Spinner Dolphin

## Description

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.

## Appearance

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. This playful animal is the most frequently seen cetacean in some tropical open seas. The animal is known for its acrobatic tricks, which include spinning high in the air or bow-riding.

## Distribution

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.

## Behavior

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.

## Diet

These carnivorous (piscivorous) cetaceans mainly feed upon vertically migrating species. They also consume mesopelagic fish as well as epipelagic and mesopelagic squid and shrimp.

## Reproduction

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.

## Population

### Population threats

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.

### Population number

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.

## Fun Facts for Kids

Spinner dolphins are so called due to their amazing ability of spinning multiple times in one jump. These dolphins are very playful animals, known for their acrobatic tricks such as jumping, flipping, and twisting above the water's surface. According to scientists, these dolphins spin for a number of reasons such as having fun, communication, or removing parasites.

They communicate with each other through a system of whistles and clicks. Each animal has its own unique frequency, which helps identify individuals.

When foraging, these animals are capable of diving at a depth of 900 feet, remaining submerged for up to 8 minutes.

Spinner dolphins can feed at any time of the day. However, they usually forage at night, when their prey comes to the water's surface. This makes the hunting process much easier and effective since thus the dolphins are able to find a maximum of food while making minimum efforts.

These animals also use body movements as a form of communication, slapping the water with different parts of their body. Thus, they are known to perform ‘nose-outs’, thrusting their beak from the surface. They usually do this when moving in groups after resting. They use 'tail slaps' to inform conspecifics of a threat or as a signal to a dive. When a group of Spinner dolphins starts picking up speed, they use head slaps, side slaps, and back slaps. However, this animal is best known for performing multiple spins in one jump with each spin getting smaller and smaller and finishing the performance with an expressive side slap.