Sara Brenes’ arms were pretty tired after pulling in 200 feet of very heavy fishing line attached to a 40-pound weight – and a 10-foot hammerhead – off Duck Key recently.

But the Boca Raton Preparatory School sophomore didn’t mind too much – because she was the one who organized the shark-fishing trip.

“I think they’re so cool,” Brenes said of the six sharks caught that day.

Brenes, 16, and her party of about two dozen schoolmates and their parents volunteered as shark researchers aboard the R/V Endsley — a 61-foot research vessel chartered by the R.J. Dunlap Marine Conservation Program at the University of Miami. The citizen scientists paid $50 each for the trip with captain Curt Slonim and several UM students to help catch, take samples, and release as many sharks as possible in a single day.

“Very scary, but very exciting,” said 9-year-old Anna Farronay after clipping part of the fin from a 51/2-foot male tiger shark.

The RJ Dunlap center, launched in 2010 by shark scientist Neil Hammerschlag, might be unique among university research facilities because it relies heavily on middle- and high-school student volunteers to help conduct hands-on marine research. Some have gone on to pursue college degrees in marine science, but even those who chose other courses of study have made valuable contributions to the body of knowledge about sharks – their movements, habitat, reproduction, diet and behavior.

“We actively engage school kids in getting real data that appears in real scientific journals,” Hammerschlag said. “The science is paramount, but for me, being able to share that amazing experience with the public, there’s nothing like it.”

Brenes is one of the most dedicated student volunteers of the more than 1,000 who have helped the Dunlap researchers work with sharks. The Coconut Creek teen has established her own charity, sharkwhisperer.org, raising more than $4,000 for the Dunlap center and other shark conservation groups. She organized Shark Week in April at her school to show her classmates and younger students that the apex predators are key components of the marine ecosystem that should be conserved – not slaughtered.

“A lot of sharks are being overfished, and a lot of sharks are being caught for their fins,” Brenes said.

Brenes has been a certified scuba diver since age 14 and has dived with sharks in South Florida, the Bahamas, Fiji and Australia – always accompanied by her mother Dori. She hopes to study marine biology in college – with a concentration on sharks.

“Ever since I was little, I’ve just been drawn to them,” Sara said. “My mom let me loose in the library and I went straight for the aquatic section – all these shark books. I found them fascinating. They’ve been around a long time – before the dinosaurs.”

Besides pulling sharks onto the deck of the Endsley, Sara got to take a small sample of muscle tissue from a the tiger shark. UM researchers planned to perform a biopsy to check for mercury and other toxins.

The crew had a very busy day on the Endsley. UM students James Komisarjevsky, Virginia Ansaldi, Laurel Zaima and Dominique Lazarre deployed 10 lines with 30-pound weights attached to poly balls in about 140 feet of water off the middle Keys. The 900-pound test lines were baited with hunks of barracuda and amberjack on large circle hooks designed to hook the animals in the corner of the jaw and allow them to swim in circles until the lines were retrieved.