Whale Shark Tags Transmit Data

October 5, 2005

Release from: Kevin Lollar
The News-Press.com (South Florida)

SARASOTA — The "pop off" tags attached to two whale sharks a month ago have popped off and started beaming their data to a satellite and ultimately to scientists at Mote Marine Laboratory.

On Aug. 31 and Sept. 2, Bob Hueter, director of Mote, and Mexican scientists attached satellite tags to two 20-foot immature male whale sharks off Isla Holbox, Mexico, which lies off the northeast tip of the Yucatan Peninsula.

The tags were programmed to pop off Oct. 1, float to the surface and relay information about the animals' movements, including location and depth, to a satellite.

One of the tags surfaced 75 miles south of Cozumel, which means the fish traveled 155 miles in a month. The other tag came up 175 miles south southeast of Brownsville, Texas, 625 miles from the tagging site.

"The interesting thing is that the animals were the same size, the same maturity stage and the same sex, and one went west while one went south," Hueter said. "That's one more piece of evidence that Holbox is an important feeding ground for whale sharks coming from all over, not just the Gulf of Mexico or Western Caribbean.

"You don't write a paper on whale shark migration based on two tags, but this is exciting."

Early data from the tags, which will be streaming in over the next 10 to 12 days, showed that the southbound shark made a dive to 998 feet, while the westbound fish dived to 2,366 feet.

Other scientists have recorded whale shark dives to 3,185 feet.

Nobody knows why whale sharks, which feed mainly on plankton, dive to such depths, but one theory is that the fish are diving for food, senior biologist John Tyminski said. Some plankton are vertical migrators — they spend part of the day at the surface and then migrate to deeper water.

Another possibility, Hueter said, is regulation of body temperature.

"They're not warm-blooded, but they're big animals and they build up a lot of body heat, especially swimming at the surface," he said. "So they execute deep dives to dump heat. But there's no data to support that."

Every summer, whale sharks gather in large numbers off Holbox, which makes that corner of the world a good place to tag the biggest fish in the sea.

Hueter and Tyminski would love to tag a few whale sharks off Southwest Florida, but animals are only occasionally seen here.

"We can't mount an expedition off Southwest Florida and say, 'This is the season: We're going to find some,'" Hueter said. "They're too unpredictable.

"We do get reports from boaters, but by the time we get there, the animal is gone."

The scientists encourage anyone seeing a whale shark to contact Mote as quickly as possible, preferably while the fish is still in sight of the boat. Reports of whale shark sightings tend to make the rounds days or weeks after the fact.

"The last thing we want to hear is: 'You should have been here last week,'" Tyminski said.