Physical Characteristics

Bottlenose Dolphins

Physical Characteristics

Size

  1. In general, bottlenose dolphins are 2 to 3.9 m (6.6-12.8 ft.). Their average weight is 150 to 200 kg (331.5-442 lb.).
  2. Differences in size may be related to coastal and offshore ecotype variances, and geographical locations. Offshore ecotypes, adapted for cooler waters, tend to be larger than inshore ecotypes.

    The sizes and skull shapes of bottlenose dolphins vary greatly by region.

  3. On average, full-grown males are slightly longer than females, and considerably heavier.

    Although male and female bottlenose dolphins are close in size,
    full grown males are generally slightly longer than females.

  4. Coastal bottlenose dolphins measured off Sarasota, Florida average 2.5 to 2.7 m (8.2-8.9 ft.) and weigh between 190 and 260 kg (419-573 lb.).
  5. Large bottlenose dolphins in the Pacific may be 3.7 m (12 ft.) and weigh 454 kg (1,000 lb.). In the Mediterranean, bottlenose dolphins can grow to 3.7 m (12 ft.) or more.

Body Shape

  1. A bottlenose dolphin has a sleek, streamlined, fusiform body.

    The bottlenose dolphin's streamlined body, together with its flippers, flukes,
    and dorsal fin, adapt this mammal for life in an aquatic environment.

Skin

  1. A dolphin's skin is smooth and feels rubbery. The skin has no hair or sweat glands.
  2. A dolphin's outer skin layer, the epidermis, is about 10 to 20 times thicker than the epidermis of terrestrial mammals.
  3. Just like human skin, dolphin skin constantly flakes and peels as new skin cells replace old cells. A bottlenose dolphin's outermost skin layer may be replaced every two hours. This sloughing rate is nine times faster than in humans. This turnover rate ensures a smooth body surface and probably helps increase swimming efficiency by reducing drag (resistance to movement).
  4. A bottlenose dolphin's skin color is gray to dark gray on its back, fading to white on its lower jaw and belly.
    • This coloration, a type of camouflage known as countershading, may help conceal a dolphin from predators and prey. When viewed from above, a dolphin's dark back surface blends with the dark depths. When seen from below, a dolphin's lighter belly blends with the bright sea surface.
    • Some bottlenose dolphins show spots on their bellies or light streaks along their sides. Many populations of Indo-Pacific bottlenose dolphins are ventrally spotted.
    • A bottlenose dolphin's color is gray to dark gray on its back, fading to white on its belly.
      This color pattern is known as countershading.

  5. The skin layer beneath the epidermis is the dermis. The dermis contains blood vessels, nerves, and connective tissue.
  6. A dolphin's blubber (hypodermis) lies beneath the dermis. Blubber is a layer of fat reinforced by fibrous connective tissue.
    • Blubber contributes to a dolphin's streamlined shape, which helps increase swimming efficiency.
    • Blubber stores calories, which provide energy when food is in short supply.
    • Blubber reduces heat loss, which is important for thermoregulation.
    • Blubber thickness fluctuates by season as well as with body size and health status.

Pectoral Flippers

  1. A dolphin's forelimbs are pectoral flippers. Pectoral flippers have the major skeletal elements of land mammal forelimbs, but they are foreshortened and modified. The skeletal elements are rigidly supported by connective tissue.
  2. A dolphin's pectoral flipper contains
    five digits similar to that of a human hand.

  3. Pectoral flippers are curved back slightly and pointed at the tips.
  4. Pectoral flipper length averages 30 to 50 cm (11.7-19.5 in.).
  5. Dolphins use their pectoral flippers mainly to steer and, with the help of the flukes, to stop.
  6. Blood circulation in the flippers adjusts to help maintain body temperature.
    • Arteries in the flippers are surrounded by veins. Thus, some heat from the blood traveling through the arteries is transferred to the venous blood rather than the environment. This countercurrent heat exchange aids dolphins in conserving body heat.
    • To shed excess body heat, circulation increases in veins near the surface of the flippers and decreases in veins returning to the body core.

Flukes

  1. Each lobe of a dolphin's tail is called a fluke.
  2. Flukes are flattened pads of tough, dense, fibrous connective tissue, completely without bone, cartilage, or muscle.
  3. From tip to tip, an adult's flukes measure about 60 cm (23.4 in.) across. Fluke spread is about 20% of the total body length.
  4. Longitudinal muscles of the back and peduncle (tail stock) move the flukes up and down to propel a dolphin through water.
  5. Like the arteries of the flippers, the arteries of the flukes are surrounded by veins to help conserve body heat in cold water.

Dorsal Fin

  1. A bottlenose dolphin's dorsal fin is often falcate (curved back), although the shape is quite variable. It is located at the center of the back.

    The dolphin's dorsal fin contains no bone, cartilage, or muscle.
    The shape varies among individuals but it is usually falcate.

  2. Like the flukes, the dorsal fin is made of dense, fibrous connective tissue, with no bone, cartilage, or muscle.
  3. As in the flukes and the flippers, arteries in the dorsal fin are surrounded by veins to help conserve or dissipate body heat.
  4. The dorsal fin may also help maintain balance as a dolphin swims, but is not necessarily essential. In fact, some whales and porpoises don’t have dorsal fins at all.

Head

  1. The rounded region of a dolphin's forehead is called the melon. The melon contains fat and plays an important role in dolphin echolocation.
  2. In front of the melon, a bottlenose dolphin has a well-defined rostrum (snoutlike projection). The rostrum is typically 7 to 8 cm (3 in.) long, marked by a lateral crease.
  3. Teeth are conical and interlocking.
    • Teeth are designed for grasping (not chewing) food.
    • Bottlenose dolphins have 18 to 26 teeth on each side of the upper and lower jaws, a total of 72 to 104 teeth.
    • A tooth's diameter measures about 1 cm (0.4 in.).
    • Dolphin teeth are not replaced.
  4. Eyes are on the sides of the head, near the corners of the mouth.
    • Glands at the inner corners of the eye sockets secrete an oily, jellylike mucus that lubricates the eyes, washes away debris, and probably helps streamline a dolphin's eye as it swims. This tearlike film may also protect the eyes from infective organisms.
    • A dolphin's eyes may move independently of each other.
  5. Ears, located just behind the eyes, are small inconspicuous openings, with no external pinnae (flaps).

    The dimple below this dolphin's eye is the
    very small external opening to its inner ear.

  6. A single blowhole, located on the dorsal surface of the head, is covered by a muscular flap. The flap provides a water-tight seal.
    • A bottlenose dolphin breathes through its blowhole.
    • The blowhole is relaxed in a closed position. To open the blowhole, the dolphin contracts the muscular flap.
    • At the surface, the dolphin quickly inhales and then will
      relax the muscular flap to close its blowhole.