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Biological parameters for managing the fisheries for Blue and King Threadfin Salmons, Estuary Rockcod, Malabar Grouper and Mangrove Jack in north-western Australia

Pember, M.B., Newman, S.J., Hesp, S.A., Young, G.C., Skepper, C.L., Hall, N.G. and Potter, I.C. (2005) Biological parameters for managing the fisheries for Blue and King Threadfin Salmons, Estuary Rockcod, Malabar Grouper and Mangrove Jack in north-western Australia. Fisheries Research and Development Corporation

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Abstract

Data have been collected on those crucial aspects of the biology of Blue and King Threadfins, Estuary Rockcod, Malabar Grouper and Mangrove Jack that are required to develop appropriate management plans for conserving the stocks of these five commercially and recreationally important species. The following biological data have been obtained. (1) The size and age at which each species reaches sexual maturity. (2) The size and age at which the two species of threadfin change from male to female and the Estuary Rockcod and Malabar Grouper change from female to male. Note that, unlike the above four species, the Mangrove Jack is not hermaphroditic and thus does not change sex. (3) The habitats, size and age compositions, duration and location of spawning, and mortality of each species. As the two threadfin species are largely restricted to areas over bare substrate in nearshore waters, they are particularly accessible to fishers. Our results indicate that, currently, the Blue Threadfin is fully exploited and the King Threadfin is over-exploited, whereas the fisheries for the Estuary Rockcod, Malabar Grouper and Mangrove Jack are apparently sustainable at current fishing levels. However, our results emphasize that fishing mortality has a very marked adverse impact on the abundance of the ultimate sex of the four hermaphroditic species, and this needs to be considered when specifying legal lengths for retention. Managers also need to monitor the status of the stocks of Mangrove Jack which, because of its high value, is attracting an increasing amount of attention from the recreational, commercial and charter boat fishing sectors. Finally, the results of this study emphasize the pressing need to develop better methods for determining the natural mortality of fish species and thus being able to derive more robust estimates of fishing mortality.

Publication Type: Report
Murdoch Affiliation: Centre for Fish and Fisheries Research
School of Biological Sciences and Biotechnology
Series Name: FRDC project 2002/003
Publisher: Fisheries Research and Development Corporation
Notes: December, 2005
URI: http://researchrepository.murdoch.edu.au/id/eprint/19792
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