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Anatomy
Rostrum: the beak area of the dolphin
Did you know? Bottlenose dolphins are mammals, meaning just like humans and all other mammals they have hair,
except they only have hair for just a few days after birth before they loose it and this hair is found on the rostrum!
Melon: The bulbous portion of the dolphins head
Did you know? The melon is full of complex fat used to focus and send out sound, also known as echolocation!
Blowhole Open
Blowhole Closed
Blowhole: The blowhole is equivalent to the human nose; this is how the dolphins breathe. First they expel the old air, or
“blow” it out and than suck in new air before they close the blowhole to dive back down again. But their “nose” is located
on their back!
Did you know? A way to tell the difference between a dolphin and a whale is the number of blowholes they have! Where
whales have two, dolphins only have one.
Dorsal Fin: the main fin located on the back or “dorsal” side of the dolphin.
Did you know? The dorsal fin is unique to each individual dolphin! It is equivalent to the human finger print and dolphin
researchers use it for identification to distinguish different individuals from one another.
Peduncle: the area behind the dorsal fin to the flukes.
Did you know? The peduncle is where the dolphin generates all its power and is the reason why bottlenose dolphins
can swim
up to 30 miles per hour!
Fluke: The “tail” of the dolphin
Did you know? The fluke has no muscle in it at all! It actually works as a thermal window to “dump” heat when the
dolphin becomes over heated!
Anus: the rectal opening of the dolphin
Did you know? Dolphin poop is usually green!
Urogenital Opening: where male or female genitalia are found.
Did you know? Male reproductive organs are actually found inside the body so researchers can’t necessarily tell if the
dolphin is male or female by just taking a quick look!
Mammary Slits: just above the urogenital opening where mothers nurse their calves, and researchers collect milk
samples from.
Did you know? This is where calves nurse from and gain all of the essential nutrients necessary for them to survive
through the beginning stages of their lives! Also just because a dolphin has mammary slits doesn’t necessarily mean that
it is female. Scientists have found an odd male with mammary slits too!
Umbilicus: the “belly button” of the dolphin
Did you know? The umbilical cord is short and stretched taut right when the forehead of the young dolphin protrudes
from the mothers genital opening, which prevents the calf from drowning in its mothers own amniotic fluid before being
fully expelled from her body.
Flippers: the side appendages of the dolphin
Did you know? The fins of the dolphin are actually used for steering and not for swimming! Also it is possible to use the
bones in the fins to help determine age, but usually dolphins are aged by looking at their teeth.
Can you tell the difference? Which is male and which is female?
(See 2 pictures)
To tell the difference between a male and a female bottlenose dolphin is actually not as easy as one might think!
The male and female reproductive organs are actually located inside the urogenital opening. Usually if the dolphin has
mammary slits it is a female; however, there have been a few cases where males have mammary slits as well! You can
be sure by determining the distance between the umbilicus, genital opening and the anus. If the umbilicus, genital
opening and anus are evenly spaced the dolphin is a male, if the genital opening is closer to the anus than the bottlenose
dolphin is a female.
Male Bottlenose Dolphin
Contaminants
A contaminant is anything that harms, poisons, or pollutes when
released into the environment. We often think of contaminants as
things specifically harmful to humans but, while this is certainly true,
contaminants can also pose a threat to any organism, whether it
lives in a marine, aquatic, or terrestrial environment.
Through a process called biomagnification, some contaminants
become progressively more concentrated in animals at successively
higher levels in a food chain, ultimately reaching the highest
concentrations in top predators. Contaminants are often stored in
fatty tissues and, as a result, may occur at especially high levels in
blubber-rich top predators such as the bottlenose dolphin.
Most contaminants fall into one or another of three broad categories:
chlorinated hydrocarbons; compounds containing heavy metal
atoms; and hydrocarbons derived from petroleum.
DDT
DDT, a key ingredient in some insecticides, is a chlorinated hydrocarbon that has
been present in the environment for more than 40 years. While DDT was—and in
some places still is—sprayed mostly on land, often far from water, it eventually
finds its way to the ocean via runoff and aerial dust. DDT in rain runoff reaches
streams, rivers and, ultimately, the ocean. DDT locked in aerial dust can
accumulate in rain clouds that release moisture and contaminants over land,
streams, rivers, or directly over the ocean.
Over time, DDT becomes concentrated in animals‟ fatty tissues. Alarmingly high
concentrations of DDT and other toxic contaminants have been found in bottlenose
dolphin populations and scientists are concerned that high levels of these toxins
may cause serious birth defects or could be responsible for the failure of some
individuals to reproduce.
Current research on the bottlenose dolphins in Sarasota Bay suggests that levels of
several toxic environmental contaminants are significantly lower in lactating females than in adult males in the same population.
One hypothesis to account for this is that lactating females are “offloading” stored contaminants to young calves through their milk.
If this proves to be the case, high calf mortality in Sarasota Bay may be an example of the far-reaching and harmful effects of
environmental contamination.
Distribution & Taxonomy
The bottlenose dolphin, Tursiops truncatus, is a mammal and, like humans and other mammals, is warm-blooded, gives birth to live
young, and nourishes its young with milk. Unlike most mammals, the bottlenose dolphin lives its entire life in the ocean. Bottlenose
dolphins are marine mammals, as are seals, sea lions, manatees, polar bears, and sea otters. These species spend most or all of
their lives in marine (ocean or sea) environments.
In terms of scientific classification, the bottlenose dolphin belongs to the group of mammals—the Cetaceans—that includes baleen
whales (the “great whales”) and toothed whales such as sperm whales, as well as narwhals, porpoises, and dolphins. The cetaceans
have been living an aquatic existence for more than 45 million years.
The bottlenose dolphin has a cosmopolitan distribution: it is found around the world in tropical and temperate ocean waters in both
inshore and offshore (pelagic) habitats. For many years, scientists believed there was only one species of bottlenose dolphin—the
one we are studying in Sarasota Bay, Tursiops truncatus. Recently, scientists discovered a great deal of variation among different
populations, leading to speculation that there may be anywhere from two or three or more different species of bottlenose dolphins.
At present, most scientists agree on the more conservative interpretation that there are at least two species: Tursiops truncatus,
the “original” species and the one we refer to today simply as the “bottlenose dolphin,” and a newly described species, Tursiops
aduncus, the Indian Ocean bottlenose dolphin, which has a coastal Indo-Pacific distribution that may extend as far south as
temperate waters off the east coast of Australia.
A Possible New Species: The Victorian Coastal Dolphin
The bottlenose dolphin of southern Australia‟s coastal waters, sometimes
called the Victorian coastal dolphin, is a possible candidate to be named a
distinct species. Animals in this population have distinct spots on their
undersides and their bodies are smaller and their beaks are shorter than
the two currently accepted species. This population also appears to be
geographically, and possibly reproductively, isolated from other
populations, meaning that there‟s a good chance it‟s on its way to
becoming a new species, if it isn‟t already. The Victorian coastal dolphins‟
mitochondrial DNA sequences also show significant divergences from
those of both T. truncatus and T. aduncus, adding further support to the
notion that it may be a unique species.
More Species Still?
Other purported bottlenose dolphin species have been suggested,
including Tursiops gilli, a name sometimes applied to dolphins found off
the coast of southern California and Baja California, and Tursiops
ponticus, the Black Sea bottlenose dolphin. However, scientists are unsure as to whether these two populations appear to be
genetically distinct and most specialists still believe these populations belong to either T. truncatus or T. aduncus. Nevertheless,
given the growing list of contenders for species status, scientists now believe that speciation in the bottlenose dolphin group is more
complex than originally thought.
Inshore v. Offshore
To add to the confusion, other studies have revealed differences in morphology, hemoglobin profiles, nuclear genetic markers, diet,
and parasite loads between inshore and offshore (pelagic) populations of the bottlenose dolphin, so they may be diverging rather
rapidly. For example, in the eastern northern Pacific, inshore types are larger than their offshore counterparts, while in the western
northern Atlantic it is the offshore population that is larger. It is far too early to tell yet, but it is possible that these two habitat
variants of the bottlenose dolphin may eventually diverge sufficiently to become different species.
Diving for Dinner
The study of the distributional ecology of a marine mammal is directly related to that of its food resources. Like all animals, marine
mammals must find and locate enough food to live and reproduce, and bottlenose dolphins have to track highly mobile and patchily
distributed food resources, such as schools of fish, to survive. To add another dimension, literally, to the matter, the prey of
bottlenose dolphins usually occurs deep in the water column, not at the sea surface, making it very difficult for scientists to
accurately determine exactly what they are eating.
Scientists are now using state-of-the-art technology, such as satellite-linked
time-depth recorders, to learn about the diving behavior and foraging ecology
of wild bottlenose dolphins. Recent research using these devices found that
offshore dolphins regularly dive below 500 meters (about 1,640 feet) and
sometimes to depths of 900 to 1000 meters (2,950 to 3,280 feet). Daytime
dives tend to be shorter and shallower than night dives, and most, about 55
percent, are within 50 meters (about 165 feet) of the surface.
Bottlenose dolphins are superbly adapted to handle the extreme pressures
they encounter at great depths. Scientists believe that beyond depths of 70
meters (230 feet), a dolphin's alveoli of the lungs and the respiratory
bronchioles collapse completely, preventing nitrogen from diffusing into the
blood. In this way, dolphins escape the effects of nitrogen narcosis, a
potentially lethal condition also know as “the bends” or decompression
sickness.
The heart rate of diving bottlenose dolphins also slow (called bradycardia) from a normal rate of about 100 beats per minute to
between 30 and 40 beats per minute. Cardiovascular changes associated with a slowed heart rate and constriction of peripheral
blood vessels substantially reduces blood flow, heat loss, and oxygen expenditure during a dive. As the dolphin surfaces at the end
of the dive, heart rate, blood vessel diameter, and blood flow increase, allowing the dolphin to quickly “dump” excess heat built up
during the dive, primarily through the flukes and dorsal fin, and quickly absorb the influx of oxygen when it breathes at the surface.
Bottlenose dolphins have a high volume of blood for their body size, giving them a relatively high number of blood cells, and
therefore more hemoglobin for oxygen storage and transport. During long dives, some tissues may become depleted of oxygen
stores and resort to anaerobic metabolism until the dolphin again reaches the surface to re-oxygenate.
Echolocation
Echolocation, an acoustic sensory mechanism, is perhaps the most important way small toothed whales, such as the bottlenose
dolphin, navigate and obtain information about the world around them. Echolocation may function better than vision in dark, murky
ocean waters.
In echolocation, sound produced in the bottlenose dolphin‟s nasal sacs is emitted
and focused through fatty connective tissue in the melon (the rounded region of a
dolphin's forehead). When the emitted sound waves strike an object, some bounce
back (or echo—hence the term echolocation) to the dolphin where they strike a fatfilled cavity in the lower jaw. This sound-wave energy is transferred mechanically
through the jaw to the inner ear, where it is converted to neural impulses that are
transmitted to the brain for processing.
Using echolocation, a bottlenose dolphin can tell how far away an object is, as well
as its density, size, and possibly even its shape. When a dolphin processes a
returning sound wave from an object, the mental image it constructs might be
similar to an x-ray, in which the object is registered as a shape containing elements
with different image densities. The strength and direction of the returning acoustic
signal help the dolphin determine where and how far away the object is, and
possibly even what it is. Early research on bottlenose dolphins suggested that dolphins might turn on echolocation after first
detecting sounds of prey, but we now know that dolphins are
actually using echolocation to scan the environment all the time!
Scientists have described two types of echolocation sounds: click
sequences and pure tone whistles. Click sequences are separated
into high-frequency “discrimination clicks” and low-frequency
“orientation clicks.” Low-frequency clicks are less precise and are
thought to give a more generalized profile of features in the
environment while high-frequency clicks provide fine resolution.
Pure tone whistles may have two functions, one having to do with
prey location and the other having a social function.
While foraging, bottlenose dolphins also occasionally produce
sudden, short, high-amplitude “pops.” These loud sounds
apparently have nothing to do with echolocation but appear to be
used to startle potential prey into revealing its location.
In the wild, bottlenose dolphins are confronted with many unnatural acoustic disturbances, including noise from motorized boats
and coastline construction. It is possible that the amplitude of these sounds could mask some of the echolocation sounds dolphins
use to navigate their environment and find food.
Feeding
Bottlenose dolphins eat a wide variety of small fish, squid, crabs, shrimp, and other small marine animals. The dolphins in Sarasota
Bay exhibit seasonal variation in foraging habitat preference. They feed more frequently in sea grass flats in the summer and in
deep water passes and coastal gulf waters in the winter.
Bottlenose dolphins use a variety of techniques to find and catch food. They usually actively hunt for prey, using echolocation, but
sometimes they just wait silently for an animal to make a sound that reveals its location, then suddenly strike at it. They also may
form coordinated hunting coalitions that launch group attacks on large schools of fish. Sometimes dolphins use powerful bursts of
sound to startle or stun prey. They also use their tails to strike the water
surface to stun fish, a behavior called “halking.”
In a technique called “kerplunking,” a dolphin whacks the top of the water
with its peduncle and fluke to produce an underwater cloud of air bubbles
that scares fish. A group of dolphins uses this technique to create an
impenetrable circle of bubbles in which prey becomes trapped. Some
dolphins place a sponge on their beaks while foraging along the sea
bottom. Others root around in sediment, hunting for buried prey, a
behavior called “crater feeding.” They also steal fish and bait from fishing
lines, boats, and nets.
Threats
The bottlenose dolphin is found around the world. The species is
relatively secure and not in imminent danger of extinction. However,
it, and all other marine mammals, faces anthropogenic threats to its
health and survival.
The greatest threat is undoubtedly habitat degradation, a worldwide
phenomenon affecting a plethora of marine species. As growing
numbers of people move to coastal areas, housing development and
commerce cause increased pollution, sewage outflow, and
sedimentation in marine waters. All of these factors threaten fragile
coastal ecosystems and the marine organisms living in them,
including the bottlenose dolphin.
There are more
subtle threats as well. Scientists think that boat traffic and other forms of acoustic
disturbance confuse communication within bottlenose dolphin groups. Marine debris
from trash thrown into the oceans, if swallowed, can lethally clog a dolphin‟s
digestive tract. Dolphins drown by becoming entangled in fishing gear abandoned
or lost by fishermen. In some parts of the world, fishermen kill dolphins for food or
because they are perceived as threats to their livelihoods. Despite the best of
intentions, tourists may also have a negative affect on wild bottlenose dolphins by
approaching groups too closely and disturbing resting or foraging animals.
But it‟s not all doom and gloom: You can do a lot to help protect bottlenose
dolphins and other marine species.
Get involved by volunteering with a research or conservation group in a coastal area or a dolphinarium.
Organize local beach clean-ups and practice green behavior such as picking up your trash at the end of a day at the beach.
Do not harass local wildlife: Watch from a distance and let animals behave naturally.
Teach others how they can help protect their favorite marine mammal, even if you don‟t live near the ocean.
By working together, we can make a difference to vulnerable marine species in need of help.
Nursing
Bottlenose dolphin calves rely entirely on their mothers’ milk to meet
their nutritional needs for at least the first six months of life. After that,
milk continues to be an important food source while calves are learning
to forage and gradually converting to a fish diet. However, the precise
age at which young dolphins stop being dependent on their mothers’
milk is not yet known.
When it is ready to nurse, a calf approaches its mother’s mammary slits
(see Anatomy) from behind and gently nudges the mammary area with
its rostrum. Scientists have seen mothers turn to the side to give their
calves easier access to the mammary slit. Because each nursing bout is
short and hard to observe underwater, scientists are still unsure how
milk is transferred from the mammary slit to a calf’s mouth.
One hypothesis is that a calf sucks milk from the nipple (located inside the mammary slit) after wrapping its tongue
around it, and another is that a mother squirts milk into the calf’s mouth through contractions of abdominal muscles.
But the truth of the matter is that we really don’t know exactly how any cetacean (whales and dolphins) nurses and we
have only a few clues.
Regardless of how cetaceans nurse, lactating mothers need a significant amount of extra energy to produce enough highquality milk to feed their growing calves. Lactating bottlenose dolphins require around twice as many calories per
kilogram of bodyweight as males and females that are neither pregnant nor lactating. Experimental studies of bottlenose
dolphins in dolphinaria showed that adult males and non-pregnant, non-lactating females consume two to four percent of
their body weight per day and about 2,000 kilograms (4,400 pounds) of fish per year. Food intake is about the same for
pregnant females throughout the gestation period but increases by 60 to 95 percent from early to late lactation.
Bottlenose dolphin calves are completely reliant on their mothers for all their nutritional needs in the first few months of
life. Milk continues to be an important food source while calves learn to forage and gradually convert their diets to fish.
Nursing bouts are numerous and short at the beginning of a calf’s life, but increase in duration and decrease in frequency
as the calf ages. When ready to nurse, the calf approaches the mother’s mammary slits from behind and gently nudges
the mammary area. In some bottlenose dolphin populations, moms have been observed turning to the side to give the calf
easier access to the nipple.
Scientists are still unsure of how the milk is transferred from the mammary slit to the
calf’s mouth. One hypothesis is that the calf may create a suctioning effect by wrapping
its tongue around the nipple. Another is that dolphin mothers may squirt milk into the
calf’s mouth by contracting her abdominal muscles.
But the truth of the matter is that we really don’t know exactly how any cetaceans nurse
and we have only a few clues. As seen in this picture, the tongue of the humpback whale
is large, strong and has “frills” around the edge. Could these structures be used to form a
grip around the nipple?
Regardless of how cetaceans nurse, it takes a great deal of energy for lactating mothers to
produce a sufficient quality and quantity of milk for their growing calves. Lactating
bottlenose dolphins obtain the energy and nutrients they need from their food and require around twice as many calories
per kilogram of bodyweight as bottlenose dolphins that are neither pregnant nor lactating.
Research Partners
Our research team has learned a great deal about bottlenose dolphins from this project, however; none of this
would have been possible without the aide of our research collaborators. Please click on the links below to
learn how each collaborator made our project possible.
Sarasota Dolphin Research Program
The Sarasota Dolphin Research Program is the longest running wild dolphin research program
in the world. Their research efforts involve a full time year round staff and aim to contribute to
a better understanding of cetaceans in Florida and elsewhere around the world.
Without a working relationship with our Sarasota Dolphin Research Program partners, this
project would not have been possible. The milk project conducted by our team is a small part
of a much larger and longer (37 years) dolphin research program in Sarasota. With their help
we were able to analyze wild dolphin milk samples from known individuals in Sarasota Bay
waters. They have obtained an unprecedented amount of knowledge including age, size,
lineage and reproductive history of each photographically identified dolphin. We would like to
express our sincerest gratitude to the world’s longest running dolphin research program for
their participation in this partnership.
To learn more about current research in Sarasota Bay and updates on the wild dolphin
population visit the Sarasota Dolphin Research Programs website at the link below:
http://www.sarasotadolphin.org
Dolphin Quest
Dolphin Quest opened in 1988 and is an international organization committed to public
education and conservation of marine wildlife. Their state of the art husbandry practices
provides a unique opportunity for research efforts on dolphins.
Without the cooperation from our partners at the Dolphin Quest Hawaii and Bermuda facilities
this project would not have been possible. Our team’s milk project is just one example of the
type of research opportunities Dolphin Quest facilities provide to scientists. With their help we
were able to analyze dolphin milk from the same individuals over time and determine what is
“normal” for lactating dolphins with healthy calves. These animals also provide us an
opportunity to conduct controlled experimental studies and validate our preliminary findings in
a way that is not possible with wild dolphins. The dedication of Dolphin Quest trainers and staff
to make research a priority at their facilities is much appreciated.
To learn more about Dolphin Quest facilities and current public education and marine wildlife
projects visit Dolphin Quest website at the link below:
http://www.dolphinquest.org
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O‟Shea, T.J., Brownell, R.L. Jr., Clark, D.R. Jr., Walker, W.A., Gay, M.L., Lamont, T.G. 1980 Organochlorine pollutants in small
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Wang, J.Y., Chou, L.S., White, B.N. 1999. Mitochondrial DNA analysis of sympatric morphotypes of bottlenose dolphins (genus:
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Wells, Randall., John E. Reynolds III., Samantha D. Eide. 2000. The Bottlenose Dolphin: Conservation and Biology. Gainesville:
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