Common bottlenose dolphin
The common bottlenose dolphin or Atlantic bottlenose dolphin is one of three species of bottlenose dolphin in the genus Tursiops. While formerly known simply as the bottlenose dolphin, this term is now applied to the genus Tursiops as a whole. As considerable genetic variation has been described within this species, even between neighboring populations, many experts think additional species may be recognized and split out.
The common bottlenose dolphin is a very familiar dolphin due to the wide exposure it receives in human care in marine parks and dolphinariums, and in movies and television programs. Common bottlenose dolphins inhabit temperate and tropical oceans throughout the world, absent only from polar waters.
Description
Common bottlenose dolphins have a grey coloration, a short beak, a single blowhole, and a hooked dorsal fin. The bottlenose is between long, and weighs between. Males are generally larger and heavier than females. In most parts of the world, adult length is between ; weight ranges between. Dolphins have a short and well-defined snout that looks like an old-fashioned gin bottle, which is the source for their common name.Their necks are more flexible than other dolphins' due to five of their seven vertebrae not being fused together like in other dolphins.
Taxonomy
Until 1998, all bottlenose dolphins were considered one species T. truncatus. That year, the Indo-Pacific bottlenose dolphin was recognized as a separate species. The two species are thought to have split during the mid-Pleistocene, about 1 million years ago.Currently, four common bottlenose dolphin subspecies are recognized:
Bottlenose dolphins along the southern California and Baja California coasts were previously recognized as the Pacific bottlenose dolphin, T. t. gillii, originally described as distinct species T. gillii. The name has since been reclassified as a junior synonym of Tursiops truncatus. Additionally, bottlenose dolphins along the Pacific coast of Central America were described as T. nuuanu in 1911. A review of T. gillii and T. nuuanu specimens supported T. gillii as a synonym of T. truncatus and T. nuaanu as a unique subspecies.
A 2020 study identified four distinct lineages within T. truncatus, each of which could be a distinct subspecies: a lineage native to the coastal regions of the western North Atlantic, an offshore lineage found worldwide in pelagic ecosystems, a lineage native to the Mediterranean, and a lineage restricted to the Black Sea. The study noted only weak differentiation between the Black Sea and Mediterranean lineages, and found them to form a sister group to the offshore lineage, indicating that they likely descended from offshore bottlenoses that colonized the Mediterranean and Black Seas. The clade containing the offshore, Mediterranean, and Black Sea populations was sister to the western North Atlantic lineage, indicating deep divergence between the two. An analysis of the morphology, genetics, and evolutionary divergence of the western North Atlantic coastal and offshore ecotypes supported the coastal form as being a distinct species. While the offshore type was retained within T. truncatus, the coastal dolphins are now recognized as Tamanend's bottlenose dolphin.
Ecology and behavior
As a very social species, the common bottlenose dolphin lives 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 1,000 animals for short periods of time. Group structure depends on the sex and age of the dolphins, but may change depending on the group. Their geographic range dictates a lot of their behaviors including the densities of dolphins while traveling. The types of groups include: nursery groups, juvenile groups, and groups of adult males. Male dolphins tend to form pair bonds, which are the strongest of dolphin bonds, while females stay with their calves for 3-8 years and then tend to stay in social groups. Typically, common bottlenose dolphins are more social after they have eaten in the mid-day or evening. During these times, they are often seen engaging in group interactions, including play, vocalizations, and cooperative swimming behaviors.Echolocation
Dolphin use of their blowholes and nasal sacs to communicate and their ability to echolocate with their melon are keys to their success. Echolocation uses sound waves that are emitted and received to understand their surroundings. As sound waves are emitted they are bounced back and received as nerve impulses in the brain which can be interpreted at a frequency of 120 kHz. This allows dolphin to know the location, shape and size of objects aiding in navigation, communication, hunting, and awareness of predators nearby. Dolphins can emit both high and low frequency sounds, but lower frequencies travel best in the water allowing for the best results while using echolocation.Communication
In addition to echolocation, dolphins communicate through whistles, squeaks and pulses. Dolphins address each other individually by matching each other's signature whistle. Body language is also a key method of communication, including gestures, postures, and physical contact, used to convey information, reinforce social bonds, and coordinate group activities.Body language and contact is also used in conflict over mates and resources. In conflict, bottlenose dolphins grab ahold of each other with their teeth, which can form unique "rake marks". These primarily superficial knicks and notches on the body or the dorsal fin makes dolphins individually identifiable. These unique marks are universally used to identify dolphins in studies around the globe.
Calf-directed communication
Common bottlenose dolphin signature whistles, which are in a higher frequency range than humans can hear, have an important role in facilitating mother–calf contact. In the Sarasota Dolphin Research Program's library of recordings were 19 female common bottlenose dolphins producing signature whistles both with and without the presence of their dependent calf. In all 19 cases, the mother dolphin changed the same signature whistle when the calf was present, by reaching a higher frequency, or using a wider frequency range. Similarly, humans use higher fundamental frequencies and a wider pitch range to inflect child–directed speech. This has rarely been discovered in other species. The researchers stated that CDS benefits for humans are cueing the child to pay attention, long-term bonding, and promoting the development of lifelong vocal learning, with parallels in these bottlenose dolphins in an example of convergent evolution.Diet
Its diet consists mainly of eels, squid, shrimp and a wide variety of fishes. It does not chew its food, instead swallowing it whole. Dolphin pods 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 pods varies depending on area. Along the U.S. Atlantic coast, the main prey includes Atlantic croakers, spot and American silver perch, while in South Africa, African maasbankers, olive grunters, and pandora are common bottlenose dolphin's typical prey. Their hunting strategies depend on what they are eating; for example, with fish they will circle the school and use their echolocation to feed on them one by one. They can also stun fish using sonar or smash them into corals depending on their speed.
According to combined stomach content and stable isotope analyses in the Gulf of Cádiz, although European conger and European hake are most important prey of common bottlenose dolphins, mass-balance isotopic mixing model, using δ13C and δ15N shows that Sparidae species; seabreams, rubberlip grunt, and common pandora, and a mixture of other species including European hake, mackerels, European conger, red bandfish and European pilchard are the assimilated diet.
Research indicates that the type and range of fish in a dolphin's diet can have a significant impact on its health and metabolism. Dolphins eat 10–20% of their body weight each day, with pregnant and nursing females eating the most.
Reproduction
Mating behavior of the bottlenose dolphin is polygamous. Although they can breed throughout the year, it mostly occurs in spring, and with a 12 month gestation period mating season and birthing season overlap. Males form alliances, or pair bonds, to seek an estrous female and they attempt to breed the most while keeping other males away from viable females. 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 long and weigh between. The calf's suckling lasts between 18 and 20 months and they are weaned between three and eight years of age. Females typically reproduce every 3 to 6 years when sexual maturity is reached, and there is no recorded menopause in the bottlenose dolphin species. Sexual maturity varies by population, and ranges from 5–14 years of age; sexual maturity occurs between 8 and 13 years for males and 5 to 10 years for females.Life expectancy
The average life span of common bottlenose dolphins is at least 40 years old and up to 60 years old, with females typically living longer than males. but in captivity they have been known to live to up to 51 years old.The main threats to bottlenose dolphins depends on their geographic range. Dolphins living in shallow coastal waters tend to be the top predator with the exception of young dolphins having to be protected from sharks by their mothers. Dolphin communities out in the deep ocean have more threats with shark attacks but living in pods allows them to survive. Other predators, mainly impacting newborns, include stingrays and orcas.