Sexual Dimorphism in Wild Bottlenose Dolphins (Tursiops truncatus) from Sarasota, Florida

We examined sexual dimorphism in external morphometric characters from 19 male and 32 female bottlenose dolphins (Tursiops truncatus) that were physically mature. These animals are long-term residents of the coastal waters near Sarasota, Florida, and were examined as part of an ongoing capture-release project. Males were significantly larger than females in 20 of 29 measurements; only one of eight measurements of the head showed significant absolute dimorphism. Proportional dimorphism (i.e., dimorphism corrected for body size) was less pronounced; only four linear measurements and three girth measurements exhibited significant differences between sexes. In addition, scarring of the dorsal fin occurred more frequently on males than on females. The occurrence of sexual dimorphism in this population of bottlenose dolphins is consistent with the model of a polygamous mating system.