In 1999, the classification of the Shark Bay dolphins was changed from bottlenose dolphins (Tursiops truncatus) to Indian Ocean or Indo-Pacific bottlenose dolphins (Tursiops aduncus). Today, the taxonomic status of the Shark Bay dolphins remains unclear because they have haplotypes that are typical of both T. aduncus and T. truncatus species. Some features of T. aduncus are actually closer to features of another genus, Stenella (spotted and spinner dolphins). Sophisticated genetic methods are being used to revise the taxonomic status of several cetacean species.
There are five superfamilies of toothed whales. Three superfamilies are referred to as “dolphins” –two superfamilies of river dolphins (Platanistoidea and “incertae sedis”) which include four families and species (Susu, India river dolphin or the Ganges susu [Platanista gangetica]; La Plata dolphin [Pontoporia blainvillei]; Boto or Amazon River Dolphin [Inia geofirensis]; and Baiji or Chinese river dolphin [Lipotes vexillifer]).
In the superfamily Delphinoidea, there are three families (Delphinidae, Monodontidae, and Phocoenidae), but only Delphinidae are commonly called “dolphins.” Delphindiae includes 36 species. The largest dolphin is the killer whale (Orcinus orca). Most scientists use the word “dolphin” to refer to one of the 36 species of delphinids.
Porpoises are in the Phocoenidae family; they are closely related to delphinids and are in the same superfamily, Delphinoidea. Porpoises are smaller than delphinids (dolphins), have no beaks, and the teeth are spade-shaped, whereas dolphin teeth are conical-shaped. In addition, porpoises breed faster than dolphins but they do not live as long. The size of the brain, relative to body size is smaller in porpoises than it is in dolphins.
Bottlenose, Irawaddy, Spotted, Spinner, Indo-pacific humpback, Southern right whale dolphin, Rough-toothed, Risso’s, Common, Dusky dolphin, Hourglass, Killer whale, False killer whale, Long-finned pilot whale, Short-finned pilot whale and Melon-headed whale.
Mainly spotted and spinner dolphins. Because yellowfin tuna associate with these dolphin species, fisherman encircle the dolphins with purse-seine nets in order to capture the tuna below. Problems arise when either the dolphins get entangled in the nets and drown or if calves get separated from their mothers.
Tursiops truncatus can reach 3-4 metres in length. The Monkey Mia dolphins tend to average about 2 metres, or around 6 and a half feet. Males and females grow to the same size.
On average, they weigh 200kgs (440lbs.), with a maximum of one extraordinary weighing in at 650kgs (1430lbs.) The Monkey Mia dolphins probably weigh much less – around 100kgs.
Wild bottlenose dolphins can live at least into their late forties. Dolphins can be aged by counting the rings inside their teeth, and new genetic methods of aging are also being developed. Puck was approximately 42 years old when she died.
In the wild, mothers nurse their calves for at least three years, but nursing up until the age of ten has been reported. She always weans her calf before the birth of her next calf. Thus, the calving interval is a minimum of three years if the calf survives. If the calf dies, the mother stops lactating, begins cycling again and may get pregnant in less than a 4-year interval. Dolphins virtually never have twins. One female called “Lick” who occasionally visits the beach, nursed from her mother for 8-9 years. Lick had her first calf, Lolly, in 1998, when Lick was about 14 years old.
Beneath each of the female’s two mammary slits are teats. The calf places his/her beak, slightly ajar, into the slit, and forms a “cone” with its tongue, which latches onto the teat. “Let-down” or milk-ejection, is under voluntary control of the mother. This way, none of the milk is lost into the water. During the first few weeks of infant life, the mother may aid the infant in nursing by lying on her side, presenting the mammaries to her calf. Later, the infant often angles on his/her side to nurse. The mother often slows down her travel speed or may hang at the surface during nursing. You can see nursing from the jetty but females rarely nurse their young very close to shore.
Dolphin milk is extremely rich and fatty compared to human milk or cow’s milk. Mothers nurse their young about four times per hour during the first week of life, and gradually reduce nursing frequency thereafter. Since it is difficult to identify nursing among wild dolphins, data on nursing frequency comes from captive studies of dolphins. During a nursing bout, the calf suckles for several seconds.
Not necessarily. Although juvenile and adult females appear to be very interested in young calves, they do not assist in the birth and may or may not escort the calf while the mother forages. When the mother forages the calf is often alone, foraging as well or following the mother.
Newborns can swim and breathe right from birth, but may need some assistance from the mother. The mother sometimes pushes her infant to the surface. Mothers and infants synchronize their breathing during the first few weeks of life. Newborns are a bit uncoordinated for the first few days of life, and seem to pop up to the surface like a cork. By the end of two weeks, infants are fairly coordinated and can begin taking deeper dives.
Tursiops truncatus weigh up to 30kg and measure between 0.7-1.2 metres at birth. Monkey Mia dolphins probably weigh much less and are less than one meter at birth.
Dolphins can reach seven times their birth weight in the first year, though Shark Bay dolphins continue to keep growing until age 15 or so.
Dolphins are mammals. They are warm-blooded, suckle their young, and breathe air.
Like most mammals, newborn dolphin teeth are still embedded in the gums. The teeth will start erupting in the first 5 weeks of life. Dolphins can be aged by the rings in their teeth.
Bottlenose dolphins have 40-50 teeth per upper and lower jaw, that is 80-100 teeth in total. Dolphins have only one set of teeth to last a lifetime. Older animals have worn teeth towards the front of the beak. Dolphins use their teeth to grip their prey, not to chew. They also occasionally rake each other with their teeth during fights.
Calves are born tail first. The mother does not eat or seem interested in the placenta, which she expels some time after birth. Birth can take a couple of hours. Calves are born during the Spring/Summer months. At Monkey Mia, births peak in October and November.
By about 4-5 months of age, calves can catch and consume small fish. They often catch tiny garfish using a technique that we call “snacking” where the calf rapidly swims belly-up just under the water surface and traps tiny fish between the surface and air. You can often see calves snacking just off the Monkey Mia beach. Occasionally seagulls or terns dive down and steal the dolphin’s fish.
They can see quite well in and out of water. It is thought that their eyesight is comparable to human eyesight.
Yes. The ears are visible only as tiny holes on the side of the head.
Dolphins use their sonar for hunting and navigating. During echolocation a dolphin produces a rapid train of clicks which are produced just beneath the blowhole and are emitted through the fatty melon (forehead). The sound bounces off objects and these echoes are picked up by the lower jaw where they are conducted to the inner ear by a pathway of fat. The echoes are then processed by the dolphin’s brain to determine the shape, density, distance, speed and direction of the object. Dolphin echolocation clicks can be emitted at a rate of several hundred per second. When dolphins close in on a fish, they increase the click rate to produce a very precise picture of the fish. Human-made sonar devices, such as those used to locate submarines, work on the same principal, but are not as sophisticated as dolphin sonar/echolocation.
The Monkey Mia dolphins develop speckles on the belly at 8-12 years, approximately at “puberty” and a little before reaching full sexual maturity. They get speckles around the genital area first, then on the belly and finally on the sides and even up around the eyes. Very old animals, like Holeyfin were heavily speckled. Nicky and Puck are moderately speckled. Calves have no speckles at all.
Dolphins are also fond of squid and cuttlefish and will occasionally eat rays. On two occasions, the researchers saw an old male eat a small shark! They probably also eat prawns as bottlenose dolphins elsewhere in Australia are known to do.
Dolphins swallow fish whole, head first. This way, the dolphin may avoid injury from the fin or tail spines of the fish. They do not use their teeth to chew. If they have a large fish, they may use their beak to break the fish upon the bottom of the seafloor. When they do this, they often do not consume the head of the fish.
To catch prey the dolphins need to be fast! They can attain speeds of up to 40kph. Typically, they travel less than 5kph.
Offshore bottlenose dolphins (Tursiops truncatus) can reach depths of almost 1000 metres. However, most of Shark Bay is quite shallow. Thus the dolphins at Monkey Mia typically don’t dive much deeper than 12-15 metres. The deepest dives recorded by a cetacean are by Cuvier's beaked whale at over 3000 metres.
They can stay submerged for periods of up to 20 minutes. However, they typically stay down for 2-3 minutes between deep dives. The longest recorded dive for the Shark Bay dolphins is 7 minutes.
Dolphins sleep by shutting down half their brain at a time. This semi-conscious state is necessary because breathing is under voluntary control. For this reason, dolphins cannot be anesthetized. They would stop breathing. During sleep, dolphins frequently close one eye and spend a lot of time ‘hanging’ or ‘floating’ at the surface. Dolphins spend approximately one-third of the day sleeping. They may sleep for several minutes, or for over two hours at a time. Scientists currently debate whether dolphins experience rapid-eye-movement (REM) or dream sleep.
Dolphins are sexually active all year round but have a peak breeding season in the spring/summer.
No. Dolphins are not monogamous. A female may mate with several males during her estrus (when she is ovulating). Males compete aggressively for access to sexually receptive females. Alliances of 2-3 or more males cooperate to keep a cycling female with them.
The genitals are internal, but there are some external differences. On the lower ventral (belly) side of the dolphin, near the tail stock is a genital slit. Both sexes have a genital slit, but the female also has two mammary slits, one on each side of the genital slit. Also, males frequently have erections, whereas females do not. We can also frequently identify the sex of an individual by sequencing their DNA obtained from a small skin sample.
Occasionally, large numbers of dolphins are stranded on beaches where they die from over-exposure to the sun and the weight of their internal organs on land. Scientists debate about the causes of stranding in dolphins and whales. Some think that internal parasites may affect their sense of direction or brain functioning. Others suggest that they follow a sick ‘leader’ onto the beach, or that they get confused amongst sand bars or mud banks. It’s thought that some dolphins and whales use magnetic fields to guide their migrations. Common stranding areas might be where such magnetic fields are disrupted. Bottlenose dolphins rarely strand. Since bottlenose dolphins are coastal, they are familiar with shallow coastal waters and they do not migrate. Mass strandings tend to occur among species with highly stable groups, such as pilot whales and false killer whales.
No, this is a myth. Sharks do prey on dolphins, especially calves. Dolphins probably can outmaneuver sharks if they detect them. The dolphin’s beak/rostrum is also a very powerful weapon, and some scientists have suggested that dolphins can kill a shark by ramming it in the belly. The major predator of the Monkey Mia dolphins is the tiger shark. However, hammerhead sharks and dusky sharks are also common to the area.
A party or a group. Dolphin parties range from 2-50 animals, although a party size of 4-5 animals is most typical. Bottlenose dolphins live in what is called a fission-fusion society. This means that party membership changes frequently. Individual dolphins join and leave different parties constantly, although they clearly have preferred associates. Party membership may remain stable for a few minutes, or for several weeks. This complex social system demands that dolphins ‘know’ where others are, so they can join, or avoid particular individuals. Bottlenose dolphin parties are not called “pods” because “pods” are considered to be consistent or stable. For example, killer whales have stable pods, and members of that pod are typically found together.
Dolphins generally do not migrate. Dolphins clearly have a home range, but they may travel over 70km per day. The researchers see the Monkey Mia dolphins generally within a 130 square km range of their study area. Currently, the researchers are trying to determine whether dolphins have community boundaries that are “closed” or “open”. That is, do members of different dolphin communities mix freely or are there definite community boundaries? They usually spend most of their day in a small area. Offspring of both sexes seem to remain in the area of their mothers, and daughters spend more time with their mothers after weaning than sons.
No. There is no leader, but there may be subtle dominance relationships among dolphins. It is unclear how strict or stable these dominance relationships are. There is no strict “pecking order” as one might see among baboons or hyenas. In addition, dolphins, especially male dolphins, do form alliances. These male alliances may compete with each other for access to females.
This depends on how you define language. Dolphins do have a very complex communication system. Scientists are still trying to work out what the variety of whistles, clicks, squawks, squeals, barks, and other sounds mean. A significant portion of the dolphin’s extraordinarily large brain is devoted to acoustic processing, which suggests that communication is an extremely important feature of dolphin life.
At other bottlenose dolphin research sites it has been shown that each individual dolphin develops a distinctive “signature whistle” during the first year of life. This whistle remains stable over time. The apparent function of this whistle is similar to a name. The dolphins use these whistles to announce or identify themselves to others. This is obviously very important in the aquatic environment, where visibility is limited and dolphins join and leave each other frequently. Furthermore, sound travels five times faster in water than in air, making sound a very efficient means of communication. Many dolphin sounds are produced well out of the range that humans can hear.