What Gamefish Do Sharks Eat?

Shark depredation can occur on the flats, all the way out to deep oceanic waters. A recent study looked at what Southeast U.S. offshore anglers were experiencing the last couple years.
Courtesy Return ‘Em Right

Sharks are a problem. At least that’s what many anglers point out when fishing for bottom fish in the Southeast. Scientists call it “shark depredation” — when your catch gets eaten before you can bring it to the boat. Sometimes anglers are left with half a fish, other times it’s no fish at all. Researchers from Florida Atlantic University’s Harbor Branch Oceanographic Institute set out to quantify exactly what recreational anglers were encountering on the water.

Using multiple methodologies that included social media, online angler surveys, cooperative fishery-dependent charters, and genetic analysis, the study uncovered the scope and impact of shark depredation in Florida’s recreational fisheries. Other regions were included too, but the majority of anglers involved were fishing in Florida.

“Our research provides crucial insights into the growing challenge of shark depredation, helping to build a comprehensive understanding of this human-wildlife conflict and how different fishery sectors are being affected by it,” said Matt Ajemian, Ph.D., senior author, an associate research professor and director of the Fisheries Ecology and Conservation Lab (FEC) at FAU Harbor Branch.

No Fish, No Problem

Many bottom fishermen, especially Florida anglers, are having more and more run-ins with sharks. It’s a bad situation.
Courtesy Return ‘Em Right

From June 2022 to September 2023, Ajemian and his team from other universities and agencies gathered the frequency and impact of shark depredation to “analyze spatial and temporal trends.” As part of the study, researchers partnered with local fishing charters to collect genetic samples from depredated fish carcasses. Sterile swabs were used on bite wounds to capture transfer DNA, but many depredation events resulted in “bite-offs,” leaving no carcass to sample.

“We quickly realized that getting those perfectly bitten carcasses that fishermen posted on social media were more the exception than the rule on the fishing charters,” said Michael P. McCallister, lead author of the study, a Ph.D. student, and research coordinator, FEC program at FAU Harbor Branch. “So, we had to quickly adapt in order to salvage those sampling events.”

To overcome that obstacle, researchers swabbed the ends of the monofilament fishing line as an alternative DNA source. It was the first time this technique has been used. Results were successful nearly half the time, showing promise for improving depredator species ID in both recreational and commercial fisheries.

What Fish Are Eaten by Sharks?

Some fishing spots are overloaded with sharks. Anglers are forced to leave the area to prevent their catches from getting destroyed.
Courtesy Return ‘Em Right

The top species eaten by sharks were snapper, grouper and greater amberjack, according to the study. Other species included king mackerel, dolphin, wahoo, blackfin tuna and Atlantic sailfish. If you can’t tell, the majority of fishing recorded was based out of Florida, but also areas such as The Bahamas, Australia, Caribbean and Mexico.

Sharks were the most frequently identified “depredator,” with bull, lemon and sandbar sharks top offenders. Depredations by sandbar sharks were highest in May, whereas depredations by bull sharks were highest in February and March. Besides sharks, dolphin, barracuda, goliath grouper and alligators also stole anglers’ catches.

The frequency of depredation varied by season and region, with the highest occurrences in the spring in the Florida Keys, as well as the southeast and Gulf regions of the state. The large number of depredation samples collected in April and May by charter fishing partners could correspond to seasonal increases in shark abundance during these months. Many of the mature adult shark species identified in this study are known to give birth and mate during this time of year.

Beginnings of Shark Depredation Research

Still, depredation rates (the percentage of total catch lost to depredation) were not affected by season or location, while frequency was affected by those variables. “Factors such as water depth, habitat type, fishing pressure, specific fishing locations, and fishing techniques may play a more direct role in determining depredation rates, influencing patterns on a finer scale beyond broader seasonal or regional trends,” said McCallister.

The results from this study will help build a comprehensive understanding of shark depredation in a recreational fishing hotspot such as southern Florida. And the authors of these findings hope to open discussions between stakeholders and fishery managers as they work to develop actionable management measures to address this conflict.

One tip for anglers trying to release bottom fish back to the depths is to use a descender device. A descender device trumps a venting tool, especially if sharks or other predators are around. The descender tool quickly helps send a fish back down deep, where fish are able to recover from barotrauma. It immediately removes them from the hungry eyes of the man in the grey suit too. The organization Return ‘Em Right offers a free online training of best practices to release fish. Upon completion, anglers receive $100 worth of release gear at no cost.