Sexual dimorphism in long-beaked common dolphins (Delphinus capensis) from KwaZulu-Natal, South Africa

Abstract

We examined external morphometric parameters in incidentally caught long-beaked common dolphins (Delphinus capensis) from the east coast of South Africa for evidence of sexual dimorphism. We evaluated sexual dimorphism and allometric growth in 26 external body measurements from 211 individuals and assessed size and shape dimorphism. Most characteristics analyzed showed a negative allometric relationship to total body length for both males and females. Twenty-one measurements showed significant differences between the sexes. Among these were the 3 girth measurements, the length of the dorsal fin base, the distance between the tip of the upper jaw to the midpoint of the umbilicus, and the distance between the tip of the upper jaw to the center of the anus. Fourteen of the 26 characteristics analyzed showed significant differences in body shape between the sexes. Our results indicated that moderate sexual dimorphism is present in long-beaked common dolphins from this region, with males being both significantly longer and more robust than females. Sexual dimorphism in this species may be related to their mating or foraging strategies.