Pantropical Spotted Dolphin

## Description

The pantropical spotted dolphin (Stenella attenuata ) is a species of dolphin found in all the world's temperate and tropical oceans. The species was beginning to come under threat due to the killing of millions of individuals in tuna purse seines. In the 1980s, the rise of "dolphin-friendly" tuna capture methods saved millions of the species in the eastern Pacific Ocean and it is now one of the most abundant dolphin species in the world. The pantropical spotted dolphin (PSD, Stenella attenuata) is the most common cetacean species observed within the Agoa Sanctuary, located in the Lesser Antilles, Eastern Caribbean. Because PSD is common within the sanctuary it is considered a resident species, however, no research has been carried out to estimate its population status and movement patterns between islands.

## Appearance

This species is identified by the spots, covering the body of adult individuals. The Pantropical spotted dolphins are born unspotted. However, as they age, a varying amount of light spots appear on the upper surface of their body as well as dark markings - on their underside. Adult individuals generally display white tip of the beak. Females of this species are a bit smaller than males. A subspecies of this dolphin typically exhibit larger and stockier body, thicker beak and are more densely spotted.

## Distribution

Endemic to tropical and subtropical areas of the Atlantic, Indian, and Pacific oceans, the Pantropical spotted dolphin is a migratory animal, travelling seasonally to the Japanese coast. This dolphin is the most commonly found cetacean in the Gulf of Mexico. The animal generally favors offshore waters with constant temperature of the deeper water. However, the Pantropical spotted dolphin is also known to occur in inshore areas.

## Behavior

The Pantropical spotted dolphins gather into groups, varying from several individuals to several thousands. Meanwhile, inshore schools of this species are typically smaller than offshore groups. Schools of Pantropical spotted dolphin have been observed together with schools of tuna. The reason of such behavior is probably the similar diet. In addition, as it is said, there is safety in numbers, so groups of these two species unite, evidently to increase protection from predators. This fast swimmer can frequently be observed preforming various acrobatic tricks such as bow-riding. Young individuals of this species are known to make surprisingly high vertical leaps out of water. However, once in tuna fishing grounds, the animal usually avoids vessels. As night feeders, these dolphins locate their prey through echolocation. The Pantropical spotted dolphins spend their daytime hours in shallower waters, where they associate with conspecifics.

## Diet

Pantropical spotted dolphins are carnivores (piscivores and molluscivores). In certain parts of their range, their diet mainly consists of flying fish. These animals also eat squid, crustaceans as well as small species of fish.

## Reproduction

Currently, there's no information on the breeding system of Pantropical dolphin. However, the animal is thought to be polygynandrous (promiscuous) as the spinner dolphin, which is a close relative of the Pantropical dolphin. They breed at any time of year. Gestation period lasts for 11 months, yielding a single baby, which is most commonly born is spring or autumn. Females give birth with an interval of 2 - 3 years. Within 3 - 6 months, the calf starts eating solid food, though lactation still takes place, often lasting for 1 - 2 years. Males of this species are sexually mature by 12- 15 years old, whereas females reach maturity within 9 - 11 years.

## Population

### Population threats

The tuna purse-seine fishery usually uses the Pantropical spotted dolphins to locate tuna populations, since these two species are known to closely associate. This causes serious threats to the schools of spotted dolphin, which becomes a target for the tuna fishery. There are recorded cases of the spotted dolphins being caught in the nets and as a result, suffocated. Moreover, in many developing countries, these animals are often caught in fisheries. Concerns to the population of Pantropical spotted dolphins also include degradation of their natural habitat and human disturbance. In certain parts of their range, namely, in Japan, Solomon Islands and the Philippines, these animals are hunted for food and as fishing bait.

### Population number

According to the IUCN Red List, the total population size of the Pantropical spotted dolphin is more than 2.5 million individuals, including estimates of specific populations in following areas: in the eastern Pacific - 228,038 dolphins; the north-eastern offshore population - about 737,000 dolphins; the western/southern offshore stock - about 876,075 animals; in Hawaiian waters - 8,978 dolphins; in Japanese waters - 438,000 individuals; in the northern Gulf of Mexico - 34,067 dolphins; along the east coast of the United States - 4,439 dolphins; in the eastern Sulu Sea - about 14,930 animals; in the Tañon Strait, between the islands of Negros and Cebu - 640 dolphins. Currently, Pantropical spotted dolphins are classified as Least Concern (LC) on the IUCN Red List.

## Fun Facts for Kids

The spotted dolphins communicate with each other through a system of clicks and whistles, which are used in various situations. By means of these clicks, the dolphins can inform conspecifics of food, nearby threats or a desire to mate.

The spotted dolphins usually dive at depths of less than 200 feet. However, when hunting at night, these animals are known to dive as deep as 700 feet.

In order to breathe, dolphins have to come to the water's surface. And since they do not breathe underwater, they have separate holes for each function, which prevent them from being drowned: they eat through their mouths while breath through their blowholes.

Dolphins give out all sounds, including the identifying squeaks and whistles, through their blowholes instead of their mouths.

These animals have two stomachs: one is intended for storing food, while the other is for digesting the food.

Dolphins do not drink water in order not to get sick. So, living in salt water, they usually obtain most of the required moisture from their food, primarily from fish and squid. Dolphins are also known to generate water by burning their fat.

## References

https://animalia.bio/pantropical-spotted-dolphin