PERRIN ET AL.: GROWTH AND REPRODUCTION OF SPOTTED PORPOISE 



The division between this and the pre- 

 vious category is somewhat subjective and 

 arbitrary. 

 3. Speckled stage. Same as two- tone but with 

 discrete, very dark-gray spots on the ven- 

 tral surfaces; discrete light-gray spots on the 

 upper, darker surfaces present on some 

 animals but lacking on others; about 140 to 

 190 cm. 



120- 

 110- 

 100 - 

 90 - 

 80- 

 70- 

 60- 

 50- 

 40- 

 30- 

 20- 

 10- 



o 



z 



1x1 

 O 



dd 



FUSED 

 (604) 



AVERAGE 





 30 



20- 



10 - 



: 



50- 

 40- 

 30- 

 20- 



10- 



 



30 



20 



10 



MOTTLED 

 (138) 



AVERAGE 



_tj_ 



SPECKLED 

 (255) 





 20 



10 







AVERAGE 



' i 



. i>-i .1:1 



2- TONE 

 (288) 



NEONATAL 

 (72) 



1 I i 



70 60 90 100 110 120 130 140 150 160 170 180 190 200 210 220 230 



TOTAL LENGTH (cm) 



Figure 13. — Length-frequency distributions of males of 

 Stenella attenuata from the offshore eastern Pacific, by color 

 pattern phase. 



Mottled stage. Ventral spots converging and 

 overlapping in places, but patches of the 

 lighter gray background still visible, yield- 

 ing a mottled effect; discrete or merging 

 light-gray spots present on the upper sur- 

 faces; about 155 to 210 cm. 

 Fused stage. Ventral spots completely 

 convergent, to give the effect of a uniform, 

 medium-gray to dark-gray surface; on close 

 inspection, the individual overlapping spots 

 still discernible; about 160 to 230 cm. 



REPRODUCTION 



Seasonality 



Nishiwaki et al. (1965) suggested that S. at- 

 tenuata in Japanese waters breeds in the spring 

 and in the autumn. Harrison et al. (1972) stated 

 that lengths of fetuses indicate that parturition 

 in the eastern tropical Pacific (of S. graffmani = 

 S. attenuata ) also occurs both in the autumn and 

 in the spring. The postnatal length-frequency 

 data for large samples (Figures 15, 16; April 1968 

 and October 1972, for example) support the thesis 

 of major reproductive seasons in spring and au- 

 tumn but also suggest that there is a reproduc- 

 tive peak in summer as well. There is year-to- 

 year variation in the timing of reproductive 

 peaks, and there is some reproduction occurring 

 throughout most of the year. It is difficult to 

 define the reproductive seasons with precision be- 

 cause most of the sampling effort was in the early 

 (January- April) and late (October-December) 

 parts of the calendar year. The sampling inter- 

 sected obvious calving seasons in April 1968, 

 January 1972, October 1972, January 1973, and 

 June 1973 (Figures 15, 16). Calving peaks were 

 probably also present in some of the other sam- 

 pling months, but the samples were too small to 

 detect them or were biased in some fashion. A 

 summary of predicted birth dates for 373 fetuses 

 more than 15 cm long collected in 1971, 1972, and 

 1973, however, indicates that there may have been 

 three calving peaks in each of the 3 yr (Figure 17). 

 In each year there was a definite calving low in 

 winter. The synchrony was diffuse, and some 

 peaks were much sharper than others. The statis- 

 tical evidence for three annual peaks in calving is 

 weak, and when the data for all years are com- 

 bined, all that can be said with certainty is that 

 the calving season is prolonged, with a low point in 

 winter and a tendency for high points in spring 

 and fall. 



The Male 



Sexual development of the male was examined 

 under three criteria: 1) weight of testes, 2) aver- 

 age diameter of seminiferous tubules, and 3) 

 amoimt of sperm in the epididymis. Each of these 

 was examined relative to total length, weight, 

 and age (number of postnatal dentinal layers). 



Weight of the testes (Figure 18) increases pre- 

 cipitously at body length of about 175 to 190 cm, 



243 



