GROWTH AND REPRODUCTION OF THE NORTHERN RIGHT WHALE DOLPHIN, LISSODELPHIS-BOREALIS, IN THE OFFSHORE WATERS OF THE NORTH PACIFIC-OCEAN

Biological samples and data were obtained from 229 northern right whal e dolphins, Lissodelphis borealis (99 males and 130 females), taken in Japanese squid driftnets in the central North Pacific Ocean, May - No vember of 1990 and 1991. Length and sex were recorded for an additiona l 188 males and 272 females. Ages were determined by counting dentinal growth layer groups. Female reproductive status was determined by mac roscopic examination of ovaries; 67 were mature. Sixteen percent were pregnant, 3% were pregnant and lactating, 33% were post partum, 24% we re lactating (no recent pregnancy), 10% were resting, and 14% were of unknown condition. Testis and epididymis were examined for evidence of spermatogenesis; 28 were mature. Three estimates of length at birth w ere 99.7, 100.6, and 103.8 cm. The gestation period was 12.1-12.3 mont hs. The sex ratio at birth was not significantly different from 1.0; t he male component decreased with age. Estimates of the average age at sexual maturation among males were 9.9 and 10.1 years; average length at sexual maturation was estimated at 215.1 and 214.7 cm. Mature testi s masses ranged from 117.4 to 1300 g. Estimates of the average age at sexual maturation among females were 9.7 and 10.4 years; the average l ength at sexual maturation was estimated at 201.1 and 199.8 cm. Males reach an asymptotic length of 265 cm, females 210 cm. Ovulation rates were < 1.0/year. Calving appeared to peak in July and August; the mini mum calving interval was 2 years.