Dolphin & Porpoise Diet

Intelligent, graceful and intriguing marine mammals, more than 30 species of dolphin and eight species of porpoise currently swim the world's oceans. From the familiar, smiling bottlenose to the misleadingly named killer whale, the diversity of these creatures is astonishing. Yet, thanks to differences in size, temperament and habitat, each species has developed its own diet of staple and favorite foods--and what's on the menu varies accordingly.

Differences

• Both members of the Cetacea group, which also includes whales, there are a few slight distinctions between porpoises and their dolphin relatives. For example, porpoises are almost always smaller with less pronounced, more rounded snouts. They also have different teeth. While dolphins have pointed, rather conical teeth, porpoise teeth look a bit like spades with a sharpened end. While both animals use a similar means of communication, the human ear can only discern "discussions" among dolphins because porpoises communicate using frequencies beyond human hearing capabilities.

Common Food Sources

• As toothed carnivores, all dolphins and porpoises eat meat. That is largely consumed in the form of fish, especially those that swim in vast schools of thousands. Most of these cunning and opportunistic aquatic mammals also regularly supplement their fish-based staple diet with tasty squid and even a crustacean or two. As for the type of fish each species prefers, that is typically determined by size and habitat.

Habitat-Determined Diet

• As with all animals, the nutritional resources available to these ocean dwellers vary depending on where they make their home. While schooling fish comprise the dietary staples for both porpoises and dolphins, habitat ultimately determines what types of fish and other food sources are available for consumption.

  Bottlenose and other similar-sized dolphins flourish throughout both the Pacific and the Atlantic, and tend to feed on mackerel, catfish and mullet. Yet they'll just as happily dine on shrimp, eels and crab. The much smaller black dolphin, found exclusively off the coast of Chile, eats only diminutive crustaceans, cephalopods and relatively small fish. In the Pacific, white-sided dolphins consume salmon, pollock, anchovies, squid and herring. The Hector's dolphins of New Zealand prefer to nibble red cod, yellow-eyed mullet and other creatures from the ocean floor. And the granddaddy of all dolphins, the killer whale, which is only called a "whale" because of its size, earns its name as the only member of the Cetacea group to eat other dolphins, whales and even sharks. Found in both hemispheres, particularly in cooler waters near the poles, their habitat affords them access to larger marine mammals, such as sea lions, penguins, turtles and seals.

Daily Dietary Demands

• There are two primary conditions that determine how much these creatures must consume to maintain a healthy diet--their size and the nutritional value of their prey. Most species, including the bottlenose, common and gray dolphin as well as most porpoises, weigh an average of 200 to 550 lbs. and are 6 to 8 feet long. In order for porpoises and dolphins of this general size to survive, they must consume between 20 and 50 lbs. of food each day, and the more nutrient-rich the catch, the better. Indeed, feeding on fatty mackerel or herring is far more satiating than a snack of squid. Larger species, such as pilot whales and the apex dolphin--the killer whale--naturally must consume a great deal more than their smaller brethren. Rather than sampling small schools of fish, their diet chiefly consists of blubbery marine mammals and meaty, large fish.

Food-Finding Strategies

• A blow from the killer whale's tail renders prey dazed and defenseless

  Social creatures that often travel in pods, dolphins and porpoises have mastered a number of strategies to trap and consume their prey--both cooperatively and individually. Some species employ a "corralling" method, in which they chase fish into shallow-water traps where they can't escape back to deeper water without first running into a hungry dolphin. Another popular strategy known as "herding" involves a group of dolphins encircling a school of fish, while individuals wait for their turn to plunge into the school and feed. Larger dolphins often will use their immense tails to slap and stun their prey, allowing them to eat their catch without risk of injury from a struggling animal. Killer whales often use this maneuver on seals and sea lions, but even bottlenose dolphins have been known to use the same tactic on fish.