GROWTH AND REPRODUCTION OF THE COMMON DOLPHIN, DELPHINUS-DELPHIS LINNAEUS, IN THE OFFSHORE WATERS OF THE NORTH PACIFIC-OCEAN

A total of 707 common dolphins, Delphinus delphis Linnaeus, (376 males and 331 females) taken in Japanese, Korean, and Taiwanese drift nets in the central North Pacific Ocean from February to November 1990 and 1991 were examined. Sex, total length, date, and location of capture w ere recorded. Biological samples were collected from 152 of the dolphi ns examined (93 males and 59 females). Ages were determined by countin g dentinal layers. Female reproductive status was determined by macros copic examination of ovaries (n=43). Eight females were mature, two we re pregnant, three were resting, two were lactating, and one was of un known condition. Testes and epididymes were examined for evidence of s permatogenesis (n=70); 21 males were mature. A preliminary estimate of gestation period was 11.1 months. The sex ratio appeared to favor mal es; segregation during the sampling period may be responsible for diff erences from 1.0. Male average age at sexual maturation was estimated to be 10.5 years. The largest sexually immature male was 179 cm; the s mallest sexually mature was 182 cm. Mature testis weights ranged from 273.2 g to 1,190 g. Females reached sexual maturation at about 8.0 yea rs; estimates of length at sexual maturation were 172.8 and 170.7 cm. Predicted asymptotic lengths for males and females were 188.1 cm and 1 79.4 cm, respectively. Calving appeared to peak in May and June. Sampl ing effort moved northward through September; infrequent sampling of p arturient females and neonates during the projected calving mode sugge sts they were segregated outside the fishing area at that time.