Whale sharks (Rhincodon typus) are the ocean's vagabonds, roaming far and wide, and often for reasons inexplicable to humans. To make matters even more complex, despite their massive size—fully grown adults are around the length of a school bus—these gentle giants have a frustrating habit (for the scientists who study them) of simply disappearing.
There's a whole lot that marine biologists still don't know about whale sharks. For example, data gathered from tracking devices reveals that individuals can swim up to 8,000 miles to dine on plankton blooms, but will often disperse in seemingly random directions after feeding time is over. Whale sharks have been recorded diving down more than 6,000 feet, yet scientists remain uncertain of their motives for hanging out at such depths. And even though experts know that pregnant females deliver live pups, as opposed to releasing eggs like some other shark species, no one has ever actually witnessed a whale shark birth.
These persistent marine mysteries were part of the impetus for Conservation International's recent whale shark tracking project. And now, with approximately 12 months worth of data, the organization has launched a near-real-time tracking map that allows biologists, and anyone else in the world, to watch as their enigmatic journeys unfold.
Last year, a team of biologists affiliated with the nonprofit visited the Bird's Head Seascape—a luminous reef system located off West Papua, Indonesia—for the sole purpose of outfitting resident whale sharks with special fin-mounted satellite tracking tags.
"We can speculate that they went somewhere—or dived to a certain depth to feed or to get cleaned or to mate or to give birth, but we really don't know. This is the world's largest fish, but we still know very little about them. No one knows where they mate, where they give birth, or even where the babies, females, and large adults spend their time," Mark Erdmann, a marine scientist and senior advisor at Conservation International-Indonesia, told me.
According to Erdmann, this project marks the first time that fin-mount tags have been used to monitor whale sharks. In the past, scientists usually opted for spear-inserted titanium dart tags that would tow behind individuals on stainless steel tethers.
"After a pre-programmed time, the tag would release from the tether and float to the surface and transmit its data back to the ARGOS satellite network, allowing the researcher to see where it had moved and dived," added Erdmann. "The problem with this technique is that the tags would frequently pull off the animals within a few weeks—or might even be bitten off by other sharks or barracuda—and the data you would get back would be less than optimal."
But the whale sharks that occupy the Bird's Head Seascape have a particular taste for silverside baitfish, which meant that biologists could safely approach them as they fed on the catches of local fishermen. While the sharks were somewhat immobilized, the team would drill a series of holes through their fins and bolt special satellite tags, custom-made by Wildlife Computers, into place. Erdmann admitted the process "probably sounds barbaric, but in reality there are very few nerve endings in the shark fin so they don't appear to feel any pain at this operation."
So far, the 16 whale sharks the crew managed to tag have pinged back a bounty of valuable data. By tracking their movements, scientists have been able to theorize that the sharks of Bird's Head Seascape are more or less "homebodies." Since this type of behavior contradicts the popular belief that whale sharks are migratory, following seasonal spawns of fish and plankton, it's possible that these individuals' anomalous behavior is due to the year-round buffet that the local fishing industry provides them.
Indonesia's whale sharks also have a habit of going on "quick road trips" along the coastline of Papua New Guinea, the western Pacific, and even the southern Mariana Trench. One shark covered a distance of 2,485 miles but, like the others, turned right back around and returned to familiar waters (and probably a nice, easy meal).
However, like all technology, satellite tags are as useful as their limitations and drawbacks.
"Having this information doesn't tell you why they moved to a certain area or what they were doing when they dived to 5,000 feet. The tags also won't tell you if they were alone at the time, or with other sharks," Erdmann said.
Furthermore, all of the individuals the team tagged were adolescent males (according to Erdmann, more than 97 percent of the 100-plus whale sharks they've identified from Bird's Head have been male), which provides even more mental fodder regarding the perplexing behavior of female sharks.
The whale sharks will continue to be monitored for as long as their tags remain active, which according to their battery life, should be around two years. You can follow along on their tracking map, but be warned that a lag-time has been induced to minimize the risk of poachers using the satellite data to hunt the sharks.
Right now, it looks like the 13-footer named "Moby" is taking a nice little cruise up through warm waters of Palau.