MIAMI — Florida anglers say sharks are snatching their catches at unprecedented rates, calling it an “overwhelming problem” and blaming a boom in Gulf shark numbers.

But scientific research paints a more complicated picture.

Scientists who study sharks acknowledge that depredation — the act of fish being eaten by an underwater predator while on a fisherman’s line — is a growing concern in some areas, especially Florida. They cite several potential drivers of increased shark-human conflict, including climate change-related shifts in shark behavior and rebounding populations of some species.

But they note that changes in human behavior — such as more people fishing and heightened awareness of shark encounters through social media — may also play a role.

Now, researchers are working to learn when and why these encounters happen and how to prevent them.

Matt Ajemian, an associate research professor studying the issue at Florida Atlantic University’s Harbor Branch Oceanographic Institute, cautions against calling shark depredation a crisis, noting that historical accounts show similar encounters have long occurred.

“I don’t call it a problem,” he said. “I try to call it a challenge.”

Researchers explore increased reports of shark encounters

Ajemian and research coordinator Mike McCallister are leading a NOAA-funded project launched in 2021 to study when and where depredation happens and what might reduce it. Their team has turned to anglers for help, gathering information through surveys, video footage, genetic testing and social media reports to identify patterns.

In their surveys, about 43% of Florida anglers said sharks had stolen their catch, with rates ranging from 10% to 60% depending on the region, season and species, researchers said. When it happened, sharks took nearly a third to almost half of the day’s haul.

The data came from quarterly surveys of 4,000 randomly selected saltwater fishing license holders over a year, with about 2,200 responding. Because participation was voluntary and limited to license holders, researchers said, the results don’t represent all Florida anglers.

They also tracked posts in a Facebook group with more than 6,500 members, logging real-time reports from offshore anglers across the state.

Researchers said survey responses and online reports point to clear patterns in when and where depredation occurs. It was most common in the spring and summer, with hotspots in Southeast Florida, the Keys and the Panhandle. Rates spiked during busy fishing periods such as red snapper and grouper season openings.

‘Not always sharks that are the problem’

Snapper and grouper were the most frequently lost catches, followed by king mackerel, cobia, tuna and sailfish, according to the study. McCallister said the data also showed longer fights gave sharks more time to strike, and anglers targeting deep-water or migratory species were more likely to be affected than those fishing inshore.

Bull sharks and sandbar sharks were the main culprits, based on angler accounts and genetic swabs from bitten fish, but they weren’t the only ones.

“The videos have shown us that it’s not always sharks that are the problem,” said Mike McCallister, FAU research coordinator.

McCallister said goliath grouper, a massive fish that can weigh up to 800 pounds, is another species that can target an angler’s catch underwater.

“Most of these depredations occur below the water line, where people can’t see them,” said McCallister.

Are shark numbers increasing?

Many anglers blame a growing shark population for increasing depredation. Researchers say that while some shark populations appear to be rebounding after past declines, their numbers likely remain below historical levels.

“My inkling is that sharks are returning on an increasing trajectory thanks to solid management and a lot of federal effort,” Ajemian said.

He and McCallister note that in the 1960s and 1970s, U.S. agencies even encouraged commercial shark fishing to diversify the seafood supply. But when shark populations declined sharply in the 1980s and early 1990s, it prompted the launch of national management plans in 1993.

Recently, NOAA Fisheries credited these management efforts with increases in several shark species in the Atlantic, including blacktip, sandbar, tiger and white sharks.

Mahmood Shivji, director of the Guy Harvey Research Institute at Nova Southeastern University, also cites research that juvenile bull shark numbers are rising in Gulf estuaries.

However, scientists say that it’s important to put the numbers in context.

Mike Heithaus, a marine ecologist at Florida International University, says that while some populations are recovering, most remain below historical levels.

For younger anglers, today’s encounters may feel unprecedented, but researchers say they could be closer to historic norms.

“That shifting baseline concept is real,” McCallister said.

Is climate change affecting shark behavior?

Scientists say broader environmental changes may also be driving shark encounters.

Overfishing and warming waters could be affecting where sharks go and what they eat, Shivji said, and climate change is altering how deep they dive and how they reproduce.

“Environmental conditions also impact the distribution of natural prey species that sharks eat, and as these prey species move to different locations, the sharks follow their food,” Shivji said.

Sharks themselves are also vulnerable. Heithaus says that climate change could further disrupt food webs, create low-oxygen zones and push predators and prey into new areas.

“Climate change is also going to have big effects on shark prey and their competitors, which is likely to disrupt predator-prey interactions,” Heithaus said.

Researchers say more study is needed to pinpoint the causes of angler-shark encounters and whether depredation is actually increasing or simply being reported more often, including through social media. To help answer that question, McCallister is examining long-term recreational fishing records for his doctoral research.

Anglers adjust to shark conflicts

In the meantime, McCallister says many frustrated anglers are already adjusting tactics, switching gear, moving spots or cutting trips short to account for shark behavior.

“Most anglers are trying to reduce depredation on their own,” McCallister said.

Researchers are also testing ways to keep sharks at bay, including deterrent devices that use magnets to disrupt their electrical senses. So far, they’ve shown mixed results.

One device, called the Zeppelin, showed early promise but only works for bottom fishing, as it can cling to metal parts of a boat or tackle, fouling lines, researchers said. It costs around $80. Other deterrents being tested, such as devices that emit electric pulses, can cost more than $1,000. Some anglers told Ajemian and McCallister the price is too high, especially since the device can be lost during use.

Shark concerns spark legislation

The search for answers is also playing out at the federal level. The SHARKED Act passed the House in January. If it gets signed into law, it would create a federal task force to study shark depredation and recommend solutions.

Until then, scientists say continued research will be key to helping anglers, policymakers and the public better understand the challenge and the best ways to address it.

While recognizing that shark activity can frustrate anglers, scientists also emphasize that the predators play a vital role in the ecosystem — one that is important to protect as their populations continue to decline globally.

“We are still learning a lot about how important they can be, but they can keep populations of prey in check and help protect the base of food webs, like seagrasses, by keeping them from being overgrazed,” Heithaus said.

“The big picture is that many shark species have been severely overfished worldwide, and many species, especially the ones that live in the open ocean and on reefs, have declined by around 50 to 90%,” Shivji said.

“Their now-rapid population declines are very concerning given the essential roles that sharks play in keeping our oceans in balance and healthy,” Shivji added, “making it very important to appreciate these amazing animals, their essential place and role in ocean ecosystems, and helping to prevent many species from going extinct.”

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