Long-beaked dolphin, Long-snouted dolphin
The spinner dolphin (Stenella longirostris ) is a small dolphin found in off-shore tropical waters around the world. It is famous for its acrobatic displays in which it rotates around its longitudinal axis as it leaps through the air. It is a member of the family Delphinidae of toothed whales. This playful animal is the most frequently seen cetacean in some tropical open seas.
The Spinner dolphin is a small and slender cetacean with comparatively long and slender beak as well as a triangular fin on its dorsum. The size and color pattern of this animal varies greatly, depending on locality. However, all Spinner dolphins are generally dark grey on their back, lighter grey on their sides, having white or very light grey underparts. These animals exhibit darker grey band, which stretches from the eye to the flipper and is fringed above with a thin light stripe.
The Spinner dolphin is generally a pelagic animal, distributed across the Atlantic, Indian and Pacific oceans. The dolphin usually favors tropical and subtropical areas, though it is also known to occur in warm temperate waters. The Spinner dolphin can be found in both shallow waters and deep waters of the open sea. The closest appearance of this animal to the coast has been recorded in Hawaii.
Spinner dolphins gather in groups, which may be quite small (just a few individuals) or very large (more than 1,000 animals). Schools of these dolphins have been seen mixed with groups of Pantropical spotted dolphins or Small toothed whales. During the day, these animals usually spend their time resting at inlets, often using the same locations every day. At sunset, the Spinner dolphins typically start looking for food. These dolphins are migratory animals, traveling long distances when chasing their prey as well as in order to stay in warm waters. Conspecifics usually find each other by using echolocation. Spinner dolphins are also known to communicate through touch, which strengthens their relationships. They perform their famous acrobatic tricks, including the well-known jumps and spins, during the nighttime hours.
These carnivorous (piscivorous) cetaceans mainly feed upon vertically migrating species. They also consume mesopelagic fish as well as epipelagic and mesopelagic squid and shrimp.
These dolphins have polygynandrous (promiscuous) mating system. Usually, members of a school mate with each other without selection. Spinner dolphins are seasonal breeders with 1 - 2 peak periods. Females give birth with an interval of 2 - 3 years. The gestation period lasts for 10.6 months, yielding a single baby. Newborn dolphins grow up very quickly due to feeding upon maternal milk for about 6 months, after which they complement their diet with other types of food. The young is nursed by its mother for the first two years of its life. The mother and baby usually form a close, lifelong relationship. Males of this species are sexually mature by 10 - 12 years old, whereas females are ready to breed within 5.5 - 10 years.
Currently, the biggest threat to the population of this animal is fishing. Thus, Spinner dolphins often associate with tuna, which makes them a target, and the animals are often caught in fishing nets. They are often entangled in fishing gear as well as hunted in the Caribbean, Sri Lanka, and the Philippines. On the other hand, the animals suffer from coastal development, reaching sheltered bays, which are used by these dolphins as resting areas during the day.
According to the IUCN Red List, the total population size of the Spinner dolphin is unknown for today, but there are estimates for specific populations in the following areas: in the northern Gulf of Mexico - 11,971 animals; in Hawaiian waters - 3,351 individuals; in the southern part of the Sulu Sea and north-eastern Malaysian waters - 4,000 dolphins; in the southeastern Sulu Sea - 31,000 animals; and finally, the Eastern spinner dolphin sub-species - 613,000 individuals. Currently, Spinner dolphins are classified as Data Deficient (DD) on the IUCN Red List.
