SPINNER DOLPHIN (T) 



Stenella longirostris Gray 1828 



Other Common Names 



Long-snouted dolphin, long-beaked porpoise, spinner 

 porpoise, rollover (St. Vincent). 



Description 



Spinner dolphins reach a maximum length of about 7 feet 

 (2.1 m). The body is slender. The beak varies from extremely 

 long and slender (Fig. 123) to relatively short (Fig. 125); the 

 beak is usually dark on top and clean white below, though 

 there may be some white above. The tip of the snout and the 

 lips are distinctly black, while those of both species of spotted 

 dolphins are light. The back is dark gray to black, the sides 

 are tan to yellowish brown, and the belly is white. Some of the 

 larger animals appear almost all black with faint, light 

 speckling. The dorsal fin is generally moderately falcate, but 

 may be almost triangular in adult males. It is often a lighter 

 gray near the middle, bordered by black or dark gray. 



Natural History Notes 



Spinner dolphins derive their common name from 

 their habit of leaping clear of the water and spinning 

 on their longitudinal axis. The reasons for this behavior 

 are unknown. Individuals may rotate 2 times, or more, 

 in one leap but spinning behavior is not observed as 

 frequently in the western North Atlantic as it is in the 

 eastern tropical Pacific. 



Spinner dolphins occur in herds of up to several hundred 

 individuals and are often seen jumping clear of the water, 

 working the sea surface into a froth. They frequently come to 



the bow of a boat from considerable distances to ride in the 

 bow wave and may ride for protracted periods. 



May Be Confused With 



Spinner dolphins may be confused with saddleback 

 dolphins. Both species occur in large herds and often come to 

 moving vessels to ride the bow wave. The two can be 

 distinguished, however, by these differences: 



Spinner Dolphin 



Saddleback Dolphin 



COLORATION 



Dark gray on back; tan or 

 yellowish tan on sides; white 

 on belly; lacks crisscross 

 pattern on sides; distinct 

 black stripe from flipper to 

 eye. 



Dark gray to brownish gray 

 on" back; white on belly with 

 crisscross or hourglass pat- 

 tern of tan to yellow on sides; 

 distinct black stripe from 

 flipper to middle of lower 

 jaw. 



Spinner dolphins might also be confused with bridled 

 dolphins, but may be distinguished by the differences 

 summarized on p. 108. 



Distribution 



Spinner dolphins are distributed in oceanic and coastal 

 tropical waters. Though one specimen was collected from 

 South Carolina, they have been more frequently reported 

 from both coasts of Florida, the Gulf of Mexico, the 

 Caribbean, and the West Indies. They have also been 



3S 



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Fi^re 122. — Spinner dolphins occur in large herds 

 in tropical waters. As illustrated by these photos of 

 animals off Venezuela in 1969, spinner dolphins 

 often leap clear of the water and may come to a 

 moving vessel from considerable distances away to 

 frolic in its bow wave. {Photo by M. Bartlett.) 



110 



