OBSERVATIONS ON A MASS STRANDING OF SPINNER DOLPHIN, 

 STENELLA LONGIROSTRIS, FROM THE WEST COAST OF FLORIDA 



James G. Mead,' Daniel K. Odell,^ Randall S. Wells,'' and Michael D. Scott" 



ABSTRACT 



The spinner dolphin, Stenella longirostris, while well known in portions of the Pacific Ocean, has rarely 

 been available for study in the Atlantic. Data from 28 individuals from a mass stranding in Florida 

 enabled us to make preliminary estimates of mean size and age at sexual and physical maturity, 

 reproductive seasonality, and sexual dimorphism for this species in the southwest Atlantic. Our 

 sample most closely resembles the Hawaiian populations described by Perrin, but further work in the 

 Atlantic is likely to demonstrate other populations differing morphologically from this one. 



The spinner dolphin, Stenella longirostris, is 

 widely distributed in tropical to warm temperate 

 waters of the world (Perrin 1975), but due to its 

 predominately pelagic habits, is seldom found 

 stranded and is not generally taken in coastal 

 fisheries. As a result, very little is known of its 

 biology except in the eastern tropical Pacific, 

 where it is taken in considerable numbers inciden- 

 tal to purse seining for yellowfin tuna. Perrin et al. 

 (1977) have recently published investigations on 

 the eastern population of spinner dolphin from the 

 Pacific. 



The species is apparently common in the Carib- 

 bean (Caldwell et al. 1971; Erdman et al. 1973; 

 Taruski and Winn 1976), but there are few rec- 

 ords, all of them strandings, from the Gulf of 

 Mexico. Gunter (1954) did not find any evidence 

 of this species in the Gulf of Mexico. Layne (1965) 

 reported on a mass stranding of this species from 

 Dog Island, Fla. (lat 29 48' N, long. 84 38' W), 

 where 36 animals stranded on September 1961. 

 Lowery (1974) reported a single adult male from 

 Fort Walton Beach, Fla. (lat. 30^24 ' N, long. 84°47 ' 

 W). Schmidley and Shane^ reported a 158 cm male 

 which stranded alive at Sabine Pass Beach, Tex., 

 on 16 May 1976, and a pregnant 188 cm female 



'Division of Mammals, Smithsonian Institution, Washington, 

 DC 20560. 



^Rosensteil School of Marine and Atmospheric Sciences, Uni- 

 versity of Miami, Miami, FL 33149. 



^Department of Zoology, University of Florida, Gainesville, 

 Fla.; present address: Center for Coastal Marine Studies, Uni- 

 versity of California, Santa Cruz, CA 95060. 



■•National Fish and Wildlife Laboratory, Gainesville, FL 

 32601. 



=Schmidley, D. F., and S. H. Shane. 1978. A biological as- 

 sessment of the cetacean fauna of the Texas coast. Final Rep., 

 U.S. Marine Mammal Commission Contract MM4AC008, avail- 

 able Natl. Tech. Inf Serv., Springfield, Va., as PB 281763, 38 p. 



Manuscript accepted October 1979. 

 FISHERY BULLETIN; VOL. 78, NO. 2, 1980. 



found on Padre Island, Tex., during March 1975. 

 Shane ( 1977) reported two additional records from 

 Padre Island: a 173 cm female which stranded 

 about January 1976 and a 183 cm male on 4 June 

 1977. The present study is based on 28 animals 

 from a single mass stranding on the west coast of 

 Florida. 



At this point it is not possible to determine 

 whether the occurrences recorded from the west 

 coast of Florida were derived from a population in 

 the Gulf of Mexico or were strays from the Carib- 

 bean. While there is a small fishery for mixed 

 species of dolphins in the Caribbean (Caldwell et 

 al. 1971), catches of spinner dolphin are relatively 

 infrequent and are unlikely to have an apprecia- 

 ble effect on the population. In contrast, the popu- 

 lations studied by Perrin and others in the Pacific 

 are taken in large numbers incidental to purse 

 seining for yellowfin tuna. 



The causes of mass strandings of cetaceans are 

 still very little understood (see Geraci 1978 for a 

 recent review of the subject). It is clear that this is 

 a very complex problem which goes far beyond the 

 scope of this paper. It is also clear that much of our 

 lack of understanding is based upon a lack of in- 

 formation on the species involved. We have felt 

 that it was also important to include material on 

 the circumstances of the stranding itself, even 

 though this is not directly related to the conclu- 

 sions drawn from examination of the specimens. 



CIRCUMSTANCES OF 

 THE STRANDING 



The stranding occurred on the north end of 

 Casey Key, with most of the dolphins concentrated 



353 



