Developing a management procedure robust to uncertainty for southern bluefin tuna: a somewhat frustrating struggle to bridge the gap between ideals and reality |
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Authors: | Hiroyuki Kurota Kazuhiko Hiramatsu Norio Takahashi Hiroshi Shono Tomoyuki Itoh Sachiko Tsuji |
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Institution: | (1) National Research Institute of Far Seas Fisheries, Fisheries Research Agency, 5-7-1 Orido, Shimizu, Shizuoka Shizuoka, 424-8633, Japan;(2) Atmosphere and Ocean Research Institute, University of Tokyo, 5-1-5 Kashiwanoha, Kashiwa Chiba, 277-8564, Japan;(3) Fisheries and Aquaculture Department, FAO, Viale delle Terme di Caracalla, 00153 Rome, Italy |
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Abstract: | Fisheries management is conducted to achieve sustainable use of fishery resources, mainly through regulation of fishing activities.
For almost a decade, the Commission for the Conservation of Southern Bluefin Tuna (CCSBT) struggled to reach agreement on
a total allowable catch (TAC) for southern bluefin tuna (SBT) because of stock assessment uncertainties. To address this,
in 2002 the CCSBT commenced development of a management procedure (MP), a pre-agreed set of rules to determine how the TAC
will be adjusted as new monitoring data become available. The CCSBT Scientific Committee tested various candidate MPs using
operating models which simulate fish population and fishery dynamics as well as incorporate process, observation, and model
uncertainties. Candidate MPs were evaluated using performance measures related to the following management objectives: maximize
catches, avoid stock collapse, and minimize interannual catch variation. Of the MPs explored, some relied solely on empirical
data i.e., adjusted TAC based on catch per unit effort (CPUE) trends], whereas others were more complicated, based on population
models. In 2005, the CCSBT adopted a model-based MP that realized a moderate catch with low variability and avoided stock
collapse. This MP struck a compromise between the risk-prone and risk-averse standpoints of the different stakeholders. However,
despite this concerted scientific effort, the MP was not implemented because, shortly after its adoption, it became evident
that historical catches may have been substantially underreported. This complication necessitates returning to near the beginning
of the development process. MP approaches have various advantages and challenges to be explored further. However, it is essential
to lessen human-introduced uncertainty (such as catch misreporting) by enhanced enforcement, and to increase management robustness
to biological uncertainties by implementing MPs. |
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Keywords: | CCSBT Fisheries management Harvest control rule Management strategy evaluation Precautionary management |
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