Dolphin Web

Physical characteristics, such as the shape of the animal’s head and the type of teeth present, largely determine the diet of toothed whales. Dolphins have conical (cone-shaped), interlocking teeth. The number of teeth varies for each individual, but there are usually between 72 and 104 teeth in the mouth. These teeth are small and sharp, designed to grasp slippery fish, as dolphins do not chew their food. Dolphins retain the same set of teeth throughout their lives and the degree of wear on the teeth is often used as an indication of age.

Dolphins are predators and actively hunt for their food. Their speed and agility in the water enables them to catch many species of fish including those which are fast swimmers. Dolphins feed predominantly on fish and cephalopods (squids) and may occasionally eat crustaceans such as prawns. Most species of dolphins appear to feed opportunistically on whatever prey species are most abundant. The number of fish they eat depends on their availability in each habitat. However, dolphins can be quite fussy eaters when there are choices of different food available. Dolphins possess taste buds in the root of their tongue which allows them to taste their food. They tend to prefer soft fleshy fish with a high fat content, such as mullet, grinners or silver biddy.

Dolphins demonstrate a remarkable range of feeding techniques in various circumstances. In open waters dolphins may herd large schools or may feed individually in rocky reef areas. In shallow habitats dolphins are often seen driving fish toward the shore and almost stranding themselves in an attempt to catch them. In many parts of the world, dolphins swim behind fishing boats feeding on “by-catch” discarded by the fishers. The dominance hierarchy within the pod is commonly seen in these feeding situations where the dominant individuals, generally adult males, have first choice of the by-catch, while females and juveniles animals have the “leftovers”.

Each day dolphins consume an amount of fish comparable to approximately five percent of their body weight. Fish are swallowed whole and head first so as to avoid impediment by fins and scales. Because the trachea (wind pipe) and oesophagus (food passage) are completely separate, dolphins are able to swallow their food underwater without risk of choking. Dolphins’ throats tend to be quite narrow, so as to reduce the ingestion of sea water. All of their freshwater requirements are achieved through the fish they eat, and as a result dolphin’s do not drink.

Because dolphins are large predators, they are near the top of the marine food chain. The fish they consume feed on smaller fish which in turn feed on even smaller marine organisms. It is well known that toxic substances pass upwards through the food chain and accumulate in the tissues of large predators such as dolphins. Pollution by industrial, agricultural and domestic waste is an increasing problem and unfortunately dolphins are often poisoned due to an accumulation of heavy metals and pesticides. Such pollution is thought to be responsible for recent die-offs of thousands of dolphins along the coasts of North America and Europe.

Rubbish from boats also poses threats to dolphins. Plastic wastes may be mistaken for food, blocking a dolphins digestive tract, causing terrible suffering before they eventually die. Fishing line and nets are also responsible for the deaths of many dolphins, as they often become entangled and suffocate.

Although dolphins occupy a relatively high position in the food chain, they are not without predators. Despite the stories that dolphins can attack and kill sharks, sharks are actually dolphins’ main natural predator. Dolphins and sharks feed on similar food types and are often seen feeding in the same areas and at times some dolphins are attacked by large sharks. Over one third of the dolphins in Moreton Bay on the east coast of Australia have large scars as evidence of shark bites. However, it appears that many dolphins survive these attacks and the wound soon heal. There is currently no firm evidence that dolphins have the capability to kill a large shark.

There have also been reports that Killer Whales (Orcinus orca) will attack and kill smaller dolphins. It is not yet known how common this is.