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.----------------------------------------DESCRIPTION OF THE FOCUS OF THE CASE STUDYSouthern 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 IMPORTANCEThe 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 STUDYThe 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 1951-2014.2016年《环境状况报告》（State of the Environment，简称SoE）的海洋章节整合了多套基于多组海洋数据流开发的专家模板。本元数据记录（metadata record）围绕案例研究《南方蓝鳍金枪鱼（Southern bluefin tuna）》展开说明。本记录附件包含完整案例研究内容，涵盖相关图表（如已提供）。若可获取，生成该案例研究所使用的海洋数据流（Data Stream）可通过本记录的“在线资源”板块获取。 ——案例研究核心内容说明 南方蓝鳍金枪鱼（SBT）是澳大利亚海洋环境中的重要顶级捕食者：幼鱼夏季会在大澳大利亚湾季节性集群；亚成体与成体主要在冬季活动于澳大利亚南部及东南海域；成体则主要于春夏季在澳大利亚西北海域的该物种唯一产卵场集群。 南方蓝鳍金枪鱼是国际商业捕捞及国内休闲垂钓领域极具价值的目标捕捞物种。在澳大利亚海域内，夏季于大澳大利亚湾海域开展的围网渔业可捕捞2至4龄的幼龄南方蓝鳍金枪鱼，该产业每年可为区域经济带来约1.5亿澳元的产值，经济效益显著。冬季在澳大利亚东部沿海海域开展的延绳钓渔业以大型南方蓝鳍金枪鱼为目标，仅能捕捞到澳大利亚商业配额中的少量份额。 ——关键关切问题 据估算，受捕捞活动影响，南方蓝鳍金枪鱼的产卵群体生物量（成体种群规模的衡量指标）已锐减至原始规模的极低占比。该种群的枯竭状态使其被《环境保护与生物多样性保护法案》（Environment Protection and Biodiversity Conservation Act，简称EPBC Act）列为“依赖保护”物种，同时被国际自然保护联盟（International Union for Conservation of Nature，IUCN）列为“极危”物种。与南方蓝鳍金枪鱼丢弃渔获、未报告捕捞及休闲捕捞相关的未统计死亡量，可能会影响南部蓝鳍金枪鱼保护委员会（Commission for the Conservation of Southern Bluefin Tuna，简称CCSBT）设定的当前种群修复目标的达成。 ——案例研究所用数据流 本案例研究基于南部蓝鳍金枪鱼保护委员会（CCSBT）及其扩展科学委员会年度报告中的种群评估信息。相关评估基于覆盖该委员会管辖海域、时间跨度为1951年至2014年的渔业捕捞数据、航空调查数据以及亲缘标记重捕法相关数据开展。