Size and maturity status of the whale shark ( Rhincodon typus) at Ningaloo Reef in Western Australia

Abstract

Between 1995 and 1997, 360 observations of whale sharks at Ningaloo Reef revealed that approximately 85% were males (4–12 m TL). Based on the external morphology of claspers, all males <7 m TL were immature. Only 9.3% of males between 7 and 8 m TL were found to be mature, compared to 36.6% of those between 8 and 9 m TL. All but one of the 79 male whale sharks >9 m were considered mature. A logistic equation fitted to the percentage of mature males in each size class predicted a length at first maturity ( L 50) of ∼8.0 m TL, while 95% ( L 95) of males were mature by ∼9.0 m TL. Female whale sharks at Ningaloo Reef during this study were generally smaller and ranged in length from 4 to 8 m TL. The small size and general absence of female whale sharks from Ningaloo Reef suggest that the region may be important for feeding rather than breeding.