-- MAIN LINKS --

-- EVOLUTION & ADAPTATION -- BALEEN WHALE SPECIES --
-- CLASSIFICATION -- CHARACTERISTICS OF BALEEN WHALES --
-- TOOTHED WHALE SPECIES -- DOLPHINS -- SEALS --
-- ENDANGERED SPECIES -- THREATS -- GAMES --

---Diet composition

Dolphins feed mainly on fish. They are opportunistic feeders, usually going after the most abundant species available. As a result, their diet depends on the geographic region they are living in and the time of year. For instance, in the North Sea, they feed mainly on herring, small sharks, haddock and sole. In other areas, they feed among others on mackerel, mullet, squid and occasionally shrimp.

At Särkänniemi, the dolphins get a variety of food species, including herring, mackerel, sprat, whiting, capelin and squid. The fish they are fed is caught mainly in the clean waters of the North Atlantic Ocean.

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---Water availability

Although dolphins live in water, getting sufficient water is a problem for them. The surrounding sea water is too salty for them to drink. If they would drink it, they would lose more water trying to get rid of the excess salt than they drank in the first place. So they have to get most if not all of their water from the food they eat, either directly or as a by-product of metabolising the fat and proteins.

Since water is so scarce for them, they have special adaptations for saving water. In a way, dolphins have to live like desert animals. Their kidneys are very efficient in reclaiming water and as a result, their urine is very concentrated.

---Diet requirements

How much a dolphin needs to eat depends in part on the composition of its diet. Some fish species, like mackerel and herring, are high in fat and consequently have a high energy (caloric) value. Other food items, like whiting and squid, contain very little fat and have a low energy value.

On an average diet, dolphins eat about 4-5% of their body weight in fish each day. For a 250 kg dolphin, that means 10-12.5 kilo/day. Lactating females may need up to double that amount. Dolphins have a fairly high metabolic rate, in part because they need to compensate for the heat lost to the cold water they live in.

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---Feeding methods

Dolphins do not chew their food. Instead, they swallow their fish whole. They usually take them head first, so that the fins and spines get folded back and do not hurt their throat. The maximum size of the fish caught depends on the size of the dolphin. Young, small dolphins prefer smaller fishes. Adult dolphins can eat up to 5 kg of fish at a time.

---Fishing methods

How dolphins capture their food depends on the location and the species. Dolphins usually locate the fish with their echolocation system. The dolphins emit sounds (clicks) which reflect off the fish.
The returning echoes give the dolphins information about the location of the fish. They possibly use loud sounds to stun the fish. The stunned fish are easier to catch.

Often, dolphins hunt in groups. They can then chase and concentrate the fish and take what they want. When taking bottom dwelling fishes, they usually hunt individually, taking one fish at a time. In some areas, they actually chase fishes ashore, beach themselves among the fishes, take what they can and then slide back into the water. In other areas, they have learned to take small fishes from fishing nets and catch fish going overboard when the nets are hauled in.

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---How do we know what dolphins eat?

To find out what dolphins eat is hard to do. Since they catch and eat their fish under water, it is hard to see what is going on. Occasionally, dolphins take a fish to the surface and some underwater photographers have been lucky enough to see a dolphin feeding.

Most of the data comes from animals that are found dead on the beach or in fishing nets. By analysing the contents of their stomachs, you can get some idea of what species they get and how
much. Most of the information about dolphin energy requirements and dolphin physiology comes from direct measurements on dolphins in oceanaria and research institutes.

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