(Stenella longirostris)
Introduction
People are fascinated with the Spinner Dolphin and all that it entails. It is one of the most social of all species. It is also one of the most spectacular to be able to view due to their amazing jumps, flips, and spins outside of the water.
Description
This is a small and slender dolphin, and the size of them will vary based on where they reside. The common coloration for them is dark gay on the back and then lighter gray on the sides. They are white or light gray on the belly. They may have a very dark gray stripe that runes from the eye to the flipper. They have a beak that is long and thin with a dorsal fin that is triangular shaped.
The average size for a Spinner Dolphin is from 6 to 7 feet in length. They can weigh from 130 to 170 pounds. The males are longer and heavier than the females. The males also have a more distinctive postanal hump than the females. The have a small head. A dwarf subspecies of the Spinner Dolphin has been identified around the Southeastern portion of Asia.
Distribution
The open areas of the tropical seas are where most of them are found. They tend to live further from land than most other species of dolphins. They are known to live in various oceans around the world including the Pacific, Atlantic, and Indian. They may be found in shallow waters to look for food from time to time. In Hawaii, they have been seen closer to the coast than in any other regions. They will rest in the bay areas for protection during the day.
Behavior
Spinning in the air is the behavior that this particular dolphin is well known for. They are also known to ride bow waves that are created by boats in the water. They can be found living in groups that range from 100 to more than 1,000. Within those larger pods, there are many smaller sub pods that can be complex to evaluate. There is a dominant hierarchy in place.
They are extremely social within their pods as well as with other species of dolphins. They have been seen using echolocation to find each other. They also touch frequently tend to create very close bonds. The jumps and spins that they are so well known for will typically take place at night.
Resting at various inlets is a common practice during the day for Spinner Dolphins. It is common to see them returning to the same locations day after day. After they have rested and the sun is going down, they will get busy looking for food resources. Migration is a big part of life for these dolphins. They will move long distances to follow prey and to be able to stay in warm waters.
Feeding
Squid is a huge part of the diet for the Spinner Dolphins. These dolphins have no problem successfully hunting in the deeper and darker waters. Yet at night the squid are more apt to be coming to the surface of the water. They will rarely be seen feeding the daylight hours. They also consume large amounts of fish and shrimp. Most of the time, they dine on vertically migrating species. They can dive up to 984 feet to get food.
Reproduction
Females are ready to mate around 4 to 7 years of age. For males, it occurs later with an age between 7 and 10 years old. Mating rituals have been observed with the Spinning Dolphins. They tend to touch often and to pay plenty of attention to the one they plan to mate with. The time of year for mating depends on the location where these dolphins live. It is believed there are a couple of times a year when hormone levels increase which is when mating does occur.
After mating, it takes about 10 months before the single calf will arrive. The mature females give birth once approximately every 3 years. The young will be born tail first, which is the case with all dolphin young. They will grow very quickly consuming the milk from their mother. They will be completely weaned about 2 years of age.
They will be introduced to other food sources though around 6 months of age. The bonds between a mother and her young can last a lifetime. The average lifespan in the wild for Spinner Dolphins is 20 years.
Conservation Status and Threats
At this time, they are considered to be an endangered species due to pollutions diminishing. Some risks to them including getting injured or killed due to fishing nets in the water. Stress caused by human activities around them can create problems for Spinner Dolphins. Pollutant in the water has also become a concern such as chemicals and plastics.
There are some conservation efforts in place for the Spinner Dolphins. One of them involves better equipment for fishing due to so many of them getting tangled up in nets. Some of the fishing commercial entities follow these dolphins to find tuna and that increases the risk of them getting caught as well. The Dolphin Safe program in the USA has helped in this area.
Reducing stress in the environment due to boats and other elements have also been looked at. Reducing such threats is important but it can also prove to be very tricky as well. In areas of Hawaii, limits on where people can go during the day have also been looked at. It is believed the dolphins resting there were frequently having their sleep interrupted by humans and that was causing a great deal of stress for them.
Efforts to reduce pollution have been a primary focus for conservation. One of the threats that still needs to be addressed in hunting of them for sport or for meat in countries outside of the USA. Even though there are some efforts in motion to prevent such hunting, it does occur on a wide spectrum. It is hard to enforce protection from such hunting in many regions.
