FISHERY BULLETIN: VOL. 75, NO. 4 



data for two males (1,940 and 2,040 mm) and two 

 females (1,790 and 1,800 mm) from off Senegal in 

 the tropical Atlantic. Layne (1965) published 

 similar data for two males (1,845 and 1,910 mm) 

 and one female (1,965 mm) from Florida. Pilson 

 and Waller (1970) reported on an adult female of 

 S. microps [= S. longirostris] 176 cm long, from 

 the eastern Pacific. Harrison et al. (1972) pub- 

 lished detailed length, weight, and gonadal data 

 for 12 males (79 to 185 cm) and 21 females (86 to 

 188 cm) of S. longirostris from the eastern Pacific; 

 five males (150 to 182 cm) and two females (169 

 and 179 cm) of S. roseiventris [= S. longirostis] 

 from Hawaii; and nine specimens from the eastern 

 Pacific, eight males (165 to 178 cm), and one 

 female (171.5 cm) listed as "probably S. longiros- 

 tris." In their discussion of growth and reproduc- 

 tion, however, they did not differentiate between 

 S. longirostris and S. graffmani [ = S. attenuata], a 

 larger species that differs significantly from S. 

 longirostris in several features of life history 

 (compare results below with those for S. attenuata 

 in Perrin et al. (1976) and Kasuya et al. (1974)). 



Several recent reports emanating from the 

 Southwest Fisheries Center, National Marine 

 Fisheries Service (NMFS), NOAA, have dealt 

 with the developmental components of various as- 

 pects of the life history of S. longirostris other than 

 reproduction. Perrin (1972) described the de- 

 velopment of the color pattern in eastern Pacific 

 forms of the species. Perrin and Roberts (1972) 

 analyzed changes in organ weights with size, 

 based on 14 specimens. Dailey and Perrin (1973) 

 described differences in parasite frequencies cor- 

 related with age in 19 specimens. Perrin (1975a, b) 

 described developmental variation in morphology 

 in the eastern Pacific and defined three geograph- 

 ical forms (subspecies), of differing adult size: the 

 less-than-2-m-long "eastern spinner," the subject 

 of this report; the slightly larger "whitebelly spin- 

 ner," found farther offshore; and the "Costa Rican 

 spinner," which is restricted to the coastal waters 

 of Central America and attains a total length of 

 well over 2 m. 



This paper treats only the eastern spinner, the 

 form of S. longirostris most heavily involved in the 

 tuna fishery through 1975 in terms of numbers of 

 seine net sets and numbers killed (Perrin 1975a). 

 Some data for the whitebelly spinner are included 

 in certain of the analyses of the eastern spinner, 

 including those of length at birth and of brain 

 weight relative to body length, for reasons ex- 

 plained below. A preliminary report on the white- 



726 



belly form of S. longirostris appeared in Perrin et 

 al. 5 



METHODS AND MATERIALS 



The Field Program 



Nearly all of the data were collected by NMFS 

 scientific observers aboard commercial tuna ves- 

 sels. The data collection procedures were the same 

 as previously described for the spotted dolphin 

 (Perrin et al. 1976). Data on S. longirostris were 

 collected on 1 cruise in 1968, 4 in 1971, 12 in 1972, 

 21 in 1973, 33 in 1974, and 30 in 1975. Some 

 specimens were also collected in 1970 by personnel 

 of the Inter- American Tropical Tuna Commission 

 aboard chartered purse seiners. 



The Sample 



In 1971 and early 1972, when the observer pro- 

 gram was very limited, adult female specimens 

 were selected for dissection when available, and 

 the samples for those periods are, therefore, biased 

 with regard to the age and sex structures of the 

 kill. In 1968 and on cruises from October 1972 on, 

 no selection was practiced in determining which 

 animals were to be examined, and those samples 

 are assumed to be cross-sectional with respect to 

 the kill. Fetuses were not collected in 1968. 



The sample of animals for which life history 

 data including at least, but not restricted to, sex 

 and body length includes 2,675 specimens, 2,663 

 from precisely known localities (Figure 1) and 12 

 from imprecisely known localities, from the east- 

 ern tropical Pacific between lat. 2 1 °N and 3 °S and 

 west to long. 117°W. Because of the seasonal na- 

 ture of the tuna fishery, the sample is heavily 

 biased toward the early months of the year, with 

 minimal coverage of the latter part of the year and 

 practically no specimens from the summer months 

 (Table 1). Length-frequency distributions by 5-cm 

 increments for males and females, including 

 fetuses, are presented by year and month in Fig- 

 ures 2 and 3. 



5 Perrin, W. F., D. B. Holts, and R. B. Miller. 1976. Preliminary 

 estimates of some parameters of growth and reproduction of the 

 whitebelly spinner dolphin, a geographical form ofStenella lon- 

 girostris, in the eastern tropical Pacific. Working document 

 submitted to Meeting of Subcommittee on Small Cetaceans, Sci- 

 entific Committee, International Whaling Commission, London, 

 7-8 June 1976. SWFC Admin. Rep. LJ-76-12, Natl. Mar. Fish. 

 Serv., NOAA, La Jolla, Calif., 36 p. (Unpubl. rep.) 



