Spinner Dolphin: Stenella longirostris

Abstract

The spinner dolphin is the most common small cetacean in most tropical pelagic waters. It can be seen at a great distance as it spins high in the air and lands in the water with a great splash. It can be identified externally by its relatively long slender beak, color pattern, and dorsal fin. The spinner dolphin is a member of the subfamily Delphininae sensu stricto. Morphologically and behaviorally it is most similar to the Clymene dolphin, but in a cladistic phylogenetic analysis based on cytochrome b mtDNA sequences it was not closely linked to that species. The spinner dolphin is pantropical, occurring in all tropical and most subtropical waters around the world between roughly 30–40°N and 20–40°S. It is typically thought of as a high-seas species, but coastal populations and races/subspecies exist in the eastern Pacific, Indian Ocean, Southeast Asia, and likely elsewhere. In the ETP, the habitats of the pelagic eastern subspecies and the eastern/Gray's intergrade/hybrid or “whitebelly spinner” are similar to that of the pantropical spotted dolphin: tropical surface water characterized by a shallow mixed layer, shoal and sharp thermocline, and relatively small annual variation in surface temperature. The whistles and burst pulses produced by spinner dolphins have been intensively studied in several areas; they vary in complexity geographically and with activity, serving functions that are only beginning to be understood. Gestation is about 10 months. Average length at birth is about 75–80 cm. Length of nursing is 1–2 years. Calving interval is about 3 years. Females attain sexual maturity at 4–7 years and males at 7–10 years. As is the case for other small cetaceans caught in fishing nets, local human consumption of bycaught animals in several regions has led to the development of markets and large directed catches from unassessed populations.