Marine Life of Midway AtollHawaiian Spinner Dolphin / Stenella longirostris
Midway Population A population of approximately 250 spinner dolphins inhabit the lagoon and nearshore waters at Midway Atoll. Feeding Feed actively at night. Move long distances as a coherent group to prey on small fish, cephalopods (squid) and shrimp. Dives to 200-300 meters. Breeding Little is known about the breeding pattern of spinner dolphins. Females probably mate with several males from their community and paternity differs for their consecutive calves. Females give birth to one calf. Newborns are closely monitored by their mother and several other adults. Babysitting is frequent. Nursing females with calves and several other grown females and large males form nursery groups, which increase the safety of young calves. These groups provide conditions where calves can learn skills important to their adult life. Calving Eleven month gestation period. Calving occurs throughout the year, with a peak during June-August months. At birth, calves are approximately 66 cm (2 ft) long, have a pinkish tint and have been seen trying to spin. Behavior Aerial activity occurs in dolphins which swim in groups. Spins, leaps, tail over head leaps, back and head slaps are common. The spin for which the dolphin is named is a well defined body movement, and can be as high as 14 spins in a row. It can be vertical or horizontal. When within the Midway lagoon, spinner dolphins are seen predominantly resting and socializing. This low energy activity is characterized by slow and silent movement within a relatively limited area. Frequently, bursts of joyful play, with numerous leaps and spins, can also be seen. An investigation of passing vessels is common. Predators Tiiger and cookie-cutter sharks are the spinner dolphin's main predatory threat at Midway. Dolphins best avoid shark predation by staying in groups. |
Last updated:
May 21, 2009
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