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Humans have been breeding Atlantic bottlenose dolphins in
human care for decades. The knowledge gained from this
activity has been invaluable for scientists around the
world. Understanding the reproductive
and maternity cycles of dolphins and whales not
only broadens our knowledge base, but also provides essential
information when dealing with stranded juvenile cetaceans
as well as the potential re-population of endangered
species.
Breeding in Human Care
During the mid 1980s, peers within the marine
mammal care industry instituted a voluntary
agreement to refrain from taking any more Atlantic
bottlenose dolphins from the wild. Part of the reasoning
behind such an agreement was due to how well Atlantic
bottlenose dolphins breed in human care.
Dolphin Research Center has been trying to breed dolphins
since its foundation. Because not all of the dolphins
at DRC are breeding
dolphins (due to age & health), we must
be very careful about genetic ties. Some marine mammal
facilities participate in loaning programs to facilitate
genetic diversity within their breeding programs. DRC
does not partake in this activity, as we presently have
no need. We have a diverse enough breeding population.
(We would also miss them if they left—they are
our family!)
Gender Differences
Dolphins have no secondary
sex characteristics. The only way to determine a dolphin’s
gender in the wild is to see a clear view of their
genitals, or to observe an erection, act of intercourse,
or a baby swimming close to an adult presumed to be
a female.
Males have two slits that look similar to an exclamation
point. The long anterior slit houses the genitals, while
the smaller posterior slit houses the anus. Two small
pores are present on either side of the genital-anal
slit, which have been considered possible vestigial nipples.
Females have one continuous
slit which houses both the anal and genital openings,
the anus located towards the posterior. Females also
have a set of slits housing the mammary glands. These
slits flank either side of the genital slit. Occasionally
females will have extra false sets of mammary slits.
These extra slits are generally non-functional and
could be a hold over from the dolphin’s
terrestrial ancestor.
Amorous Activities
There is no actual mating season for dolphins. They
mate 365 days a year. Ninety percent of their mating
activity, however, is foreplay. Intercourse only takes
seconds. Males become sexually mature between 8 to 12
years of age. Females become sexually mature a little
sooner at around 5 to 10 years of age (Wells 1999).
Much of the amorous activity
between dolphins includes chasing each other around
and raking each other with their teeth. Dolphins have
a tendency to get lazy looking eyes and lie on their
sides, sinking like a log, when they feel amorous.
This seems to be the height of erotic behavior for
a dolphin. The more dominant dolphin is usually found
beneath the more passive, which is playing the “floating log”.
Dolphins are indiscriminately amorous. They have sex
with the opposite gender, the same gender, and engage
in masturbation with inanimate objects. Female dolphins
have been observed suctioning things (like plates) to
their genital region when they feel amorous. They also
seem to enjoy buzzing on each others' slits using echolocation
(Samuels 1989).
What are the possible reasons for this type of behavior
as it is not just procreational? It is believed that
dolphins may engage in this type of behavior to learn
about sex as well as to maintain strong social bonds
for many sorts of cooperative activities (Nguyen 1999).
Male Reproductive Tract
Dolphins must maintain a
streamlined body to move efficiently through the ocean.
Therefore, male dolphins have their penis and testicles
packed inside their body. On mammals, testicles are
usually found outside the body since sperm dies at
body temperature. Dolphins compensate for the extra
heat that their testicles must endure by utilizing
a special feature of their circulatory system. A network
of blood vessels goes from the testicles to the dorsal
fin and flukes, drawing heat away from the sperm/testicles,
returning with cooled blood which then surrounds the
testicles and keeps them below the dolphin’s core
body temperature ( Harrison 1948). This same network
of blood vessels surrounds a female dolphin’s uterus,
also keeping the fetus below the dolphin’s core
body temperature.
Male dolphins are also designed
to have quick erections. They do not require stimulus
(foreplay) to become erect, unlike humans. Ejaculation
seems to be under voluntary control. In fact, some
of DRC’s dolphins have been
trained to ejaculate on signal. Mating must occur quickly
in the wild, so this is advantageous to a male dolphin.
Imagine if you were in the middle of mating and a bull
shark appeared. You would certainly want to be able to
finish spreading your genes and get out of the area in
a hurry!
Female Reproductive Tract
Female dolphins have a bicornate uterus, meaning they
have two internal reproductive horns that each act as
uteri ( Harrison 1969). It is thought to be a possible
evolutionary link to their land ancestors. Their uterine
system is similar to a horse or cow.
Each female dolphin tends
to use either the right or left ovary. There is some
indication that they switch the ovary/uterus they are
using later in life. Female dolphins are thought to
be “spontaneous” ovulators
and don’t necessarily have a set cycle. The cervix
itself is also unique. It has annular folds (or pseudocervix)
seen in only cetaceans and manatees. There is also a
mucous plug between the folds and actual cervix. Depositing
and storing sperm here protects it from the salt water,
which would kill sperm instantaneously (Robeck 1948).
The fold of the pseudocervix
contains some muscle bundles and appears capable of
some movement. Perhaps the retraction of the penis
triggers muscular contractions of the pseudocervix,
thereby shutting out lethal seawater and assisting in
the sperm’s movement through the mucous plug to
the true cervix (Boyd 1999).
Seasonality
Presently, DRC has had a
birth in each month of the year. There do seem to be
peaks, however, in the spring and in the fall. How
can we tell if a female is ovulating? By tracking when
a calf was born and figuring approximately a year earlier,
we can estimate when the female ovulated. We are still
unsure when or how often females ovulate. This seems
to be a highly individualized process. Through blood
sampling we have seen that some females have ovulated
six times a year and others once a year, and some even
skip a year. DRC can also detect follicular growth on
the ovary by using an ultrasound machine on female dolphins.
Females can ovulate without males around, but male company
seems to sometimes stimulate a female’s ovulation
cycle.
Pregnancy
Recent research indicates that bottlenose dolphin pregnancy
lasts about 12 months (Wells 1987). During this time,
there is very little room in the uterus for a baby to
develop. As a result, and to make birth easier, the tail
fluke and dorsal are cartilaginous and are folded over
in the uterus. The organs are also located beneath the
developing baby, which could be the reason for a female
gaining more girth during pregnancy and not developing
a bulge (Cockroft 1990).
Mothers double their intake of food following the birth
of their babies. Intervals between calves vary from about
three to five years.
Social Groupings
We take blood tests and urine
samples to analyze hormone levels. High progesterone
levels can indicate if a female is pregnant. If a dolphin’s progesterone levels
indicate a possible pregnancy we then perform an ultrasound.
An ultrasound allows us to “see” into the
dolphin’s belly, confirm a pregnancy and estimate
how far along the mother is in the process.
This knowledge gives us the opportunity to place the
mom in a good birthing situation. When a female has been
confirmed to be pregnant, we ensure that she is in a
positive birthing environment, which includes a protected
lagoon and compatible female pool mates that have some
birthing experience. Males are not present during or
after a birth at Dolphin Research Center, as they can
present a danger to a small calf.
Groupings of females with calves occur naturally in
the wild. The groupings are called maternity pods (Wells
1999). DRC tries to emulate these natural formations.
It is important to have other females available to a
mother dolphin. Female dolphins have been seen assisting
in birth, and more consistently as baby-sitters or aunties
helping to rear young dolphins. One of the best ways
a female dolphin can learn how to care for a calf is
to be around a baby and other more experienced females.
Once a calf is born, DRC continues to watch the relationship
between the females. We also conduct observational studies
to learn more about the entire maternity process.
Adult male dolphins generally
do not appear around females unless mating. Male dolphins
tend to congregate in groups of two or three and sometimes
form what is known as a “pair bond”. Pair
bonded males will stay together for an extended period,
if not all of their lives. Male dolphins play no role
in raising their young. In fact, male dolphins have
been known to be a threat to baby dolphins (Wells 1999).
Adolescent dolphins also congregate in separate groupings
called juvenile pods. This will occur once a calf is
old enough to leave its mother (Wells 1999).
Mothering Style
Each female dolphin seems to have a unique
mothering style. Some mothers are very
protective parents, while others seem more relaxed
with letting their calves explore. These variations
have also been observed in the wild.
Babies
Babies are usually born tail first, weigh 25-40lbs,
and are generally three to four feet long (Wells 1999).
We can get an approximate idea of how old a baby is by
looking at the dorsal fin. It is thought that the dorsal
fin stiffens within a few hours. The tail flukes seem
to take a bit longer.
A baby dolphin swims in a
position next to its mother called the echelon position.
The baby swims in this position to catch mom’s
slipstream, allowing the calf to work less hard in
order to keep up with its mother.
When babies are born they
have lighter colored bands spanning their mid section.
These are called fetal bands and are caused from being
scrunched up in the mother’s
womb. These bands will slough off after multiple weeks.
Newborn dolphins are very
dark in color. It is possible that this dark shading
is used for camouflage as the baby travels in the mother’s
shadow. This coloration also sloughs off after multiple
weeks.
When we assess the health
of a newborn, we look for good body weight and good
breathing. Another way we can get a good indication
of the baby’s health is from
the mother’s behavior. If she is relaxed and comfortable,
it is a good sign. If a baby is not healthy, a mother
will usually display frantic and erratic behavior.
When babies are new to the
world, they have to get used to their bodies not only
swimming, but also breathing. They have to get comfortable
with their blowhole’s
location. As a result, babies do something called chin
slap breathing, which involves lifting their heads farther
out of the water than necessary to breathe.
Echolocation is an ability that babies learn how to
use over time. For this reason babies end up with a few
cuts and scrapes within the first weeks of life.
Due to the need to look out
for a clumsy calf, you sometimes see mothers “steering” their calves
away from what might be considered a danger. Merina had
a lot of steering to do within her daughter Pandora’s
first very active days of life. Pandora was quite spirited
and would often try and race in front of her mother.
We often saw Merina physically pick Pandora up with her
rostrum and place her in another part of the pool.
Nursing
Babies nurse an average of about every twenty minutes
or more for 24 hours a day. In the first few weeks of
life this can happen in more frequent intervals. They
nurse, on average, a minimum of two years, but have been
observed nursing up to four and a half years (Wells 1999).
Calves have many fringes
along the edges of their tongue, believed to be an
aid in nursing. Calves apparently roll their tongue
and clasp the fringes together in order to form a watertight
funnel for the milk to flow through. Mothers take the
active role in nursing by squirting the milk into the
baby’s mouth. The milk is very
high in fat and contains colostrum. Colostrum provides
antibodies that help protect the calf against infection
during those critical first months of life.
Watching the maternity aspect
of a dolphin’s
life is an amazing experience. The knowledge that we
can gain by studying this facet of cetacean life can
provide valuable insights into the life of a dolphin.
References:
Boyd, I., Lockyear, and Marsh. “Reproduction
in Marine Mammals.”218-286. In J. E. Reynolds III
and S. A Rommel, eds, Biology of Marine Mammals. Washington,
DC: Smithsonian Institution Press, 1999.
Cockroft and Ross. Observations on the Early Development
of a Captive Bottlenose Dolphin Calf. The Bottlenose
Dolphin. Chapter 27, 1990.
Harrison, R.. “The
Comparative Anatomy of the Blood-Supply of the Mammalian
Testis.” Proceedings
of the Zoological Society of London 119 (1948):
pp 325-44.
Harrison , R. Reproduction and Reproductive Organs.
The Biology of Marine Mammals. Academic Press, New York,
New York, 1969. pp 253–348.
Nguyen, D. and Mann. “Sociosexual Development
in Bottlenose Dolphin Calves,” Proceedings of the
Seventh Annual Atlantic Coastal Dolphin Conference, Virginia
Beach, Va., March 19-21, 1999. p 11.
Robeck et al. “Reproductive
Biology of the Bottlenose Dolphin (Tursiops truncatus)
and the Potential Application of Advanced Reproductive
Technologies.” Journal
of Zoo and Wildlife Medicine. 25, no. 3, 1994. pp 321-36
Samuels, A. et al. “Gentle Rubbing Among Bottlenose
Dolphins.” Proceedings of the Eighth Biennial Conference
on the Biology of Marine Mammals, Pacific Grove, CA,
December 1989. p 58.
Wells and Scott. “Bottlenose
Dolphin Tursiops
truncatus Montagu, 1821,” 137-82. In S.
Ridgeway and R. Harrison, eds., Handbook of Marine
Mammals. Vol. 6, The Second Book of Dolphins
and Porpoises. New York: Academic Press, 1999.
Wells et al. “The Social Structure of Free-Ranging
Bottlenose Dolphins,” 247-305. In H.G. Genoway’s,
ed., Current Mammalogy. Vol. 1. New York: Plenum
Press, 1987.
 Copyright © 2007 Dolphin Research Center
Information Can Be Used with Proper Citing
Dolphin Research Center, 58901 Overseas Highway, Grassy Key, FL 33050-6019
305-289-1121 www.dolphins.org
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