Shark vs. Dolphin Battles Can Have Surprising Outcomes
Battles between sharks and dolphins appear to pit brawn against brains, with new research finding that many dolphins survive attacks using everything from karate-type moves to ganging up on the shark.
The study, published in the journal Marine Mammal Science, suggests that at least some dolphins are up to the shark challenge.
Lead author Kelly Melillo Sweeting told Discovery News that when dolphins are attacked, they "may cooperate to drive a shark away, whether by chasing or ramming it."
"Some shark-induced scars seen in our study suggest the possibility that a dolphin may roll to try to escape a shark's bite," added Sweeting, who is the Bimini Research Manager at the Dolphin Communication Project.
Sweeting and her team studied shark attack failures by looking at shark bite scars present on healthy Atlantic spotted dolphins swimming in the waters near Bimini, The Bahamas. The scientists discovered that 14 out of the 92 studied dolphins showed some sign of shark attack, while another 15 had scars that could not conclusively be classified as shark induced or not.
Tooth marks and observations at the site suggest that tiger sharks and bull sharks were the ones going after dolphins at this particular area.
"The frequency with which sharks prey on dolphins varies between species and geographies," Sweeting said. "I suspect that off Bimini, bull and tiger sharks prey on dolphins regularly enough that this pressure might cause behavioral changes for the dolphins, such as habitat use."
The researchers could find no difference in shark-induced scars between the sexes, suggesting that the sharks went after both adult male and female dolphins. More scars were, however, detected on dolphin calves, so sharks appear to target smaller dolphin prey.
Another finding is that shark attack "fails" usually happened when the shark bit in or around the dolphin's dorsal fin. The researchers suspect that sharks are more successful when they bite into the softer lower side of the dolphin.
While not investigated in this study, dolphins are also known to attack sharks. Sweeting explained that "larger dolphins, like the killer whale -- the largest dolphin species, have successfully preyed on large sharks, but the frequency of this is unknown."
Given that both dolphins and sharks can be formidable on both offense and defense, they likely prefer to seek out other easier-to-kill prey, such as fish and squid. While white sharks often hunt marine mammals, and some sharks consume seabirds, most sharks eat a lot of fish and shellfish.
Kathleen Dudzinski, Director of the Dolphin Communication Project, believes that photographing and examining scars on dolphin bodies that seem to be from sharks could offer clues as to how dolphins and sharks interact.
"We do not fully understand how dolphins might escape or fight off predatory sharks because so few shark attacks on dolphins are directly observed," she told Discovery News.
Once researchers get a better sense of how these kinds of species relate to each other, she explained, we can "better understand how we humans might impact that system."