DAUPHIN ISLAND, Alabama -- A trio of anglers from Mobile cruised triumphantly back to the weigh station of the Alabama Deep Sea Fishing Rodeo just before scales closed Friday.

They thought they'd landed a pair of bull sharks that would possibly make the leaderboard, and that the crowd of spectators would line the fence to "ooh" and "ahh" as the animals were lifted out of the boat and weighed.

Instead, University of South Alabama researcher Marcus Drymon told them they had landed two sandbar sharks, a protected species that would not be weighed or counted in the tournament. Drymon and other USA researchers took the shark carcasses for research studies.

Sandbar sharks are a ridgeback species, meaning there's an elevated ridge between their dorsal fins. Most ridgeback species are protected in the Gulf due to overfishing, with the exception of tiger sharks, oceanic white tips or smoothhound sharks. Sandbar sharks closely resemble bull sharks, often leading to confusion for anglers.

"If you see a shark that you think is a bull shark, the first thing you'd want to do is to check and see if it has that inter-dorsal ridge," Drymon said. "If it does, that means it's a species that you're not allowed to harvest as a recreational fisherman or a commercial fisherman."

In addition to the ridges, sandbars have a taller front dorsal fin that is closer to the front of the shark's head than a bull shark.

"Typically, the fishermen are genuinely making mistakes by bringing in a species that's hard for them to identify," Drymon said. "It's unfortunate that some of these guys end up being landed in this tournament, but being as they are already dead, we make the best possible use of it by taking a multitude of different samples that will ultimately help better inform the next stock assessment of this species."

Alabama Deep Sea Fishing Rodeo rules committee chairman Todd Bishop said that prohibited species of sharks or other fish are not accepted at the scales.

"We certainly try to educate our anglers on what the prohibited species are," Bishop said. "We have fliers here at the rodeo site for them to take so they can take a look at the prohibited species."

According to the Florida Museum of Natural History's ichthyology department, sandbar sharks were one of the primary targeted species for commercial and recreational fishing along the eastern United States. Some believe the sandbar shark population dropped by as much as two thirds from the 1970s to the 1990s. Sandbar sharks are more vulnerable to overfishing because they are relatively slow to mature, have a long gestation period and small litter size.

Drymon and a team of University of South Alabama scientists, graduate students and interns measure the reproductive organs of the sharks, take samples of blood, bile, muscle and vertebrae to learn what they can about the sharks' age, maturity and history.

See the video and gallery above for more on the scientific samples that took place on the sandbar sharks Friday at the rodeo.