Spinner Dolphin

The spinner dolphin is the most acrobatic and abundant of all cetaceans in Sri Lankan waters.

Appearance: a small, slender dolphin with a long, slim beak. The head is very slim at the apex of the melon.

Key Characteristicsspinner-dolphin

  • Performs high, spinning leaps
  • Three-tone colour pattern
  • Streamlined slender body
  • Long, slender, dark-tipped beak
  • Long, poited flippers
  • Tall, falcate fin
  • Gently sloping forehead
  • Frequently bow rides
  • Usually found in large schools

Dorsal Fin: tall and falcate

Flippers: long and pointed at the tips.

Flukes: slight median notch

Teeth: sharp, pointed and conical. Upper jaw 90-130, lower jaw same.

Colouration: The surface pattern is a three-tone arrangement: dark grey along the cape, medium grey on the sides and pale grey, creamy white or pink on the belly. Some may have a dark lateral stripe between the medium-grey flanks and belly. A pink belly indicates a flush: the animal is radiating excess heat by dilating blood vessels near the surface of its skin. A dark stripe extends from the eye to the flipper. The tip of the beak and ‘lips’ are black.

Behaviour: Spinners ‘commute’ to shallow coastal waters during the daytime. Here they rest, play, care for their young and socialize while avoiding oceanic predators such as sharks, bill fish and larger odontocetes. They return to pelagic waters in the afternoon or evening to feed off the nearby continental slope. Several pods will often congregate inshore to form an aggregation of thousands, a so-called super-pod.

Foraging behavior is cooperative and well orchestrated, particularly when prey density in deeper waters is high.

Spinner dolphin society is leaderless and very fluid. Associations change daily. There is no strict hierarchy of dominance.

The trademark surface behavior of a spinner dolphin is a twisting leap into the air, rising three of four meters above the surface while the body is bent a series of graceful curves, making as many as five complete spins before diving back into the Ocean. Typically, a spinner will perform a series of gyrations, each less energetic than the  previous one, often concluding with an emphatic slap. Spins are most frequently performed while the school is spread out across the water.

Other frequent surface activities include lobtailing, flipper-slapping, partial breaches and porpoising, as well as bow-riding and other play with boats. Their high-pitched squeals and whistles can occasionally be heard when their heads are above the surface.

Group Size: varies from paris to schools of up to a thousand. Super-pods of cover three thousand have been observed.

Associates: a variety of other cetaceans, as well as yellowfin tuna and seabirds preying on baitfish schools. Most associations with other cetaceans are in pelagic waters.

Fishing-boats will often follow pods of spinner dolphins in the hope of locating tuna. Spinners that encounter sperm whales may harass them, causing the whalesto sound.

Diet: epipelagic and mesopelagic fish, shrimp and squid, taken mostly at night.

Dive Depth: 200-300m. Nocturnal foraging depth 60-100m.

Distribution: breeding residents, widely and abundantly distributed all round Sri Lanka and in adjacent waters. Super-pods in excess of a thousand individuals are frequently seen off Kalpitiya.

Sightings: all year round. Sri Lanka: extremely abundant, extremely so off Kalpitiya. Maldives:  extremely abundant. India: common.

Taxonomic Notes: Four subspecies of the spinners dolphin, Stenella longirostris, are recognized. These are geographically defined and differ in body shape, size and colour. The subspecies known as the Gray’s or Hawaiian spinner dolphin S.I.longirostris, with its typical tripartite colour pattern, is thought to be the subspecies present in Sri Lanka. Some spinner dolphins in Sri Lanka and Maldives, however, show a dark lateral and strip between their medium-grey flanks and belly. Representatives of subspecies, or other undescribed stocks, may exist here-and elsewhere in the world as well.