Dolphins are related to whales and porpoises, all belonging to the Order Cetacea. Cetaceans may be either filter feeding or toothed, dolphins being the later. There are 34 species of dolphins in the world, with the Hector’s Dolphin being the smallest at about 3 feet, and the Orca (Killer Whale), the largest, being up to 26 feet. The dolphin seen in the lowcountry, and the one we are focusing on, is the Atlantic Bottlenosed Dolphin. Dolphins live in social groups called pods, ranging in size of a handful in local waters, but up to hundreds in the open ocean. We have 300 or so dolphins that live in the waters of Hilton Head year round, but this number grows substantially with transient dolphins during the warmer months, hence increasing the chance of a sighting. Although these amazing creatures the spend their entire lives in the water like fish, dolphins are mammals, like the furry creatures of the forest (and us!).
What Makes a Dolphin a Mammal?
- They are vertebrates, meaning they have a backbone and internal skeletal structure.
- They are warm-blooded.
- They breathe air with lungs.
- They give live birth, but then, so do some reptiles. What truly distinguishes a mammal is that they nurse their young with milk produced by mammary glands, hence the name mammal.
- Bonus: they have a middle ear containing three bones.
The Major Anatomy of the Bottlenose Dolphin
- The dolphins living within our estuaries and tidal creeks range in size from 8 to 9 feet, and 400 to 600 pounds, while those living in open ocean waters can be 12 feet and 1,000 pounds.
- The head contains the melon, a round organ used for echolocation (more about that later).
- The eyes. located on the sides of the skull, not in the front like ours, move independently of the other, offering about 180 degree field of vision. But this is monocular vision, whereas humans have binocular vision; they only have binocular vision looking down.
- The blow hole at the top of the head is used for breathing (left side) and sound production (right side). In fact, dolphins do not breath or make sounds through their mouths at all!!
- There is no external ear, being reduced to a small hole behind the eye.
- The dolphin has between 80 and 100 conical teeth used for gripping.
A How are dolphins adapted to life in the water?
- A dolphin’s body is gracefully streamlined.
- The front legs have been reduced to the pectoral fins, or flippers, used to steer, and back legs are gone. The skeletal structure inside this fin is very similar to a human’s arm and hand, including 5 phalanges, or finger bones.
- The dorsal fin acts as a rudder, stabilizing the dolphin.
- The external nose and ears have been reduced to holes.
- The mammalian coat of fur has been replaced by a subcutaneous layer of fat.
- A modification of the pupil shape allows dolphins to see both in and out of the water clearly.
- Increase in lung capacity and the ability of muscles to store oxygen, allowing them to only have to take a breath every 3 to 4 minutes. They can hold their breath up to 10 minutes for deep dives.
- Their urine is saltier than the saltwater in which they live, balancing the internal and external salt concentrations.
- Their coloration patterns camouflage them, lighter underneath to match the sky if looking up from below the dolphin, and darker on top to blend into the water if looking from above.
I recorded the video below while conducting a dolphin cruise program on Broad Creek during May 2016. The video is a great example of not only the types of dolphin sightings we have during a dolphin cruise, but if you watch the dolphins as they roll over, you see the variation in coloration described above.
A Most Interesting Skin
The outer layer, the epidermis, of the dolphin’s skin is 10 times thicker than any land mammal, and this entire layer sloughs off every 2 to 4 hours, leaving the dolphin streamlined and free of external attachments while traveling through the water. The skin feels extremely smooth and cool, like touching an inflated inner tube. Looking at the skin under magnification, micro-dermal ridges can be seen.; these ridges trap water molecules on the surface of the skin, allowing the dolphin to travel through the water with less resistance. The skin is very pliant. When moving quickly through the water. the usual smooth flow of water becomes turbulent, and the dolphin’s skin actually ripples at accelerated speeds to counter the effect of this turbulence.
Super Cool Dolphin Facts
- Dolphins have an average life expectancy of 25 years, but can live up to 50 years.
- Dolphins form strongly bonded relationships that are not sexual in nature, and may last a lifetime, much like your BFF.
- Although they are warm blooded, the internal temperature of dolphin’s is around a chilly 36 degrees.
- They usually swim 3-7 mph, but can go over 20 mph if needed.
- The dorsal fin shape, size, markings, and any deformities are unique to each dolphin and can be used to identify them, much like our fingerprints.
- Bottlenosed dolphins eat 20 to 30 pounds of food a day, mainly fish, but sometimes crabs, shrimp, squid, and small mammals.
- Remember those conical teeth? Those are shaped for grabbing because dolphins do not chew their food, they swallow it whole, and preferably head first. Muscles at the back of the throat squeeze out excess water as they swallow.
- Like cows, dolphins have 3 chambered stomachs, and the first chamber breaks up the food before being digested in the other chambers.
Dolphins have the ability to “see” in our murky waters through the use of a sonar-like process called echolocation. With a range up to 650 feet, dolphins can sense the size, shape, speed, distance, and direction of objects as small as 2 inches. A series of short clicks are sent from an organ called a melon in the forehead. The return signal is picked up by acoustic fat filling the lower jawbone and is transferred to the middle ear and on to the brain for processing. Echolocation is an active process that the dolphin chooses to use, unlike vision which is always “on”, and young dolphins are taught how to use it by their mothers. Besides being used to navigate and locate food, echolocation can be used to stun food. Dolphins can feel echolocation clicks as a gentle caress or a strong punch, depending on the strength.
Dolphins communicate with each other through a complex system of sound. Every dolphin has it’s own unique whistle that other dolphins recognize as a particular individual. Even a baby dolphin (calf) recognizes it’s mother’s whistle soon after birth. Dolphins are not born with this signature sound, but develop during the first 4 to 6 months of life. Dolphins use other sounds besides whistles to communicate, such as pulsed squeaks if in distress, pulsed yelps during courtship, or buzzing clicks during an aggressive confrontation. Dolphins do not have vocal cords, producing sound through valves and 4 air sacs below the right blowhole and emit this sound through the the blowhole. The frequency levels range 10 times beyond what humans can hear.
These Highly Social Creatures Also Communicate in Other Ways
When a mother and calf swim together there is often contact between the base of the mother’s tail and the body of the calf, giving the calf a feeling of safety and security, while assuring the mother of the proximity of her calf. Strongly bonded dolphins often swim side-by-side, with pectoral fins touching, much in the way we hold hands. Touch varies from the loving stroking of courtship to the aggressive contact of tail slaps, butting, or even biting. An open mouth of teeth is a threat or warning, and as the threat increases the dolphin will add a head nod. Bubbles blown through the blowhole may indicate surprise, excitement, or agitation. The ultimate warning is the “S” position in which the dolphin lowers it’s head and tail and arches it’s back to form an “S”. If the warning is not heeded, a head-on attack is likely. Play is an important part of dolphin culture, playing with seaweed or play fighting other dolphins. They’ve been known to harass other social creatures like seabirds and turtles. Dolphins enjoy riding the waves, frequently surfing the coastal swells and leaping over wake.
The following video I recorded while conducting a dolphin cruise on Broad Creek during May 2016.
So how Smart Are They?
Comparing absolute size and weight, the average bottlenose dolphin brain is about 20% larger than a human brain, but comparing the ratio of brain to body size, dolphins have larger brains than any other animal except humans. Dolphins possess self-awareness, unique to only the great apes (us!), elephants, and dolphins. This means they recognize their own image in the mirror and have demonstrated the ability to relate their body parts to those of humans, for example, bobbing their head to mimic a human. Dolphins have been known to use tools, a skill that was once believed to be possessed by humans. An example is holding a sea sponge in the beak and using this to stir up food from the sea grass beds, a skill taught to young dolphins by their mothers.
Dolphins will work together in many ways, including helping an injured individual, other females giving assistance to a calving mother, or attacking an intruder as a group- even killing a large shark by ramming it as a group. Working together, dolphins can herd schools of fish for group feedings, some even making air bubbles or clicking sounds to direct the fish. The dolphins inhabiting the lowcountry of South Carolina and Georgia will herd fish up onto the muddy marsh banks, eating the fish they have stranded there before sliding back into the marsh waters. This feeding strategy, called Strand Feeding, occurs at mid to low tides when the banks are exposed, and is observed only in this area of the world, so like the use of tools, is a learned behavior passed down through generations.
I have not yet been fortunate enough to see this for myself, but please take a few minutes to watch this video from Kiawah Island, SC.
How Do Dolphins Sleep?
Here’s your vocab term for the day kids- Unihemispheric Slow Wave Sleep. A dolphin’s brain is divided into 2 independent halves. To sleep the dolphin shuts down half it’s brain, along with the opposite eye, while the other half of the brains stays awake at a reduced level of alertness. This “awake” side watches for obstacles, predators, and signals the body when it is time to surface for a breath of air. About every 2 hours the dolphin will switch sides, resting the active half and awakening the rested half. Dolphins sleep for about 8 hours a day like this. Again demonstrating their intelligence, dolphins will often sleep in pairs or groups, sharing the responsibility of watching for obstacles and predators, and will switch their resting halves together.
Reproduction and Child Rearing
Externally you cannot tell a male from a female dolphin, excepting that adult males tend to be larger than adult females (but how do you know if a dolphin is full grown?). This is because the reproductive organs are contained within a genital slit on the underside of the animals.
Females reach social and sexual maturity between 5 and 10 years of age, while the males do not reach sexual maturity until they are about 12. Even then they not be socially mature enough to take a mate. Unlike most animals, dolphins may mate year-round, which is unique to humans, dolphins, and chimps. Dolphins are not monogamous and a female may mate with several males during her fertile times.
Mothers will carry their pregnancies for 11 to 13 months (wow), and although they may mate at any time through the year, calving in South Carolina more often happens from May through July.
Birth occurs just below the surface of the water. Once uterine contractions begin, the mother floats on the surface with her tail hanging down, or will swim in slow circles. Labor lasts for an hour or two, and the mother may be assisted by another female during and after delivery. Unlike any other mammal, the babies are born tail first. The mother will immediately assist the calf to the surface to take it’s first breath of air. A newborn is about 3 feet long and 40 pounds. The calves will start eating fish at about 4 months of age, but the mothers will continue to nurse them until about 18 months old. Even once a calf is weaned, it will stay very close to it’s mother for up to 6 years.
Threats to Dolphins
Although smaller dolphins, especially calves, may potentially be attacked by lager, aggressive sharks such as the Bull or Great White, this is rare. The only true threat to dolphins comes from humans, with some species, such as the Amazon River Dolphin, are critically or seriously endangered.Human development contaminates the habitat of dolphins with pesticides, heavy metals, plastics, and other industrial and agricultural pollutants that do not disintegrate easily in the environment. These pollutants concentrate in both predators, such as dolphins, and their prey. In some parts of the world, such as Taiga in Japan. dolphins are traditionally considered food and killed in massive harpoon hunts. Loud underwater noises, such as those resulting from naval sonar testing, live firing exercises, or offshore construction projects are harmful to dolphins, increasing stress, damaging hearing, and causing decompression sickness by causing them to surface too quickly to escape the noise.
What Can You Do?
Never, never,never feed dolphins, even taking care in dumping the castoff from fishing. Dolphins may become dependent on humans for food, and not withstanding dependency, it encourages the dolphins. to come dangerously close to boats. Scores of dolphins are injured or killed by propeller strikes each year. Bag all liter immediately when near the water. Plastic waste materials are especially lethal to dolphins (and sea turtles). If mistaken for food and consumed, these materials do not digest, leaving a feeling of fullness in the animal, who will not eat if not hungry.. This leads to the eventual starvation death of the effected animals. The National Marine Fisheries Service encourages the public to keep a distance of 50 feet from dolphins. Boaters and jet skiers should not chase dolphins as this puts the dolphins at risk of injury.
Love Dolphins and Want to Know More?
I could not recommend the book Voices in the Ocean by Susan Casey more. Be forewarned, it made me cry at times.
A New York Times Bestseller…
Inspired by a profound experience swimming with wild dolphins off the coast of Maui, Susan Casey set out on a quest to learn everything she could about these creatures. Her journey takes her from a community in Hawaii known as “Dolphinville,” where the animals are seen as the key to spiritual enlightenment, to the dark side of the human-cetacean relationship at marine parks and dolphin-hunting grounds in Japan and the Solomon Islands, to the island of Crete, where the Minoan civilization lived in harmony with dolphins, providing a millennia-old example of a more enlightened coexistence with the natural world. Along the way, Casey recounts the history of dolphin research and introduces us to the leading marine scientists and activists who have made it their life’s work to increase humans’ understanding and appreciation of the wonder of dolphins—the other intelligent life on the planet.