Bigeye tuna expected to be second species to have a harvest strategy in place at IOTC

May 12, 2022

May is gearing up to be a big month for the Indian Ocean Tuna Commission (IOTC), as members plan to hold four policy and science meetings over the next two weeks. Two of those meetings – the Technical Committee on Management Procedures (TCMP) on May 13-14 and IOTC’s annual Commission meeting on May 16-20, will be crucial to the development and adoption of the RFMO’s harvest strategy portfolio. While a variety of harvest strategies, also known as management procedures (MPs), will be discussed at the TCMP, including those for albacore, skipjack, yellowfin, and swordfish, the big-ticket item will be the bigeye tuna MP. In development since 2014, a draft proposal of a comprehensive bigeye tuna management procedure, submitted by Australia, will be reviewed by the TCMP. Next week’s Commission meeting will then have the tremendous opportunity to adopt the measure, marking IOTC’s first-ever full MP, joining the skipjack tuna harvest control rule as the Commission’s only two pre-agreed frameworks for calculating and recommending catch quotas. 

The Commission now has two main decisions to make regarding management objectives and candidate MPs. The management objective for the bigeye tuna fishery includes a mandate to avoid both overfishing and an overfished state, often referred to as being in the “green zone” of the Kobe plot. Objectives should be specific and measurable in the context of management procedures, but the probability by which the final MP must achieve this objective has yet to be decided. As part of the adoption process, the Commission still has to select between a 60% and 70% probability of being in the Kobe green zone in the specified years 2034-2038, with the latter providing a stronger assurance that the MP will be successful and maintain a sustainable stock. 

The Commission must also decide between the two final candidate management procedures that the Scientific Committee recommended in 2021 after rigorous management strategy evaluation (MSE) testing. The two candidates are not too different, with both operating under a 3-year management cycle and limiting the fluctuation in catch limits between management periods to 15%. One of the candidate MPs takes a “hockey stick” approach, with catch rates increasing as the population increases, up to a certain population size where the target catch rate levels out resembling a hockey stick when plotting both catch and biomass on an X/Y graph. The other candidate MP relies more on the specified management objective, using internal projections to prescribe a catch limit that can best hone in on and achieve the objective. 

Both candidate MPs were able to achieve the prescribed management objective with both a 60% and 70% probability. Performance between the two differs only slightly. The hockey stick MP shows slightly higher average catches while the other has more stable catches, including potentially a higher initial catch. Regardless of which management procedure the Commission selects, they will be choosing one that performs in a robust manner and is likely to succeed. 

Although bigeye is not currently overfished, overfishing is occurring, and the MP can help to ensure that fishing levels are again sustainable. This will avoid depleting the stock to a dangerously low level that would likely then require tough management decisions to recover the stock, as IOTC is currently facing for yellowfin tuna.

While a few tuna-RFMOs have a management procedure or harvest control rules in place, no tuna-RFMO has adopted a second MP for another species under its jurisdiction, let alone a full MP for any of the tropical tunas. IOTC will have that chance when Australia champions the bigeye tuna MP at the meeting later this week, and if adopted, the RFMO would position itself as a global leader of management procedures. Hopefully, the dominant bigeye fishing members will join Australia in this effort.