Fisheries WA has identified Shark Bay as a priority area for developing a formal management process for its fisheries and the habitats occupied by its commercial and recreational fish species (Fisheries Western Australia 1999). Such management plans are needed to sustain the commercial and recreational fish stocks and biodiversity of the fish communities of the region, both of which are considered essential for maintaining the value of Shark Bay both socially and as a World Heritage area (Fisheries Department of WA 1996; Fisheries WA 1999).
Appropriate advice for managers to develop plans for conserving western yellowfin bream, baldchin groper, blackspot tuskfish, blue tuskfish and bluespotted tuskfish stocks in Shark Bay requires for those species (1) reliable data on the age and size compositions, growth rates, lengths and ages at first maturity, fecundity, and the proportions of each sex in each age and size class of these hermaphroditic species and (2) a thorough understanding of the types of habitat occupied at sequential stages in the life cycle so that critical habitats can be protected.
Data have been collected on the biology of western yellowfin bream and four tuskfish species that are of the type and quality required by managers for developing appropriate plans for conserving the stocks of these five commercial and recreational species. Emphasis was thus placed on determining (1) the size and age at which each species reaches sexual maturity, (2) the size and age at which the first species, a protandrous hermaphrodite, changes from male to female and the other four species, which are protogynous hermaphrodites, change from female to male and (3) the proportions of individuals of each species that change sex. The marked interspecific variations in the above characteristics imply that each species should be considered independently when developing management plans. We are using the experience gained during this study to assist Dr Rod Lenanton, the chief supervising scientist for finfish at WA Fisheries, to produce a document on the importance of considering carefully the implications of hermaphroditism in managing fish species. During this study we developed an improved method for determining natural and total mortality in fish populations, which will be invaluable for managers of all fisheries for which there are appropriate data. The new method for estimating mortality has been provided to and discussed with Dr Lenanton.
Keywords: reproduction, hermaphroditism, protandry, protogyny, age composition, growth, mortality, habitat.