AGE, GROWTH, AND REPRODUCTIVE PATTERNS OF THE PACIFIC WHITE-SIDED DOLPHIN (LAGENORHYNCHUS OBLIQUIDENS) TAKEN IN HIGH SEAS DRIFT NETS IN THECENTRAL NORTH PACIFIC-OCEAN

Biological data were collected from 341 Pacific white-sided dolphins ( Lagenorhynchus obliquidens; 171 males and 170 females) taken in high s eas drift nets in the central North Pacific Ocean in June-September of 1990 and 1991. Age was determined for 149 dolphins (73 males and 76 f emales) by counting dentinal growth layer groups and measuring postnat al dentine thickness. Reproductive status was determined for 76 female s and 71 males. Ten females were sexually mature (3 pregnant and 7 lac tating), as were 11 males. The estimated average length at birth was 9 1.8 cm (SE = 0.4787 cm; n = 4). The estimated gestation period was 11- 12 months. The sex ratio was not significantly different from 1:1. The youngest sexually mature male was 10 years of age and the oldest sexu ally immature male 11 years. The youngest sexually mature female was 8 .3 years of age and the oldest sexually immature female 11 years. The average length at sexual maturation was 173.7 cm (SE = 0.8953 cm) for males and 177.5 cm (SE = 1.5 cm) for females. Males and females reache d an estimated asymptotic length of 184 and 177 cm, respectively. Esti mates of early postnatal growth rates were complicated by poor growth model fit; however, both sexes appeared to grow about 4.5 cm/month dur ing the first half year. A calving period preceded sampling during lat e winter and spring.