Dolphin Information
Frequently Asked Question
What is an Atlantic
Bottlenose dolphin’s taxonomic classification?
What are the differences between
dolphins and porpoises?
How many different species of dolphins
are there?
What is the average lifespan of a dolphin?
Where do bottlenose dolphins live?
What do dolphins use their dorsal fin
for?
How do dolphins use their pectoral
fins?
How do dolphins use their flukes?
How many teeth do dolphins have?
Why do dolphins have teeth if they don’t
chew their fish?
What do dolphins eat?
How much do dolphins eat?
How do dolphins breathe?
Do dolphins sleep?
How can you distinguish between a male
and female dolphin?
Do dolphins have a sense of smell?
Do dolphins have good eyesight?
What is echolocation? How does
it work?
How well do dolphins hear?
How deep do dolphins dive?
When do dolphins reach sexual maturity?
How is a dolphin born?
What does a newborn calf look like?
How many calves does a female
typically have in her lifetime?
Do dolphins mate for life?
What are some common threats to
marine mammals?
What is an Atlantic Bottlenose
dolphin’s taxonomic classification?
Kingdom: Animalia (Animals)
Phylum: Chordata (Chordates)
Subphylum: Vertebrata (Vertebrates)
Class: Mamalia (Mammals)
Order: Cetacea (Cetaceans)
Suborder: Odonoceti (Odontocetes)
Family: Delphinidae (Marine Dolphins)
Genus: Tursiops
Species: truncatus
Atlantic bottlenose dolphins, or Tursiops truncatus, are cetaceans. The Order Cetacea is divided into two suborders, Odontoceti (toothed whales) and Mysticeti (baleen whales). Mysticetes do not have teeth but have triangular plates of baleen that extend from their upper jaw and are composed primarily of keratin, a type of protein that is also found in our hair and nails! They use their baleen plates to filter food from the water column. There are two, general feeding modes. Some of these whales are “gulpers”, which means they engulf large quantities of water into their huge mouths and strain the water out through the baleen, thus trapping their meal in the baleen fibers. Some are called “skimmers’, which means they cruise through the water column, with their mouths slightly open, trapping small, planktonic creatures as they move. Interestingly, the size, length, and diameter of the baleen fibers differ between species and relates to the type of prey they target. Mysticetes also have two nasal openings (blowholes) and include species such as the gray whale (Eschrichtius robustus), the Southern right whale (Eubalaena australis), and the bowhead whale (Balaena mysticetus). Odontocetes have a single nasal opening and anywhere from 2-250 teeth, though in some species the teeth of females do not emerge past the gumline. Odontocetes include approximately 70 species of whales, dolphins, and porpoises, including the Atlantic bottlenose dolphin, sperm whales (Physeter macrocephalus), narwhals (Monodon monoceros), belugas (Delphinapterus leucas), killer whales (Orcinus orca), and the Amazon River dolphin (Inia geoffrensis).
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What are the differences between
dolphins and porpoises?
There are several differences between dolphins and porpoises:
1) Dolphins have long, pronounced beaks (or rostra), and porpoises do not have a distinct beak.
2) Most of the vertebrae in a dolphin’s neck are separate units, which gives them the ability to turn their head. Some portion (2 – all 7) of a porpoise’s neck, or cervical, vertebrae are fused, which limits neck mobility.
3) Porpoises are generally smaller than dolphins.
4) Dolphins have cone-shaped teeth, while porpoises have spatulate, or spade-shaped, teeth.
5) Porpoises also have smaller and more triangular dorsal fins than dolphins, and one porpoise species has no dorsal fin (the finless porpoise - Neophocaena phocaenoides).
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How many different species of
dolphins are there?
The Family Delphinidae is the largest and most diverse group of odontocetes, with approximately 35 species and 17 genera. Many species are represented by large numbers of individuals, so the majority of oceanic cetaceans are represented by this group and include killer whales (Orcinus orca), Hector’s dolphins (Cephalorhynchus hectori), the short-finned pilot whale (Globicephala macrorhynchus), the Atlantic bottlenose dolphin, southern right whale dolphins (Lissodelphis peronii), and the Irrawaddy dolphin (Orcaella brevirostris).
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What is the average lifespan
of a dolphin?
The lifespan of bottlenose dolphins varies greatly between regions and populations. The average range is approximately 20-50 years, depending on the population.
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Where do bottlenose dolphins live?
Bottlenose dolphins are distributed all over the world in both temperate and tropical waters. They occupy a variety of habitats, including nearshore coastal areas (e.g. bays, lagoons, harbors, and river mouths) and deep, offshore waters. In some areas, dolphins exhibit high site fidelity (i.e. a limited home-range), and in others they are migratory. Two, distinct groups of bottlenose dolphins, called ecotypes, have been identified. Though they are not considered different species, they are characterized by their distribution (nearshore/coastal vs. offshore) and exhibit different physical and physiological characteristics. There is a second species of Tursiops that lives in the Indian Ocean, called Tursiops aduncus.
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What do dolphins use their dorsal
fin for?
A dolphin’s dorsal fin has two, main functions: stability and thermoregulation. The fin acts similarly to the keel of a sailboat, helping the dolphin swim through the water in a straight line.
The dorsal fin is also used to regulate body temperature. All marine mammals have fur and/or blubber to help them maintain a constant, internal body temperature (warm-blooded). Fur and blubber keeps them warm, but it’s a little like wearing a winter coat year-round. So, marine mammals need a way to cool off from time to time and have adapted to this by utilizing areas of their body that are thinly covered by hair and/or blubber as “thermal windows”. The dorsal fin is a thermal window, as it is primarily composed of cartilaginous tissue and lacks blubber. Thus, it allows dolphins to dump excess heat to their environment when their internal body temperature gets too high. There are large veins in the dorsal fin that lie close to the surface of the skin. Warm blood from the body is transported to these veins and is cooled by the ambient water.
Like a human fingerprint, there are no two dorsal fins that are exactly identical. Each has its own unique shape, height, thickness, and notches. Scientists utilize the appearance of dorsal fins to identify individuals in the wild. Many populations are extensively catalogued by dorsal fin photographs, which allow scientists to study specific groups of resident dolphins for many years.
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How do dolphins use their pectoral
fins?
The pectoral fins aid a dolphin in stopping, steering, and the coordination of fine movements.
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How do dolphins use their flukes?
Dolphins use their flukes for propulsion through the water. Fish move their tailfins laterally, from right to left (side-to-side), and dolphins move their flukes dorsoventrally, or up and down. Dolphins have extra space between their vertebrae, which creates a flexible vertebral column. Therefore, they are able to produce more powerful undulations by increasing the trajectory of their flukes. These movements are powered by a very strong muscle called the peduncle, which enables bottlenose dolphins to swim upwards of 20 mph! An important characteristic of dolphin propulsion is that they produce movement via both the up and down stroke of their flukes. Imagine a dog paddling through the water. The dog moves forward when its paws are moving toward the back of its body (called the “power phase”). When they reposition their paws back to the front of their body, they are not producing movement (called the “recovery phase”). Dolphins lack a recovery phase, which conserves energy and makes swimming much more efficient.
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How many teeth do dolphins have?
Atlantic bottlenose dolphins have 80-100 cone-shaped teeth. They possess only one set of teeth, which erupt as calves and are called “milk-teeth”. Therefore, if they lose or break a tooth, it will not be replaced by another. They are considered homodonts, which means they only have one type of tooth in their mouths. In comparison, humans are heterdonts, possessing 4 different types of teeth (incisors, canines, premolars, and molars).
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Why do dolphins have teeth if they
don’t chew their fish?
Dolphins do not chew their food but rather swallow their prey whole. This type of consumption eliminates the need for differentiated teeth to grind or tear food. They typically swallow large fish head first, so that they do not scratch their throat and esophagus with the fish’s scales and fins. They do need their teeth to catch their prey, and the cone-shape aids in firm grasping.
Dolphins also use their teeth socially, in a behavior called “raking”, in which they use their teeth to scratch each other. This behavior is typically used as a way to establish dominance, exhibit aggression, or to moderate behavior. Dolphins have a very thick outer (epidermal) skin layer. The surface of their epidermis is replaced up to once every 2 hours to promote a smooth hydrodynamic surface (decreases drag when swimming) and to prevent the colonization of fouling organisms on their skin.
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What do dolphins
eat?
At Dolphins Plus, the dolphins typically eat an assortment of herring, capelin, sardines, silversides, and smelt. Sometimes, we feed them live shrimp and live snapper. The dolphins also catch mangrove snapper and grunts in their houses and love to chase glass minnows and shrimp. In the wild, dolphins eat predominantly fish (piscivorous), but they also consume significant amounts of squid and crustaceans. However, diet varies by region, season, sex, age, and reproductive status. For example, Barros and Odell (1990) discovered 43 different types of prey in the stomachs of stranded bottlenose dolphins, but a few species were most abundant. Similarly resident bottlenose dolphins in Sarasota, Florida, exhibited a variety of prey in their stomach, but pinfish accounted for approximately 70% of their diet (Barros and Wells 1998).
Bottlenose dolphins employ an impressive repertoire of individual and group hunting techniques. This includes things like intentional beaching, where dolphins guide prey up onto muddy shorelines; fish whacking, where dolphins smack fish clear out of the air with their flukes, often into the mouths of their podmates!; the use of marine sponges as tools to forage for organisms living in the substrate; “kerplunking”, which involves the creation of a ring (or seine “net”) of bubbles around a school of fish by dolphins driving their flukes through the surface of the water repeatedly; and mud-ring feeding, which is similar to the above but involves the suspension of mud into the water column that presumably startles and corrals fish.
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How much do dolphins eat?
An average dolphin eats about 2-4% of their body weight each day. An adult male typically eats about 20 pounds of fish, while a nursing mother can eat upwards of 40 pounds of fish daily! Although it is not uncommon for bottlenose dolphin calves to nurse for up to 4 years, they usually begin to supplement their diet with fish at approximately 6 months of age. A dolphin’s caloric needs vary based on age, season, reproductive status, changes in water temperature, and activity level.
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How do dolphins breathe?
Dolphins breathe through a nasal opening on the top of their heads called a blowhole. When resting, their blowhole remains tightly shut, and in order to breathe, they must contract muscles surrounding this nasal passage. Breathing in all mammals involves both a voluntary and involuntary process. For example, we as humans can intentionally hold our breath while diving to the bottom of a pool. However, if you were to lose consciousness, involuntary mechanisms would take over, and your body would continue breathing.
In cetaceans, although there may be an involuntary characteristic to their breathing that relates to reflexes stimulated by surfacing and submerging (i.e. water passing over their blowhole), their respiration is predominantly voluntary in nature. Thus, many scientists believe dolphins must think about every time they want to take a breath. This may seem like a huge burden, but remember dolphins breathe air yet live in an aquatic medium. So, there is already a deliberate physical requirement, involving coordinated body movements, needed to get to the surface of the water to take a breath.
Bottlenose dolphins are able to hold their breath for an average of a few minutes and a maximum of about 10 minutes. Dolphins are efficient breathers. They are able to exchange 80% of the air in their lungs with each breath, while humans are only capable of exchanging 17%. They also have greater blood volume vs. body size than terrestrial mammals, which means they have more blood in their bodies, which in turn carries more oxygen. Marine mammals also have a greater capacity for oxygen storage in their lungs, blood (e.g. increased hemoglobin and hematocrit), and muscles (increased myoglobin). All of this creates a more efficient use of the oxygen in their bodies and is what allows many species to dive for extended periods of time.
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Do dolphins sleep?
Due to the voluntary nature of breathing in dolphins, they cannot sleep the same way terrestrial mammals sleep. One theory on sleeping in dolphins is that they alternately rest each hemisphere of their brain for short intervals throughout the course of the day. Dolphins have cross-ocular connections like humans do, so they may close one eye when resting the opposing side of their brain. Therefore, half of their brain remains alert, enabling them to surface when they need to breathe and constantly be aware of predators.
In general, it’s believed that dolphins require less sleep than terrestrial mammals. Large marine mammals have low field metabolic rates (the rates of metabolism associated with normal, daily activity) that converge with basal, or resting, metabolic rates with an increase in size. This means that the larger they are, the less energy they spend going about their daily lives. Thus, some scientists believe low levels of activity in large marine mammals are equivalent to rest or sleep in terrestrial mammals. So, in theory, dolphins may not need to sleep the way, or amount that we do, because they are achieving sufficient rest by limiting movements and by the virtue of comparatively lower metabolic rates.
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How can you distinguish between
a male and female dolphin?
Even though male and female genitalia are internal, it’s fairly easy to discriminate one from the other. On the underside of their peduncle, males have two, separate slits, or grooves. One is called the genital groove and the other the anal groove. They lie in line with each other such that the grooves of a male resemble an exclamation point. Females have one anogenital slit or groove and a mammary slit on either side, which produce milk when they are reproductively mature. Therefore, a female’s underside resembles a division sign.
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Do dolphins have a sense of smell?
Dolphins lack olfactory receptors (the olfactory tract and bulb only exist in the fetal stage of development) and therefore, do not have a sense of smell.
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Do dolphins have good eyesight?
Dolphins have excellent vision both above and below the water. They are able to see in both environments, because they can control the way light enters their eye via a specialized, horizontal, crescent-shaped pupil. In humans, light enters our eyes and is bent first at the surface of the eye (i.e. the cornea) and again as it passes through the lens. This two-step bending of light, and the possession of an adjustable, comparatively flattened lens, works to focus light beams on the retina, which then forms an image. Dolphins have large, non-adjustable, spherical lenses with high refractive power, which compensates for the lack of refraction at the cornea-water interface. In contrast to air, water and the cornea have similar refractive indices, which means light doesn’t bend when transitioning between the two. Therefore, when viewing an object underwater, light does not bend as it enters a dolphin’s eye, but they compensate for this with a static, rounded lens (i.e. it has more light-bending ability). So, when a dolphin is above water, they reacquire the corneal light bending properties, and there is an over-refraction or bending of light that enters the eye (loss of a focused image). So, it’s hypothesized that, when viewing an object above water, dolphins close the central part of their pupil completely. Thus, light coming in only through the periphery of their crescent-shaped lens would need the additional refractive, or light-bending, strength of the air-cornea interface in order to create an image on the retina.
Since their eyes are on the sides of their head, dolphins (and most small, toothed whales) have both monoscopic and stereoscopic vision. Seeing monoscopically means a dolphin is able to independently process two different images at the same time. Dolphins are also able to see stereoscopically, focusing both eyes downward toward their stomach (most in focus about 3-5 feet away). Dolphins see 173 degrees to each side from the tip of their rostrum to the tip of their tail. They have three known blind spots – directly above them, directly in front of them, and directly behind them.
There is no evidence for color discrimination in dolphins. Though they posses cones in their eyes, which are the structures known to translate colors to the brain, they only have what are called green cones. Animals require at least 2 types of cones (humans and many terrestrial mammals have 3 types – blue, green, and red) to discriminate color. So, the possession of only a single type of cone suggests functional color blindness in dolphins.
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What is echolocation? How
does it work?
Echolocation works similarly to an ultrasound. It gives a dolphin the capacity to explore their environment 3-dimensionally and aids in navigation and hunting in low light and low visibility environments. The emit sounds, or clicks, from their nasal passages, which are then passed through their melon (forehead). The melon is filled with fatty tissue and fluid and acts like an acoustic lens to focus the sounds in different directions. The sound waves then bounce off of objects of interest and are received by the dolphin’s lower jaw as an echo. This information is then passed to the brain via the inner ear. Echolocation is very efficient. Bottlenose dolphins are capable of distinguishing an object the size of a ping-pong ball from a football field away.
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How well do dolphins hear?
Dolphins hear about 7.5 times better than we do. As a matter of fact, odontocetes in general can hear at a wider range of frequencies than any other mammals, covering both low frequency communication signals and high frequency echolocation signals. Dolphins’ hearing range is between 0.2 – 150 kHz, with peak sensitivity falling between 8 - 90 kHz. A human’s hearing range is between 0.2 – 17 kHz, with peak sensitivity falling between 0.5 – 4 kHz. Thus, humans are incapable of hearing a large range of sounds both produced and heard by dolphins.
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How deep do dolphins dive?
An average dive for a bottlenose dolphin can be anywhere
from 10ft to 150ft.
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When do dolphins reach sexual
maturity?
The age at sexual maturity varies greatly in bottlenose dolphins between regions and populations. Sexual maturity is usually a function of size, not age. A female typically reaches sexual maturity when she has attained 85-95% of her mean adult body length. This ranges from 7-12 years, depending on the population. Males attain sexual maturity later than females, typically occurring between 10-15 years. This phenomenon of sexes achieving reproductive maturity at different times is called “bimaturism”.
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How is a dolphin born?
Dolphins are mammals and therefore, give birth to live young. The gestation period for bottlenose dolphins is approximately 12 months, and calves are usually born tail first. The birth process can take anywhere from 30 minutes to 3 hours.
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What does a newborn dolphin calf
look like?
At birth, a bottlenose dolphin calf is about 3 – 4 feet long and weighs 30 – 40 pounds. They are born with their dorsal fin flat on their back, and their tail flukes curled. The dorsal fin is usually standing erect by about 24-48 hours after birth, though it may remain wobbly for many years. Their flukes also flatten out within 24-48 hours. A newborn calf is generally dark in color with light stripes called fetal folds.
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How many calves does a female
typically have in her lifetime?
For all marine mammals, the normal number of offspring at birth is 1, which is believed to reflect the immense amount of care invested in a single offspring. It’s unlikely that a mother would be able to offer the care necessary to survive to multiple neonates at the same time.
Females begin to reproduce successfully at about 7-12 years of age, and males tend to mature even later. Due to a high investment in maternal care, the average interbirth interval in bottlenose dolphins is about 4-5 years. There is no clear evidence of reproductive senescence (“old-age”) in dolphins, with female dolphins successfully reproducing into their late forties. Therefore, it would be possible for a dolphin to give birth to 11+ calves in their lifetime, though not all births in the wild are successful.
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Do dolphins mate for life?
Dolphins are not monogamous animals and do not typically mate for life. Atlantic bottlenose dolphins live in what are called fission-fusion societies, where pods are constantly changing size and members. Some believe bonds between males are the strongest and most enduring in bottlenose dolphin societies. Females, on the other hand, tend to maintain weak-to-moderate bonds with other females that are more complex and less stable over time.
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What are some common threats to marine mammals?
Unfortunately, one of the characteristics marine mammals share is that most are, or have been, exploited by humans. Whales, sea otters, sea cows, and seals have been historically overexploited, which has resulted in the extinction of some species (e.g. Stellar sea cow, Caribbean monk seal, and the Atlantic gray whale) and the endangered status of many. Though there are laws that protect marine mammals, not all countries abide by these laws. So, the direct harvesting of whales, seals, walruses, dugongs, and dolphins still occurs today in various places throughout the world.
Another threat to marine mammals is entanglement in fishing gear and nets. Many marine mammal species are accidentally caught in nets used by fishermen. This is called “bycatch”, which is the non-target portion of the catch. Bycatch includes not only marine mammals but other species of fish, invertebrates, reptiles, and even birds and is a very wasteful practice. Passive, or discarded, gear and trash can also cause a significant amount of marine mammal mortality each year. Lost and discarded nets wreak havoc on marine organisms as they drift for many miles and sometimes many years. When a marine mammal gets entangled in a net, they often lose the ability to swim to the surface to breath and then drown.
Marine pollution you can’t see, specifically toxins, can cause serious health issues in marine mammals. Chemicals such as PCBs, organochlorides, pesticides, and heavy metals are related to reduced immune function (i.e. the ability to ward off infections and disease), an increase in the mortality of newborns (also called “neonates”), sterility, fewer births, birth defects, skeletal abnormalities, various types of cancer, and neurological dysfunction.
Oil spills suffocate marine environments and cause serious issues for many marine organisms. Marine birds and marine mammals tend to suffer heavily from exposure to oil, because they lose their ability to float and insulate themselves when their feathers/fur become soaked with oil. The long-term effects on marine mammals from oil spills are associated with the ingestion of the oil and the inhalation of hydrocarbon vapors. The Exonn Valdez spill in Alaska in 1989, resulted in the death of approximately 250,000 seabirds, sea lions, 2800 sea otters, 300 harbour seals, 22 killer whales, and billions of fish. The recent BP oil spill is said to be the equivalent of 13 Exxon Valdez spills as of July 2010.
Other threats to marine mammals include sound pollution (interferes with communication, breeding, diving, migrating, and feeding), collision with vessels (particularly manatees but also occurs between dolphins and whales and large ships), river regulation devices (causes drowning of manatees and river dolphins), habitat destruction, and climate change (e.g. global warming and the loss of polar bear habitat and prey).
References:
Barros NB and Odell DK. 1990. Food habits of bottlenose dolphins in the southeastern United States. In: The bottlenose Dolphins (S Leatherwood and RR Reeves, eds), Academic Press, San Diego. pp. 309-328
Barros NB and Wells R. 1998. Prey and feeding patterns of resident bottlenose dolphins (Tursiops truncatus) in Sarasota Bay, Florida. Journal of Mammalogy 79: 1045-1059
Hoelzel AR (ed) et al. 2002. Marine Mammal Biology: An Evolutionary Approach. Blackwell Publishing, Oxford. 432 pp.
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