Common bottlenose dolphin

Appearance

The common bottlenose dolphin is grey in color and may be between 2 and 4 m long, and weighs between 150 and 650 kg. Males are generally larger and heavier than females. In most parts of the world, the adult's length is between 2.5 and 3.5 m with weight ranging between 200 and 500 kg. Dolphins have a short and well-defined snout that looks like an old-fashioned gin bottle, which is the source for their common name.

Like all whales and dolphins, though, the snout is not a functional nose; the nose has instead evolved into the blowhole on the top of their heads. Their necks are more flexible than other dolphins' due to five of their seven vertebrae not being fused together as is seen in other dolphin species.

Distribution

The common bottlenose dolphin can be found in the temperate, subtropical and tropical oceans worldwide. The global population has been estimated at 600,000. Some bottlenose populations live closer to the shore and others live further out to sea. Generally, offshore populations are larger, darker, and have proportionally shorter fins and beaks. Offshore populations can migrate up to 4,200 km in a season, but inshore populations tend to move less. However, some inshore populations make long migrations in response to El Niño events. The species has occurred as far as 50° north in eastern Pacific waters, possibly as a result of warm water events. The coastal dolphins appear to adapt to warm, shallow waters. It has a smaller body and larger flippers, for maneuverability and heat dispersal. They can be found in harbors, bays, lagoons and estuaries. Offshore dolphins, however, are adapted to cooler, deeper waters. Certain qualities in their blood suggest they are more suited to deep diving. Their considerably larger body protects them against predators and helps them retain heat.

Status

The North Sea, Baltic, Mediterranean and Black Sea populations of the common bottlenose dolphin are listed on Appendix II of the Convention on the Conservation of Migratory Species of Wild Animals of the Bonn Convention), since they have an unfavorable conservation status or would benefit significantly from international cooperation organized by tailored agreements.

Estimated population of a few specific areas are including:

The species is covered by the Agreement on Small Cetaceans of the Baltic, North East Atlantic, Irish and North Seas, the Agreement on the Conservation of Cetaceans in the Black Sea, Mediterranean Sea and Contiguous Atlantic Area, the Memorandum of Understanding for the Conservation of Cetaceans and Their Habitats in the Pacific Islands Region, and the Memorandum of Understanding Concerning the Conservation of the Manatee and Small Cetaceans of Western Africa and Macaronesia.

Behavior

As the very social animal, common bottlenose dolphins live in groups called pods that typically number about 15 individuals, but group size varies from pairs of dolphins to over 100 or even occasionally over 1000 animals for short periods of time. The type of group is include; nursery groups, juvenile groups, and groups of adult males.Dolphins also use sound for communication, including squeaks emitted from the blowhole, whistles emitted from nasal sacs below the blowhole, and sounds emitted through body language, such as leaping from the water and slapping their tails on the water. Their heads contain an oily substance that both acts as an acoustic lens and protects the brain case. They emit clicking sounds and listen for the return echoes to determine the location and shape of nearby items, including potential prey.

Habitat

They inhabit temperate and tropical oceans throughout the world, and are absent only from polar waters. Until recently, all bottlenose dolphins were considered as a single species, but now the Indo-Pacific bottlenose dolphin and Burrunan dolphin have been split from the common bottlenose dolphin. While formerly named simply as the bottlenose dolphin, this term is now applied to the genus as a whole. The dolphins inhabit warm and temperate seas worldwide. As considerable genetic variation has been described among members of this species, even between neighboring populations, many experts consider that additional species may be recognized.

As the very social animal, common bottlenose dolphins live in groups called pods that typically number about 15 individuals, but group size varies from pairs of dolphins to over 100 or even occasionally over 1000 animals for short periods of time. The type of group is include; nursery groups, juvenile groups, and groups of adult males.

Reproduction

Mating behavior of bottlenose dolphin is polygamous. Although they can breed throughout the year, it mostly occurs in spring. Males form alliances to seek an estrous female. For a chance to mate with the female, males separate the female from her home range. Females bear a calf every three to six years. After a year-long gestation period, females bear a single calf. Newborn calves are between 0.8 and 1.4 m long and weigh between 15 and 30 kg. They can live as long as 40–50 years. The calf suckling lasts 18 and 20 months. Sexual maturity varies by population, and ranges from 5–14 years of age; sexual maturity occurs between 8 to 13 years for males and 5 to 10 years for females.

Food

Their diets consist mainly of eels, squid, shrimp and a wide variety of fishes. They do not chew their food, instead swallowing it whole. Dolphin groups often work as a team to harvest schools of fish, though they also hunt individually. Dolphins search for prey primarily using echolocation, which is a form of sonar.

The diet of common bottlenose dolphin varies depending on area. Along the U.S. Atlantic coast, the main prey includes Atlantic croakers, ‘spot’ fish, and American silver perch, while dolphins in South Africa typically feed on African massbankers, olive grunters, and pandora.