Do sharks really eat dolphins? How do we know sharks attack dolphins?
The threat that sharks pose to dolphins is greater than we once thought. Most shark species won’t attack dolphins, but there are some species that do! Although it is very rare, people have seen and filmed dolphins being attacked by sharks. That means that we have to use other methods to figure out how big a threat sharks are to dolphins. We can see if particular shark species have dolphins in their stomachs or use chemical markers in the blood or muscle of sharks to see if they have eaten dolphins.
|A scar on the back of a dolphin in Shark Bay|
What sharks are a threat to dolphins?
|A tiger shark cruises the shallows|
How do dolphins avoid being attacked?
Even for shark species that are major threats to dolphins, it is unlikely that they go too far out of their way to try to eat dolphins. But, dolphins will make major changes to their behavior in order to reduce the chances that they are attacked! The success of these anti-predator behaviors is probably one reason that dolphins aren't found in diets of sharks very often.
|A dolphin in the shallows when tiger sharks are not around|
|Spotted dolphin with two scars|
If a dolphin does run into a shark, their best defense is speed and maneuverability. Dolphins are much more maneuverable than most sharks so they are able to keep out of the way once they see a shark. Dolphins also are faster over the long haul. In Shark Bay, we saw a white shark approach a group of dolphins that didn’t see the shark until the last second. Even though the shark didn’t attack, the dolphins scattered and leapt away from the shark for a long time before slowing down! Sometimes, dolphins may group together to “mob” a shark, much like small birds will do to a hawk. They harass the shark until it swims away. This behavior has been observed in several locations around the world.
Can a dolphin kill a shark?
They can. Smaller dolphins - like the well-known bottlenose dolphin - will attack and kill small sharks occasionally, but sharks are not a part of their diets. Accounts of dolphins killing large and dangerous sharks by ramming them in the gills have not been verified.
Some populations of killer whales (yes, they are dolphins), eat sharks, and can even kill a great white shark. Off New Zealand, killer whales eat many rays and sharks. Off the western coast of North America, there are several types of killer whales. "Resident" whales eat fish like salmon while "transient" killer whales eat marine mammals including seals and sea lions, dolphins, porpoises, and whales. The "offshore" whales are not as well known and appear to eat a large number of sharks, especially Pacific sleeper sharks which live in fairly deep water.
False killer whales also have been observed taking dolphins.
Heithaus lab publications on shark-dolphin interactions:
Connor, R. C. and M. R. Heithaus. 1996. Approach by great white shark elicits flight response in bottlenose dolphins. Marine Mammal Science 12: 602-606.
Heithaus, M. R. 2001. Shark attacks on bottlenose dolphins (Tursiops aduncus) in Shark Bay, Western Australia: attack rate, bite scar frequencies, and attack seasonality. Marine Mammal Science 17: 526-539.
Heithaus, M. R. 2001. Predator-prey and competitive interactions between sharks (order Selachii) and dolphins (suborder Odontoceti): a review. Journal of Zoology (London) 253:53-68.
Heithaus, M. R. and L. M. Dill. 2002. Food availability and tiger shark predation risk influence bottlenose dolphin habitat use. Ecology 83: 480-491.
Heithaus, M. R. and L. M. Dill. 2006. Does tiger shark predation risk influence foraging habitat use by bottlenose dolphins at multiple spatial scales? Oikos 114:257-264.
Heithaus, M. R., J. J. Kiszka, A. Cadinouche, V. Dulau-Drouot, V. Boucaud, S. Perez-Jorge, and I. Webster. In press. Spatial variation in shark-inflicted injuries to Indo-Pacific bottlenose dolphins (Tursiops aduncus) of the southwestern Indian Ocean. Marine Mammal Science
Selected other publications on shark-dolphin interactions:
Cockcroft, V. G., Cliff, G. and G. J. B. Ross. 1989. Shark predation on Indian Ocean bottlenose dolphins Tursiops truncatus off Natal, South Africa. South African Journal of Zoology 24:305-310.
Corkeron, P. J., R. J. Morris and M. M. Bryden. 1987. Interactions between bottlenose dolphins and sharks in Moreton Bay, Queensland. Aquatic Mammals 13:109-113.
Ford, J. K. B., G. M. Ellis, C. O Matkin, M. H. Wetklo, L. G. Barrett-Lennard, R. E. Withler. 2011. Shark predation and tooth wear in a population of northeastern Pacific killer whales. Aquatic Biology 11: 213-224.
Kiszka, J., Perrin, W. F., Pusineri, C. and V. Ridoux. 2011. What drives island-associated tropical dolphins to form mixed-species associations in the southwest Indian Ocean? Journal of Mammalogy 92:1105-1111.
Melillo‐Sweeting, K., Turnbull, S. D. and T. L. Guttridge. 2014. Evidence of shark attacks on Atlantic spotted dolphins (Stenella frontalis) off Bimini, The Bahamas. Marine Mammal Science 30:1158-1164.
Norris, K. S. and T. P. Dohl. 1980. Behavior of the Hawaiian spinner dolphin, Stenella longirostris. Fishery Bulletin 77:821-849.
Pyle, P., M. J. Schramm, C. Keiper, and D. Anderson. 1999. Predation on a white shark (Carcharodon carcharias) by a killer whale (Orcinus orca) and a possible case of competitive displacement. Marine Mammal Science 15: 563-568.