(Lagenorhynchus obscurus)
Introduction
The Dusky Dolphin is very closely related to the Pacific White Sided Dolphin. However, the scientific studies conducted show that there are enough variations for them to be classified as two separate species. What you may not know is that their name was originally going to be Fitzroy's Dolphin which was given to them by Charles Darwin.
Description
This is a small dolphin species and it is simple enough to identify it from other species out there. This is due to the head that is evenly sloped. It also lacks a beak at the end of the snout. They feature a bluish black color on the tail and along the back. They also have a dark band that is featured from the flanks to the tail diagonally. The belly is white with a dark color for the lower jaw and snout. They have gray from the eye to the flipper and then two white or cream stripes that run between the dorsal fin to the tail.
They are about 6 to 6 ½ feet long. They weigh from 150 to 187 pounds. The males and the females look very similar in size. The male does have a dorsal fin that is more curved than the females.
There are teeth found in both the upper and the lower jaws. They may have from 24 to 36 pairs of teeth that are very small and pointed. Usually, the upper jaw will have 2 sets less than what is found in the lower jaw.
Distribution
The Dusky Dolphin resides in the coastal waters of the Southern Hemisphere. The best known locations for them include New Zealand, the Southern region of Australia, The Southwest area of Africa, and in Tasmania. There are small populations of this dolphin living along the Western coast of South America.
They are coastal and can be located around both the slopes and the continental shelves. They stick to the warmer regions, but from time to time they have been found living in cooler temperatures as well.
Behavior
The Dusky Dolphin is very social, and their pods can be more than 1,000 members. However, it is more common to find them in much smaller numbers. They typically will range from 20 to 500 members. It is believed that the larger numbers come together for feeding and that there are plenty of subgroups within a larger pod. This allows a level of hierarchy to work for them that can be difficult for observations to fully identify.
They are very acrobatic and can be seen leaping out of the water. They are known to tumble in the air. They are also commonly found approaching boats so that they can bow ride. Playing and leaping are types of activities they often take part in as they socialize. They can swim very fast too. Communication includes the use of squeals, clicks, whistles, and squeaks. They are loud sounds and can be heard almost 2 miles away when they occur while the dolphins are out of the water.
Feeding
There are plenty of types of food that the Dusky Dolphin feeds upon. They include shrimp, squid, various fish, and anchovy. They can feed during the day or at night, and generally do so in highly sophisticated collaborative efforts. They are able to feed both at the surface of the water and at the bottom of it which gives them plenty of opportunities.
They tend to take part in efforts that involve up to 300 dolphins working as a team to successfully herd larger schools of fish. What is very interesting though is that they can change their strategies for foraging to fit the circumstances. Their communication each other is key to making sure they are able to get enough food for survival.
Reproduction
Spring is the time of year when the Dusky Dolphin is most likely to take part in mating. It takes about 11 months for the calf to be born. The males compete aggressively with each other in order to be able to mate with the females. There seems to be less involved with mating rituals with this species than with other dolphins. However, the bonds that do form seem to be apparent within a pod.
The age for matting seems to vary in different locations. It is believed that it could be determined based on food resources, stress, the length of the dolphin, and more. There needs to be additional research conducted to back up such theories. The females and their young will form nursery groups and they tend to stay in the water that is shallow so that they can rest.
The young will be fully weaned at about 18 months from the milk the mother produces. However, about 6 to 8 months of age they will be introduced to other food resources. They will be taught how to successfully hunt so that they can one day take care of their needs by contributing to the collaborative hunting efforts.
Conservation Status and Threats
It has been difficult to get a good count on the number of Dusky Dolphins in the wild. However, it is believed that they do endure huge losses of numbers due to getting tangled up with fishing nets or illegal harpoon hunting. Efforts to help with improving fishing methods has proved to be helpful. In Peru there is a huge demand for the meat of this dolphin and efforts to stop illegal killing can be difficult to implement even though it has been banned since 1996.
Some have been worried about the volumes of tourists that come to watch the dolphins around New Zealand. However, the experts don't feel that this process has caused any major stress factors for the Dusky Dolphins to contend with. Studies that will help to identify environmental problems as well as to get a better count on the number of them are in progress. Right now, they aren't in serious danger but hopefully conservation steps will also prevent their numbers from ever dropping low enough for them to be at risk of extinction.
