The Idea That Sharks Fear Dolphins May Just Be an Old Sailor’s Myth

If you picture a showdown between the chirpy dolphin and the toothy shark, you might imagine a pod ramming into the ocean’s iconic predator enough times to eventually kill it. To see such a predator done in by the animals we perceive as the underdogs certainly makes for a compelling role reversal.

“You’ve got these amazingly intelligent, incredible dolphin predators, in social groups with complex social lives, and then the iconic shark,” says Michael Heithaus, a professor in the Department of Biological Sciences at Florida International University and expert in marine predator-prey interactions. “What’s not to love about it?”

However, the actual work of observing and recording direct encounters between the two species is where the waters get murkier. Today, does the sailor’s myth that sharks fear dolphins hold true? 

Are Sharks Afraid of Dolphins?

(Credit: Tharuka Photographer/Shutterstock)

The idea that sharks fear dolphins is, really, just an old sailor’s myth, according to Heithaus. Though he began looking into the hypothesis as he began his graduate work, he could not find scientific data to back it.

“I wanted to work on actually flipping it and asking, ‘Are dolphins afraid of sharks?’” he says. 

Heithaus, who worked in Australia at the time, noted that many of the dolphins in the area sported scars and wounds from sharks’ mean bites. This contradicted the notion that dolphins needn’t worry if swimming alongside sharks, for they could always just beat them up. 

“What we found is actually the reverse – that dolphins were actually quite afraid of sharks,” he says, “and changed their behavior in relation to when sharks were there and what habitats the sharks were in.”

Read More: What Makes These 7 Shark Species Stand Out Among the Rest?

How Sharks and Dolphins Really Get Along

There are over 500 species of sharks in the world, so the actual behaviors stemming from any encounters between the two animals will vary. For the most part, Heithaus says a shark and dolphin would probably ignore one another.

The nature of their interactions also depends on their respective sizes. Larger tiger sharks, for example, are more of a threat than smaller sharks, who may avoid bigger dolphins. On the flip side, the largest and most killer dolphins, orcas, might prey on sharks.

“Those sharks are afraid of those giant dolphins and are moving out of areas to stay safe because they don’t want to become a meal themselves,” Heithaus says. 

It’s difficult to generalize how one species might react to another without knowing more specifics. Some dolphins might view sharks as fellow competitors feeding from the same schools of fish, while others might avoid sharks out of awareness that they’re predators they should fear. 

“For those kinds of combinations of shark and dolphin, where one might eat the other, it’s basically like we see with predators and prey in any other situation,” Heithaus explains. “The species that might be prey will do lots of different things – including form groups, if you’re a dolphin – and go to areas where there’s less risk. It becomes a really big part of their lives, staying safe from this predator.” 

Read More: What Can Shark Brains Tell Us About Their Fascinating Intelligence and Behaviors?

Do Sharks Eat Dolphins?

So, who eats who? Heithaus says the most regular predators of dolphins are tiger sharks, white sharks, and bull sharks. Tiger sharks pose the greatest threat as they often frequent the same shallow coastal areas as dolphins. 

(Credit: Jsegalexplore/Shutterstock)

Dolphins don’t make a regular habit out of hunting down sharks. However, according to one of Heithaus’ papers, which was published in the Journal of Zoology in 2001, some predation does happen. There are records of bottlenose dolphins eating elasmobranchs — groups of fish, including sharks, whose skeletons are cartilage instead of bone — in the waters of South Africa, the Atlantic, and the Gulf of Mexico. 

More commonly, though, dolphins enjoy snacking on squid or fish. Killer whales, which specialize in consuming larger prey, have been observed attacking and killing big sharks, such as basking and white sharks. 

“False killer whales have been seen eating sharks occasionally, but after that, you know, bottlenose dolphins might occasionally kill a small shark,” Heithaus says. “To reverse it, it’s really about killer whales.”

Read More: How These 4 Deep Sea Sharks Lurk in the Ocean

How Often Do Sharks Attack Dolphins? 

Observing shark-dolphin interactions is challenging, but researchers have gained some insights into the frequency of these encounters over the years. 

A 2017 study conducted in Florida’s Sarasota Bay cataloged 262 individual bottlenose dolphins, of which 93 had verifiable scars from shark attacks. This meant the shark attack rate among residents of Sarasota Bay was about 35.5 percent.

Shark bites were also the largest sources of injury to Sarasota Bay’s dolphins, according to the study authors, compared to other potential causes, such as wounds resulting from stingray barbs or boat collisions.

But these numbers aren’t the definitive rate of how often sharks successfully attack and eat dolphins. These recorded instances are of shark attack survivors — in other words, sharks’ failed predation attempts. Dead dolphins aren’t observable, and living dolphins who survive attacks may not always bear scars. 

What’s clear, though, is that dolphins can survive shark attacks, as a 1987 investigation of shark-dolphin encounters in Australia’s Moreton Bay also supports. In order to survive, fellow pod members might band together to drive the offending shark away from the injured individual. 

Instances where dolphins might turn on sharks, though, are more in line with trying to survive predation, Heithaus explains.

“It really depends,” he says. “These animals are really good at figuring out, ‘Are you a real threat or not?’ and change their behavior based on it.”

Read More: Why Do Sharks Attack Humans?

How Do Dolphins Behave Around Sharks?

(Credit: Nicolas-SB/Shutterstock)

Dolphins have methods to avoid getting killed by sharks, some of which might include forming groups and seeking safety in numbers, mobbing predators to chase them away, or evading sharks altogether. They might tweak their foraging habits to avoid sharks during their busy hours.

Of course, not all shark-dolphin encounters are of predator-prey nature. For example, when sharks and dolphins share the same resources as competitors, they might not get aggressive — as long as there’s enough to go around.

Limited resources can strain this conviviality and lead sharks to begin preying on dolphins — who, in turn, change their behaviors to better survive. 

Ultimately, it’s all about trade-offs, Heithaus says.

“The biggest thing that we noticed is that they really change where they spend their time,” he says. “In the place where we did the most studies — and we’re seeing similar results in other places — when there are no sharks around, you basically find the dolphins where there’s the biggest buffet table.” 

Where there are sharks, though, dolphins might opt for survival over a hearty meal.

“The dolphins, a lot of them will say, ‘You know, it’s not worth getting the big feed,’ and they move off to areas where it’s safer. But they’re kind of eking out an existence, getting less food,” Heithaus says. “They’re giving up food to stay safe.” 

Read More: Dolphins and Whales Apparently Sleep With One Eye Open

The Importance of Shark and Dolphin Conservation

Sharks face a major threat of overfishing, with researchers estimating that about 273 million sharks are killed each year at an unsustainable rate. This is especially concerning considering sharks, who have slower reproduction rates, are unable to bounce back as quickly from such depletions.

Dolphins similarly face threats, from fishing nets preventing them from surfacing for air, should they get entangled, to strains on their prey supplies due to warming ocean temperatures

The loss of these creatures is felt not only by their surrounding ecosystems but also by scientists. Overfishing, Heithaus says, has knocked out many bigger individual sharks within their respective populations, posing a major challenge for researchers looking into shark-dolphin interactions. 

“There’s just not as many sharks, and especially big sharks, as there used to be,” he says. 

Plus, healthy oceans depend on sharks and dolphins. Tiger sharks, for example, are like wolves in that they keep the populations that graze seagrass beds in check. 

“Although studying shark-dolphin interactions is intriguing and fun, it’s also really important, because we’ve got to find ways to protect and manage these populations so we’ve got healthy populations and healthy oceans for generations to come,” Heithaus says. “That’s not just so we can have great images and inspire the next generation.”

Read More: How Citizen Scientists Are Helping Sharks Around the World

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Source : Discovermagazine