Dolphins: they attract sharks wherever they swim | Photo: Creative Commons

The empirical theory that the presence of dolphins in the water protects surfers and swimmers from shark attacks has been debunked.

Scientists from Murdoch University concluded that sharks are more likely to attack dolphins in sheltered waters than in the open ocean.

Researchers made over 600 boat trips and collected data from 343 dolphins swimming in more than 540 square kilometers of sheltered and open coastal waters off Bunbury and Busselton in Western Australia.

"We wanted to know whether any particular group of dolphins were more vulnerable to shark attacks," explains Kate Sprogis, a researcher at Murdoch University's Cetacean Research Unit.

"So, we looked for patterns by grouping dolphins based on age and sex, seasonality and annual trends, and also the location in open versus sheltered waters."

Sheltered Waters vs. Open Ocean

The results of the study were quite revealing and indicated that 25 percent of dolphins in the sheltered waters of Koombana Bay, Leschenault Inlet, and Leschenault Estuary had bite wounds, compared to just 13 percent of dolphins tracked in coastal waters.

"We believe that because water is more shallow in sheltered waters, with less space and fewer escape routes, altercations between sharks and dolphins are more likely to happen," Sprogis notes.

Dolphins: they are more likely to be attacked by sharks in sheltered waters | Photo: Sprogis/Murdoch University

"But it could also happen because the acoustic detection of predators may be more difficult with more underwater noise from ships and boats in these areas or because the murkier waters make it more difficult for dolphins to spot sharks."

Contrary to popular belief, the number of shark attack incidents can be higher when dolphins swim around near the shore, increasing even more the number of encounters with humans.

Actually, the real scenario could be even worse. Dolphins may very well be dangerous shark magnets.

"We could not account for dolphins that may have died from interactions with sharks. We worked with data from dolphins who have survived. So, this figure could be even higher," concludes Kate Sprogis.

The study published in the Journal of Experimental Marine Biology and Ecology also highlights the fact that the number of shark bits on dolphins increased yearly between 2009 and 2013 as water temperature increased.

According to previous studies, the odds of a surfer being attacked and killed by a shark are 1 in 3,748,067. In other words, that's 0,000026 percent.

To put things into perspective, surfers are 47 times more likely to die from a lightning strike than from a shark attack.

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