Bottlenose Dolphin

Bottlenose dolphins can become more than 50 years old and have been reported giving birth successfully up to an age of 48. During mating the dolphins usually swim on their side at least during penetration which lasts only 3.8s on average. Pregnancy lasts for one year followed by a nursing period of 1-5 years but sometimes the young attempt to suckle much longer. Birth was reported to last between 20 minutes and 2 hours and occurs during the whole year with a peak in one season in some areas or only during three or four summer months in other regions. One single calf is usually born every 3-6 years. Unfortunately infant mortality is often high. Female bottlenose dolphins become sexually mature with an age of 5-13 years whereas males do not reproduce before they are 8-14 years old.

The area used by the dolphins, called home range, can be very different in size depending on the number of animals within the dolphin group. Groups of 40-70 animals cover areas of up to 1000km². Daily movements vary between about 30 to 90km. Very long movements have been observed in response to environmental changes like El Niño events. Some populations are seasonally migrating between different regions others show side fidelity. Often different localizations are used for different purposes. So there are hunting areas, socializing areas, resting areas and reproduction areas.

Most of this information however corresponds to coastal bottlenose dolphins since little is known about offshore populations. Bottlenose dolphins also show a high variability in their diet. These animals feed on whatever seasonal and local circumstances provide rather than being specialized on a certain kind of prey. So food encompasses many different species of fish but also squid and sometimes shrimps. Offshore animals frequently follow fish schools. During feeding bottlenose dolphins are often observed to circle around fish schools with one or more individuals regularly heading into the school to feed. Sometimes they even push fish onto the shore where it can't escape and nearly beach to feed on it. To find prey not only the echolocation system is used. Dolphins also hunt by eyes and often use passive acoustic to localize fishes. That means the dolphins do not produce sounds themselves but hear for the noise which is caused by the prey.

Group size, as you probably have already expected, varies a lot as well. Usually 2-15 animals swim together but occassionally more than 1000 individuals are seen to build one huge group. Basic social units are either nursery groups, consisting of several females and their offspring, or mixed-sex groups of juveniles. Composition of the group often changes daily or even between some hours. Adult males are mostly seen traveling alone but sometimes strong bonds exist between two or three animals. Some females are also more social than others.

Many discussions took place in the past about the question, if the bottlenose dolphin, Tursiops truncatus, is one species or not because of all these variations between different geographic regions. Today there is much agreement to distinguish between Tursiops aduncus which occurs in the coastal waters of the Indian Ocean and western part of the South Pacific and Tursiops truncatus which inhabits the central and eastern South Pacific as well as the North Pacific, the Atlantic Ocean, Caribbean, Mediterranean Sea, Black Sea, North Sea, Baltic Sea and Red Sea.