10.11.2013

Spinner Dolphins

Spinner dolphins (Stenella longirostris)
Spinner dolphins (Stenella longirostris) are easily spotted as they swim in the clear waters of coral reefs. Named for their ability to spin during acrobatic jumps, these dolphins are slender, with long thin beaks, sloping foreheads, and a stripe that runs from the eyes to the flippers. An adult measures 4.25 to 6.89 feet (1.3 to 2.1 m) long, and weighs between 100 and 165 pounds (45 and 75 kg). There are several varieties of spinners in different geological locations, and they vary slightly in shape and color.

Spinner dolphins feed at night on fish and squid in the deeper waters of the reef, although they will also eat organisms that live on the reef floor. Their mouths are equipped with 45 to 65 pairs of sharp teeth in each jaw. After feeding, spinner dolphins can often be found resting in protected areas of shallow water.

As social animals, spinners depend on interaction with others for hunting, defense, and reproduction and form small, long-lasting social groups called pods. In this species, pods do not have a highly organized social structure with a leader or dominant animal; instead, spinner pods are loose associations of a few key individuals, as well as dolphins who come and go.

A pod of spinner dolphins may also spend time with other sea animals, such as pilot whales, spotted dolphins, or tuna. Like most dolphins, spinners have good eyesight; however, they primarily rely on their sense of hearing and two kinds of voices, the sonic voice and the sonar voice, to let them know about their environment. The sonic or audible voice includes a vocabulary of clicks and whistles that are performed above or below the water. Along with these sounds, these mammals incorporate several mechanically produced sounds like jawsnapping, flipper slapping, and crash dives. Sonic voice and mechanical sounds are associated with communication between animals. The sonar or echolocation voice is used to navigate. Spinners send out high frequency sounds that are reflected back to the senders as echoes. The dolphins listen for the echoes and use them to locate objects.

A female spinner calves (has offspring, called a calf) once every two or three years. After a gestation period of about 10 1/2 months, a single newborn, 29.5 to 33.5 inches (75 to 85 cm) long, is born. The calf is immediately pushed to the surface by its mother, so it can take in its first breath. A nursing mother lies on her side at the surface, enabling her offspring to feed and breathe. The mother’s fat-rich milk supports the young dolphin for about seven months.

Spinner dolphins may use their pectoral fins to reach out and stroke each other, acts that strengthen the social bonds between them. Pairs of dolphins often swim along face to face, touching their flippers. Closely bonded animals, such as mother and calf, may swim in perfect synchrony as if mirror images of each other. The dolphins are also playful animals that make “toys” from materials in the environment and pass them back and forth to each other.