Open water swimmers around the world, especially channel swimmers and marathon swimmers, often tell newcomers that when dolphins or porpoise are near them in the open water, there is no need to fear sharks.

It is often said to be a sign of good luck and protection.

The belief is that sharks fear dolphins and porpoises that can easily defend themselves against the apex predators – and will, in turn, protect swimmers, their mammalian friends.

Experienced escort pilots of channel swimmers throughout the Pacific, from the Catalina Channel to the Hawaiian Islands, also back up this understanding.

But is it true?

According to Peter Klimley and David Ainley who wrote a book Great White Sharks: The Biology of Carcharodon carcharias, Great white sharks attack dolphins and porpoises from above, behind or below to avoid being detected by the friendly mammal’s echolocation. The targeted species include dusky dolphins, Risso’s dolphins, bottlenose dolphins, Humpback dolphins, harbour porpoises, and Dall’s porpoises.

This discomforting information is supported by Michael Heithaus who presented his study, Predator–prey and competitive interactions between sharks (order Selachii) and dolphins (suborder Odontoceti): a review” in the Journal of Zoology (Cambridge University Press). “White, tiger, bull and sevengill sharks are probably the major predators on nearshore cetaceans, but dusky sharks may also represent a risk. The risk that nearshore cetaceans face from sharks will vary with location. For example, the risk of shark predation is probably higher in tropical waters than in higher latitudes because of the diversity and abundance of large, predatory sharks in warm waters.”

Heithaus, who directs the Shark Bay Ecosystem Research Project in Shark Bay, Western Australia, encourages further study of the natural relationship between sharks and dolphins where more information and understanding about the nature of shark-dolphin interactions is needed.

A MythBusters episode on the Discovery Channel explored the question, Are Sharks Afraid of Dolphins?:



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