Kauai Spinner Dolphins (Stenella longirostris) are seen daily on our morning boat tours to Napali and Niihau. They will frequently display the behavior which gives them their common name and for which they are most famous: Acrobatic displays in which they will spin longitudinally along their axis (like a top) as they enthusiastically leap out of the water and through the air. They are a remarkably lively creature and perhaps the biggest crowd pleaser on our Kauai sightseeing tours.
The bulk of the Spinner Dolphin is dark grey, with darker patches in the tail stock, back and throat. It will often have a creamy-white patch on the belly, though this varies considerably. It has a distinctively long and thin beak, with a dark tip. The fins tend to be lengthy for its size. The dorsal fin is erect and may even lean forward in some older males. Spinner Dolphins are the most variable in form of all cetaceans so you’ll do best to recognize them by their dance.
Adults vary in size from 129 cm to 235 cm (4 to 7.5 feet) and weight from 23 kg to 78 kg (50-170 lbs) . The gestation period is 10 months with maturity reached at 4-7 years (females) and 7-10 years (males). Longevity is unknown.
The total current population is unknown but considered Endangered after the dramatic population loss incurred after the introduction of purse seine fishing for tuna in the 1950’s.
Spinner Dolphins are nocturnal feeders, feeding on the ocean’s “scattering layer” of marine life (fish, jellyfish, krill, shell-less snails and squid), which rises toward the surface in the evenings to feed on microscopic plant material.
Spinners congregate in groups that vary from just a few dolphins to great schools numbering in the thousands. The reason for the creature’s spinning is not known. One suggestion is that the great cauldron of bubbles created on exit and re-entry may act as a target for echolocation by other individuals in the school. It may also be simply play-acting, or more likely, a combination of both.
See Wikipedia, “Spinner Dolphin”, http://en.wikipedia.org/wiki/Spinner_dolphin