Bottlenose Dolphins
(Tursiops truncatus)

The prey of bottlenose dolphins consists of "shoaling and bottom-dwelling species (e.g. shrimp, crabs, eels), [highly mobile schooling] fish, squid, and octopi," but consists primarily of schooling fish (www.cetacea.org). An individual dolphin eats 6-7kg of fish per day (animaldiversity.unmz.umich.edu). Coastal bottlenose dolphins eat fish that are typically found in shallow water, between 2 and 3 metres (Barros and Wells, 1998). Seagrasses are an important feeding habitat because they harbour various large dolphin prey fish and serve as a nursery grounds for resident dolphins. This habitat offers juveniles relatively high protection from predators, as the former can hide among dense seagrass beds. These beds also provide juvenile dolphins with an area rich in prey, in which they can practice and refine their hunting skills.

Stomach content analyses of resident bottlenose dolphins feeding primarily in seagrasses in Sarasota Bay, Florida, showed that sound-producing fish were their primary prey type. These analyses suggest that dolphins passively listen, in addition to using echolocation, to locate schools of prey (Barros and Wells, 1998).

Bottlenose dolphins actively and cooperatively hunt their prey. Schooling fish are herded into tight clumps by several dolphins in order to facilitate a catch. Another method that dolphins use to assist them in their hunt was described by Acevedo-Gutierrez (1999). Off the coast of Costa Rica, Acevedo-Gutierrez (1999) observed an increase in aerial behaviour during hunting and feeding. These leaps, which are loud, fast and cause much disruption in the water, likely confuse and immobilise fish in the immediate vicinity, thereby making it easier for the dolphin to capture its prey. In addition, bottlenose dolphins use bubble bursts to capture prey. Dolphins will emit a burst of air/water into the centre of a school of fish. This burst pushes the fish near the surface of the water and probably confuses or even immobilises them, so that they can be easily captured from below (Dagmar and Wilson, 1997). Hunting also occurs in solitary situations, with the same herding, confusing and immobilising strategies being used (Dagmar and Wilson, 1997).

www.wdcs.org  Example of aerial behaviour which theoretically helps capture prey by immobilising and confusing them.

www.earthtrust.org This photo is an example of a small bubble burst emitted by bottlenose dolphins during prey capture.

Aside from humans, sharks are the only known predators of bottlenose dolphins. Scars from shark bites are commonplace on bottlenose dolphins, suggesting that encounters with these rivals occur frequently, but do not always end in death for the dolphin. Calves are most vulnerable to shark attacks, but mothers will actively chase and attack potential predators (Mann and Bernett, 1999). Other dolphins in a group –whether related or not- will also defend against predator attacks by following a mother closely when she chases a shark or by staying with her calf (Mann and Bernett, 1999).