Marine Mammal of the Month

Characterized by their curious and fun-loving nature, dolphins have become a well-known figure across all of the world’s oceans. Hawai‘i is home to three main species of dolphins -- the bottlenose (Tursiops truncatus), the spotted (Stenella frontalis) and the spinner dolphins. Spinner dolphins (Stenella longirostris) have been seen across every tropical ocean around the world, and with advances in technology and better surveying techniques, we are just now beginning to understand their true nature.

Spinner dolphin (Stenella longirostris) leaps into the air. Photo by: Na Pali Riders, Flickr.

Spinner dolphins received their name from the way that they leap out of the water. Unlike all other dolphin species, spinner dolphins “rotate” or “spin” themselves when they jump. This “spinning” however, is more than just some performance. Scientists and psychologists believe the purpose of spinning out of the water is to remove attached fish/parasites and to communicate through signaling -- signals like “Let’s go” or “Watch out.” Another unique characteristic of spinner dolphins is that they are mostly nocturnal. During the night, spinner dolphins dive into ocean depths of 3,000 feet to hunt for their prey. The pod is divided into subgroups which then take turns diving for food, looking out for predators, and supervising the young as they are not yet ready to make the long dives. A pod of spinner dolphins can be as many as a few dozens to a couple thousand in size in which they are more efficient in finding prey. After the pod is well fed, they make their way into the coastal areas of islands to rest and recharge for the next night -- this is when most tourists spot the dolphins. Parents, having done all the work getting the food and feeding the young, tire out and fall into a resting state where they can still supervise their young and recharge their energy, while the play amongst each other.

According to the ICUN, the total population of spinner dolphins is still to be determined. With that said, there have been many records of spinner dolphin deaths as a result of bycatch and boating accidents. In oceans in the Eastern Pacific, spinner dolphins are known to associate with yellowfin tuna (Thunnus albacares), a very desired fish in the market. Without the commercial use of radar technology, however, many fishermen resorted to using spinner dolphins to locate yellowfin tuna for them. Knowing that the spinner dolphins will surround their prey, fishermen herd the dolphins into a tight ball while driving around in speedboats. They then drape a large net over the entire pod, ensnaring both the dolphins and the tuna. This method killed as many as six million spinner dolphins, discarding them back into the ocean. Thanks to the environmental protection agencies, a ban was placed on this highly unsustainable fishing method and fines are distributed out to anyone who fishes/swims within 50 yards of these dolphins. As a result, we have seen a huge decline in dolphin deaths and populations of spinner dolphins are expected to make a comeback.

Spinner dolphins are not new faces to the nearcoastal areas of O‘ahu. Known for their unique acrobatic ability, spinner dolphins catch the eyes of the hundreds of beach tourists every day. As humans on this Earth, it is our responsibility to respect these animals and monitor our impact to their environment so that we may enjoy their company in the future. •