THE AGE, GROWTH AND REPRODUCTION OF THE HUMPBACK DOLPHIN, SOUSA CHINENSIS, IN KWAZULU-NATAL
Zianca Nolte, William Froneman and Stephanie Plön
Rhodes University, Department of Zoology and Entomology, Nelson Mandela Metropolitan University

 

Abstract
Globally inshore cetaceans are being threatened by a number of anthropogenic activities. The Indo-Pacific humpback dolphin, Sousa chinensis, is currently listed as ‘near threatened’ by the International Union for the Conservation of Nature (IUCN) and likely population declines in KwaZulu-Natal are primarily due to the incidental capture of dolphins in shark nets. In order to revise any management strategies, knowledge on the life history of the species is required to optimise conservation actions. To date very little is known about the biology of humpback dolphins. The aim of this study was to determine basic life history parameters, such as age, growth and reproduction of humpback dolphins incidentally caught in shark nets. Age was estimated by counting the growth layer groups (GLGs) in the dentine or cementum of sectioned and stained teeth. The age and length at which male humpback dolphins become physically mature is estimated to be 24 GLGs and 266.48 cm, whereas for females it is estimated at 16 GLGs and 239.29 cm total body length. Sexual maturity was histologically assessed from gonal material in males and is attained between 9 and 10 GLGs. In females, ovaries were assessed macroscopically for the presence of corpora, which indicate past ovulatory events. Females attain sexual maturity at roughly 7.6 GLG. Results from this study can assist in assessing the status of existing population structures and help to determine the urgency and need for the implementation of conservation and management strategies, such as the management of shark nets or the installation of deterrent devices like “pingers” to ensure the continued survival of humpback dolphins in KwaZulu-Natal waters.

 

Presentation Topic
THE AGE, GROWTH AND REPRODUCTION OF THE HUMPBACK DOLPHIN, SOUSA CHINENSIS, IN KWAZULU-NATAL
Contact Ms Nolte:
Email Zianca Nolte