Do Dolphins Protect Humans From Sharks? Stories vs Science

Famous dolphin rescue stories

Tales of helpful dolphins are ancient. The Greek historian Herodotus told the legend of Arion, a musician thrown overboard by sailors and carried safely to shore on a dolphin’s back.

Modern stories involve sharks. In 2004, four lifeguards swimming about 100 m (330 ft) off the coast near Whangārei, New Zealand, reported that bottlenose dolphins herded them together and circled them for about 40 minutes while a large shark, said to be a great white, was nearby. In 2007, a surfer bitten by a white shark off Marina State Beach in Monterey Bay, California, reported that a group of dolphins appeared around him as he made it back to shore, and he survived.

Dolphins also seem to help other animals. In 2008, a bottlenose dolphin known locally as Moko appeared to guide two stranded pygmy sperm whales off a sandbar at Mahia Beach, New Zealand, and back to open water.

How dolphins really deal with sharks

For dolphins, sharks are predators, not just neighbors. Tiger, bull, dusky and great white sharks all prey on bottlenose dolphins, especially calves and weak animals. In Sarasota Bay, Florida, about 36% of resident dolphins carry at least one shark bite, mostly from bull and tiger sharks, and fresh bites are most often seen between June and November.

Dolphins have several defenses. The first is avoidance: research in Shark Bay, Western Australia, found that dolphins spend less time in rich but risky feeding areas when tiger sharks are most abundant, trading food for safety. Mothers with young calves often favor very shallow water, which may make approaching sharks easier to detect. Living in groups means more eyes and ears on the lookout.

When a shark comes close, a group of dolphins may chase, charge and ram it with their beaks, a behavior called mobbing. This can drive off smaller sharks, but a large shark remains dangerous, and well-documented cases of bottlenose dolphins killing sharks are rare. The orca is a different story: as the largest dolphin, it hunts sharks, including great whites, as described in orca vs great white shark.

Why scientists are cautious

Researchers do not doubt that some of these encounters happened. What they question is the explanation. There are several reasons for caution:

• Anecdotes cannot be tested. No one can repeat the event, check whether a shark was really there or measure what the dolphins were doing.
• Only happy endings get reported. A swimmer whom dolphins ignored, or pushed out to sea rather than toward shore, has no story to tell. This bias makes dolphin rescues seem more common than they are.
• Other explanations fit. Dolphins circling a swimmer may be reacting to a shark as a threat to themselves, guarding their own group with the people simply in the middle, or showing curiosity. Dolphins also herd fish in tight circles, a very similar movement.

Dolphins do help their own kind: they have been seen supporting injured or newborn companions at the surface so they can breathe. Whether that care ever extends deliberately to humans is unknown. Dolphins can also be aggressive toward people. In Brazil, a solitary bottlenose dolphin called Tião injured many swimmers and killed one man in 1994, after months of close contact with crowds of swimmers.

Myths about dolphins and sharks

• “If dolphins are around, there are no sharks.” False. Both follow the same schools of fish, and sharks hunt dolphins.
• “Sharks are afraid of dolphins.” There is no evidence of a general fear; many dolphins carry shark-bite scars.
• “Dolphins kill sharks by ramming their gills.” A popular claim with little scientific documentation for bottlenose dolphins.
• “A dolphin will always push a drowning person to shore.” Dolphins push and nudge many floating objects, and there is no reason to think they always push toward land.

For the bigger picture of how these two animals differ, see dolphin vs shark.

Why you should not approach wild dolphins

Treat wild dolphins as wild animals. Adults can weigh several hundred kilograms and bite or ram if they feel crowded. Dolphins that are fed by people learn to approach boats and swimmers, which leads to more injuries for both people and dolphins, and more dolphins tangled in fishing line or hit by boats.

In the US, feeding or harassing wild dolphins is illegal under the Marine Mammal Protection Act, and NOAA advises watching from at least 50 yards (about 46 m) away for no more than 30 minutes. In Hawaii, a federal rule bans swimming within 50 yards of spinner dolphins. In the UK and the EU, dolphins are strictly protected, and deliberately disturbing them is an offense.

Shark bites on people remain rare; see How often do sharks attack humans? for real numbers. If you see a shark, leave the water calmly and tell a lifeguard. If anyone is bitten by a shark, a dolphin or any other marine animal, seek emergency medical help immediately by calling 911 in the US, 112 in the EU or 999 in the UK.

To learn more about the dolphins in these stories, see our profile of the common bottlenose dolphin.