Tursiops truncatus (Montagu, 1821)

Russell A. Mittermeier & Don E. Wilson, 2014, Delphinidae, Handbook of the Mammals of the World – Volume 4 Sea Mammals, Barcelona: Lynx Edicions, pp. 410-526 : 515

23.

Common Bottlenose Dolphin

Tursiops truncatus

French: Grand Dauphin / German: GroRer Tummler / Spanish: Delfin mular

Other common names: Black Porpoise, Bottlenose Dolphin; Black Sea Bottlenose Dolphin (ponticus)

Taxonomy. Delphinus truncatus Montagu, 1821 ,

“in Duncannon Pool, near Stoke Gabriel, about five miles up the River Dart,” Scotland, UK .

Although bottlenose dolphins are one of the most well-studied species of all cetaceans, their taxonomy is still in dispute.

Until as recently as 2000, all bottlenose dolphins were considered to belong to a single species, 1. truncatus . Evidence from morphological, osteological, and genetic studies later highlighted differences between 7. truncatus and 1. aduncus . Nevertheless, there is still confusion about the taxonomy of 7. truncatus due to its great geographical variation. This genus will likely be divided into more species in the future as more knowledge is gathered. One recognized subspecies exists in the Black Sea (7 t. ponticus), which exhibits genetic and morphological differences from other 7. truncatus in the eastern and western Mediterranean Sea and from those in the north-eastern Atlantic Ocean. Two subspecies recognized.

Subspecies and Distribution.

1. t. truncatus Montagu, 1821 — worldwide in temperate and tropical waters as far S as New Zealand and generally as far as 45° N, but reaching the Faroe Is in the N Atlantic. 1: 1. ponticus Barabash-Nikiforov, 1940 — inhabits the Black Sea, Kerch Strait along with the connecting part of the Azov Sea, and the Turkish Straits system.

Descriptive notes. Total length 190-380 cm; weight 136-635 kg. Neonates are 84— 140 cm long and weigh ¢.30 kg. Although there is variation in body shape throughout the distribution of the Common Bottlenose Dolphin, it has robust, medium-sized build. Body size is perhaps related to water temperature, except in the eastern Pacific Ocean. The Common Bottlenose Dolphin has short and robust beak, with distinct crease separating it from melon. Dorsal fin is located at middle of back and is tall and moderately falcate. Flippers are recurved and slightly pointed at tips. Skin pigmentation varies from pale gray to black dorsally and laterally, with pale, and sometimes pinkish, coloration on belly. Spotting is rare but, when present, generally appears as small flecks on belly and lowersides. Pale brush marking is sometimes found on sides of Common Bottlenose Dolphins, especially on face, and sometimes there is faint spinal blaze. Wide, faint stripe can be found extending from flipper forward to gape. The Common Bottlenose Dolphin is somewhat sexually dimorphic in size, with adult males tending to be slightly larger than females. Each jaw contains 18-27 pairs offlattened teeth.

Habitat. Temperate and tropical waters, typically along coasts and over continental shelves. Off coasts of North America, Common Bottlenose Dolphins generally inhabit waters with sea-surface temperatures of 10-32°C. They may also occur in bays, lagoons, channels, river mouths, and deep oceanic waters. They can be found as far south as Tierra del Fuego, South Africa, and New Zealand. In the North Pacific Ocean, Common Bottlenose Dolphin frequent waters as far north as the southern Sea of Okhotsk, Kuril Islands, and central California. In the North Atlantic Ocean, they can occur as far north as Nova Scotia, Canada, as well as Norway and the Lofoten Islands. The Common Bottlenose Dolphin generally is not found in waters pole-ward of 45° in either hemisphere, except in northern Europe and southern New Zealand.

Food and Feeding. The Common Bottlenose Dolphin is primarily a generalist feeder and eats a large variety of fish and squid. Generalist feeding is most common, but individuals may show some specialization within populations. Some preference has been shown forfish belonging to the families Sciaenidae , Scombridae , and Mugilidae . Most prey is benthic, but pelagic fish are often eaten. Noise-producing fish (i.e. sciaenids) represent a large portion of the diet, which sometimes also includes shrimps, squid, and other crustaceans. In some cases, different age and sex classes of Common Bottlenose Dolphins eat in different areas, with lactating females and their young feeding nearshore, adolescents frequenting more offshore waters, and adult males and resting females feeding even farther offshore. Common Bottlenose Dolphins exhibit variable feeding strategies, but they generally capture fish individually. Cooperative feeding (chasing fish onto shore to trap them and feeding from shrimp trawlers) is not uncommon. Individual feeding strategies vary greatly and include high-speed chases, knocking fish out of the water with flukes, producing bubbles to herd prey toward the water's surface, and stunning fish with percussive leaps and tail lobs (“kerplunking”).

Breeding. Mating activity and births of Common Bottlenose Dolphins can occur throughout the year. Breeding, however, is most frequent during spring and summer. Captive studies have shown that females ovulate spontaneously and multiple times within one season. Mature males can be sexually active throughout the year. Gestation lasts c.12 months. Birth intervals are typically ¢.3-6 years. Occasionally, female Common Bottlenose Dolphins are pregnant and lactating at the same time. Lactation can lasts 1-5-2 years. Males reach sexual maturity later (9-14 years) than females (5-14 years). Females as old as 48 years have produced offspring, and genetic studies have matched paternity of progenyto males that were 13-40 years old. Common Bottlenose Dolphins canlive up to 58 years, but most often, femaleslive to ¢.50 years and males live to 40-45 years.

Activity patterns. Common Bottlenose Dolphins are active throughout the day and night. Common behaviors include traveling, feeding, resting, and socializing. They can be aerially active and bow-ride. Populations of Common Bottlenose Dolphins living in deep waters can dive for at least five minutes to depths of more than 500 m in pursuit of prey. Populations inhabiting shallow water do not dive for as long and generally surface every 30 seconds.

Movements, Home range and Social organization. Groups of Common Bottlenose Dolphins most often consist of 2-15 individuals, although groups of more than 1000 individuals have been reported. Group structure varies greatly with factors such as sex, age, reproductive status, and kinship. Relationships between mothers and their young are very strong, but other affiliations may or may not be stable over time. Common subgroups consist of nursery groups, juveniles of mixed sex, strongly bonded pairs, and individual adult males. Common Bottlenose Dolphins occur in mixed-species groups with a variety of other delphinid species, often including the Indo-Pacific Bottlenose Dolphin (7. aduncus ), the Atlantic Spotted Dolphin ( Stenella frontalis ), the Indo-Pacific Humpback Dolphin ( Sousa chinensis ), and the Atlantic Humpback Dolphin ( Sousa teuszii ). Echolocation vocalizations of Common Bottlenose Dolphins have a peak frequency of 40-130 Hz. Movements and home ranges of the Common Bottlenose Dolphin vary greatly throughout its distribution. Most inshore individuals are not migratory and reside long-term in a particular area; some retain multigenerational home ranges. Some coastal populations residing in the cold-water extremes of the species’ distribution may migrate seasonally. Average daily movements of Common Bottlenose Dolphins are 33-89 km, but offshore dolphins may travel as far as 4200 km.

Status and Conservation. CITES Appendix II. Classified as Least Concern on The [UCN Red List. The “Black Sea Bottlenose Dolphin” (7. t. ponticus) is listed as Endangered, the Fiordland (New Zealand) subpopulation of Common Bottlenose Dolphinsis listed as Critically Endangered, and the subpopulation in the Mediterranean Sea is listed as Vulnerable, with a current estimate in the low 10,000s. Abundance of the Common Bottlenose Dolphin is estimated at ¢.600,000 individuals world-wide. About 52,000 individuals are estimated in the northern Gulf of Mexico, ¢.126,000 off the east coast of North America, ¢.243,500 individuals in the eastern tropical Pacific Ocean, ¢.3215 individuals in Hawaiian waters, ¢.2000 individuals off the west coast of the USA, ¢.168,000 individuals in the north-western Pacific Ocean, ¢.900 individuals off KwaZulu-Natal, €.2628 individuals in the eastern Sulu Sea, ¢.7654 individuals in the north-western Mediterranean, ¢.584 individuals in the Alboran Sea, ¢.1000 individuals around the Faroe Islands, ¢.610 individuals off the Atlantic coast of Europe, ¢.12,600 individuals in western European continental shelf waters, ¢.122 individuals off Belize, and c.66 individuals in Doubtful Sound, New Zealand. Population trends of Common Bottlenose Dolphins are unknown. The Fiordland (New Zealand) subpopulation is estimated to contain ¢.205 individuals. The population size of the Black Sea Bottlenose Dolphin is unknown, but it is thought to be at least several thousand, and there is uncertainty as to the population trend. Threats of most concern are direct and incidental catch. Direct takes of the Common Bottlenose Dolphin often occur for display, research, and use by the military. Public display of the Common Bottlenose Dolphin started in 1883 at the Brighton Aquarium in the UK. In the past, they were deliberately hunted in the Black Sea for human consumption, oil, and leather. Human consumption of the Common Bottlenose Dolphin still occurs offJapan, Peru, Sri Lanka, and the Faroe Islands. They are known to regularly feed from fishing gear making incidental entanglement and ingestion of fishing gear a serious threat to the species. Gillnets, trawls, purse seines,driftnets, and hook-and-line fishing gear can cause mortality. Populations of Common Bottlenose Dolphins in coastal waters where pollution is prevalent are at high risk of immunotoxicity, pathological problems, and reproductive impairment from contaminants, including PCBs, chlorinated hydrocarbons, and DDT metabolites. Other threats include noise disturbance from military sonar and seismic surveying, ship strikes, biotoxins, and habitat destruction.

Bibliography. Barros & Odell (1990), Barros & Wells (1998), Bearzi et al. (2012), Birkun (2008), Currey et al. (2011), Curry & Smith (1997), Hammond et al. (2008q), Herzing et al. (2003), Jefferson et al. (2008), Klatsky et al. (2007), Leatherwood & Reeves (1990), Pate & McFee (2012), Read et al. (1993), Rogers et al. (2004), Wang et al. (1999, 2000), Wells & Scott (2009).

Figures

On following pages: 33. Commerson’s Dolphin (Cephalorhynchus commersonii); 34. Chilean Dolphin (Cephalorhynchus eutropia); 35. Heaviside's Dolphin (Cephalorhynchus heavisidii); 36. Hector’s Dolphin (Cephalorhynchus hector).

Subspecies and Distribution. 1. t. truncatus Montagu, 1821 — worldwide in temperate and tropical waters as far S as New Zealand and generally as far as 45° N, but reaching the Faroe Is in the N Atlantic. 1: 1. ponticus Barabash-Nikiforov, 1940 — inhabits the Black Sea, Kerch Strait along with the connecting part of the Azov Sea, and the Turkish Straits system.