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Atlantic Bluefin Tuna MSE
(Thunnus thynnus)
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Overview
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Atlantic bluefin tuna exhibits complex dynamics involving two stocks
(eastern and western), characterized by long-distance movements and
mixed-stock fisheries. Management Strategy Evaluation (MSE) for Atlantic
bluefin tuna, incorporating stock mixing between the two stocks, has
been under development since at least 2014. Following substantial
efforts by both the SCRS and the Commission, a Management Procedure (MP)
was adopted in 2022 (Rec. 22-09), and Total Allowable Catches (TACs) for
both stocks were set for 2023–2025 based on this MP (East: Rec. 22-08;
West: Rec. 22-10).
The Commission also adopted the Exceptional
Circumstances (EC) protocol in 2023 (Rec. 23-07, Annex 4), which
includes annual evaluation of ECs by the SCRS. No ECs have been invoked
since its adoption.
The SCRS has scheduled the application of the
MP in 2025 to set TACs for the period 2026-2028. In addition, the
Commission plans to conduct a stock assessment and review the Operating
Models (OMs) and the MP over 2026-2028.
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OM Developed
in 2014-2021
Recondition
in 2028
MP Adopted
in 2022
MP since 2022
ECP adopted
in 2023
EC evaluation
No EC since 2023
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History
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A detailed account of the Management Strategy Evaluation (MSE) process
for Atlantic bluefin tuna (BFT) is available in the SCRS Reports and in
the documents and activity reports of the ICCAT Atlantic-Wide Research
Programme for Bluefin Tuna (GBYP). The BFT MSE process was initiated in
2013 with a kick-off meeting held in Gloucester, USA (Anon., 2013).
During the development of the Operating Models (OMs), the SCRS began
consultations with Panel 2 in 2019 to define operational management
objectives, as outlined in Resolution 18-03.
Following the
adoption of the OMs in 2021 (Anon., 2021), the SCRS focused on the
development and evaluation of candidate Management Procedures (MPs), and
maintained regular engagement with the Commission to support the
adoption process. This engagement was facilitated through intersessional
meetings and a series of “Ambassadors webinars,” which were used to
communicate MSE results to stakeholders and decision-makers.
In
2023, the Commission adopted the Exceptional Circumstances Protocol
(Rec. 23-07, Annex 4). These milestones represent the culmination of a
decade-long, iterative process to establish a scientifically robust and
operationally viable management framework for Atlantic bluefin tuna.
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Contents
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Operating Models
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The SCRS developed a novel population dynamics model for the Atlantic bluefin tuna Operating Models (OMs) that explicitly accounts for stock mixing between the two biological populations. This model integrates multiple data sources, including otolith microchemistry, genetic analyses, and electronic tagging data. The development of this modelling framework required several years of effort, beginning around 2015, and culminating in the adoption of the OMs in 2021. Progress was partly constrained by the need for the SCRS to also conduct full stock assessments for the eastern and western Atlantic bluefin tuna stocks in 2017 (E/W), 2020 (E/W), 2021 (W), and 2022 (E). The adoption of these OMs in 2021 represented a significant milestone in addressing the complexities associated with stock mixing, achieved despite the concurrent demands of multiple assessment cycles.
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Materials
More materials can be found in Reference
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Management Objectives
Rec. 22-09
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Stock Status
Prob. >= 60% in green quadrant for both W,E stocks
Safety
Prob. < 15% of stock falling below Blim
Yield
Maximize overall catch in both W,E areas
Stability
TAC changes between periods +20%/-35%
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Candidate Management Procedure
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Seven Candidate Management Procedures (CMPs) were initially developed
since 2019,
following 2 CMPs were sent to the Commission for their
final selection in 2022.
- CMP-BR by Butterworth Rademeyer
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CMP-LW by Lauretta et al.
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Management Procedure
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The Commission adopted the BR Management Procedure in 2022 (Rec.22-09, Annex 2).
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The BR Management Procedure (MP) is an empirical approach that utilizes standardized abundance indices as its primary input. These indices are initially standardized for magnitude and subsequently aggregated using a weighted average of ten indices representing both the eastern and western Atlantic areas. The resulting composite index is then smoothed over three years to reduce the influence of observation error and interannual variability. Total Allowable Catches (TACs) are determined by applying a fixed harvest rate to the estimated abundance, as derived from the aggregated and smoothed indices.
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Exceptional Circumstances
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The Commission adopted the Exceptional Circumstances Protocol in 2023 (Rec.23-07 Annex 4).
The SCRS have evaluated Exceptional Circumstances annually since 2023, and there have been no Exceptional Circumstances declared yet.
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Principles of ECs
a: When there is evidence that the stock and/or fishery dynamics are in
states not previously considered to be plausible in the context of the
management strategy evaluation (MSE);
b: When there is evidence that
the data required to apply the management procedure (MP) are not
available or sufficient, or are no longer appropriate; and/or,
c:
When there is evidence that total catch for either the West area or the
East area is above the total allowable catch (TAC) for the respective
area set using the MP.
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References
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Materials
Rec/Res
Meetings
SCRS Docs
Others
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Updated: July 7, 2025
