WCPFC Harvest Strategy
Harvest Strategy CMM 2014-06
Pursuant to paragraph 13 of CMM 2014-06, WCPFC12 agreed on a Workplan for adoption of Harvest Strategies under CMM 2014-06 Workplan for the adoption of Harvest Strategies under CMM 2014-06 (506.05 KB). The Commission agrees updates to the workplan annually and this website records the progress of the WCPFC Harvest Strategy development. The latest version of the Workplan can be accessed here.
For the development of a harvest strategy framework, the Scientific Committee noted three expert consultation workshop reports on management strategy evaluation: 1) SC12-MI-WP-05 Report of the Expert Consultation Workshop on Management Strategy Evaluation, 2) SC15-MI-IP-03 Report of the Second Expert Consultation Workshop on Management Strategy Evaluation, and 3) SC16-MI-IP-11 Report on the third external MSE review: Developments in the South Pacific albacore MSE framework).
The following information largely follows the structure and contents of the Recent progress in the technical development of harvest strategies for WCPFC stocks and fisheries (WCPFC18-2021-12).
II. Skipjack tuna in the WCPO
1. MSE framework for WCPO skipjack
The technical details of the MSE framework for WCPO skipjack were described in SC16-MI-IP-08. This paper outlined the analyses undertaken to develop the operating models (OMs) that comprise the MSE uncertainty grid and sets the range of scenarios across which candidate management procedures (MPs) will be tested. A selected MP is the combination of an agreed data collection program, estimation model and harvest control rule. A description of the generation of simulated data within the framework that will feed into the MP is in SC16-MI-IP-10.
The operating models are divided into a reference set and a robustness set. The reference set is considered to reflect the most plausible hypotheses of fishery and stock dynamics and forms the primary basis for selecting the ‘best performing’ MP. The robustness set comprises scenarios that are considered less likely though still plausible and are used to give a secondary indication of the performance of a reduced subset of MPs. Work continues to finalise the outstanding elements of the OMs that will comprise the robustness set for WCPO skipjack (SC15-MI-WP-06 Considering uncertainty when testing and monitoring WCPFC harvest strategies).
Performance indicators (PIs) measure the expected performance of each MP in relation to defined management objectives. They allow managers to identify and select the best performing MP. PIs are calculated from the evaluations across the range of scenarios included in the reference set. The methods for the calculation of the PIs are described in SC14-MI-WP-04 (Performance indicators for comparing management procedures using the MSE modelling framework). The skipjack MSE results are presented for a subset of six PIs (see SC17-MI-WP-04/WCPFC18-2021-13 Evaluations of candidate management procedures for skipjack tuna in the WCPO).
The interim target reference point for skipjack (CMM 2015-06) has been reviewed by SC17 and WCPFC18 (WCPFC18-2021-10 Further updates to WCPO skipjack tuna projected stock status to inform consideration of an updated target reference point: update of SC17-MI-WP-02). This paper includes examination of candidate revised interim skipjack TRPs between 36% and 50% of SBF=0 and requests of the TTMW1 (Tropical Tuna Measure Workshop 1) for estimated fishing mortality under each candidate depletion level.
Management procedures can be broadly classified as either empirical (in which the estimate of stock status is based on relatively unprocessed data e.g., CPUE trends) or model-based (in which the estimate of stock status is determined from an analytical stock assessment). Given the challenges associated with the interpretation of purse seine CPUE, the development of MPs for WCPO skipjack have focused on model-based approaches. The details of the MP for WCPO skipjack are provided in the appendices of SC17-MI-WP-04 (Evaluations of candidate management procedures for skipjack tuna in the WCPO), and the development, testing and performance of the EM is described in SC16-MI-IP-09 (Developing management procedures for WCPO skipjack: The Estimation Model). The evaluation of candidate management procedures for WCPO skipjack are described in SC17-MI-WP-04 and the results are available online for viewing and interrogation using the PIMPLE application (https://ofp-sam.shinyapps.io/pimple/).
2. Monitoring strategy
The monitoring strategy: 1) collects the necessary data from the fishery to calculate performance indicators (PIs) that are the same as (or as close as possible to) the PIs calculated from the evaluations, and routinely checks that the observed performance of the management procedure is consistent with expected performance from the evaluations (SC16-MI-IP-02); and 2) monitors the collection of new data to ensure that the basis of the evaluation framework and scenarios included in the uncertainty grid remain valid and appropriate.
As part of the monitoring strategy a stock assessment may be conducted. This stock assessment is different from the very tightly specified assessment that is conducted as part of the MP. Its purpose is to calculate PIs that are generated from stock assessment outputs (e.g. SB/SBF=0) and to check that the evaluation framework continues to adequately represent the stock and fishery dynamics.
3. Summary of harvest strategy development status
For WCPO skipjack, the modeling and evaluation framework is well advanced. At this point further technical work is focused on finalising the outstanding elements of the robustness set of operating models.
III. South Pacific albacore tuna in the WCPO
Interim target reference point for South Pacific albacore
WCPFC15 agreed on an interim target reference point (TRP) for South Pacific (SP) albacore at 56% of spawning stock biomass in the absence of fishing (0.56SBF=0) with the objective of achieving an 8% increase in CPUE for the southern longline fishery as compared to 2013 levels. If a future stock assessment indicates that this interim TRP will not result in the desired longline CPUE, then the interim TRP will be revised in order to meet this objective. The TRP shall be reviewed every 3 years, consistent with the SP albacore assessment schedule. In order to manage the required reduction in catches, the timeline for achieving the interim target reference point shall be no later than 20 years.
As requested by the SC17, SPC-OFP recalibrated the WCPFC interim TRP that would on average achieve the agreed objective of an 8 % increase in vulnerable biomass (CPUE proxy) for the southern longline fishery as compared to 2013 levels, and undertook projections to estimate the constant catch levels that would achieve the recalibrated TRP, on average, over the long-term. The results of the requested analyses are in WCPFC18-2021-17 (Recalibration of SP albacore TRP).
Trajectories to achieve the South Pacific albacore interim TRP
As requested by WCPFC15, the SC15 reviewed performance of stochastic stock projections across the grid of 72 assessment models under future fishery scenarios to examine their performance in recovering the stock to the TRP (SC15-MI-WP-02, Alternative trajectories to achieve the South Pacific albacore interim TRP). This paper was updated for the WCPFC16 (WCPFC16-2019-19) and for SC16 (SC16-MI-IP-01) considerations. Given the new stock assessment agreed at SC17, and the corresponding TRP recalibration, trajectories to achieve a recalibrated TRP will be the subject of further discussion.
1. MSE framework for South Pacific albacore tuna
An initial MSE framework for South Pacific albacore was first outlined in SC15-MI-WP-08 (South Pacific albacore management strategy evaluation framework) and the MSE framework was externally reviewed in SC16-MI-IP-11 (Report on the third external MSE review: Developments in the South Pacific albacore MSE framework). The modeling framework, including conditioning of the OMs and the elements of the MSE uncertainty grid for South Pacific albacore may be reviewed in the light of the most recent stock assessment (SC17-SA-WP-02 and SC17-SA-WP-02a) and could be revised if the current ranges of uncertainty are considered insufficient or inappropriate. The derivation and calculation of performance indicators for South Pacific albacore is detailed in SC15-MI-WP-03 (Performance indicators for comparing management procedures for South Paciﬁc albacore using the MSE modelling framework).
Recent work has focused on resolving a number of key technical challenges, most notably the process for generating simulated catch and effort data that sufficiently reflect the level of variability observed in real data. Unlike skipjack, the assessment of South Pacific albacore is heavily reliant on available CPUE information. A CPUE hindcasting analysis to examine how effectively catch and effort can be simulated within the South Pacific albacore evaluation framework was outlined in SC16-MI-IP-04 and is further developed in SC17-MI-IP-01. It highlights the difficulty in generating realistic nominal CPUE at the fishery level but indicates that, for some model regions, simulated CPUE for standardised index fisheries may be used as a basis for testing empirical MPs. However, it will also be necessary to develop candidate model-based management procedures (MPs) for South Pacific albacore following the recent testing of a range of empirical approaches.
2. Candidate management procedures
Under the initial technical workplan for developing harvest strategies for South Pacific albacore (SC14-MI-WP-02 Technical aspects of a potential South Pacific albacore harvest strategy), the primary focus was to develop empirical MPs using longline CPUE as the indicator of stock status that is input to the HCR. SC16-MI-IP-05 (HCR design considerations for South Pacific albacore) presented the results of South Pacific albacore MSE analyses conducted for empirical MPs along with a number of design considerations for HCRs that take either CPUE or size composition data as input. SC15-MI-WP-07 (CPUE analysis for South Pacific albacore) examined CPUE data and standardisation approaches (both traditional CPUE analysis and geostatistical analysis) to inform this process.
Analyses conducted to date have demonstrated the relative advantages and disadvantages of empirical MPs. On the one hand, they are very simple in concept, often require minimal processing of input data and can be more closely aligned with economic objectives related to catch rates and vessel profitability. On the other, they rely heavily on having a CPUE index that reliably tracks overall stock abundance. Such indices can be difficult to identify for a very widely dispersed stock for which multiple assessment regions are considered. Model-based approaches can address some of these issues (below) and a next step in the development of harvest strategies for South Pacific albacore would be to develop and test model-based MPs that use relatively simple biomass dynamic assessment models.
CPUE for South Pacific albacore
Noting the comments of CCMs concerning the stability of the simulated CPUE for South Pacific albacore, a retrospective forecasting was performed to test model predictions using existing historical data (SC16-MI-IP-04 Retrospective CPUE forecasting for the South Pacific albacore), which was updated in SC17-MI-IP-01 (Retrospective forecasting of CPUE for South Pacific albacore). Retrospective forecasting or hindcasting is a method for testing the performance of a predictive model using existing historic data. Results from the retrospective analysis showed evidence of a trend for underestimation of adult biomass with successive removal of years from the data in some model regions. However, in some instances, the forecasted standardized CPUE time-series showed potential to be used as a stock status indicator in the harvest strategy of South Pacific albacore.
Further work is required to test the performance of MPs using CPUE as a stock status indicator to drive future fishing opportunities, and it was recommended that alternative approaches to estimating stock status within the MP using simple models (i.e. biomass dynamic model) be explored and compared with the empirical CPUE approach.
3. Monitoring strategy
The monitoring strategy for South Pacific albacore has received relatively little attention to date, although much of the work undertaken to develop the monitoring strategy for skipjack can be similarly applied to South Pacific albacore, particularly in situations where the management objectives and hence performance indicators for the stocks and fisheries are similar.
4. Summary of harvest strategy development status
For South Pacific albacore, it may be necessary to re-visit the conditioning of the operating models and structural uncertainties in the light of the most recent assessment, although this depends to a large extent on the outcome of the stock assessment modeling work, the development on model-based MPs, and the considerations of the Scientific Committee. Following the initial investigation of empirical management procedures, that used estimates of stock status determined from longline CPUE as inputs to the harvest control rule (SC15-MI-WP-08), current work focusses on the development of model-based management procedures.
IV. Bigeye and yellowfin tunas in the WCPO
WCPFC12 agreed to a workplan for the adoption of harvest strategies for WCPO skipjack, bigeye, yellowfin and South Pacific albacore tuna. These four stocks are caught by an overlapping mix of fisheries. Management measures for one stock will impact fisheries that catch other stocks. An important consideration when developing harvest strategies for these stocks is to account for mixed fishery interactions.
1. TRPs for bigeye and yellowfin tuna
At SC15, risk-based TRPs for bigeye and yellowfin tuna were introduced (SC15-MI-WP-01, Minimum Target Reference Points for WCPO yellowfin and bigeye tuna consistent with alternative LRP risk levels, and multispecies implications) and the ‘minimum’ spawning-biomass-depletion-based TRPs for yellowfin and bigeye tuna were updated for WCPFC16 by applying the 2019 skipjack tuna stock assessment (WCPFC16-2019-15, Minimum target reference points for WCPO yellowfin and bigeye tuna consistent with alternative LRP risk levels, and multispecies implications).
Noting the request from WCPFC16 to provide advice on the formulation of TRPs for bigeye and yellowfin tuna (paragraphs 273-275, WCPFC16 Summary Report), SC16 reviewed SC16-MI-WP-01 (Further consideration of candidate target reference points for bigeye and yellowfin tuna in the WCPO) and requested the Scientific Services Provider undertake the analyses for bigeye and yellowfin tuna according to the criteria outlined in the Paragraph 211-212 of the SC16 Summary Report. Accordingly, WCPFC17 reviewed WCPFC17-2020-12 (SC16-requested analyses to inform WCPFC17 discussions on candidate target reference points for WCPO bigeye and yellowfin tuna), and agreed that it would be difficult to identify TRPs for bigeye and yellowfin during WCPFC17 and to continue its consideration in the future. SC17 reviewed SC17-MI-WP-01 (Updated WCPO bigeye and yellowfin TRP evaluations), noting that impacts on skipjack tuna depletion associated with relative changes to fishing levels to achieve a candidate bigeye tuna TRP are contingent on the proportion of fishing scalars related to purse seine fishing that target skipjack tuna.
This paper was updated in WCPFC18-2021-11 (Updated WCPO bigeye and yellowfin TRP evaluations with considerations for SP albacore) by presenting results of analyses, requested by SC16, WCPFC16 and SC17, to assist WCPFC18 in the identification of interim target reference points for WCPO bigeye and yellowfin tuna stocks and to consider the implications of candidate bigeye and yellowfin TRPs for all four key tuna stocks.
2. Mixed fishery framework
The mixed fishery framework involves developing stock specific MPs for skipjack, South Pacific albacore and bigeye, in line with the agreed WCPFC harvest strategy workplan. The interaction of these MPs, as well as their impact on yellowfin, would then be evaluated using a combined evaluation framework. An implementation of this approach for skipjack, bigeye and yellowfin is described in the latest document SC17-MI-WP-05 (Mixed-fishery harvest strategy developments) which demonstrates an initial attempt at considering multi-species and mixed fisheries interactions based on single stock operating models (OMs) for skipjack, bigeye and yellowfin.
This proof of concept analysis demonstrates that the technical challenges involved in implementing the multi-species modeling framework can be addressed and the conceptual approach remains tractable. The initial results are sufficiently encouraging to support the continued development of this approach.
3. Summary of harvest strategy development status
The next steps in the further development of the mixed fishery approach involve: i) the conditioning of OMs for both bigeye and yellowfin; ii) the development of candidate MPs for bigeye for the tropical longline ﬁshery, iii) the development of mixed fishery, multi-species performance indicators and iv) the inclusion of South Pacific albacore in the mixed fishery evaluation framework. In order to fully develop PIs under the mixed fishery approach, the adoption of TRPs for both bigeye and yellowfin tunas will be useful.
V. Stakeholder engagement and capacity building
The roles of scientists and managers and the key decisions and areas for advice from both the Scientific Committee and the Commission have been outlined in previous reports (SC14-MI-WP-05 Key decisions for managers and scientists under the harvest strategy approach for WCPO tuna stocks and fisheries). SPC-OFP provided a number of web-based tools in SC17-MI-IP-02 (Capacity building and stakeholder engagement activities for WCPFC harvest strategies) related to capacity building, decision making, and a harvest strategy Moodle course.
1. Capacity building tools
Interactive R-Shiny training tools allow users to explore the development and performance of HCRs and MPs:
- Introduction to Harvest Control Rules (https://ofp-sam.shinyapps.io/amped-intro-hcr/)
- Introduction to Performance Indicators (https://ofp-sam.shinyapps.io/amped-intro-indicators/)
- Comparing Performance of Management Procedures (https://ofp-sam.shinyapps.io/amped-comparing-performance/)
2. Decision making tools
A key component of the harvest strategy process is selection of preferred MPs using performance indicators. To help facilitate this process, interactive decision making tools have been developed by SPC.
These tools allow stakeholders and managers to explore the results of the skipjack and South Paciﬁc albacore MSE simulations and compare the relative performance of the candidate MPs. Manuals and cheat-sheets for these tools are available via the tool websites.
Additional tools may be necessary to explore the results of the mixed-ﬁshery MSE simulations. Conditioning of operating models (OMs) is an important component of the MSE development process. An interactive tool has been developed to explore the diagnostics of the OMs currently used in the skipjack evaluation process: Hierophant (https://ofp-sam.shinyapps.io/hierophant/). Similar tools can be developed for the OMs of the other stocks.
3. Harvest strategy Moodle course
Moodle is a widely used on-line learning platform that facilitates the delivery of training materials in multiple formats. An ‘Introduction to Harvest Strategies’ training course is being developed using the SPC’s Moodle site. It is anticipated that this will become a key source of reference and learning material for WCPFC members and currently contains information on many aspects of harvest strategies, including management objectives, performance indicators, reference points, MPs and MSE.
It is possible to access the course (still under development) from the main page by using a ‘guest’ login (https://spc.learnbook.com.au/login/index.php).
Paciﬁc Island Fisheries Professionals (PIFP) are one year positions at SPC where the PIFP works alongside SPC staﬀ on a speciﬁc project, before returning to their home country. The PIFP positions provide a longer-term type of capacity building for asmall number of people. SPC has had one PIFP (in 2020) focused on harvest strategies, and aims to have another PIFP working in this area in 2022.
SPC are also running training workshops with fisheries agencies throughout the region, that have so far involved over 260 people across 17 workshops.
A harvest strategy poster will soon be distributed to members and stakeholders to help raise awareness of the process. This will be followed up by short information leaﬂets that focus on particular harvest strategy components. A series of short information ﬁlms are being produced that will complement the other engagement material, the first training movie can be accessed here (https://www.youtube.com/watch?v=zM3B9DLmtZg)
A harvest strategy Slack group has been set up to provide an informal communication channel with members. There are now over 70 members. Please contact Dr. Finlay Scott at SPC (email@example.com) if you would like to join. For enquiries to SPC on the technical work supporting the development of harvest strategies or training workshops, please contact: firstname.lastname@example.org
VI. Limit reference points (LRPs)
WCPFC8 approved a number of the SC7 recommendations related to limit reference points.
1) The agreed working definition for LRPs is to be based on the following principles:
- they define a state of the fishery that is considered to be undesirable and which management action should avoid;
- the probability of breaching an LRP should be very low;
- management actions should be taken before the fishery falls below or is at risk of falling below an LRP.
2) The hierarchical approach (as outlined in SC7-MI-WP-03) to identify key LRPs for key target species in the WCPFC is as follows:
A reliable estimate of steepness is available
FMSY and BMSY
Steepness is not known well, if at all, but the key biological (natural mortality, maturity) and fishery (selectivity) variables are reasonably well estimated.
Applied species: bigeye, yellowfin and South Pacific albacore
FX%SPRo and either
The key biological and fishery variables are not well estimated or understood.
Applied species: skipjack
Note: SPR refers to the spawning-potential-per-recruit, and SBrecent,F=0 refers to the estimated average spawning biomass over a recent period in the absence of fishing).
SC10 noted that the Commission endorsed SC’s recommendation for a 10 year time window in relation to the LRP 20%SBF=0, t1-t2 based on the years t1=ylast-10 to t2=ylast-1 where ylast is the last year used in the assessment. It was also note that the Commission had not seen the need to adopt an equivalent F-based reference point as this was seen as redundant given the adoption of a biomass-based LRP.
VII. Acceptable risk level of exceeding LRP
At WCPFC12, the Commission noted that the SC10 had considered levels of risk associated with breaching the LRP within the range 5-20% and that the identification of acceptable risk is a management issue. The Commission agreed to identify the level of acceptable risk which should be applied to breaching a LRP for the key target species, noting that the UN Fish Stocks Agreement states that the risk of exceeding LRPs should be very low.
At WCPFC13 (Paragraph 296, WCPFC13 Summary Report), the Commission agreed to:
a) not specify, at this time, acceptable levels of risk of breaching the limit reference point for each stock;
b) consider any risk level greater than 20 percent to be inconsistent with the LRP related principle in UNFSA (as referenced in Article 6 of the Convention) including that the risk of breaching limit reference points be very low; and
c) determine the acceptability of potential HCRs where the estimated risk of breaching the limit reference point is between 0 and 20%.
VIII. North Pacific striped marlin - Stock Reguilding Plan
The Commission at WCPFC16 adopted the Interim Rebuilding Plan for North Pacific Striped Marlin (Attachment L, WCPFC16 Summary Report).
IX. Links to WCPFC MOW and HSW materials and outcomes
Four WCPFC workshops have been held on Management Objectives and Harvest Strategies from 2012 - 2014. These workshops were held as informal meetings of stakeholders with an interest in WCPO tuna fisheries, that were convened by the Commission to facilitate and support the development of harvest strategies by Commission Members. Links to the relevant meeting pages and reports:
- MOW1: 28 - 29 November 2012, Manila, Philippines: https://www.wcpfc.int/meetings/wcpfc-management-objectives-workshop
- MOW2: 28 November 2013, Cairns, Australia: https://www.wcpfc.int/meetings/wcpfc-management-objectives-workshop-2
- MOW3: 28 November 2014, Apia, Samoa: https://www.wcpfc.int/meetings/wcpfc-management-objectives-workshop-3
- MOW4/HSW: 30 November - 1 December, Bali, Indonesia: https://www.wcpfc.int/meetings/wcpfc-harvest-strategy-workshop
North Pacific Albacore
I. Interim Harvest Strategy for North Pacific Albacore Fishery
At the sixth session of the Northern Committee (NC6) in 2010, and consistent with Article 6 (Application of the precautionary approach) of the WCPFC Convention, Canada submitted a paper (NC6-DP-02) on the development of a precautionary approach based fishery management regime for the northern stocks. Building on this paper, NC7 agreed to incorporate this development into its Work Program for 2012-2015.
The NC9 determined that it was best to delay discussions on the framework until the completion of the 2014 North Pacific albacore stock assessment. In July 2014, the International Scientific Committee for Tuna and Tuna-like Species in the North Pacific Ocean (ISC) concluded that the North Pacific albacore stock is “healthy and that current productivity is sufficient to sustain recent exploitation levels, assuming average historical recruitment in both the short and long term”. The ISC also provided further advice regarding candidate limit and target reference points.
Based on the advice from the ISC, the NC10 in 2014 recommended, and the 11th regular session of the Commission (WCPFC11) adopted a Precautionary Management Framework for North Pacific Albacore. In December 2017, the Commission (WCPFC14) adopted an Interim Harvest Strategy for North Pacific Albacore Fishery (HS-2017-01) as recommended by the NC13, which replaced the Precautionary Management Framework for North Pacific Albacore, and the contents are listed below.
1. Interim management objective
The management objective for the North Pacific albacore fishery is to maintain the biomass, with reasonable variability, around its current level in order to allow recent exploitation levels to continue and with a low risk of breaching the limit reference point.
2. Biological reference points
Based on ISC’s stock assessment advice and following the hierarchical approach adopted by the Commission, North Pacific albacore is to be treated as a Level 2 stock. The following is based on an average recruitment scenario:
The limit reference point (LRP) for this stock is established at 20%SSBcurrent F=0. This LRP is consistent with the Annex II of the UN Fish Stocks Agreement (UNFSA) and recent WCPFC decisions on LRPs for the three tropical tuna species and South Pacific albacore, where 20%SSBcurrent F=0 was adopted. If this point is breached, management actions will be taken to return the stock to a predetermined level as outlined in the subsequent section on Decision Rules.
The target reference point (TRP) for this stock will be determined following a comprehensive analysis under a management strategy evaluation (MSE) approach as outlined in section 4 on “Future Work”. Historical fishing activity, anticipated fishing activity, and the source of increased fishing mortality will also be considered when evaluating a suitable TRP. Socioeconomic factors, as per UNFSA Article 6.3.c., will be further considered. The existing conservation and management measure (CMM) for the stock (WCPFC 2005-03) establishes through limits on current effort an overall management regime for the stock.
3. Decision rules
NC recommends a management strategy for the stock that ensures that the risk of the biomass decreasing below the LRP is low.
LRP rule: In the event that, based on information from ISC, the spawning stock size decreases below the LRP at any time, the NC will, at its next regular session or intersessionally if warranted, adopt a reasonable timeline, but no longer than 10 years, for rebuilding the spawning stock to at least the LRP and recommend a CMM that can be expected to achieve such rebuilding within that timeline. The NC will take into account historical fishing activity and the source of increased fishing mortality when developing management strategies to rebuild the stock, including in establishing effort reductions. The NC will further consider socioeconomic factors, as per UNFSA Article 6.3.c., as well as which the NC members, if any, contributed to exceeding the LRP.
4. Future work
This framework may be periodically reviewed and revised. To support such revisions, the NC endorses the ongoing development and implementation of an MSE for the stock and fishery, which would yield new information that would enhance the robustness of this framework.
II. North Pacific Albacore Management Strategy Evaluation
Management Strategy Evaluation (MSE) is a process that, given management objectives conveyed by stakeholders and managers, uses computer simulations to assess the performance of candidate harvest strategies under uncertainty. The goal of this MSE is to examine the performance of alternative harvest control rules and associated reference points for North Pacific albacore. Since the 1st ISC NPALB MSE Workshop in April 2015, there were several workshops to develop the framework and several meetings with managers and stakeholders. Performance was evaluated based on management objectives pre-agreed at the 3rd ISC NPALB MSE Workshop in October 2017, where candidate reference points and harvest control rules for testing were also agreed upon. The ALBWG then started developing the MSE framework and running simulations and presented the initial set of results at the 4th MSE Workshop in February 2019, where managers and stakeholders recommended to focus on the assessment of the performance of additional candidate harvest control rules with the best performing TRPs, F40 and F50. During 2020 and 2021, There were three ALBWG workshops focusing on the NPALB MSE, as well as three MSE workshops for managers and stakeholders. All workshops were held online due to COVID-19 related travel restrictions. Details of the NPAWG MSE activities are in the final Report of the North Pacific Albacore Tuna Management Strategy Evaluation (NC17-IP-06).
NC17 reviewed the progress of the ISC’s MSE process and encouraged members to work with their domestic stakeholders to deepen understanding of the MSE process and to be prepared to discuss and advance the process collectively at NC18. NC17 developed a 3-year work plan for further development of harvest strategies for North Pacific albacore, including adoption of a TRP and establishment of a harvest control rule and threshold reference point in due course.
Pacific Bluefin Tuna
Harvest Strategy for Pacific Bluefin Tuna Fisheries
WCPFC17 adopted a Harvest strategy for Pacific Bluefin Tuna Fisheries (HS-2017-02) and based on the HS-2017-01, the Commission in December 2021 adopted a revised Conservation and Management Measure for Pacific Bluefin Tuna (CMM 2021-02). In addition, WCPFC18 adopted a revised Harvest strategy for Pacific Bluefin Tuna Fisheries (HS 2021-01), which included new rules in section Harvest controls rules during second rebuilding period. Contents of the HS 2017-02 is listed below.
Introduction and scope
This harvest strategy has been prepared in accordance with the Commission’s Conservation and Management Measure on Establishing a Harvest Strategy for Key Fisheries and Stocks in the Western and Central Pacific Ocean.
Although the provisions of this harvest strategy are expressed in terms of a single stock, they may be applied to multiple stocks as appropriate and as determined by the Northern Committee.
1. Management objectives
The management objectives are, first, to support thriving Pacific bluefin tuna fisheries across the Pacific Ocean while recognizing that the management objectives of the WCPFC are to maintain or restore the stock at levels capable of producing maximum sustainable yield, second, to maintain an equitable balance of fishing privileges among CCMs and, third, to seek cooperation with IATTC to find an equitable balance between the fisheries in the western and central Pacific Ocean (WCPO) and those in the eastern Pacific Ocean (EPO).
2. Reference points
Because steepness in the stock-recruitment relationship is not well known but the key biological and fishery variables are reasonably well estimated, the stock of PBF is to be treated as a Level 2 stock under the Commission’s hierarchical approach for setting biological limit reference points.
2.1 Rebuilding targets
Initial rebuilding target: The initial rebuilding target for the PBF stock size is the median SSB estimated for the period 1952 through 2014, to be reached by 2024 with at least 60% probability.
Recruitment scenario during initial rebuilding period: The low recruitment scenario (resampling from the relatively low recruitment period (1980-1989)) or the recent recruitment scenario (resampling from the last 10 years), whichever is lower, will be used for the ISC’s SSB projections until 2024 or until the SSB reaches the initial rebuilding target, whichever is earlier.
The ISC is requested to periodically evaluate whether the recruitment scenario used during the initial rebuilding period is reasonable given current conditions, and to make recommendations on whether a different scenario should be used. If ISC recommends a different scenario, this will be considered by the NC.
Second rebuilding target: The second rebuilding target for the PBF stock size is 20%SSBF=0, to be reached by 2034, or 10 years after reaching the initial rebuilding target, whichever is earlier, with at least 60% probability.
However, if: (1) the SSB reaches the initial rebuilding target earlier than 2024; (2) ISC recommends a recruitment scenario lower than the average recruitment scenario; and (3) the SSB projections indicate that the second rebuilding target will not be achieved on this schedule, the deadline for rebuilding may be extended to 2034 at the latest.
Also, if there is a recommendation from the Northern Committee that 20%SSBF=0 is not appropriate as the second rebuilding target, taking into account consideration from IATTC, scientific advice from ISC, IATTC or WCPFC SC, and socioeconomic factors, another objective may be established.
Recruitment scenario during second rebuilding period: After the initial rebuilding target is reached and until the second rebuilding target is reached, the recruitment scenario to be used for the SSB projections will tentatively be the average recruitment scenario (resampling from the entire recruitment period).
The ISC is requested to periodically evaluate whether the recruitment scenario used during the second rebuilding period is reasonable given current conditions, and to make recommendations on whether a different scenario should be used. If ISC recommends a different scenario, this will be considered by the NC.
2.2 Development of reference points
The Northern Committee will develop more refined management objectives as well as limit reference point(s) and target reference point(s) through MSE process specified in Section 6.
3. Acceptable levels of risk
Until the stock is rebuilt, the Northern Committee will recommend conservation and management measures as needed to ensure rebuilding in accordance with the probabilities specified in sections 2.1 and 5 for each of the two rebuilding targets.
Once the stock is rebuilt, in accordance with Article 6.1(a) of the Convention, the Northern Committee will recommend conservation and management measures as needed to ensure that any target reference point(s) (once adopted) are achieved on average in the long term, and ensure that the risk of the stock size declining below the B-limit (once adopted) is very low.
4. Monitoring strategy
The ISC will periodically evaluate the stock size and exploitation rate with respect to the established reference points and the report will be presented to the Scientific Committee. Until 2024, while the MSE is being developed (see section 6), the ISC is requested to conduct stock assessments in 2018, 2020 and 2022.
In order to cope with the adverse effects on the rebuilding of the stock due to drastic drops of recruitment: (1) all the available data and information will be reviewed annually, including recruitment data provided by the ISC and in National Reports; and (2) the ISC is requested to conduct in 2019, and periodically thereafter as resources permit and if drops in recruitment are detected, projections to see if any additional measure is necessary to achieve the initial rebuilding target by 2024 with at least 60% probability.
5. Decision rules
Harvest controls rules during initial rebuilding period: The interim harvest control rules below will be applied based on the results of stock assessments and SSB projections to be conducted by ISC.
(a) If the SSB projection indicates that the probability of achieving the initial rebuilding target by 2024 is less than 60%, management measures will be modified to increase it to at least 60%. Modification of management measures may be (1) a reduction (in %) in the catch limit for fish smaller than 30 kg (hereinafter called “small fish”) or (2) a transfer of part of the catch limit for small fish to the catch limit for fish 30 kg or larger (hereinafter called “large fish”). For this purpose, ISC will be requested, if necessary, to provide different combinations of these two measures so as to achieve 60% probability.
(b) If the SSB projection indicates that the probability of achieving the initial rebuilding target by 2024 is at 75% or larger, the WCPFC may increase their catch limits as long as the probability is maintained at 70% or larger, and the probability of reaching the second rebuilding target by the agreed deadline remains at least 60%. For this purpose, ISC will be requested, if necessary, to provide relevant information on potential catch limit increases.
Harvest controls rules during second rebuilding period: The harvest control rules during the second rebuilding period below will be applied based on the results of stock assessments and SSB projections to be conducted by ISC.
- If the SSB projection indicates that the probability of achieving the second rebuilding target by 2034 or 10 years after reaching the initial rebuilding target, whichever is earlier, is less than 60%, management measures shall be modified to increase it to at least 60%. For this purpose, the ISC will be requested, if necessary, to provide information on possible management measures to achieve 60% probability.
- If the SSB projection indicates that the probability of achieving the second rebuilding target by 2034, or 10 years after reaching the initial rebuilding target, whichever is earlier, is at 75% or larger, fishery controls may be changed, including adjustment of catch limits, as long as the probability is maintained at 70% or larger. For this purpose, ISC will be requested, if necessary, to provide relevant information on potential fishery controls.
- Any adjustments to management measures shall be considered in cooperation between the two RFMOs taking into account historical and future projected proportional fishery impacts on SSB between fisheries in the EPO and fisheries in the WCPO. For this purpose, ISC will be requested, if necessary, to provide relevant information, including projected proportional fishery impact of potential management measures changes.
- This harvest control rule will be reviewed and modified, as necessary, if depletion estimates across the time-series have been adjusted due to changes in assumptions and/or settings of the stock assessment model.
The Northern Committee will, through MSE development process, develop decision rules related to the limit reference points once adopted including for the case of their being breached.
6. Performance evaluation
Until the stock is rebuilt, the Northern Committee will work with the ISC and the Scientific Committee and consult with the IATTC to identify and evaluate the performance of candidate rebuilding strategies with respect to the rebuilding targets, schedules, and probabilities.
The ISC is requested to start the work to develop a management strategy evaluation (MSE) for Pacific bluefin tuna fisheries in 2019 and have a goal of completing it by 2024.
To support development of the MSE, ISC is encouraged to identify at least two experts and the NC members are encouraged to provide additional funds for the ISC’s work on the MSE.
The Joint WG will start to discuss in 2018, and aim to finalize no later than 2019, guidelines for the MSE, including at least one candidate long-term target reference point (TRP), two candidate limit reference points (LRPs) and candidate harvest control rules (HCRs), which will be provided to the ISC. Those candidate TRPs, LRPs and HCRs will be tested and changed if appropriate during the MSE development process.
In preparation for the Joint WG meeting in 2019, the ISC is requested to organize workshops in early 2018 and 2019 to support the identification of specific management objectives, including level of risks and timelines. The workshops will include managers, scientists and stakeholders, taking into account any recommendations of the Joint WG, and the number of representatives should be relatively small, as it was for the MSE workshop for North Pacific albacore.
Northern Committee, in consultation with the ISC and the Scientific Committee, should consider the following criteria:
- Probability of achieving each of the rebuilding targets within each of the rebuilding periods (if applicable).
- Time expected to achieve each of the rebuilding targets (if applicable).
- Expected annual yield, by fishery.
- Expected annual fishing effort, by PBF-directed fishery.
- Inter-annual variability in yield and fishing effort, by fishery.
- Probabilities of SSB falling below the B-limit and the historical lowest level.
- Probability of fishing mortality exceeding FMSY or an appropriate proxy, and other relevant benchmarks.
- Expected proportional fishery impact on SSB, by fishery and by WCPO fisheries and EPO fisheries.
Recognizing that developing the operating model and other aspects of the MSE will take time and additional resources, and might require further dialogue between the Northern Committee, the ISC, and the IATTC, while the MSE is in development the ISC is requested to perform this work using the best means at its disposal.
 See the information provided by the International Scientific Committee for Tuna and Tuna-like Species in the North Pacific Ocean (WCPFC-NC9-2013/IP-03) in response to a request made by the Northern Committee at its Eighth Regular Session (Attachment F, NC8 Summary Report).
 SSBF=0 is the expected spawning stock biomass under average recruitment conditions without fishing.
 WCPFC13 agreed that any risk level greater than 20 percent to be inconsistent with the limit reference point related principles in UNFSA (as references in Article 6 of the Convention) including that the risk of breaching limit reference points be very low.
North Pacific Swordfish
The NC14 agreed to adopt the following management objectives for NP swordfish; “The management objective is to support thriving swordfish fisheries in the North Pacific while maintaining the stock size at levels capable of producing maximum sustainable yield. The Northern Committee will develop more refined management objectives.” In December 2019, the Commission accepted the recommendation from the NC15 on the harvest strategy for North Pacific swordfish fisheries (WCPFC16 – Attachment K). WCPFC16-Attachment K - HS for SWO.pdf
Currently, no conservation and management measure is available for North Pacific swordfish, and NC17 planned to consider proposals for developing the CMM for North Pacific Swordfish at NC18.