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Population Status: Bottlenose dolphins are not an endangered species. They are, however, protected (as are all marine mammals) in U.S. waters by the Marine Mammal Protection Act of 1972. The worldwide population is unknown as there is insufficient data but there are certain populations that are depleted. Threats to the species include pollution, habitat destruction, accidental catches in fishing gear and nets, and human activities such as boating. Human interactions of feeding and swimming with wild animals also pose a threat to dolphins by altering their natural behavior.
Diet: Active predators, dolphins eat a wide variety of fish, squid and crustaceans such as shrimp, consuming approximately 4to 6% of their body weight. Feeding behavior is adapted to the animal’s habitat and available food sources. Dolphins employ different feeding strategies: they may hunt their prey individually or they may hunt cooperatively herding fish into a tight ball for easy feeding. They also chase fish onto mud banks or herd them into shallower waters where catching their prey may be easier. They often will feed in association with human fishing as well. After capturing their prey, dolphins will swallow it whole. They do not chew their food; larger fish is broken up by shaking or rubbing on the bottom.
Predators: Some species of sharks (tiger, dusky and bull sharks) and orcas will occasionally prey upon dolphins, however humans pose a greater threat either through harassment or incidental catches.
Social Groups: Bottlenose dolphins are very social animals that live in groups called pods. The size of a pod varies from two to 15 animals. Pods may join temporarily to form larger groups or herds. Up to several hundred animals have been observed traveling in one herd. It is believed pod composition may be based on age, sex and reproductive status.
Females with their young often comprise one group type. At three to six years of age the juveniles leave the maternal group and a form juvenile groups. Young male dolphins join bachelor groups where the young males will form strong social bonds that may last their entire lives. Often juvenile females will return to the maternal group.
Reproduction: Males reach sexual maturity at 7–12 years old and females between the ages of 5 and 10 years. Breeding may occur throughout the year, however there are peak seasons depending on location. A single calf is born after a 12-month gestation period. Usually born tail first, the calf weighs approximately 40 pounds and is about 40 inches long. The calf nurses from the mother’s nipples that are concealed in the mammary slits. Dolphin milk has a very high fat content. The calf may nurse for up to six years, however usually by the time a calf is 18 months old fish is a significant portion of its diet. The usual calving interval is 2–4 years.
Factoids:
• Their streamlined bodies allow for ease of movement through the water. Bottlenose dolphins outinely swim at speed of 3 to 7 miles per hour and they are capable of reaching burst speeds of 18 to 22 miles per hour. They can jump into the air as high as 20 feet.
• Most dolphins dive to depths of 10 to 150 feet. However a dive to 1,795 feet was recorded under controlled conditions.
• Their coloration aids in avoiding predators.
• Dolphins have between 86 to 100 coned shaped teeth used to catch and hold onto their prey.
• All dolphins breathe through the single blowhole located on top of their head. On average they breathe 1–2 times per minute, their maximum dive time is about 8 minutes.
• Their ability to echolocate enables them to navigate murky water and find food. This is accomplished by the dolphin sending out a series of high frequency sounds through its melon (forehead). These sounds travel through the water and bounce off objects, returning to the dolphin’s inner ear by way of their lower jaw. Echolocation allows dolphins to determine size, shape, density and texture of objects. It’s like seeing with sound!
• A “signature whistle” is a sound produced by dolphins that may be used for individual dolphins to recognize or remain in contact with other dolphins.
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