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 Editorials | Environmental | August 2005 
It's All About the Dolphins...
 Erich Haubrich - PVNN
Prominent throughout our oceans and rivers, dolphins take on a persona that is adored worldwide. We see them jumping, playing, and even hear them laughing as they have fun in the ocean. Dolphins are some of the most highly intelligent creatures on earth.
These warm-blooded mammals belong to a group of mammals called Cetaceans which also encompass all whales. Dolphins are referred to as "toothed whales" or Odontocetes differentiated from baleen whales which have horny plates connected to their upper jaw.
It takes all kinds...
Dolphins come in many colors from the black and white killer whale (which is actually in the dolphin family) to the false killer whales and pilot whales which are almost solid black. There are 67 total species of dolphins 32 of them oceanic with river dolphins, sperm whales, beaked whales, beluga, narwhal and porpoises rounding out the other 35 species. Porpoises are often confused with dolphins, but while dolphins have rounded interlocking teeth while porpoise teeth are squared. Pacific Bottlenose Dolphins are the variety most commonly observed in and around Banderas Bay.
The colors of life...
The bottlenose and spotted dolphins benefit from their coloring as camouflage in the water with darker colors on the top to blend into the ocean from above with lighter coloring on the bottom which blends into the sunlight coming through the water. Older animals in some regions sometimes show inconspicuous spotting along their sides and underbellies.
Is it just a fluke?
The front limbs on dolphins are called flippers, with a very similar bone structure to the human hand. Dolphins don't possess hind limbs of any kind, they have only flukes which we often call tails. The flukes are flattened pads of tough, dense, fibrous connective tissue completely without bone or muscle, the spread of the fluke is usually about 20% of the animals overall body length. The tails are used for propulsion while the flippers are used for steering as well as to control body temperature. Most dolphins have a prominent dorsal fin similar to that of a shark, which works much like a rudder on a boat, much like the flukes the dorsal fins contain connective tissue but no bones.
Ladies' choice...
Females are receptive to mating throughout most of the year and are generally responsible for initiating courtship and breeding behavior, although males can become territorial and aggressive during courtship. Average females become sexually mature at around 5 to 12 years while males are about 10 to 12 years when they reach sexual maturity.
A new baby is born...
On the west coast of Mexico calving generally happens in the fall months. Deliveries can be either tail or head first. "Auntie" dolphins, either male or female may assist with the birth and are generally the only other dolphin allowed near the calf. Dolphins have a relatively close relationship with their offspring with a long period of parental care through maturation. Dolphins are birthed like most mammals via the birth canal in the female abdomen. Generally there is only a single offspring.
When a new baby dolphin is born it immediately heads for the surface of the water with the help of its mother for its first breath. It is nursed on the surface as the mother turns on her side to allow the calf to breathe easily while nursing.
As the baby matures it is able to suckle underwater. The nipples of the mammary glands are located within small slits on either side of the reproductive opening. The large mammary glands are large reservoirs where milk collects and is forced by contraction of muscles, through the nipples, into the mouth of the baby. Each nursing session lasts about 5 to 10 seconds about 4 times per hour for the first 4 to 8 days.
The baby will generally nurse for up to 18 months, while the milk, which is about 33% fat helps the calf establish a thick layer of blubber for insulation. The rapid growth of the baby dolphin is related largely to the high fat, calcium and phosphorus content of the mother's milk. In zoological environs calves can start to take a few fish at about 90 to 120 days. Mother-calf bonds are long-lasting with calves staying with their mother 3 to 6 years or more.
They keep growing and growing...
Because dolphins spend their whole life in an aquatic environment they don't need to support their own weight, thus they can attain great size. In most cases dolphins don't reach their maximum size until many years after sexual maturity. Bottlenose dolphins can reach over eight feet in length and can weigh up to 575 pounds.
All shapes and sizes...
An average bottlenose dolphin calf is a little over 3 feet at birth and can grow to eight or nine feet long. After the gestation period that ranges from 9.5 to 17 months.
Dinner time...
Adult bottlenose dolphins usually dine on other fish, squid and crustaceans such as shrimp depending on their geographical location, consuming about 4 or 5 percent of their body weight per day. Bottlenose dolphins often cooperate when hunting and catching fish. In open waters, a dolphin pod sometimes encircles a large school of fish and herds them into a small, dense mass, sometimes using their tail flukes to stun the fish. The dolphins take turns charging through the school to feed. Occasionally dolphins herd schools of fish against a sand bar or shoreline to trap them in shallow water where they are easy prey.
Dolphins also feed on individual, non-schooling fish. To hunt larger fish, a bottlenose dolphin may even use its tail flukes to kick a fish out of the water, then retrieve the stunned prey on the surface. They don't actually chew their food, they swallow fish whole head first for the most part or shake them or rub them on the ocean floor to aid in digestion. There conical, interlocking teeth are highly effective for this purpose, they have about 40 teeth on top and about 48 on the bottom.
Dolphin talk...
Bottlenose dolphins identify themselves with a signature whistle. However, scientists have found no evidence of a dolphin language. Sounds are probably produced by movements of air in the trachea and nasal sacs. During some vocalizations, bottlenose dolphins actually release air from the blowhole, but scientists believe that these bubble trails and clouds are a visual display and not necessary for producing sound.
Bottlenose dolphins produce clicks and sounds that resemble moans, trills, grunts, squeaks, and creaking doors. They also produce whistles. They make these sounds at any time and at considerable depths. The sounds vary in volume, wavelength, frequency, and pattern. A mother dolphin may whistle to her calf almost continuously for several days after giving birth. This acoustic imprinting helps the calf learn to identify its mother.
The senses...
The dolphin's senses are very highly developed, with acute hearing, eyesight and sense of touch. Like all toothed whales dolphins have a limited sense of smell. Little is known about a dolphin's sense of taste, although they do have taste buds and show strong preferences for certain types of food fishes.
Where am I?
Although the dolphins have large eyes located near the corners of their mouths with acute vision both in and out of the water, a great deal of their location of food is done through echolocation. The term echolocation refers to an ability that dolphins possess that enables them essentially to "see" with their ears by listening for echoes. Dolphins echolocate by producing clicking sounds and then receiving and interpreting the resulting echo. Dolphins produce directional clicks in trains. Each click lasts far less than a second.
The click trains pass through the melon (the rounded region of a dolphin's forehead), which is made up mostly of fatty tissue. The melon acts as an acoustical lens to focus these sound waves into a beam, which is projected forward into water in front of the animal. Sound waves travel through water at a speed of about one mile per second which is 4.5 times faster than sound traveling through air. These sound waves bounce off objects in the water and return to the dolphin in the form of an echo.
High frequency sounds don't travel far in water. Because of their longer wavelength and greater energy, low frequency sounds travel farther. Echolocation is most effective at about 5 to 200m for objects about 2 to 6 inches in length. The returning sound is received in the fatty portions of the lower jaw where they are then sent to the ear and onto the brain. Through this echolocation dolphins are able to determine the size, shape, direction and speed of objects in the water. Many details of this ability in dolphins have yet to be understood fully by science.
Going for a swim...
Bottlenose dolphins can often be found "surfing" on the bow of a boat, this is done for the purpose of "hitching a ride" on the currents pushed forward by the boat and considered to be good luck by boaters around the world. The bottlenose routinely swims at speeds of about 3 to 7 miles per hour and can burst to speeds of 18 to 22 miles per hour for short periods.
Although bottlenose dolphins generally do not need to dive very deep to catch their food, they regularly dive to depths of up to 150 feet. Under experimental conditions a deep trained dive was made to over 1,700 feet. They can dive for up to 8 to ten minutes and maintain a slower heartbeat while diving to slow the metabolism of oxygen.
Dolphins are quite acrobatic and can be seen doing complex and artful aerial maneuvers that awe spectators both in marine parks and in the wild. They are able to execute spins and flips that place them well out of the water during mating, demonstrations of hierarchical dominance or even just while being playful.
Take a deep breath...
In about a third of a second a dolphin exchanges 80% of the air in it's lungs in one breath both inhaling and exhaling, as compared to humans that exchange a mere 17%. The dolphin always holds its breath underwater, exhaling just before reaching the surface of the water. Dolphins breathe through a blowhole in front of the dorsal fin which is closed in the relaxed position and opens by flexing a muscular flap to breathe. A dolphin's respiratory rate is about 2 or 3 breaths per minute.
Heating and cooling...
Bottlenose dolphins are warm-blooded creatures with an average body temperature of 98.4 degrees, which is very close to that of humans. Bottlenose have most of their body fat in a thick layer of blubber that lies just underneath the skin. This blubber layer insulates the dolphin and streamlines the body. It also functions as an energy reserve. A bottlenose dolphin's body fat generally accounts for about 18% to 20% of its body weight.
Bottlenose dolphins also use their circulatory system to regulate their body temperature and the circulation to their flukes, flippers and dorsal fins play a big part in this, shedding excess heat to the appendages when needed. They can also shed body heat when exhaling, like most mammals and do this often due to the amount of body heat generated by their high metabolism.
A little shuteye...
Dolphins are like humans in many ways, one of which is that they spend up to 33% of their day asleep. Some researchers have theorized that sleep in bottlenose dolphins occurs in one hemisphere of the brain at a time, allowing them to maintain normal breathing patterns. Dolphins are rarely seen "logging" or remaining on the surface in a sleep state.
Our friend the dolphin...
More than just being a fascinating sea creature and fellow mammals, dolphins and humans have a history of positive interaction with one another. Dolphins routinely interact with swimmers and divers in a very playful fashion, swimming closely, nosing around and even offering a lift when a person gently grabs onto the dorsal fin. They are quite genial and there are tales of dolphins offering aid to sailors swept overboard or injured swimmers and surfers. It's always fun to have dolphins around while swimming, diving or snorkeling, their bright, playful personalities are very endearing, creating a happy and memorable spectacle. They are also being used in aquatic therapy more and more with very positive results.
Family ties...
Dolphins live in groups referred to as pods. Pods are coherent, long-term social units that vary in size and structure although composition is largely based on age, sex and reproductive condition. Many pods are composed of mother-calf pairs and pods of mature females and their recent offspring while others occur in mixed-sex and single sex groups. Some adult males are observed to be alone, in pairs or occasional trios, moving between female groups in their age range, pairing up with females for brief periods. Adult males rarely associate with sub-adult males. Does this sound familiar? At times several pods may join for short periods to form herds or aggregations of up to several hundred animals. This is seen often and throughout the year in our bay. Whatever the size of the group, social hierarchy may often be observed in bottlenose dolphins.
The biggest kid on the block...
Aggressive behavior amongst dolphins is often observed in the wild, with dolphins maintaining or establishing dominance by biting, chasing, jaw-clapping and smacking their tails in the water. Dolphins can also often show aggression by scratching one another with their teeth, leaving superficial lacerations that heal easily without tremendous long-term effects. Traces of light parallel stripes remain on the skin of the dolphin and can be seen when the dolphin is observed closely. These marks have been seen in virtually all species of dolphins. Dolphins also show aggression by emitting bubble clouds from their blowholes. During courtship, dolphins engage in head-butting and tooth-scratching along with other types of posturing.
A long, full life...
Census data from various conservation organizations and scientific study of dental material suggests that the average lifespan of a bottlenose dolphin is about 20 years or less. While currently not endangered, it is important for us all to help conserve this beautiful creature. Their predators are generally various types of sharks, killer whales and disease such as bacteria and parasites. Pollution is also a factor in many areas, having caused the deaths of large numbers of dolphins in coastal areas. Many conservation organizations are making efforts to prevent this type of ecological disaster.
Come and see them...
Most people do not have the opportunity to observe bottlenose dolphins in the wild. The unique opportunity to observe and learn directly from live animals increases public awareness and appreciation of wildlife exists only in aquatic centers or marine zoological parks such as Vallarta Adventure's Dolphin Center here in Banderas Bay.
In the protected environment of a marine zoological park, scientists can examine aspects of dolphin biology that are difficult or impossible to study in the wild and people can observe, up close, these awesome and wonderful creatures. They are complex and amazing in ways that endear us to their species and astound our senses. |
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