The bottlenose dolphin is probably the most familiar of the small cetaceans because of its coastal habits, widespread captivity in zoos and aquaria, and frequent appearance in the media. It is a large, robust dolphin, with a short to moderate-length stocky snout distinctly set off from the melon by a crease. The dorsal fin is tall, sickle shaped, and set near the middle of the back.
Color of the back and sides varies from light gray to nearly black, fading to white (sometimes with a pinkish hue) on the belly. In rare instances, individuals’ bellies and lower sides are spotted. There is sometimes a faint dorsal cape on the back, generally only visible at close range. Often, there are brushings of gray on the body, especially on the face, and from the apex of the melon to the blowhole. Bottlenose dolphins have 18-27 pairs of robust teeth in each jaw. In older animals, many of these may be worn down or missing.
Length at birth is about 1-1.3 m. Adults range from 1.9-3.8 m, with males somewhat larger than females. There is wide variation in size between different populations, with the largest known specimens from the United Kingdom. Maximum weight is at least 650 kg, although most animals are much smaller. In many areas of the world, such as the western North Atlantic, eastern North Pacific, and Peru, there appear to be two bottlenose dolphin eco-forms, a coastal and an offshore type. These forms have been distinguished by morphological, ecological, and physiological features.
Can be Confused With
Bottlenose dolphins can be mistaken for several other species of small cetaceans, depending on the region. They are likely to be confused with long-beaked bottlenose dolphins where the two species overlap in distribution, with young Atlantic spotted dolphins (before they develop spots) in the tropical Atlantic, with dolphins of the genus Sotalia along the east coast of South America, and with humpback dolphins in the Indo-Pacific and off West Africa. When seen from a distance, they can also be confused with Risso's or rough-toothed dolphins.
Bottlenose dolphins are found primarily in coastal and continental shelf waters of tropical and temperate regions. Population densities are higher nearshore, than in deeper, offshore waters. Nevertheless, bottlenose dolphins inhabit oceanic waters, such as those in the eastern tropical Pacific. Except for their occurrence around the United Kingdom, northern Europe, and southern New Zealand, they generally do not range poleward of 45° in either hemisphere.
Ecology and Behavior
The bottlenose dolphin is a generalist in regards to habitat. Although more is known about the biology of this species than of any other dolphin, much of what we know of the general biology of dolphins comes from studies of bottlenose dolphins, both in captivity and in the wild. The bottlenose dolphin is the most common cetacean species held in captivity. It has proven highly adaptable and is easily trained. In the wild, bottlenose dolphins frequently attend fishing vessels and steal fish from nets. In some instances, solitary wild dolphins have interacted with humans for extended periods of time.
Group size is commonly less than 20 individuals, but large herds of several hundred are sometimes seen in offshore waters. Bottlenose dolphins are commonly associated with other cetaceans, and hybrids with other species are known to exist both in captivity and in the wild. Based on a number of studies of nearshore populations, bottlenose dolphins live in relatively fluid (fission/fusion) groupings within somewhat closed societies. While mother/calf bonds and some other associations strong, most dolphins associate with different individuals from day-to-day. In many inshore areas, bottlenose dolphins maintain long-term home ranges; in other localities, they are migratory, generally ranging further. The behavioral and social systems of these animals are highly diverse and adaptable. Bottlenose dolphins are quite active (especially when feeding or socializing), often slapping the water with their flukes, leaping, and performing other aerial behaviors.
Bottlenose dolphins are long lived, reaching up to 40 years of age or more. Sexual maturity varies according to population, and females breed for many years – some individuals known to be 45 years old have given birth to calves and successfully raised them in Sarasota, Florida, United States. Gestation lasts about a year, as does lactation. Spring and summer or spring and fall calving peaks have been described for most populations.
Feeding and Prey
Threats and Status
The main threats to bottlenose dolphins include direct harvests and fisheries bycatch. Bottlenose dolphins have been hunted directly in several areas and continue to be collected in some parts of the world. The largest takes in recent years have been in the Black Sea, but large numbers have occasionally been taken in Japanese and Taiwanese drive fisheries, and smaller catches are reported in the Caribbean, Peru, Sri Lanka, and Indonesia. Additionally, substantial numbers of bottlenose dolphins have been taken in live-capture fisheries for display, research, and use by the military. Incidental catches (bycatch) also occur throughout the species’ range. Catches have occurred in gillnets, driftnets, purse seines, trawls, and on hook-and-line gear. Some mortality related to recreational fishing have also been documented, in some cases exceeding bycatch numbers in commercial fisheries.
Coastal bottlenose dolphins are also susceptible to habitat destruction and degradation by human activities, including vessel collisions and contaminants. There have been several bottlenose dolphin die-offs of bottlenose dolphins in recent years, most often linked to toxic algal blooms and pollutants.
The IUCN lists the bottlenose dolphin as “data deficient,” because too little is known to evaluate its conservation status. The bottlenose dolphin is not considered threatened or endangered by the United States government, but is protected under the Marine Mammal Protection Act and has been afforded special protected status under Annex II of the European Union’s Habitats Directive (92/43/EEC). The United States National Marine Fisheries Service considers bottlenose dolphins in United States waters to belong to several distinct stocks, which are assessed separately. Because these stock delineations are often difficult to determine, population assessments should be considered dynamic, ongoing processes. The following United States stocks considered are:
• California coastal stock (generally found within 1 km of shore) – 169 (CV=0.11) based on 1994 and 1999 survey data
• California/Oregon/Washington offshore stock – 956 (CV=0.14) based on 1991-1996 ship surveys
• Hawaiian stock – 743 (CV=0.56) based on 1993, 1995, and 1998 aerial surveys
• Western Gulf of Mexico – 3,499 (CV=0.21) based on a 1992 aerial survey
• Northern Gulf of Mexico – 4,191 (CV=0.21) based on a 1993 aerial survey
• Eastern Gulf of Mexico coastal stock – 9,912 (CV=0.12) based on1994 aerial surveys
• Gulf of Mexico bay, sound, and estuary stock – estimates have been made for many of the small water bodies adjoining the Gulf of Mexico.
• Gulf of Mexico continental shelf edge and continental slope stock – 5,618 (CV=0.26) based on 1992-1994 shipboard surveys
• Gulf of Mexico outer continental shelf stock – 50,247 (CV=0.18) based on 1992 and 1993 aerial surveys
• Western North Atlantic coastal stock – Stock structure in this region is complex and estimating abundance has proven controversial.
• Western North Atlantic offshore stock – 30,633 (CV=0.25) based on 1998 shipboard and aerial surveys
Refer to the current NOAA stock assessment reports for information on each stock.
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