sharks would grab at the nets, trying to make off with an easy meal. It would appear that it runs in the family - whale sharks are opportunistic feeders, like their smaller shark cousins.

Accompanying Aw's photos in Sharing with Sharks for the October issue, on sale September 27th, and online edition of National Geographic, Jennifer Holland wrote, "The giant fish is hard to study because it is hard to find and track. By tagging individual specimens, scientists have learned that whale sharks can log thousands of miles in years-long trips. But they sometimes disappear for weeks, diving more than a mile down and resting in the chilly deep for a spell. No one has ever found mating or birthing grounds.

Whale sharks are ordinarily loners. But not in one corner of Indonesia. [Michael Aw's] photographs, shot some eight miles off the province of Papua, reveal a group of sharks that call on fishermen each day, zipping by one another, looking for handouts near the surface, and nosing the nets - a rare instance when the generally docile fish act, well, like the rest of the sharks."

One might question whether these sharks are becoming habituated or "trained" to look to the
fishermen for their food. This has been a concern leveled at others in the eco-tourism trade who are accused of attracting animals, in particular sharks, to the extant that it potentially interferes with the animals normal hunting instincts. But research has shown that what is offered as an attractant is usually insignificant compared to the animal's normal nutritional requirements and with whatever behavior modification that might take place, its effects are transitory.

But it can provide for some amazing moments, as Michael Aw's photos can attest. You can read the entire photo-article in the October issue of National Geographic or visit the National Geographic website.

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