● Dolphins have to be conscious to breath. This means that they cannot go into a full deep sleep, because then they would suffocate. Dolphins have "solved" that by letting one half of their brain sleep at a time. This has been determined by doing EEG studies on dolphins. Dolphins sleep about 8 hours day in this fashion.
● The number of dolphins killed since the fishery began in the late 1950s is estimated to be over 6 million animals, the highest known for any fishery. For comparison, the total number of whales of all species killed during commercial whaling in the 20th century was about 2 million. The bycatch of dolphins in the ETP tuna fishery has now been successfully reduced by more than 99%, but even at the present level of about 1,000 dolphins/year, it remains among the largest documented cetacean bycatch in the world.
Dolphins are mammals, not fish. They are warm blooded like man, and give birth to one baby called a calf at a time. At birth a bottlenose dolphin calf is about 90-130 cms long and will grow to approx. 4 metres, living up to 40 years. They are highly sociable animals, living in pods which are fairly fluid, with dolphins from other pods interacting with each other from time to time.
With the help of several beautiful bottlenose dolphins we can see how well the dolphin body is adapted for their life in the ocean
Dolphins use their powerful tail flukes in an up and down motion to move through the water. They also use their tails when hunting, hitting a fleeing fish up into the air with their tail, stunning it, then scooping the fish up when it falls back into the water. A dolphin slapping its tail on the water in the wild may be a sign of annoyance, or a warning to other dolphins of danger.
Their pectoral flippers are used to steer them through the water, and they also use them to stroke one another, increasing the social bond between them. Dolphin "friends" may swim along face to face touching flippers. Dolphins that appear to be closely bonded may swim in synchrony, twisting, turning and swimming in perfect harmony together.
Their teeth are interlocking rows of conical pegs, suitable for holding slippery fish. They eat their fish whole, head first. In the wild an open mouth is a sign of aggression, as is head nodding. A sign of greater aggression is violent jaw clapping.
Dolphins breathe through their blowhole located at the top of their head. A dolphin may empty and refill its lungs in less than a fifth of a second. As the dolphin breathes the air leaves the blowhole at speeds of over 100mph. Complex nerve endings around the blowhole sense pressure changes so the dolphin knows exactly when the blowhole is in or nearing the air and can be opened. Water in a dolphin's blowhole will actually drown it so powerful muscles close the blowhole as it dives under the water again.
The dolphin's eyes produce a special slippery secretion which protects the eyes from foreign objects and water friction. To sleep, a dolphin must shut down only half of its brain, as its breathing is under voluntary control. Dolphins take short cat-naps, floating just below the surface, then slowly rising to breathe. Often dolphins are very active during night time, for some this is their main feeding time.
The dolphin's skin is completely smooth allowing the dolphin to move easily through the water, and also reduce heat loss. Their skin may bear rake marks from other dolphins teeth during play or mating, and can easily become badly sunburnt if they strand. Their bodies are very streamlined so they may swim at high speeds through the water, and an example of this is their ears. Dolphin's ears are barely noticeable marked only by a small hole just behind the eye. In a bottlenose dolphin the ear is about 5-6 cms behind the eye and only 2-3 mm in diameter.
Dolphins are able to dive to great depths, and also leap to great heights. They may leap to avoid predators or to show how powerful they are to females at mating time. Noisy splashing jumps may also be used to herd fish. Bottlenose dolphins can dive to depths of over 1,640 ft (500m).
The life of a dolphin
Dolphins carry their young inside their womb and gestation is about 12 months for a bottlenose. The baby emerges tail first, and will suckle from its mother for up to 4 years (a calf may stop suckling sooner depending on circumstances).
The baby will however stay with its mother for between 3-6 years, during which time it learns all about feeding techniques, social interaction and group foraging. Females are likely to stay within the family pod with their mother and sisters, though males will leave and form associations with other males. Dolphins have defined home ranges, an area in which they will roam and feed. Though dolphins live in small groups called pods, these pods can be quite fluid and dolphins can be seen interacting with dolphins from other pods from time to time. If another dolphin is drowning, other dolphins will come to it's aid, supporting it with their bodies so it's blowhole is above the water allowing it to breathe. Dolphins main predators are sharks and unfortunately man, through direct killing for food, netting, pollution, and fishing. Dolphins spend a large part of their day looking for food, or actually feeding. They may either hunt alone, or together as a pod. They use their echolocation (sonar system) to locate fish by sending out a stream of pulses and clicks. Dolphins communicate with each other by whistling or body language. When a baby is first born, some dolphin research suggests a mother dolphin will whistle to it constantly, imprinting her sound on the baby so it will recognize her, and the baby learns to develop its own signature whistle. It is thought that each dolphin has its own individual signature whistle, just like a name.