Subspecies
The Hawaiian or Gray’s spinner dolphin (S. l. longirostris) inhabits the waters of the Hawaiian archipelago and the eastern spinner dolphin (S. l. orientalis) is found in the eastern tropical Pacific.
The eastern spinner has been declared ‘depleted’ under the Marine Mammal Protection Act of 1972.
Estimated Population
In 2002 a survey estimated the number of spinner dolphins surrounding the Hawaiian islands to be about 2,805. The eastern tropical pacific population has declined 80 percent in 20 years from 2 million to 400,000.
Biology
The spinner dolphin weighs 100 – 165lbs and measures 4.25ft – 6.89ft.
Dolphins return to the surface regularly to breathe through a blowhole on the top of their head. A dolphin can refill its lungs in less than 1/5 of a second and the exhaled air leaves the blowhole at speeds of 100mph. While sleeping, the dolphin shuts down half of its brain because breathing is under voluntary control.
Spinner dolphins have 45 to 65 sharp-pointed teeth that enable them to feed on species such as lantern fish, shrimp and squid. Hawaiian spinners feed at night in the open ocean and come into shore to rest, avoid predation, care for their young and reproduce, during the day.
Females reach sexual maturity at 5-12 years of age and normally give birth to one calf every 2-3 years.
Although it is not known exactly how long dolphins live, it is thought they live over 20 years.
Dolphins are known as playful and expressive mammals, often exhibiting emotions through flapping or slapping their fins, leaping out of the water, and playing with floating objects discarded into the open ocean such as plastic bags.
Spinners can travel in schools of thousands of individuals.
Threats
The tuna fishery has been the main reason for eastern population declines.
The Hawaiian spinner population has not been drastically affected by this fishery; however, it remains threatened by potential entanglements in marine debris, collisions with vessels, acoustic disturbance, habitat degradation and human disturbance through aquatic activity in spinner habitats.
