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Fishery Bulletin 93(3), 1995 



common dolphin extends into the driftnet 

 fisheries area of the central North Pacific 

 Ocean. On the basis of these factors, we pro- 

 visionally assign the Delphinus in our 

 sample to the short-beaked common dolphin 

 D. delphis. 



Growth 



Length at birth and gestation period 



Only two fetuses (65.0 cm and 12.6 cm) and 

 one age-0 neonate (82 cm) were collected; 

 this small sample size limited our ability to 

 calculate a length at birth with the method 

 described by Hohn and Hammond ( 1985) or 

 the modified DeMaster (1978) approach 

 described by Ferrero and Walker (1993). 



The small sample size of newborns and 

 lack of near-term fetuses also limited esti- 

 mation of the gestation period. However, if 

 we assume that the length of the age-0 neonate ap- 

 proximates the size at birth (82.0 cm) and consider 

 the collection dates and lengths of the two fetuses, 

 then preliminary estimates can be determined. We 

 explored the gestation period parameter in two ways: 

 1) by using the relationship between fetal length and 

 time described by Hugget and Widdas (1951), and 2) 

 by using the relationship between size at birth and 

 gestation period described for several species of 

 delphinids by Perrin et al. (1977). 



Following Hugget and Widdas ( 1951), we regressed 

 the lengths (y) of our two fetus specimens and the 



10 15 



Age (years) 



Figure 2 



Age-frequency distribution of 93 male and 59 female common dolphin, 

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

 nets, February to November, 1990 and 1991, in the central North Pa- 

 cific Ocean. 



age-0 neonate (we assumed this animal was recently 

 born given the complete absence of postnatal den- 

 tine) on time, indexed by day of the year of collection 

 (x), in order to estimate the linear phase of growth 

 (t g-t ), where t is the gestation period and t Q is the 

 "nonlinear" phase of growth. The regression equation 



-57.04 + 0.264* 



(1) 



was significant (r 2 =0.996, P<0.001). The linear 

 growth phase was estimated to be 10.5 months. We 

 did not attempt to estimate the nonlinear phase be- 



