Diet & Eating Habits - Dolphins

FOOD PREFERENCES & RESOURCES

1. Dolphins are active predators and eat a wide variety of fishes, squids, and crustaceans such as shrimps. The foods available to a dolphin vary with its geographic location. • Coastal dolphins tend to eat fishes and bottom-dwelling invertebrates. • Offshore dolphins tend to eat fishes and squid. • Some offshore dolphins were found with deep-sea fishes in their stomachs. This evidence suggests that offshore dolphins may dive to more than 500 m (1,600 ft.). Bottlenose dolphins are active, opportunistic predators.

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FOOD INTAKE

1. Adult bottlenose dolphins eat approximately 4% to 6% of their body weight in food per day. A nursing mother's daily intake is considerably higher: about 8%. 2. A dolphin's stomach is compartmentalized for rapid digestion.

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METHODS OF COLLECTING FOOD

1. Feeding behavior is flexible and adapted to a dolphin's particular habitat and available food resources. Bottlenose dolphins frequently use cooperative hunting strategies for locating and catching prey. 2. Hunting strategies are varied and diverse. • Bottlenose dolphins often cooperate when hunting and catching fish. ° In open waters, a dolphin group sometimes encircles a large school of fish and herds the fish into a small, dense mass. The dolphins take turns charging through the school to feed. ° Occasionally dolphins herd schools of fish against sand bars, shorelines, or mud banks to trap them in shallow water where the fish are easy prey. • Dolphins also feed on individual, nonschooling fishes. • A bottlenose dolphin may use its tail flukes to flip a fish out of the water, and then retrieve the stunned prey. • Some coastal bottlenose dolphins in Shark Bay, Western Australia seem to use a certain species of sponge (Echinodictyum mesenterium) as a shield when foraging in areas with rocky or sandy bottoms. Researchers have observed a small number of females carrying the sponges on their beaks, diving down, and then dropping the sponge just prior to surfacing and swallowing prey. Researchers theorize that the sponge acts as a shield to protect the dolphin's beak (rostrum) from spines of certain fishes or stingrays, or from sharp shells or rocks when the dolphin digs into sandy-bottomed habitats in search of prey. This sponge-carrying tool-use behavior has only been seen in several female dolphins and some of their female offspring at Shark Bay. • Bottlenose dolphins often feed in association with fishing operations. Dolphins may accompany shrimp trawls or other fishing vessels and feed on discarded fishes caught incidentally in the nets. 3. Dolphins do not chew their food. Before eating large fishes, bottlenose dolphins shake them or rub them on the ocean floor until suitable-size pieces break off. They also strip meat from spiny fishes, reducing the chance of injury from sharp spines.