Reproductive biology of yellowfin tuna in the eastern Australian Fishing Zone, with special reference to the north-western Coral Sea

Abstract

Developmental stages of oocyte maturation and degenerative stages of postovulatory follicles in yellowfin tuna from the eastern Australian Fishing Zone of the Coral Sea are described. The time of spawning of yellowfin appeared to be during the late evening and early morning. Final oocyte maturation occurred in less than 24 h; postovulatory follicles could not be identified in ovaries after 24 h. Spawning of yellowfin commenced in the north-western Coral Sea by October and had ceased in the central-western Coral Sea by late February. The duration of spawning appeared to be less protracted in the south-western Coral Sea. The average spawning frequency of female yellowfin in the western Coral Sea was once every 1.54 days. Significant differences in spawning frequency were found between different size classes of yellowfin; larger fish spawned more frequently. The spawning stock of yellowfin in the north-western and central-western Coral Sea could be the major source of recruits for the tuna fisheries off the eastern coast of Australia.