SEXUAL DIMORPHISM IN THE DORSAL FIN OF PACIFIC WHITE-SIDED DOLPHINS (LAGENORHYNCHUS OBLIQUIDENS) FROM COASTAL WATERS OFF JAPAN

Abstract

Records of external measurements of 35 male and 40 female Pacific white-sided dolphins collected from 1970 to 2020 were examined for the shape change of the dorsal fin and the difference between males and females. For mature individuals based on a body length of 200 cm, which is an approximate guideline for maturity, a significant difference was detected in the ratios of the front edge length and the tip height which were 3.8 on average with a maximum value of 5.6 in males, and 2.8 (average) and 3.1 (maximum value) in females, respectively. It was concluded that sexually mature males could be distinguished by measuring the shape of the dorsal fin.