2016 SoE Marine Chapter - Case Study - Southern bluefin tuna

The Marine chapter of the 2016 State of the Environment (SoE) report incorporates multiple expert templates developed from streams of marine data. This metadata record describes the Case Study "Southern bluefin tuna". The full Case Study, including figures and tables (where provided), is attached to this record. Where available, the Data Stream(s) used to generate this Case Study are accessible through the "On-line Resources" section of this record.

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DESCRIPTION OF THE FOCUS OF THE CASE STUDY
Southern bluefin tuna (SBT) are an important apex predator within Australia’s marine environment with juveniles seasonally aggregating in the Great Australian Bight during the summer, subadults and adults utilising southern and south-eastern waters primarily during the winter months and adults aggregating in an areas off the north western region of Australia primarily during the spring and summer months on the only spawning ground for the species.
Southern bluefin tuna are a highly prized target species of international commercial and national recreational fisheries. Within Australian waters, a purse-seine fishery catches juvenile (2-4 yr old) SBT in the waters of the Great Australian Bight during the summer months, and is of significant value to the regional economy (~$150M annually). A longline fishery targeting large SBT off the eastern Australian seaboard during the winter months catches a smaller amount of Australia’s commercial allocation.

ISSUES OF IMPORTANCE
The SBT spawning biomass (a measure of the adult population) is estimated to have been depleted by fishing to a low fraction of its original size. The depleted nature of the stock has led to the listing of SBT as Conservation Dependent under the EPBC Act and Critically Endangered by the IUCN. Unaccounted mortalities associated with discards, unreported catches and recreational catches of SBT can impact on achieving current stock rebuilding targets set by the CCSBT.

DATA STREAM(S) USED IN CASE STUDY
The case study is based on stock assessment information produced in annual reports of the Extended Scientific Committee and the Commission for the Conservation of Southern Bluefin Tuna. Assessments are based on data relating to fishery catches, aerial surveys and close-kin mark recapture methods covering the spatial area of the Commission and a temporal period of 1951-2014.