Ferrero and Walker: Growth and reproduction of Delphmus delphis 



485 



measured to the nearest millimeter. Each ovary was 

 sliced transversely into serial sections (=1 mm thick) 

 with a scalpel and examined for the presence of cor- 

 pora lutea and corpora albicantia. Two measure- 

 ments of corpus diameter, taken at right angles, were 

 recorded for well-regressed corpora; three diameters 

 were recorded for larger corpora. Total corpus counts 

 included corpora albicantia and corpora lutea from 

 both the right and left ovaries. Females were classi- 

 fied as sexually mature if at least one corpus was 

 present on either ovary. 



Corpora were examined externally for indications 

 of regression, including color change (i.e., darken- 

 ing), reduced size and surface furrowing, and were 

 classified by type following Perrin et al. (1976). 



Results 



The sample 



From February to December 1990 and 1991, a total 

 of 707 D. delphis (376 males and 331 females) were 

 examined (see Fig. 1 for approximate collection loca- 

 tions). Sex, length, collection date, and location were 

 recorded for each specimen, and biological samples 

 were collected from 152 of these dolphins (93 males 

 and 59 females). 



Postnatal growth patterns and the 

 reproductive parameters, average age 

 and average length at sexual matura- 

 tion, were measured by using the por- 

 tion of the dissected sample for which 

 both age and reproductive status were 

 determined (70 males and 43 females). 

 We tested for differences in the length 

 distributions of the total sample and the 

 reproductive sample; no significant dif- 

 ferences were detected (Kolmogorov- 

 Smirnov Test, D=0.18, P>0.05) The total 

 sample (rc=707) was used to examine sex 

 ratios, gestation period, and reproductive 

 seasonality. The spatial and temporal dis- 

 tribution of the total sample reflects the 

 movement of the driftnet fisheries north- 

 ward from February to August, then 

 southward in the fall (Gong et al., 1993; 

 Nakano et al., 1993; Yatsu et al., 1993; 

 Yeh and Tung, 1993; Table 1). 



Male D. delphis ranged from 0.4 to 

 27 years in age (n=93): 3% were calves 

 <1 year old (n=3), 23% were yearlings 

 (n=21), and the remainder were >2 

 years old. Female ages ranged from 

 to 26 years (n=59); one newborn was 



sampled, 5% were calves <1 year old (n=3), and 32% 

 were yearlings (n = 19). The age distribution of both 

 sexes (Fig. 2) declined intrinsically except between 

 the two youngest age groupings. 



Males ranged in length from 86 to 211 cm. Females 

 ranged from 81 to 199 cm (Figs. 3 and 4). 



Stock identification 



The two recently described species of common dol- 

 phin in the North Pacific Ocean are separable on the 

 basis of cranial morphometries and color pattern 

 (Heyning and Perrin, 1994). To date five cranial speci- 

 mens are available from the driftnet fisheries and of 

 these, one is from an adult animal. The rostral length 

 to zygomatic width ratio for the single adult speci- 

 men (201 cm, male) was 1.36. The mean ratio for 

 adult male short-beaked common dolphin presented 

 in Heyning and Perrin (1994) was 1.37 (SE=0.046). 

 Preliminary comparison of photographs of common 

 dolphins taken in the driftnet fisheries (color pat- 

 tern features are described in Heyning and Perrin 

 [1994]) suggests that our sample more closely re- 

 sembles the short-beaked common dolphin. Further- 

 more, the currently known distribution of both spe- 

 cies of Delphinus presented in Heyning and Perrin 

 (1994) indicates that only the short-beaked form of 



170°E 180° 170°W 160° 



Figure 1 



Approximate sampling locations of 376 male and 331 female common dol- 

 phin, Delphinus delphis, caught in Japanese, Korean, and Taiwanese drift 

 nets, February to November, 1990 and 1991. 



