HOLBOX, Mexico (1 Sep 2007) -- Whale sharks don't like rice. Last week, University of South Florida and Georgia Aquarium researchers aboard a research boat threw a handful of instant rice one meter in front of a whale shark to measure how much food the world's largest fish eats in an hour. "It's real low-tech," USF biology professor Phil Motta said. "Sometimes low-tech is good." The rice experiment wasn't as low-tech as Motta made it out to be: A laser aboard the research boat gave the exact distance of the rice grains from the shark, and a high-speed video camera recorded the grains' movement. "We play the video back frame by frame, click, click, click, and we can see the grains moving into the mouth," said Motta, who was in Holbox to study whale shark feeding habits. "We know the distance from the laser, we know how fast the grains are moving, and we can get the rate of flow into the shark's mouth. We know the size of the mouth, so we can get the volume." Whale sharks, however, are plankton eaters, and the rice grains clogged the fish's filtering pads, which look like Brillo pads, and the fish spit them out. "We call it coughing," Motta said. "The rice went in and came back out. The shark could discriminate between a handful of rice and plankton." The USF/Georgia Aquarium feeding study was only part of the whale shark science going on last week off Holbox. Every summer, deep nutrient-rich water from the Caribbean flows across the shallow continental shelf north of the Yucatan Peninsula and fuels massive plankton blooms. These blooms, in turn, attract one of the world's largest feeding aggregations of whale sharks. In 2003, Mote Marine Laboratory researchers started studying the big fish with the Domino project (Mexican scientists and tour guides who study whale sharks and regulate tourist activities around the animals — locals call whale sharks "dominos" because of the fish's spots). "The Mexicans have the central role," said Bob Hueter, director of Mote's Center for Shark Research. "The work is taking place in Mexican water. It was their project first. "Mote and USF are a small piece of the project. We focus on the biology. The Mexicans do that, too, but they also deal with the bigger picture of policy and management, the effects of tourism on Holbox, the socioeconomic benefits. We're like technical consultants for the program: They use the information we bring to extend the protection of this species." Over the past few years, Holbox has become a popular tourist destination, and part of the Domino project's role has been to make sure tourists don't harass the fish. Among the rules are snorkeling only (no scuba), no flash photography, only three people in the water with one shark, and no one can come within 2 meters of a shark. "The project started as a management tool for local people to know about these animals," project research coordinator Rafael de la Parra said. "The research part started right along with that, and we found there's so little known about these great animals." Along with Domino scientists, Mote's part of the research has been taking tissue samples from Holbox' whale sharks for DNA testing and putting external tags and satellite tags on the fish. External tags are a way to count the animals that pass through the area — so far, researchers have tagged almost 600 whale sharks, with vast majority still untagged. If people report tags, scientists can begin to understand where the animals go when they're not gorging on plankton off Holbox. Since 2003, researchers have put satellite tags on 14 whale sharks, including one last week. These "pop-off" tags, which are programmed to pop off the fish at a set time, record water temperature, pressure, which gives depth, and approximate location. When the tag detaches, it surfaces and beams its information to a satellite. | | Over the past few years, Holbox has become a popular tourist destination, and part of the Domino project's role has been to make sure tourists don't harass the fish. Among the rules are snorkeling only (no scuba), no flash photography, only three people in the water with one shark, and no one can come within 2 meters of a shark. Of the 13 previous tags, eight have reported data; the tag attached to a shark last week was set to detach after 120 days. "We find that the tagged animals go in all directions from the site," Hueter said. "We have them going into the far western Gulf of Mexico. We had one go south from the site to the western Caribbean. "That correlates with some of the visual tag sightings. We've had a number down around Utila (off Honduras) and Belize. And we've had animals go other directions, the Florida Straits, Cuba." Satellite tags have shown whale sharks dive to 4,500 feet, where the water temperature is just above freezing. But, instead of staying at that depth, they return almost immediately to the surface. "The fact that they're turning around and coming right back up is a surprise," Hueter said. "It's doubtful that they're feeding — to dive so deep when there's so little down there seems far-fetched. It must be for some other reason. "I can only speculate, but they might be going that deep to dump heat, cool off, for rest and recharge, or to get rid of parasites of some kind." In the summer, however, these fish converge on Holbox to feed, which makes the area a great lab for Motta, USF doctoral student Kyle Mara, and Georgia Aquarium nutritionist Mike Maslanka. The aquarium is home to four whale sharks. Whale sharks are in the same order as nurse sharks and, like nurse sharks, produce suction pressure to feed. So far, scientists have determined whale sharks suck in four kilograms (8.8 pounds) of plankton an hour and the fish don't like cold food (when the researchers collected plankton in a net, put it in a cooler and returned it to the water, the sharks wouldn't eat it — this was not part of an experiment, just a serendipitous observation). "Their work will crystallize our understanding of what whale sharks are feeding on, how they're feeding and how much they're feeding," Hueter said. "That will not only provide insight to why they're at Holbox, but also what their daily nutritional needs are. That translates to care and feeding in captivity." But why, aside from possible benefits to captive whale sharks, study the whale sharks of Holbox? "They're a charismatic animal because of their size and beauty — it's an aesthetic, emotional thing, and people think about that," Hueter said. "But we also want to know the population status. Are they increasing or decreasing? Is it a doom-and-gloom story again or a good story? "Whale sharks are an indicator animal for the health of our oceans. They feed low on the food chain; their food supply is not in trouble; they're not being directly depleted by man. If whale sharks can't make it in this day and age, not much can." SOURCE - The News-PressSCUBA FORUMDISCUSS THIS TOPIC - Dive in and have your say at Scuba Forum |
