Environment

University of Miami researchers bag a big -- really big -- bull shark

 

Though an ocean predator estimated at 800 to 1,000 pounds might scare tourists, a University of Miami scientist calls it an 'amazing sign' for a declining shark population

Cmorgan@Miamiherald.com

University of Miami shark expert Neil Hammerschlag has caught and tagged more than 1,000 sharks in his research career so he’s handled some big animals over the years.

Few have measured up to one he caught this week along a reef off Islamorada in the Florida Keys.

At an estimated 800 to 1,000 pounds, it ranks among the largest bull sharks ever recorded, out-weighing the official rod-and-reel world record by at least 100 pounds.

The presence of such a large and scary predator in South Florida waters might give tourists and snorkelers pause but it’s a positive sign to scientists like Hammerschlag concerned about declining populations of sharks vital to the health of marine systems. Massive females like this one are particularly important, with their size reflective of their breeding prowess.

“It’s an amazing sign to know they’re still out there,’’ said Hammerschlag, a research assistant professor at UM’s Rosenstiel School of Marine and Atmospheric Science. “This is the biggest bull shark I’ve ever seen.’’

Bulls aren’t considered in immediate danger of disappearing but their numbers have been sharply declining in the Atlantic Ocean and Gulf of Mexico. As coastal species whose young forage in the mangrove-lined shallows of Florida Bay, they’re under a host of pressures, including overfishing, pollution and the loss of both habitat and prey, Hammerschlag said.

They’re also considered among the most aggressive species, ranking behind great white and tiger sharks in attacks on humans, according the International Shark Attack File maintained by the Florida Museum of Natural History in Gainesville.

The big bull was bagged as part of a shark survey project Hammerschlag has directed for the last three years in the Atlantic and Gulf waters of the Florida Keys. Every other weekend, he and a team of researchers troll for sharks with a string of “drum lines’’ specially designed to hook sharks and safely release them.

The system includes a float or “drum” attached to a heavy weight that anchors it in place. Dangling from the float is a 75-foot length of extremely thick fishing line tipped with a circle hook, which is designed to snag in the corner of the mouth rather than in deeper, more damaging spots. The hook is baited with chunks of fish, which send out a pungent trail that keenly sensitive sharks track like bloodhounds.

Once hooked, the shark can safely swim around the float until researchers can recover it. They hold it just long enough to apply tracking or identification tags and take blood and tissue samples used to chart the health of sharks and test for environmental effects like mercury contamination.

To track the movements of sharks, researchers use both simple dart tags, which can provide information only when someone catches a tagged shark and reports it, and more expensive satellite tags that deliver data electronically.

The big bull hit on Sunday along a reef in about 150 feet of water off Islamorada.

Hammerschlag said he can normally bring in a shark himself but from the tug, he said he knew this one wasn’t an average specimen. A colleague helped him haul the shark toward the R/V Endsley, a 61-foot research vessel fitted with a special shark-hoist at the stern that allows researchers to work on sharks without having to remove them from the water.

The tawny-colored bull, estimated at 10-plus feet, was so long its tail hung off the back of the hoist. It dwarfed Hammerschlag as he jumped down to quickly do his work.

Judging by its length and massive girth, researchers calculated the bull shark at the extreme upper range estimated for the species — as much as 1,000 pounds, Hammerschlag said, and “over 800 pounds, for sure.’’

The Dania Beach-based International Game Fish Association, which maintains official world records for traditional hook and line catches, lists the largest bull shark at 697 pounds, 12 ounces. It was caught off Kenya in 2001. Bull sharks caught in South Florida waters typically run from less than 100 pounds to around 300 pounds.

Hammerschlag’s bull shark, caught with the assistance of a colleague and floating gear and not weighed on an official scale, would not qualify for any records.

Because the team had run out of satellite transmitter tags that day, Hammerschlag affixed a small tag with his project contact information before nudging it back into Atlantic, where it swam off, its current whereabouts unknown.

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