Bottlenose dolphins (Scientific name:Tursiops) are usually gray in color and have a pronounced bottle-shaped snout. Often featured in television shows and movies, they can reach lengths of three meters (10 feet) and weigh as much as 450 kilograms (1,000 pounds). They eat around 13.5 kilograms (30 pounds) of fish a day, mostly pinfish, pigfish and mullet, and come to the surface an average of once every 28 seconds to breath. Female bottlenose dolphins often live into their early 50s, while males typically live between 40 and 45 years. The maximum age recorded in the wild was a 58-year-old female,
Common bottlenose dolphins get their name from their short, thick snout (or rostrum). Fossils of Tursiops have been found in Pliocene Period (5.4 million to 2.4 million years ago) and Pleistocene Period (less than two million years old) deposits. It has been suggested that they originated in the Mediterranean region. Tursiops species are a descendant of terrestrial mammals from the family Pakicetidae, terrestrial whales from the early Eocene (56 million to 33.9 million years ago) as are other dolphins and whales.
Bottlenose dolphins have a long association with humans in regard to entertainment, tourism and research. They have been described in literature dating as far back to ancient Greece and Rome. The first bottlenose dolphins were publicly displayed in 1883 and have been a fixture of oceanarium and marine park shows around the world for a long time. The term Tursiops means dolphin-like. It is derived from the Latin word for dolphin, Tursio, and -ops, which is the Greek suffix for appearance.
The main predators of bottlenose dolphins are large sharks including bull sharks, tiger sharks, great white sharks and dusky sharks. These sharks prey on smaller dolphins and calves and females than on larger dolphins. It is not unusual to see shark bite scars on dolphins and dolphin remains in shark stomachs. Orcas also occasionally prey on dolphin species. Bottlenose dolphins defend themselves against attackers by butting them with their rostra (snout) or striking them with their tail flukes. Blubber may provide some protection against predators. Many shark populations have decreased and thus dolphins may be experiencing lower predation by sharks. Stingrays sometimes kill bottlenose dolphins.
Websites and Resources: Britain-based Whale and Dolphin Conservation Society uk.whales.org ; Animal Diversity Web (ADW) animaldiversity.org; National Oceanic and Atmospheric Administration (NOAA) noaa.gov; Fishbase fishbase.se; Encyclopedia of Life eol.org; Smithsonian Oceans Portal ocean.si.edu/ocean-life-ecosystems ; Monterey Bay Aquarium montereybayaquarium.org ; MarineBio marinebio.org/oceans/creatures
Where Bottlenose Dolphins Are Found
Bottlenose dolphins have a worldwide distribution. They are found in tropical to temperate marine waters in the Indian Ocean, Atlantic Ocean, Pacific Ocean, and Mediterranean Sea, along the coasts of all major continents and many islands.. They are found in a wide range of habitats, mostly in coastal areas and in shallow offshore banks, but also in estuarine systems and the open ocean, and sometimes even in rivers.
In the United States, common bottlenose dolphins are found along the West Coast off California, Oregon, and Washington, and in the Hawaiian islands. They are also found in coastal and offshore waters along the East Coast from New York to Florida, throughout the Gulf of Mexico, and in the Caribbean. Worldwide, bottlenose dolphins can be found in the Mediterranean and Black seas, as well as the southwestern Indian Ocean. In the Pacific Ocean, they range from northern Japan and central California to Australia and Chile. In the Atlantic Ocean, they range from at least as far north as Georges Bank (off Massachusetts) and the British Isles to Tierra del Fuego (in Argentina) and northern Namibia. [Source: NOAA]
There are a number of regional populations and groups. For example, Lance Garrison, research biologist with NOAA Fisheries, told NPR there are four near-shore populations of dolphins from New York to North Carolina. There is 1) an estuarine North Carolina population that also moves north into Virginia, 2) a southern migratory group off the coast of Virginia and 3) a northern migratory group from Delaware to New York. In addition, there is 4) a genetically distinct, offshore population. The northern group begin migrating to the coast of North Carolina coast in October. The southern group, which also begins migrating in October, moves as far south as northern Florida. [Source: Scott Neuman, NPR, August 17, 2013]
Bottlenose Dolphin Species
Bottlenose dolphins are diverse genetically and morphologically, and in terms of life histories based on habitat. Their taxonomy is still a matter of debate. They belong to the family Delphinidae (oceanic dolphins) and there are currently includes at least three species. Common bottlenose dolphins (Tursiops truncatus) are the most well-known and widely distributed species. They are found in offshore waters and are generally found in pods of up to about 30 individuals. What is written in this article applies mostly to common bottlenose dolphins. [Source: Nikki Groce, Animal Diversity Web (ADW) /=]
Two species occupy the western North Pacific — Indo-Pacific bottlenose dolphins (Tursiops aduncus) and common bottlenose dolphins. Common bottlenose dolphins and the subspecies Lahille's Bottlenose Dolphin (Tursiops truncatus gephyreus) are found in the western South Atlantic.
Pacific Bottlenosed Dolphin (Tursiops gillii) is found in the eastern North Pacific and is frequently seen off the coast of Southern California. Adults are bluish-gray or purplish-gray on the dorsal side, and white on the belly to the anus. The flukes, flippers, and dorsal fin are blackish. The dolphin's head and snout are dark, with a relatively short, but well-defined beak, approximately 7.6 centimeters (3 inches) long.
Indo-Pacific bottlenose dolphins are found in inshore waters in pods comprised of 2 to 15 individuals. They are socially and behaviorally similar to common bottlenose dolphins and occasionally form pods with common bottlenose dolphins and less often with Indo-Pacific humpback dolphins. They have been observed, in the wild and in captivity, playing by chasing and splashing each other and some have linked this behavior with learning. Indo-Pacific bottlenose dolphins are usually less social and more shy than common bottlenose dolphins. They are less frequently observed at the surface and make less frequent leaps from the water. Indo-Pacific bottlenose dolphins are hunted by at least 10 species of sharks, including bull sharks, great white sharks, tiger sharks, sixgill sharks, sevengill sharks, dusky sharks, oceanic whitetip sharks, mako sharks, Pacific sleeper sharks and Greenland sharks.
Common Bottlenose Dolphins
Common bottlenose dolphins(Scientific name: Tursiops truncatus) weigh 136 to 450 kilograms (300 to 1,400 pounds) and are 1.8 to 4 meters (6 to 13 feet) in length. Their lifespan is 40 to 60 years. They are found throughout the world in both offshore and coastal waters, including harbors, bays, gulfs, and estuaries of temperate and tropical waters (estuaries are the areas where rivers meet the sea). [Source: NOAA]
Common bottlenose dolphins are one of the most studied and well-known marine mammals in the wild. In addition, they are easy to view in the wild because they live close to shore and are distributed throughout coastal and estuarine waters. But this puts dolphins at increased risk of human-related injuries and death. They are a highly intelligent species and use sound both for communication and to hunt for food.
Common bottlenose dolphins are generally gray in color. They can range from light gray to almost black on top near their dorsal fin and light gray to almost white, sometimes with a slight pink hue, on their belly. Bottlenose dolphins living in nearshore coastal waters are often smaller and lighter in color than those living offshore.
Common bottlenose dolphins are found everywhere except polar waters. They generally stay fairly close to the surface. Deep water one come up to take breaths every one to two minutes, whereas inshore ones take breaths two times per minute. They have been known, however, to dive deep enough to go 4.5 minutes without taking a breath. Common bottlenose dolphins are found in bays, estuaries, sounds, open shorelines and large, estuarine rivers as well as in nearshore coastal waters, deeper waters over the continental shelf, and even far offshore in the open ocean. They occupy waters with surface temperatures between 10º and 32 ºC (50º and 90ºF) Some such as populations along the Atlantic coast migrate seasonally. [Source: Jessica Jenkins, Animal Diversity Web (ADW)]
Indo-Pacific Bottlenose Dolphins
Indo-Pacific bottlenose dolphins (Scientific name: Tursiops aduncus) are regarded as a distinct species — different from common bottlenose dolphins. All Tursiops species were initially included in the species common bottlenose dolphins. It is now recognized that there are at least three species. First identified in 1883 by Christian Ehrenberg, Indo-Pacific bottlenose dolphins are differentiated from common bottlenose dolphins by genetic and morphological differences. Some have suggested that Indo-Pacific bottlenose dolphins are more closely related to Stenella (spinner dolphins) and Delphinus species (common dolphins) than to common bottlenose dolphins. Research on this topic is ongoing. [Source: Kelly Diaz, Animal Diversity Web (ADW) /=]
Indo-Pacific bottlenose dolphins are found in the Indian, South Pacific, and western and southern North Pacific oceans. They tend to live in shallow water near the shore at depths of less than 300 meters. Some live in estuaries. Others can be found in coral reefs. Where they reside at a particular time often depends on seasonal and tidal conditions, water temperature and prey distribution.
Indo-Pacific bottlenose dolphins are similar to common bottlenose dolphins Their coloration is similar though Indo-Pacific bottlenose dolphins have ventral spotting that may be a sign of reproductive maturity, especially in females. Adult Indo-Pacific bottlenose dolphins are between 1.75 and four meters (5.7 and 13 feet) and weigh around 230 kilograms (500 pounds). Their pectoral fin in about 23 centimeters long and the tail fluke was 60 centimeters wide.
There are a number of physical differences between common bottlenose dolphins and Indo-Pacific bottlenose dolphins. Indo-Pacific bottlenose dolphins can be distinguished from Common bottlenose dolphins by a longer, better-defined rostrum, a smaller melon, and, in some cases, more teeth. Indo-Pacific bottlenose dolphins also have a smaller body, a smaller head, and larger flippers than Common bottlenose dolphins. They have a more slender rostrum that is tapered more abruptly near the base and taller and broader-based dorsal fins relative to other bottlenose dolphins. However, these differences are variable, which can make it difficult to distinguish them in areas of overlap. [Source: Kelly Diaz, Animal Diversity Web (ADW) /=]
Bottlenose Dolphin Characteristics
Bottlenose dolphins have a fusiform (spindle-like) body shape, with flippers, dorsal fin, and beak. Even though they are mammals their body lacks many external characteristics of terrestrial mammals, including hair, external ears and hind limbs. A fusiform body reduces turbulence and allows bottlenose dolphins to cruise underwater at high speeds. The dorsal fin is tall, curved and set near the middle of the back. Some sexual dimorphism (differences between males and females) exists (See sizes below).
Bottlenose dolphins are homeothermic (warm-blooded, having a relatively uniform body temperature maintained nearly independent of the environmental temperature) and endothermic (use their metabolism to generate heat and regulate body temperature independent of the temperatures around them). They have insulation, in the form of blubber. Their relatively small surface area for a large animal sizes and vascular shunts — that allow selective cooling of certain organs and tissues — help them thermoregulate. Bottlenose dolphins have a thermoneutral zone of 13º to 28ºC (55º to 82ºF), If the temperature of their environment drops below or rises above this zone, their metabolic rate increases. [Source: Nikki Groce, Animal Diversity Web (ADW) /=]
Males are larger than females., weighing on average of 253 kilograms (560 pounds) compared to the female average of 210 kilograms (463 pounds). Offshore populations tend to have a smaller body lengths, which average of about 3.1 meters, compared to coastal populations, which have average body lengths of about 3.25 meters. Male common bottlenose dolphins range in weight from 260 to 500 kilograms (573 to 1,100 pounds), with their average weight being around 400 kilograms (88 pounds), and range in length from 2.3 to 3.8 meters (7.5 to 12.5 feet). Females are typically between 2.3 and 3.7 meters (7.5 to 12.1 feet), and weigh about 250 kilograms (550 pounds). [Source: Jessica Jenkins, Animal Diversity Web (ADW) /=]
All bottlenose dolphins have a “melon”, the rounded structure within their forehead, for echolocation (emitting sound waves and sensing their reflections to determine the location of objects). They have an average of 98 teeth. As is true of all modern dolphins and whales, the skulls of bottlenose dolphins are telescoped — the rostra are elongated and tapered towards the front and the nostrils are moved to the top. This allows dolphins to breathe more easily during swimming. Rostrum (snout) length is longer in offshore populations than in coastal populations.
Common bottlenose dolphins have a pale-grey mark that cuts through a darker grey dorsal area towards the bottom of the dorsal fin. Indo-Pacific bottlenose dolphins do have this mark but may have dark spots on the rear bottom half of the body. Other differences in external appearance between the species include rostrum (snout) length, body size, ratios of rostrum length to body length and snout-to-eye length.
Bottlenose Dolphin Behavior
Bottlenose dolphins are motile (move around as opposed to being stationary), nomadic (move from place to place, generally within a well-defined range), sedentary (remain in the same area), migratory (make seasonal movements between regions, such as between breeding and wintering grounds), social (associates with others of its species; forms social groups) and have dominance hierarchies (ranking systems or pecking orders among members of a long-term social group, where dominance status affects access to resources or mates). The average territory size of common bottlenose dolphin is 125 square kilometers. Density estimates range from 0.06 to 1.22 dolphins per square kilometer. [Source: Nikki Groce, Jessica Jenkins, Animal Diversity Web (ADW) /=]
Bottlenose dolphins and are both diurnal (active during the daytime) and nocturnal (active at night). They are very active animals that can swim up to speeds of 30 kilometers per hour (19 miles per hour) although on average they swim between three and six kilometers per hour (two and four miles per hour). They spend their time feeding, traveling, socializing, and idling and about three quarters of their time underwater or diving, and about a quarter of the time spent at the surface. Some populations are migratory while others reside in one area. Still others are nomadic
Bottlenose dolphins may travel alone or in groups, and the groups continually break apart and reform. Their travel is characterized by persistent movement in a consistent direction. When they are resting, it may appear that they are traveling. Resting is often characterized by tight group formations, slow movement, and intervals of methodical breathing. [Source: NOAA]
Bottlenose dolphins are very intelligent animals. In captivity this intelligence is demonstrated by their ability to solve problems in experimental trials as well as during their everyday lives. Their cognitive skills are also reflected by the speed and effectiveness by which they acquire and perfect behaviors. Bottlenose dolphins sometimes engage in aggressive behavior including biting, ramming, and tail slaps. Bonding and acceptance behaviors include stroking and rubbing.
The graph to the right shows: "Examples of instantaneous heart rate (ifH) responses from individual dolphins against time before (time –20 to 0) and up to 40 s (time 0 to 40 s) during a breath-hold. (A) ifH for a LONG and SHORT dive (each preceded by a symbol with a pre-determined dive duration), and a dive without a symbol (NS), where dive duration was determined by the dolphin. (B) ifH variation during a breath-hold for 3 NS dives in dolphin D3 (Table 1). The dive durations, the time from the last breath before and first breath after a breath-hold is indicated in parenthesis."
Bottlenose Dolphin Group Behavior
Bottlenose dolphins are social animals. They typically live in groups of two to 30 individuals, although groups may exceed 1,000 or even 10,000 individuals. Females in a group tend to be related or share long histories. There are three types of groups that typically form: 1) nursery groups (mothers and calves); 2) adolescent, or juvenile, groups (young dolphins of both genders up to their mid teens); and 3) solitary or pair-bonded adult males. and 3) Pair bonds of males may last for more than 20 years. [Source: Nikki Groce, Jessica Jenkins, Animal Diversity Web (ADW) /=]
Both wild and captive bottlenose dolphins establish dominance hierarchies in both sexes. Large adult males dominate all others, while the largest females dominate smaller males and females. These hierarchies are maintained through aggressive behaviors that include contact and posturing. Captive dolphin groups are characterized by a dominance hierarchy based on age, size and gender with large adult males having dominant over other group members. In the absence of males, the largest female becomes dominant. /=\
Bottlenose dolphins participate in fission-fusion societies in which subgroups frequently join or leave the main group. They use breeding, playing, aggression, and gentle body contact (such as rubbing) as ways to have social interactions with one another. Calves maintain what is called “baby position” while swimming. The mom surfaces first, and the calf surfaces slightly after and behind its mother. [Source: NOAA]
Behaviorly, Indo-Pacific bottlenose dolphins often live in pods with a social hierarchy where the largest dolphin is usually the most dominant. According to Animal Diversity Web: In the wild there are also same sex groups, especially in subadult groups, that later join larger pods. They exhibit site fidelity and have well-established home ranges. Most males and females remain in their natal home range until maturity. In the Pacific, home ranges tend to be found around an island. Home ranges can be up to 85 square kilometers, however the range depends on gender and may change seasonally. Density estimates are reported to range from 0.06 to 4.80 per square kilometers. [Source: Kelly Diaz, Animal Diversity Web (ADW) /=]
Bottlenose Dolphin Senses and Communication
Bottlenose dolphins sense using vision, touch, sound, echolocation (emitting sound waves and sensing their reflections to determine the location of objects) and chemicals usually detected by smell and communicate with sound and mimicry.[Source: Nikki Groce, Animal Diversity Web (ADW) /=]
Bottlenose dolphins produce three types of sounds: 1) whistles, 2) echolocation clicks, and burst-pulse sounds (also called click-trains). Whistles are used to communicate identity, location, and/or emotional state. Each individual has a signature whistle, which develops a feww months after birth and is retained throughout an individual’s life. Male calves have whistles that are similar to those of their mothers’ This is not true with female calves. Kin recognize one another by their whistles and these sounds help maintain group cohesion. Bottlenose dolphins may mimic the whistle of others as a precursor to social interaction. These dolphins have the ability to vocally label objects.
Clicks, or pulses, are predominately used for echolocation. However, some burst pulse sounds are used for communication. The peak frequencies for these sounds are about 40-130 kHz. Each click lasts only about a fraction of a millisecond and is repeated as often as 600 times each second. The energy from the sound is reflected back to the source allowing the dolphin to surmise its surroundings. Echolocation is used to perceive surroundings and find prey. It is even sometimes used to stun prey. The phonic lips, enlarged folds of tissue associated with the nasal sacs, are the structures that produce the clicks and whistles. The sounds are then focused by the melon (the fatty, rounded organ their forehead) to create directional beams of sound. For incoming sounds intramandibular fat bodies focus sound to each ear.
Bottlenose Dolphin Feeding and Hunting
Bottlenose dolphins typically choose prey between five and 30 centimeters in length. They eat between 4.5 and 16 kilograms per day, depending on the size of the individual and if it is lactating. They feed on wide variety of fish, squid, crustaceans (such as, crabs and shrimp) and other ocean life, and can thrive in many environments, feed on a variety of prey, use different techniques to pursue and capture prey. They searching for food individually or cooperatively. Instead of using their teeth to chew, dolphins grip fish with their teeth, then swallow the fish whole — head first — so the spines of the fish don't catch in their throats. Their sharp teeth allow them to grasp prey while the tongue maneuvers prey down the throat. Dolphins teeth are not used to chew. They may break up their prey by shaking it in the air and striking it with their tails — a process called fish-whacking. Bottlenose dolphins use passive listening and/or high frequency echolocation to locate prey. . When prey is detected, these dolphins either rush in or alert others of the prey’s presence.[Source: NOAA]
Bottlenose dolphins prefer drums, croaker fish, mackerels, tuna and mullets. Their diet varies in accordance with local prey availability. Along the central Atlantic coast of the U.S. both fish and invertebrates are consumed. The four most commonly consumed fish for that area are weakfish (gray sea trout), Atlantic croaker. Spot and silver perch. Along the southeastern U.S. coast, fish and cephalopods such as squid are consumed. The most consumed species in this area are silver perch, croaker, sand seatrout, mullet, spot and squid species such as Atlantic brief squid.Bottlenose dolphins off the coast of South Africa eat fish including African scad, olive grunt, red pandora, chub mackerel and cephalopod species such as common cuttlefish and squid from the Loligo genus. In the eastern tropical Pacific, inshore dolphin species tend to feed on fish and invertebrates, while offshore one species feed on open ocean fish and squid. Off the coast of Peru, they feed on sardines, anchovies, and hake as well as squids. [Source: Nikki Groce, Animal Diversity Web]
Bottlenose dolphins feed in many ways and employ a number of interesting hunting techniques. Cooperative hunting often involves herding schools of prey fish into bait balls. A group may work together to bring fish together into groups and then take turns charging through the schools to feed. They may also trap schools of fish against sand bars and seawalls for an easy dinner. Sometimes they stranding themselves on shore in order to feed on prey they purposely stranded ("strand feeding"). [Source: NOAA, Jessica Jenkins, Animal Diversity Web (ADW) /=]
Most of the time, bottlenose dolphins feed individually. Among the common individual feeding methods are chasing prey to the surface before capture, hitting fish with their tail flukes, pushing prey on to the shore, and distracting fish with tail movements or by leaping. They are not shy about taking advantage of human activities and doing things like feeding behind shrimp trawls and collecting discarded fish or stealing fish from fishing gear. They have been observed driving the fish towards fishermen who reward the dolphins with a share of their catch. In some cases dolphins use echolocation calls to stun their prey. In Australia may mount a sponge on their rostrum to protect their snouts as they forage on the bottom.
According to Animal Diversity Web (ADW): Indo-Pacific bottlenose dolphins have a diet consisting of mainly bony fish and, to a lesser degree, cephalopods. While they eat a wide variety of fish species, the majority of their diet is composed of just a few species, which varies regionally. In captivity these dolphins eat six to seven kilograms of food per day. They hunt cooperatively and foraging behavior is characterized by shallow dives multiple times per minute. In shallow water they hunt by using several methods, including “kicking” fish into the sand with their tails and chasing small fish up on to the shore. While feeding and traveling they leap from the water regularly. Hunting and feeding occur most frequently in the morning and afternoon. [Source: Kelly Diaz, Animal Diversity Web (ADW)]
Bottlenose Dolphin Mating and Reproduction
Bottlenose dolphins generally begin to reproduce when they are between 5 and 15 years old, with the exact age varying by population. Female bottlenose dolphins can reach sexual maturity before males. Sexual maturity is usually achieved years before reproduction. Males often reach sexual maturity at age 10 but breed until they are at approximately 20 years old. Females can reproduce well into their late forties.
Bottlenose dolphins are viviparous, meaning they give birth to live young that developed in the body of the mother, and engage in seasonal breeding. Reproductive seasons vary from region to region. Typically, females ovulate at a particular time of year while males are active throughout the year (but with a peak of testosterone production when females ovulate).
Breeding of bottlenose dolphin off the U.S. typically takes place from September to January, peaking from October to December. Most calves are weaned by age four, with ranges from 2.7 to 8.0 years depending on the mother’s gestational status. Most calves are weaned half way through the mother’s next pregnancy. The average time between births for a female is about four years. Females employ polyestrous cycling and spontaneous ovulation. The gestation period is around 12 months. Females become sexually mature between seven and 12 years of age. Males reach sexual maturity between about 12 and 15 years.
Bottlenose dolphins are polygynous (males having more than one female as a mate at one time). Males will either go after females individually or form alliances with other males to herd and compete for females to reproduce with. Males in alliances work together to separate a female in estrus from her groups. They then compete with each other to mate with her, often flanking her to prevent other males from approaching her. An individual male will attempt to mate with a female in estrous when she enters his home range. /=\
Waiting for a female to become receptive can take several weeks. Some males do not engage in alliances. Instead they remain in their home ranges. According to Animal Diversity Web: When an estrous female enters the home range of such a male, he attempts to attract her to mate. During courtship, a male postures by arching his back. He strokes and nuzzles the female, and he may clap his jaws or yelp. Bottlenose dolphin copulation typically occurs belly-to-belly with both animals facing the same direction, although an animal facing the opposite direction is not uncommon. Intromission lasts only around 10 seconds and involves vigorous pelvis thrusts. [Source: Jessica Jenkins, Animal Diversity Web (ADW) /=]
Bottlenose Dolphin Offspring and Parenting
For bottlenose dolphins, gestation lasts about 12 months and a female gives birth to one calf. Calves can be born at any time of the year but tend to be born during warmer months. Females nurse their young from nipples on each side of their genital slit until the calf is between 18 and 20 months.
Young are precocial. This means they are relatively well-developed when born. Parental care is provided by females. During the pre-birth, pre-weaning and pre-independence stages provisioning and protecting are done by females. The post-independence period is characterized by the association of offspring with their mothers. Bottlenose dolphins are cooperative breeders, which means helpers provide assistance in raising young that are not their own.[Source: Nikki Groce, Animal Diversity Web (ADW) /=]
Bottlenose dolphins are typically 84 centimeters to 1.4 meters (2.7 to 4.6 feet) at birth, and typically weigh between 14 and 20 kilograms (30 and 44 pounds). Once calves are born, they generally stay with their mothers for 3 to 6 years. On average, females give birth every 3 to 6 years. [Source: NOAA]
Lactation lasts for at least 18-months but may last almost twice that. Females protect their young from predators, sometimes enlisting help of other females in their group. In the first few days following birth, offspring learn to swim alongside their mother, often by flanking or staying against the mother. The mothers patiently assist their young and even after this period calves often stay very close to their mothers
According to Animal Diversity Web: Lactating females require 88 to 153 cal/ kilograms as opposed to non-lactating females that typically require 34 to 67 cal/ kilograms. Bottlenose dolphins participate in allomaternal care, that is, all of the females within a group help care for each others' offspring. When a bottlenose dolphin calf is born, it learns to ride the pressure waves alongside its mother during its first few days. The mother assists the calf to keep it alongside her body. Females also protect calves from predators. [Source: Jessica Jenkins, Animal Diversity Web (ADW) /=]
Indo-Pacific Bottlenose Dolphin Mating and Young
Female Indo-Pacific bottlenose dolphins breed every 4 to six years. The breeding season typically ranges from September to January. However, breeding may occur throughout the year. The average number of offspring is one and the average gestation period is 12 months. The average weaning age is 3½ years and the average time to independence is four years. Females reach sexual maturity at seven to 12 years. Males reach sexual maturity at nine to 13 years. Female reproductive success depends on the depth of the water; shallow water allows for easier detection of predators and reduced predation overall by sharks.[Source: Kelly Diaz, Animal Diversity Web (ADW)]
Indo-Pacific bottlenose dolphins are one of the few mammal species in which males cooperate with other males to allow for easier mating with females. Males form alliances with one to three other potentially unrelated, males. These male groups herd females for mating, sometimes called “mate guarding.” Single males may also attempt to guard females for mating. Breeding females also form groups. Smaller female groups are easier to defend, whereas larger groups of females are difficult to defend. Male and female dolphins tend to mate with more than one partner. Copulation usually occurs when the dolphins are positioned belly to belly in the same direction. /=\
Adult female Indo-Pacific bottlenose dolphins invest a great deal of time and attention in their calves. Even after weaning, calves stay with their mothers for another one to three years. At birth, Indo-Pacific bottlenose dolphins are between 0.8 and 1.1 meters (2.6 and 3.6 feet) in length and between nine and 21 kilograms (20 and 46 pounds). Young are born tail first and are able to swim immediately. The highest rates of births are from October to December. The mean weaning age is 3.5 years. However, a study in Australia found a weaning age ranging from 2.7 to eight years. Adult females, in a sample population off the coast of Mikura Island, Japan, give birth once every three to 4 years. /=\
Threats to Bottlenose Dolphins
Bottlenose dolphins for the most part are not regarded as endangered or threatened although some populations and subspecies may be. They are listed as “Not Evaluated” on the International Union for Conservation of Nature (IUCN) Red List and are protected in the United States under the Marine Mammal Protection Act (MMPA). The Convention on International Trade in Endangered Species (CITES) places them in Appendix II, which lists species not necessarily threatened with extinction now but may become so unless trade is closely controlled:
In all, 61 stocks of common bottlenose dolphins have been identified in U.S. waters. Population trends for many of the U.S. stocks are unknown. Five stocks along the Atlantic Coast are considered depleted under the Marine Mammal Protection Act (MMPA) and 46 stocks along the Atlantic Coast and Gulf of Mexico are considered strategic The depleted stocks in U.S. waters are: 1) the Western North Atlantic Central Florida Coastal stock; 2) the Western North Atlantic Northern Florida Coastal stock; 3) the Western North Atlantic Northern Migratory Coastal stock,; 4) the Western North Atlantic South Carolina-Georgia Coastal stock and the Western North Atlantic Southern Migratory Coastal stock . [Source: NOAA]
Bottlenose dolphins are vulnerable to many stressors and threats including disease, biotoxin, pollution, habitat alteration, vessel collisions, human feeding of and activities causing harassment, interactions with commercial and recreational fishing, energy exploration and oil spills, and other types of human disturbance (such as underwater noise).
Interactions with Fishing Gear: One of the main threats to bottlenose dolphins is getting caught in fishing gear. Dolphins can become entangled or captured in commercial fishing gear such as gillnets, seines, trawls, trap pots, and longlines. In addition to interactions with commercial fisheries, dolphins may also encounter rod-and-reel gear used by recreational anglers or for-hire fishing vessels (such as charter boats and headboats). This problem is increasing, especially in the southeast United States and is largely the result of dolphins taking the bait and the catch directly from fishing gear, eating discarded fish, or being fed fish (illegally) by humans causing them to associate anglers with food. These interactions can cause dolphins to be injured or killed by entanglement in or ingestion of the gear. In addition, fishermen sometimes become frustrated when dolphins take their catch, and can retaliate with violence towards dolphins.
Habitat Destruction and Degradation: Common bottlenose dolphins living near shore are also susceptible to habitat destruction and degradation by contaminants and oil spills. For example, dolphins living in areas with high levels of PCBs were shown to have impacts to their immune systems. Dolphins in areas affected by the 2010 Deepwater Horizon oil spill were found to have compromised immune systems and decreased reproductive success (PDF, 685 pages). In addition to chemical contamination, physical habitat degradation due to shoreline development and increased boat traffic is also of concern.
Biotoxins: Several common bottlenose dolphin die-offs have occurred in recent years, linked to harmful algal blooms such as red tide. Several HABs (or several HAB-related die-offs) have been confirmed along the coast of Florida and others were suspected elsewhere in the Gulf of Mexico. Dolphins can be exposed to HAB toxins through the air or by eating contaminated prey. Biotoxin exposure can lead to both acute and more chronic health issues for dolphins. Extremely high concentrations of chlorinated hydrocarbon residues have been found in tissues of bottlenose dolphin species. Concentrations of polychlorinated biphenyls and dieldrin have also been measured in their blubber. Calves may inherit affects of their mother’s contaminants or received them directly through milk. These contaminants can lead to impaired testosterone production in males and reproductive infertility.
Illegal Harassment and Feeding Activities: Bottlenose dolphins are easy to view in the wild, but this also puts them at increased risk of human-related injuries and death. Feeding and attempting to feed dolphins is harmful and illegal because it changes their natural behaviors and reduces their wariness of people and vessels. They learn to associate humans with an easy meal and change their natural hunting practices by begging for handouts and taking bait/catch directly off fishing gear. Dolphins also teach these unnatural and risky feeding strategies to their calves and other dolphins. Dolphins are then more vulnerable to vessel strikes and to fishing gear entanglements and ingestion. They also may fall victim to extreme retaliatory acts (such as shooting) by frustrated boaters and fishermen.
Dolphins may also be disturbed or harassed by the presence of humans and watercraft. Harassment is illegal and occurs when any act of pursuit, torment, or annoyance has the potential to injure the animal or disrupt its s behaviors. Any human-caused change to a dolphin’s behavior may constitute disturbance or harassment. Certain critical survival behaviors are particularly vulnerable, and disturbance may lead to injuries or death. Long-term negative impacts include compromised health, reduced reproductive success, and displacement from, or avoidance of, important habitats.
Image Sources: Wikimedia Commons, NOAA
Text Sources: Animal Diversity Web (ADW) animaldiversity.org; National Oceanic and Atmospheric Administration (NOAA) noaa.gov; Wikipedia, National Geographic, Live Science, BBC, Smithsonian, New York Times, Washington Post, Los Angeles Times, The New Yorker, Reuters, Associated Press, Lonely Planet Guides and various books and other publications.
Last Updated June 2023