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The biology of the Black Bream, Acanthopagrus butcheri, in the Swan-Canning Estuary has undergone short-term, marked changes: implications for stock assessment

Cottingham, A., Hesp, S.A. and Potter, I.C. (2009) The biology of the Black Bream, Acanthopagrus butcheri, in the Swan-Canning Estuary has undergone short-term, marked changes: implications for stock assessment. In: Swan Canning Research and Innovation Program Showcase, 19 August, Perth, Western Australia.

Abstract

We compared the abundance, size and age compositions, pattern of growth, reproductive biology and body condition of Black Bream (Acanthopagrus butcheri) in the Swan-Canning Estuary, Western Australia, determined from samples collected during this study in 2007/08, and from previous studies dating back to 1993.

Our study revealed remarkable changes in the biology of this species over this relatively short period. Thus, while the abundance of Black Bream in seine net catches has increased greatly, its growth has declined substantially, as has the typical length at maturity and body condition.

The marked changes in the biology of Black Bream are likely to be associated with density-dependant processes and/or environmental changes to the estuary. This study has therefore demonstrated that the biology of the Swan-Canning Estuary population of Black Bream is highly plastic, a finding which has important implications for stock assessments for this species. Thus, many traditional equilibrium-based stock assessment approaches, e.g. per-recruit analyses, which assume that biological variables such as growth are constant, would be inappropriate. We therefore developed a non equilibrium-based approach which compared the relative biomass production of the Swan-Canning Black Bream population between the different study periods to assess the current state of this stock.

Publication Type: Conference Item
Murdoch Affiliation: Centre for Fish and Fisheries Research
School of Biological Sciences and Biotechnology
URI: http://researchrepository.murdoch.edu.au/id/eprint/20998
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