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Common Dolphins – Basic Knowledge

PHYSICAL DESCRIPTION: Common dolphins are colorful, with a complex crisscross or hourglass color pattern on the side; the long-beaked common dolphin being more muted in color. When looking at the profile of the two common dolphin species, the short-beaked common dolphin has a more rounded melon that meets the beak at a sharp angle, as compared to the long-beaked common dolphin that has a flatter melon that meets the beak at a more gradual angle.

COLOR: Color patterns on the common dolphin are the most elaborate of any cetacean. The back is dark gray-to-black from the top of the head to the tail dipping to a V on the sides below the dorsal fin. The flanks are light gray behind the dorsal fin and yellowish-tan forward of the dorsal fin, forming an hourglass pattern. Its belly is white. There are large dark circles around the eyes connected by a dark line that runs across the head behind the beak and a black stripe runs from the jaw to the flippers.

FINS AND FLUKES: The dorsal fin is triangular-to-falcate (curved). It is pointed and located near the middle of the back and is black-to-light gray in color with a black border. The flippers are long and thin and slightly curved or pointed depending on geographical location. Flukes are thin and pointed at the tips with a slight notch in the center.

LENGTH AND WEIGHT: Common dolphins can reach lengths of 7.5 to 8.5 feet (2.3-2.6 m) and weigh as much as 297 lb. (135 kg). The short-beaked common dolphin is relatively heavier, and has a larger dorsal fin and flippers than the long-beaked one.

FEEDING: Delphinus delphis feeds on squid and small schooling fish. In some parts of the world, they feed at night on the deep scattering layer, which moves towards the water’s surface during that time. Common dolphins have been seen working together to herd fish into tight balls. Like many other dolphin species, the common dolphin will sometimes take advantage of human fishing activities (such as trawling), feeding on fish escaping from the nets or discarded by the fishermen.

MATING AND BREEDING: Sexual maturity is reached at 3 to 4 years of age or when they reach 6 to 7 feet in length (1.8 to 2.1 m). Calves are 30 to 34 inches at birth (76 to 86 cm ); gestation period is 10 to 11 months.

DISTRIBUTION AND MIGRATION: The common dolphin may be one of the most widely distributed species of cetaceans, as it is found world-wide in temperate, tropical, and subtropical seas. The long-beaked common dolphin is found more in coastal waters; the short-beaked common dolphin is found in offshore waters, including the Eastern Atlantic Ocean as far south as Florida. The common dolphin throughout history has often been recorded in art and literature. It was recently proposed that two forms of this species, the short- beaked (delphis) and long-beaked (capensis) common dolphin, represent two distinct species.

NATURAL HISTORY: Like all mammals, dolphins are warm blooded, breathe air, give birth to live babies, feed their new born milk, and are born with hair. Being warm, blooded, or homeothermic, dolphins maintain a constant body temperature regardless of the surrounding water temperature. Unlike terrestrial mammals, including humans, dolphins are conscious breathers, meaning they must be aware of their breathing to avoid involuntarily taking a breath while underwater. Common dolphins can dive for as long as 15-20 minutes but typically hold their breath for only a few minutes. Common dolphins may live for 35 years or more, with females generally living longer than males. Common dolphins are often found in large herds of hundreds or even thousands. They are extremely active, fast moving, and engage in spectacular aerial behavior. They are noted for stampeding in these extremely large groups across the ocean, riding bow and stern waves of boats, often changing course to bow ride the pressure waves of fast-moving vessels and even large whales. Common dolphins can be frequently seen in association with other marine mammal species.

THREATS: Traditionally, hundreds of thousands of common dolphins have been taken incidentally, along with spinner and pan-tropical spotted dolphins, in purse seine nets used during tuna fishing operations in the eastern tropical Pacific although these numbers have improved. Common dolphins also may be caught accidentally in other fishing gear, such as midwater trawls. Turkish and Russian fishermen used to catch large numbers of common dolphins in the Black Sea for meat (to be used for fish meal) and oil. The fishery stopped after the common dolphin numbers became and remain severely depleted; there are several reports suggesting that the Turkish fishery may have recently resumed. Many common dolphins are taken in a Japanese small cetacean fishery and directly caught in the Mediterranean. Some common dolphins have been taken in Peru for human consumption. Studies suggest that the immune system of these animals can be severely affected by heavy metals, PCBs and other pollutants. The status of common dolphins, relative to OSP, in the U.S. Atlantic Eastern Economic Zone (EEZ) is unknown. The species is not listed as threatened or endangered under the Endangered Species Act. There are insufficient data to determine the population trends for this species.

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We all depend on a healthy ocean; a healthy ocean depends on us. Let us be the change we would like to see in the world.  Our new Ocean Sentinels Club is proof that conservation can be fun, rewarding and effective.  The Club unites and empowers citizens to advocate for the conservation of dolphins and the marine environment across Palm Beach County, and beyond. Join us. The time is now. It begins with you.

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Bottlenose Dolphins – Basic Knowledge

The bottlenose dolphin is the most studied and best known of all cetaceans. This is primarily due to its ready adaptability to captive environment, such as research facilities and marine parks, and its appearance on the TV show Flipper. This dolphin has an extensive range and is the most encountered dolphin species in coastal U.S. waters.

PHYSICAL DESCRIPTION: The bottlenose dolphin has a long and robust body shape, with a pronounced, stubby beak (hence the name ‘bottlenose’), and a distinct melon. Because 5 of the seven neck vertebrae are not fused together as in other dolphin species, the neck of these dolphins is more flexible. They have about 40-48 sharp conical-shaped teeth in both the upper and lower jaw.

COLOR: The color of bottlenose dolphins may range from light to dark lead gray, with lighter shading on the sides, and a white, sometimes pink to pinkish-gray belly.

FINS AND FLUKES: The dorsal fin is triangular, curved and moderate in size, up to 35 cm in height, and located near the middle of the back. The flukes are proportional, curved, with a deep median notch, and are 65-80 cm from tip to tip. Their flippers are pointed and of moderate length.

LENGTH AND WEIGHT: Adult bottlenose dolphins can reach 4 meters (12 feet) in length, and, in some geographical areas, weigh as much as 650 kg (1,430 pounds). However, in most part of the world their weight seems to be limited to about 350 kg (770 pounds). Males are typically larger than females.

FEEDING: These dolphins can be found foraging in deep and very shallow waters. They may hunt and feed individually or in a concerted effort of a group, chasing fish against the water surface, onto mud banks, and shorelines. Association with human fisheries is also reported. They consume about 8-15kg (15-30 pounds) of food each day. Their diet includes a variety of fish species, but also squid and crustaceans.

MATING AND BREEDING: Male bottlenose dolphins reach sexual maturity at age 10, females between 5 and 10 years of age. The gestation period (pregnancy) is 12 months and calves are born in all seasons although in some geographical areas seasonal peaks during spring and fall have been reported. Females give birth once every 3-4 years. At birth, calves acre about 100 cm (3 feet) in length and may weigh around 10 kg (22 pounds). Calves depend on their mother’s milk for 12-18 months but stay with their mother for up to 5 years learning how to catch fish and the social skills to become a full member of dolphin society.

DISTRIBUTION AND MIGRATION: With the exception of polar waters, bottlenose dolphins are found in every ocean around the world, in coastal waters and the open sea. They are frequently encountered in estuaries, lagoons, bays and harbors. There appears to be a coastal and offshore ecotype. Population density appears to be higher in near-shore areas. Bottlenose dolphins are known to have limited home ranges or may be migratory.

NATURAL HISTORY: Like all mammals, dolphins are warm blooded, breathe air, give birth to live babies, feed their new born milk, and are born with hair. Being warm, blooded, or homeothermic, dolphins maintain a constant body temperature regardless of the surrounding water temperature. Unlike terrestrial mammals, including humans, dolphins are conscious breathers, meaning they must be aware of their breathing to avoid involuntarily taking a breath while underwater. Bottlenose dolphins can dive for as long as 20 minutes but typically hold their breath for only 30 seconds to 3 or 4 minutes between breaths.

Bottlenose dolphins may live for 50 years or more, with females generally living longer than males. They live in social communities, sometimes called pods. Group size in near-shore populations is typically 30 or less while offshore groups may comprise several hundred individuals.

Even though they appear to live in relatively open societies, they exhibit strong social bonds that help provide protection against predators, assist in locating and catching food, and aid in the rearing of their offspring. Like in other social animals, play is an important part of learning. Behaviors such as fish toss, bow riding and seaweed-keep-away are considered play but also help dolphins develop social bonds as well as useful hunting techniques. They use multiple feeding strategies, including “fish whacking,” where they strike a fish with their flukes and knock it out of the water, and driving schools of fish into shallow areas or onto mudflats. Bottlenose dolphins use high frequency echolocation to locate and capture prey, and high-pitched ‘whistles’ to communicate with one another.

THREATS: Bottlenose dolphins are protected in U.S. waters by the Marine Mammal Protection Act. While the species is not considered endangered, they are near depletion in some areas and threatened in many others. Incidental and direct exploitation are generally reported at moderate to low levels. According to NOAA, current threats come primarily from incidental injury and mortality from fishing gear (such as gill net, seine, trawl, and long-line commercial and recreational operations), exposure to pollutants and biotoxins, viral outbreaks and direct harvest in some countries (e.g. Japan and Taiwan). Studies of large, high mortality events over the last decades suggest that the immune system of these animals can be severely affected by heavy metals, PCBs and other pollutants.

In an effort to reduce injury and mortality of coastal bottlenose dolphins along the eastern seashore of the U.S., the National Marine Fisheries Service implemented the Bottlenose Dolphin Take Reduction Plan (BDTRP). This initiative includes provisions for research and education, and requires modifications of fishing practices for small, medium, and large-mesh gill-net fisheries from New York to Florida.

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We all depend on a healthy ocean; a healthy ocean depends on us. Let us be the change we would like to see in the world.  Our new Ocean Sentinels Club is proof that conservation can be fun, rewarding and effective.  The Club unites and empowers citizens to advocate for the conservation of dolphins and the marine environment across Palm Beach County, and beyond. Join us. The time is now. It begins with you.

Read more