FORT LAUDERDALE, Fla. — Imagine pulling up to a fishing spot. You hook a fish, a beautiful snook. As you reel it in, the water boils, a shark’s tail smacks the surface. The fish stops struggling. All that’s left of the snook is a bloody stump.

On the next cast the same thing happens. There’s no reason to continue fishing in this spot, so you leave.

Anglers say this kind of shark encounter seems to be happening more and more in parts of South Florida, especially near Flamingo, in Everglades National Park.

“You can’t get away from the sharks. They are all over the place,” said Collin Ross, a recreational angler who’s been fishing in Everglades National Park nearly weekly for the past 30 years. “It is a huge issue.”

“Basically, if a fish is struggling on a line, sharks are instinctively attracted to it and can catch it much more easily than if it was free-swimming,” said Bonefish & Tarpon Trust biologist Jose Emilio Trujillo Moyano, who is leading a study to better understand the problem.

Ross has seen things change. “You used to be able to fish without any type of issues, and now you fish some areas and you have to leave immediately because of the sharks.”

He, like many, is mystified by what’s going on. “All we know is there are a lot more sharks in areas where people are fishing. Why are they congregating? Is there an overpopulation? I don’t know?”

One frustration with the intense levels of shark depredation is that it defeats the purpose of fishing regulations and the common ethos of catch-and-release; any fish you hook dies.

“It just sucks. You hate to lose the fish,” Ross said. “And what people don’t realize is that if they catch and release the fish, the shark is just swimming around the boat waiting for you to release it and he eats it.”

Does the uptick in shark depredation mean there are “too many” sharks, or is it that some sharks are learning to target fishing boats?

Trujillo Moyano embarked on a study two years ago to find out.

He used extensive workshops and surveys with anglers and professional fishing guides to look at shark depredation rates and locations for the most sought-after inshore gamefish species in the Florida Keys: permit, bonefish, adult tarpon, juvenile tarpon, snook and redfish.

— 31% of the snook that anglers hooked in the study area around Flamingo were killed by sharks.

— 23% of the hooked redfish were depredated in the same area.

— In other areas of the Keys, 10% of the hooked bonefish, tarpon and permit were depredated.

Four inshore shark species did the most damage: great hammerheads, black tips, bull sharks and lemon sharks.

But lemon sharks were by far the most destructive, with most of their predation occurring near Flamingo, in Everglades National Park, where they were most likely to take snook and redfish.

Trujillo Moyano set out to understand the Flamingo problem. Is it about shark abundance, or about sharks changing their behavior to key in on fishing spots and boats?

He tracked 56 lemon sharks in and around the Flamingo area for approximately the last eight months (the study is ongoing) and analyzed their movements and diets.

Findings

Trujillo Moyano found that there were two groups of lemon sharks using Flamingo — “resident” that were Flamingo homebodies and “transient” who would often leave the area.

About 28% of those sharks focused their time on known fishing hot spots that anglers would use on a daily basis.

Fishing boats show up at those hot spots about 8 a.m. The sharks tended to show up just before that.

One shark tracked for more than 100 days came “over and over” to a specific hot spot.

If there was a change in behavior maybe there’d be a change in the diet of lemon sharks around Flamingo.

Trujillo Moyano compared lemon shark diets around Flamingo in the 1990s to those of today. The bulk of the sharks’ diet in the 1990s came from prey low on the food chain, such as mullet, pinfish and toad fish. Fish higher on the food chain, such as snook and redfish, were not their normal fare.

But Trujillo Moyano found that 30% of the juvenile lemons in his study had snook in their diet. “That is very odd,” he said.

“No study until now has reported lemon sharks eating large prey like gamefish that are high trophic level species. The fact that we are finding snook in their diet is … not normal. That indicated that they are obtaining this resource through a new way of hunting, which we believe is depredation,” said Trujillo Moyano.

The study is ongoing, but right now, Trujillo Moyano feels “a subset of sharks may be driving most of the damage.”

A nursery with less food and cover

To understand the problem you need to understand the shark and the ecosystem.

The Flamingo area is a crucial nursery area for lemon sharks, said marine biologist Catherine Macdonald, who studies sharks with the University of Miami’s Rosenstiel School of Marine, Atmospheric, and Earth Science.

They’re not known as the fastest sharks, said Macdonald, but they are quite agile and flexible, which gives them an advantage in a tight mangrove environment such as Flamingo. They seek the area out because there’s lots of food, and its vast shallows protect them from other sharks that might eat them.

Trujillo Moyano said the lemon sharks around Flamingo and in his study are essentially all juveniles, meaning they’re young, but could still be up to 5 or 6 feet long.

But the area, which was once known as the most biologically productive in Florida Bay, has suffered seagrass die-offs since then have reduced production.

“We know that the seagrass in Florida Bay is the basis for the whole ecosystem,” said Trujillo Moyano. “Changes in the seagrass basically resonate in the whole community, in the whole ecosystem. And we know that the seagrass die-offs have resulted in declines in prey.”

Some anglers say it also gives sea trout, snook and redfish fewer places to hide from sharks.

But less food in the nursery could be a factor in increased shark depredation.

“I think that there’s lots of possible theories,” said Macdonald, “including learned behavior and attachment to fishing sites, including declines in prey populations that are sort of increasing competition between human fishers and sharks.”

Are lemon sharks on the rise?

Is there a lemon shark population boom? Watching shark after shark take snook and redfish from your line would certainly indicate there is, but Flamingo is just a small part of the shark’s range.

Macdonald said that the species has a “pretty slow rate of intrinsic increase.”

According to the Florida Museum, lemon sharks don’t reach sexual maturity until they’re about 12 or 13 years old (about 7 feet long) and only reproduce every two years and mothers give birth to four to 17 pups.

Meanwhile, female boney fish can release millions of eggs per reproductive season, Macdonald said.

Macdonald said that we have to take anglers’ experiences with sharks seriously, but that, “when we talk about populations, I think that one thing that I can say with reasonable confidence is that they’re not biologically capable of a population explosion.”

Independent data that UM collects in South Florida indicates there is not a spike in the lemon shark population. “The data is not there to support an argument that their numbers have massively changed.”

Trujillo Moyano concurs. “There’s no evidence that shows that their population has increased in crazy numbers,” he said. “There’s no evidence that their numbers have come back to what they were 50 years ago.”

But population numbers are a blind spot for now. Both Macdonald and Trujillo Moyano said the National Oceanic and Atmospheric Administration is overdue for a stock assessment in order to understand possible population ups and downs.

Solutions

It’s currently illegal to harvest lemon sharks in Florida waters, in part, because they reproduce so slowly.

Ross and some other anglers see a lemon shark harvest as a potential difference-maker if populations are healthy, but the lack of a recent stock assessment leaves wildlife managers without much recourse.

“We’re hoping that the FWC (Florida Fish and Wildlife Conservation Commission) allows changes to federal laws around lemon sharks, and then the guides can take it into their own hands and they can cull sharks as they see fit,” Ross said.

“I absolutely do not doubt the experiences of people fishing. And as scientists we’d be fools to discount what they know,” Macdonald said. But she’s skeptical of a harvest. “There have been a couple of studies that have shown that lemon sharks really can’t sustain a stable population even at a pretty low level of harvest,” she said.

The federal government has their eye on the issue as well. Earlier this year, the SHARKED Act (Supporting the Health of Aquatic systems through Research Knowledge and Enhanced Dialogue) was introduced to Congress and is currently under review in the Senate. If it passes, it would create a task force to tackle the problem of shark depredation.

The next phase of Trujillo Moyano’s study will test shark deterrents. One method, developed for surfers, generates an electrical field around the boat that overwhelms the organ sharks use to detect electrical fields when hunting. Gamefish such as snook and redfish lack the organ, so should not be bothered, he said.

“It annoys the shark,” he said. It remains to be seen just how annoyed they get.

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