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Dolphins Essay Bottlenose dolphins can grow to be thirteen feet long and weigh up to 600 pounds (Bottlenose Dolphins). This makes bottlenose dolphins the largest of the beaked dolphins (Dolphin Research Center). Bottlenose dolphins have slick and rubbery skin with no sweat glands or hair. Their epidermis is ten to twenty times thicker than that of other mammals. It can be replaced every two hours, which is nine times faster than human skin. The peeling of their skin helps to reduce drag when they swim. The skin is dark gray on their backs, and fades to white or pink on their bellies. This coloring is called countershading. From above the dolphins blend in with the dark water below, and from underneath they blend in with the sunlight. Countershading helps dolphins hide from predators and prey (Bottlenose Dolphins). Bottlenose dolphins are piscivors, or fish-eaters. They have eighty-eight to one hundred small, sharp teeth for grasping slippery squid and fish (Parker and Burton) (Dolphin Research Center). When catching fish, dolphins usually herd a school of fish together and then dash through the school one at a time to feed. It has been observed where 200 bottlenose dolphins were in a single row, working together to find food. Dolphins can also use their tail flukes to toss a fish out of the water and then retrieve the shocked prey (Bottlenose Dolphins). If a dolphin catches a large fish, it will smack the fish on the ocean floor or the water’s surface to break it into smaller portions (McClintock). After a dolphin catches its prey, it uses its tongue to swallow the fish and push the water out of its mouth (Dolphin Research Center). Dolphins can eat up to thirty pounds of fish in one day, so it is helpful that they have three stomach compartments, similar to that of a cow (McClintock) (Lockley 69). Bottlenose dolphins find fish by using echolocation. This is when a dolphin sends out a beam of short sonar pulses from its melon, or forehead. The beam reflects off of fish or other objects and echoes back to the lower jaw. The echoes are then sent to the ear bones where they are characterized. Using echolocation, dolphins are able to locate prey that is buried up to one and a half feet under the sand (Cahill 140-141). Bottlenose dolphins are excellent swimmers. They can jump up to sixteen feet in the air. Three to seven miles per hour is their normal swimming speed, but they can reach speeds of eighteen to twenty-two miles per hour. Dolphins also porpoise, which is when a dolphin swims fast enough to repetitively come out of the water and back under the water in one swift movement. This uses less effort than swimming fast at the ocean’s surface. When dolphins swim in deep open water, they often dive. They dive to 150 feet regularly, but they have been recorded diving up to 2,000 feet (Bottlenose Dolphins). When a dolphin needs to breathe, it comes to the surface, exhales, and then inhales. If a dolphin stays underwater for a very long time, it can exhale at over 100 miles per hour (Cahill 77). It only takes about 0. 3 seconds for dolphins to breathe (Bottlenose Dolphins). Dolphins exchange 80% of their lung air with each breath; when humans breathe, they exchange only 17% (Bottlenose Dolphins). They come to the surface to breathe every twenty-eight seconds when they are not diving, but they can hold their breath for up to twelve minutes (McClintock) (Bottlenose Dolphins). Before a dolphin can hold its breath for a long time, it has to slow its heart rate down to twelve beats per minute. A slow heart rate helps to conserve energy and oxygen while diving (Dolphin Research Center). In order for dolphins to be able to swim, they have to have fins. Bottlenose dolphins have three different types of fins on their bodies. The most recognizable is the dorsal fin. It is located in the center of the back and is the cause of dolphins sometimes being confused with sharks. The dorsal fin is helpful for balance but is not essential. Dolphins also have flippers on both sides of their bodies called pectoral fins that are used to steer. The bones in pectoral fins look similar to human hands because they have five digits. The two parts of a dolphin’s tail are called flukes. Tail flukes are made up of tough connective tissue with no bones or muscle. The tail’s spread is 20% of the total body length. The dolphin’s back muscles move the flukes up and down to push the dolphin through the water. All of the fins and flippers use the process of countercurrent heat exchange to conserve body heat. This means that the arteries in the fins are surrounded by smaller veins so that some of the heat from the blood is transferred to the blood in the veins instead of being released to the environment (Bottlenose Dolphins). Dolphins need to conserve heat to stay warm in cooler waters. The lifespan of a bottlenose dolphin is twenty to thirty years. They can reproduce every three years for their entire lives starting at the age of six (Bottlenose Dolphins) (Cahill 98). The gestation period lasts twelve months. Baby dolphins, called calves, are usually born tail-first to prevent drowning, and the umbilical cord between the mother dolphin and calf snaps during birth (Cahill 98) (McClintock). â€Å"85% of all firstborn calves die† (McClintock). Newborn calves typically weigh twenty-two to forty-four pounds and are thirty-nine to fifty-three inches long (Bottlenose Dolphins). Since dolphins are mammals, calves drink milk produced in the mother’s body (World Book 296). Mother dolphins have to swim constantly with their calves in their â€Å"slipstream† because newborns do not have enough blubber to easily float (Hecker). At about four months old, young start to eat fish and are entirely weaned from milk between the ages of one year and eighteen months (Lockley 169). Each dolphin develops a signature whistle at one month old. In order for calves to recognize their mothers by their whistle, mothers whistle to their calves almost constantly for several days after birth (Bottlenose Dolphins). A dolphin will stay with its mother for at least six years and some dolphins stay with their mothers for their entire lives (Bottlenose Dolphins). Bottlenose dolphins are very social animals. They travel in pods, which are groups of two to fifteen dolphins (Bottlenose Dolphins). Dolphins are very protective of each other, and they have killed sharks that were too close to their pod by repeatedly hitting them in the gills (Lockley 172). They will also try to save an injured or dead dolphin by keeping it at the surface for hours or even days (Lockley 19). Bottlenose dolphins are usually very friendly towards humans. Some wild dolphins even go into bays and interact with them (Dolphin Research Center). Dolphins also love to have fun. In captivity, they enjoy teasing each other and humans that are around their tanks (Lockley 48). In the wild, dolphins like to ride ocean waves or a boat’s stern or bow wake (Bottlenose Dolphins). They sometimes toss jellyfish and seaweed to one another and use plastic, seaweed, or other objects as â€Å"dolphin jewelry† on their fins, beaks, and necks (Cahill 93). Bottlenose dolphins truly are intriguing and individual animals. It’s hard to believe that some people actually hunt them. Beloved and admired by many, they should be protected in both captivity and the wild. Bottlenose dolphins have been entertaining people in for over eighty years, and hopefully they will continue to do so for many years to come.