Case studies of Harvest Strategies in global fisheries

Management Objectives:

• Maximum long-term yield
• A maximum annual probability of SSB falling below the limit reference point is less than 5% for all years.

Reference Points:

• Fishing mortality target = 26%F_MSY
• Bpa (MSY Biomass trigger value) = 2.58 metric tons
• Biomass limit reference point = 2.00 metric tons

^{*Bpa: biomass below which action should be taken, (pa= precautionary approach)}

Candidate Harvest Strategies:

Explored 5 harvest control rules that derive a target fishing mortality based on spwaning stock biomass, including combinations of limitations on interannual variability in total allowable catch (aka stability), and various catch banking and borrowing schemes (e.g 10% banking of total allowable catch and 10% borrowing applied in alternate years, suspended when SSB is below the biomass trigger value)

Progress Update & Workplan:

Full MSE completed by ICES. Coastal States of NEAFC must evaluate MSE results to select final elements of the management strategy.

Link to relevant policy document or update:

• Workshop on Management Strategy Evaluation of Mackerel (WKMSEMAC): Long-Term Management Strategy Evaluation – ICES (2020):
• EU, Norway, and the Faroe Islands request on the long-term management strategies for Northeast Atlantic mackerel (full feedback approach): Long-Term Management Strategy Evaluation Summary Advice – ICES (2020)

Management Objectives:

Initial Options:

• The annual probability that the stock drops below Blim should not exceed “X” probability; or the annual probability that the fishing mortality exceeds F_lim should not exceed “X” probability
• Catch is high and stable as much as possible
• Maximum interannual variation of TAC over yy period should be less than xx%.

Reference Points:

Initial biomass target and limit reference points will be based on either B_MSY or carrying capacity (K), and will include multipliers yet to be defined (e.g., X%*B_MSY and Y%*K). Fishing mortality target and limit reference points will be based on FMSY (e.g., Z%*F_MSY).

Candidate Harvest Strategies:

Evaluating empirical or model-based harvest control rules that reduce the target harvest rate and total allowable catch when biomass falls below its target level. Currently, only a harvest control rule is being developed, as opposed to a full harvest strategy.

Progress Update & Workplan:

Plan is to use the current interim stock assessment model to evaluate a short-term harvest control rule, then move on to a full MSE proccess to evaluate a comprehensive management procedure.

Link to relevant policy document or update:

1st Meeting of the Joint SC-TCC-COM Small Working Group on Management Strategy Evaluation for Pacific Saury (SWG MSE PS) Report

Management Objectives:

Tuning Objectives (for MSE purposes):

• Pr(B(2029)>=B(MSY) ) = 0.5 (SB in 2029 exceeds SB_MSY in exactly 50% of the simulations)
• Pr(B(2034)>=B(MSY) ) = 0.6 (SB in 2034 exceeds SB_MSY in exactly 50% of the simulations)

Reference Points:

• Interim Limit Reference Point: 40% B_MSY and 140% F_MSY
• Interim Target Reference Point: B_MSY and F_MSY

Candidate Harvest Strategies:

Comprehensive harvest strategy proposed by Australia. MSE evaluating model-based HCRs with these candidate constraints:

• Total Allowable Catch (TAC) to be set every 3 years (and held constant between settings)
• A maximum of 15% change to the TAC (increase or decrease) relative to the previous TAC

Progress Update & Workplan:

Evaluation of candidate harvest strategies underway via MSE. Reference set of operating models were revised in 2021 due to concerns about uncertainty in the stock assessment on which the operating models are based, strengthening the MSE.

• 2022: Refine and further develop MSE and candidate harvest strategies
• 2023: Adopt final harvest strategy

Link to relevant policy document or update:

• WCPFC Harvest Strategies: Navigate to ‘Bigeye and Yellowfin Tunas in the WCPO’ to read an overview of the current work going towards the harvest strategy

• Candidate performance indicators and monitoring strategies commensurate with candidate management objectives for southern longline fishery and tropical longline fisheries
• Updated WCPO bigeye and yellowfin target reference point evaluations
• Mixed-fishery harvest strategy developments: Updates on mixed fishery modeling framework for South Pacific albacore, bigeye, and skipjack

Management Objectives:

Initial proposals for the Southern longline, tropical longline, and tropical purse seine fishery include biological, economic, social, and ecosystem objectives.

Reference Points:

• Limit Reference Point: 20%SB_F=0
• Target Reference Point: Pending agreement on a target reference point the spawning biomass depletion ratio (SB/SB_F=0) is to be maintained at or above the average SB/SB_F=0 for 2012-2015

Candidate Harvest Strategies:

Evaluating a harvest control rule and harvest strategy through a mixed fishey modelling framework that develops model-based harvest strategies for bigeye, but is set up to achieve objectives across multiple species, including yellowfin, skipjack, and South Pacific albacore.

Progress Update & Workplan:

Initial mixed fishery framework explored via MSE; Next steps include operating model conditioning, the development of candidate management procedures for bigeye for the tropical longline fishery, and the development of mixed fishery, multi-species performance indicators. Input needed from managers on management objectives and target reference points.

Link to relevant policy document or update:

• WCPFC Harvest Strategies: Navigate to ‘Bigeye and Yellowfin Tunas in the WCPO’ to read an overview of the current work going towards the harvest strategy
• Candidate performance indicators and monitoring strategies commensurate with candidate management objectives for southern longline fishery and tropical longline fisheries
• Updated WCPO bigeye and yellowfin target reference point evaluations
• Mixed-fishery harvest strategy developments: Updates on mixed fishery modelling framework for South Pacific albacore, bigeye, and skipjack

Management Objectives:

Conceptual Management Objectives: 

• Greater than [___]% probability of occurring in the green quadrant of the Kobe matrix
• Less than [___]% probability of the stock falling below B_LIM
• Maximize overall catch levels
• Any increase or decrease in TAC between management periods should be less than [___]%.

Reference Points:

None have been adopted to date.

Candidate Harvest Strategies:

Testing a variety of harvest control rules, including constant catch and hockey stick harvest control rules (i.e., that adjust the total allowable catch up and down as the population size increases and decreases, respectively).

Progress Update & Workplan:

MSE process began in 2020. Initial MSE testing complete and an updated MSE framework was developed and presented in 2022.  Need input from managers on management objectives and performance statistics.

Link to relevant policy document or update:

Collective Volumes of Scientific Papers: Paper not yet available in ICCAT database

Management Objectives:

Aiming at ensuring harvest rates within safe biological limits, and consistent with the precautionary approach* and the maximum sustainable yield (MSY) approach.

^{*ensure with a high probability (95%) that the size of the stock is maintained above Blim}

Reference Points:

• Interim Target Fishing Mortality Reference Point: F_MSY(0.32F)
• Interim Biomass Trigger Reference Point: B_pa/MSY B_trigger(2,250,000 tonnes)
• Interim Biomass Limit Reference Point: B_lim(1,500,000 tonnes)

^{*Bpa = A stock size above which the stock is considered to have full reproductive capacity. Pa stands for precautionary approach.}

Candidate Harvest Strategies:

An interim harvest control rule (HCR) has previously been explored by ICES that sets a total allowable catch (TAC) when biomass is above/below biological reference points (B_pa,B_lim, etc.)

• If SSB≥B_pa, the TAC shall be fixed to a fishing mortality of F_MSY
• Maximum TAC change: +/- 20%
• If B_lim<SSB<B_pa, the TAC shall be fixed that is consistent with a fishing mortality given by the following formula: Target F = 0.05 + [(SSB – B_lim)*(F_MSY – 0.05) / (B_pa– B_lim)]
• If SSB<B_lim, the TAC will be fixed corresponding to a fishing mortality F=0.05

Noted Constraints:

• There are mechanisms for banking up to 10% of unutilized quota and borrowing up to 10% beyond the quota allocated subject to stock status.
• The HCR since 2017 has an annual TAC change rule different from the one evaluated: Maximum TAC change: +25%, -20%
• Development of only an HCR, as opposed to a full harvest strategy.

Progress Update & Workplan:

• 2021: The HCR based on ICES evaluation (2016) has been in place since 2017 and should have been reviewed after 5 years (no later than December 2021).
• 2021: The interim long-term management strategy may no longer be precautionary in the long term. There have been consistent deviations from the HCR (overshooting catch advice) due to an allocation dispute. During the evaluation of the management strategy, the implementation error in the form of a consistent overshoot of the TAC was not included.
• 2022: Refine and further develop management strategy evaluation (MSE) and candidate harvest control rules in collaboration with ICES.
• 2023: Adopt a full harvest strategy or updated harvest control rule.

Link to relevant policy document or update:

• Agreed record of conclusions of fisheries consultations between the European Union, the Faroe Islands, Iceland and Norway on the management of blue whiting in the north-east Atlantic in 2017: Long-Term Management Strategy (2016)
• Report of the Workshop on Blue Whiting Long Term Management Strategy Evaluation (WKBWMS): Long-Term Management Strategy Evaluation – ICES (2016)
• NEAFC request to ICES to evaluate a long-term management strategy for the fisheries on the blue whiting stock: Long-Term Management Strategy Evaluation Summary Advice – ICES (2016):

Management Objectives:

Aiming at ensuring harvest rates within safe biological limits, and consistent with the precautionary approach* and the maximum sustainable yield (MSY) approach.

^{*ensure with a high probability (95%) that the size of the stock is maintained above Blim}

Reference Points:

• Interim Target Fishing Mortality Reference Point: F_mgt (0.14F) / F_MSY (0.157F)
• Interim Biomass Trigger Reference Points: B_pa/MSY B_trigger (3,184,000 tonnes)
• Interim Limit Reference Points: F_lim (0.291F) and B_lim (2,500,000 tonnes)

^{*Bpa = A stock size above which the stock is considered to have full reproductive capacity. Pa stands for precautionary approach.}

Candidate Harvest Strategies:

A few harvest control rule (HCR) options were explored by ICES (2018). A HCR and Reference Points were adopted that set a total allowable catch (TAC) when biomass is above/below biological reference points (B_pa, B_lim, etc.)

• If SSB≥B_pa, the TAC shall be fixed to a fishing mortality of F_mgt.
• Maximum TAC change: +25%, -20%
• If B_lim<SSB<B_pa, the TAC shall be fixed at a level that is consistent with a fishing mortality given by: Target F = 0.05 + [(SSB – B_lim)*(F_mgt – 0.05) / (B_pa– B_lim)]
• If SSB<B_lim, the TAC will be fixed corresponding to a fishing mortality F=0.05.

Noted Constraints:

• There are mechanisms for banking up to 10% of unutilized quota and borrowing up to 10% beyond the quota allocated subject to stock status.
• Development of only an HCR, as opposed to a full harvest strategy.

Progress Update & Workplan:

• 2022: The HCR based on ICES evaluation (2018) has been in place since 2019 and should be reviewed after 5 years (no later than December 2023).
• 2022: The interim long-term management strategy may no longer be precautionary in the long term. There have been consistent deviations from the HCR (overshooting catch advice) due to an allocation dispute. During the evaluation of the management strategy, the implementation error in the form of a consistent overshoot of the TAC was not included.
• 2023: Refine and further develop management strategy evaluation (MSE) and candidate harvest control rules in collaboration with ICES
• 2024: Adopt a full harvest strategy or updated harvest control rule.

Link to relevant policy document or update:

• Agreed record of conclusions of fisheries consultations between Iceland, the European Union, the Faroe Islands, Norway and the Russian Federation on the management of the Norwegian spring-spawning (Atlanto-Scandian) herring stock in the North-East Atlantic in 2019: Long-Term Management Strategy (2018):
• Report of the Workshop on a long-term management strategy for Norwegian Spring-s​pawning herring​ (WKNSSHMSE​): Long-Term Management Strategy Evaluation – ICES (2018):
• NEAFC request concerning long-term management strategy for herring in the Northeast Atlantic (Norwegian spring-spawning herring): Long-Term Management Strategy Evaluation Summary Advice – ICES (2018):

Management Objectives:

• Maintain Pacific halibut, on average, at a target (fixed or dynamic) female spawning biomass equal to the stock size required to produce maximum net economic returns on a spatial and temporal scale relevant to the fishery
• Maintain Pacific halibut, above a female spawning biomass limit where the risk to the stock is regarded as unacceptable (SB_LIM), at least 90% of the time

Reference Points:

• Target Reference Point: 45% SSB₀ and 120%SSB_MSY
• Interim Trigger Reference Point: 30% SSB₀
• Interim Limit Reference Point: 20% SSB₀and 50%SSB_MSY

^{*SSB0 = spawning stock size that would exist in the absence of fishing}

Harvest Strategy:

Using MSE to evaluate several model-based harvest strategies; HS must have ≥ 50% chance of achieving the target and ≤10% chance of breaching the limit

Interim harvest control rule:

• The harvest control rules relies on the spawning potential ratio (SPR) of 46% (F_SPR=46%). The SPR is adjusted to reduce the fishing intensity at low levels of spawning biomass by linearly increasing the SPR (i.e reducing the fishing intensity) if the estimated stock status is less than a trigger at 30% SSB₀, to zero fishing intensity (SPR=100%) when the estimated stock status is less than the limit at 20% SSB₀(i.e., a 30:20 control rule).

^{*SPR = Spawning Potential Ratio, or the lifetime spawning output that a young fish is expected to produce under current fishing mortality compared to what it would produce in the absence of fishing.}

Outcome:

Interim harvest strategy in place since 2020 to set the allowable coastwide catch, but adoption of a final, formal harvest strategy has yet to occur, in part due to ongoing negotiations about how to allocate the catch among Alaska, Canada, and the U.S. West Coast. Final mortality limits are determined based on the previous year’s limits, the interim harvest strategy, and social and economic considerations. MSE development continues and is exploring size limits and stock assessment frequency as part of the harvest strategy.

Link to relevant policy document or update:

• Interim International Pacific Halibut Commission Harvest Strategy Policy: Includes harvest strategy policies from both 2019 and 2020
• Pacific halibut MSE landing page

Management Objectives:

In development and not officially adopted, but often assumed to be B_MSY based on Article VII(1)c of the Antigua Convention.

Reference Points:

Reference points being developed as part of current MSE process.

• Interim Limit Reference Point: F_0.5R0 and SSB_0.5R0, where steepness = 0.75 (this is equivalent to 8%SSB₀)
• Interim Target Reference Point:F_MSY, SSB_MSY

_{*SSB0 = spawning stock size that would exist in the absence of fishing
*R0 = recruitment (i.e., number of young fish) that would exist in the absence of fishing
*steepness – the fraction of virgin recruitment obtained when a stock is at 20% of its unfished size. A steepness of 0.75 indicates that a stock is productive enough to still produce 75% of its maximum reproductive output, even when it is depleted to just 20% of its initial population size.}

Candidate Harvest Strategies:

Candidate model-based harvest strategies are being developed as part of current MSE process.

Current interim HCR developed without MSE testing:

• F should not exceed F_MSY
• If >10% chance that F>F_limit, reduce F to ≤F_MSY with a 50% probability and a <10% chance of F>F_limit
• If >10% chance that SSB<SSB_limit, take action to get SSB≥SSB_MSY with a 50% probability and a <10% chance of SSB<SSB_limit within 2 generations or 5 years, whichever is greater

Progress Update & Workplan:

• 2020-23: MSE framework development and refinement; testing of candidate harvest strategies
• 2024: Finalize MSE; adopt HCR/HS

Link to relevant policy document or update:

• Resolution C-16-02: Harvest Control Rules for Tropical Tunas (Yellowfin, Bigeye, and Skipjack)
• 1st Workshop on Management Strategy Evaluation (MSE) for tropical tunas report
• 2^ndWorkshop on Management Strategy Evaluation (MSE) for tropical tunas report
• Example Toy Management Strategy Evaluation for Bigeye Tuna: A shiny app where users can explore the performance of candidate HCRs

Management Objectives:

Interim Objective:

• Achieve an 8% increase in catch per unit of effort (CPUE) for the southern longline fishery as compared to 2013 levels

Draft performance indicators:

• Maintain biomass at or above levels that provide fishery sustainability throughout their range
• Maximise economic yield from the fishery (average expected catch)
• Maintain acceptable CPUE
• Catch stability

Reference Points:

• Interim Limit Reference Point: 20%SB_F=0 and FX%SPR, with X TBD
• Interim Target Reference Point: 56% SB_F=0

_{*SBF=0 = spawning stock size that would exist in the absence of fishing}

Candidate Harvest Strategies:

Using MSE to evaluate several harvest strategies with model-based and empirical harvest control rules using CPUE data; HS must have <20% chance of breaching the limit reference point

Progress Update & Workplan:

Evaluation of candidate harvest strategies underway via MSE

• 2020-22: Refine and further develop MSE and candidate harvest strategies
• 2023: Adopt final harvest strategy

South Pacific albacore is also being incorporated in the mixed fishery MSE framework for the Western and Central Pacific in which the harvest strategies for bigeye, skipjack, yellowfin, and South Pacific albacore will overlap.

Link to relevant policy document or update:

• WCPFC Harvest Strategies: Navigate to ‘South Pacific albacore tuna in the WCPO’ to read an overview of the current work going towards the harvest strategy
• South Pacific Albacore Management Procedures Explorer (SPAMPLE): A shiny app where a user can compare the relative performance of South Pacific albacore HCRs

Management Objectives:

Objective:

1. The objective of the interim Management Procedure (MP) for skipjack tuna, is to ensure that:

a) the spawning potential depletion ratio of skipjack tuna is maintained on average at a level consistent with the target reference point;

b) the spawning potential depletion ratio of skipjack tuna is maintained above the limit reference point with a risk of the limit reference point being breached no greater than 20 percent;

Performance Indicators:

• Maintain SKJ, YFT, BET biomass at or above levels that provide fishery sustainability throughout their range.
• Maximise economic yield from the fishery (average expected catch).
• Maintain acceptable CPUE.
• Catch stability.
• Effort stability: effort variation relative to a reference period.
• Proximity of SB/SB_F=0 to the average SB/SB_F=0 in 2018-21.

Reference Points:

a) Target reference point: Calculated on the basis of two spawning potential depletion values:

• The first value represents the estimated average depletion of the skipjack tuna stock over the period 2018-2021 (SB_2018-2021/SB_F=0).
• The second value represents the long-term median equilibrium stock depletion that would be reached under the agreed baseline fishing conditions for skipjack tuna (purse seine effort at 2012 levels, pole and line effort at average 2001-04 levels, and the domestic fisheries in assessment region 5 at average 2016-18 levels).

Both values are expressed as a percentage of the estimated average spawning potential in the absence of fishing (SB_F=0), calculated as described in paragraph 3. Values are calculated as medians based upon the grid of assessment models as agreed by the WCPFC Scientific Committee.

The target reference point is the average of these two values (weighting of 50/50). This was estimated from the 2022 WCPO skipjack tuna stock assessment at 50 per cent of SBF=0*.

b) Limit reference point: 20 percent of the estimated recent average spawning potential in the absence of fishing, calculated as described in paragraph 3.

*SBF=0 = spawning stock size that would exist in the absence of fishing

Harvest Strategy:

While the harvest strategy was officially adopted in December 2022, it is not yet legally binding.  The harvest strategy will guide rather than direct fishing activity for WCPO skipjack tuna during an unspecified trial period.

Specifications:

• Type: Model-based
• Management cycle: 3 years
• Data inputs: Stock assessment estimates of spawning potential depletion ratio for the latest estimation year (SB_latest/SB_{F=0, t1-t2}), Stock assessment estimates of current stock biomass (B_curr) with respect to B_MSY, stock biomass at maximum sustainable yield (B_MSY), fishing mortality at MSY (F_MSY)
• Management output: Effort
• Harvest control rule:
  The HCR is a scalar (multiplier) that adjusts future catch or effort relative to a baseline of 2012 values.
• If SB/SB_F=0>0.8, output multiplier = 1.4 (alt. 1.2)
• If 0.47<SB/SB_F=0<0.8, reduce effort linearly as specified in HCR
• If 0.37<SB/SB_F=0<0.47, output multiplier = 1
• If 0.2<SB/SB_F=0<0.37, reduce effort nonlinearly as specified in HCR
• If SB/SB_F=0<0.2 (the limit), output multiplier 0.2
• Other:Maximum effort change: +/-10% for any 3-year management cycle, relative to catch and effort specified by the HCR for the previous 3-year period.

Outcome:

Adopted in 2022, the performance of the harvest strategy will be reviewed in year 2025.

Link to relevant policy document or update:

• Conservation and Management Measure on a Management Procedure for WCPO Skipjack Tuna
• Performance Indicators and Management Procedures Explorer (PIMPLE): A shiny app where a user can explore and compare the performance of alternative candidate harvest strategies

Management Objectives:

• Greater than 60% probability of occurring in the green quadrant of the Kobe matrix
• Less than 15% probability of the stock falling below B_LIM
• Maximize overall catch levels
• Any increase or decrease in TAC between management periods should be less than +20% and -35% respectively*

*An exception will be made during the first application of the harvest strategy, during which changes in TAC shall not exceed a +20% increase or -10% decrease.

Reference Points:

• Interim Target Reference Point: Dynamic SSB_MSY
• Interim Biomass Limit Reference Point: 40% dynamic SSB_MSY 

Harvest Strategy:

In 2022, ICCAT successfully adopted a harvest strategy for Atlantic bluefin tuna.  The harvest strategy is comprehensive for the West and East & Mediterranean Sea stocks.

Specifications:

• Type: Empirical
• Management cycle: 3 years
• Data inputs: Inputs are 10 fishery-dependent and fishery-independent indices of abundance covering the western and eastern Atlantic and Mediterranean Sea.
• Management output: Quota
• Harvest control rule: The indices are aggregated to produce master abundance indices for West and East and smoothed over years to reduce observation error and variability effects. Quotas are then set based on the concept of taking a fixed proportion of the abundance present, using relative harvest rates compared to a reference year (2017), as indicated by these aggregated and smoothed indices.
• Other:
  Maximum quota change: +20%/-35%

Outcome:

The MSE process began in 2014. The MSE framework was finalized in 2022 and harvest strategy adopted in November 2022.  The performance will be evaluated in year 2028.

Link to relevant policy document or update:

• Atlantic Bluefin Tuna Harvest Strategy – Official Recommendation: The full recommendation adopted at the ICCAT 2022 commission meeting.
• Atlantic Bluefin Tuna MSE – Background & Structure: Describes core concepts and provides an overview of the MSE
• Atlantic Bluefin Tuna MSE – Results, Decisions, & Next Steps: Includes recent results on candidate harvest strategy performance given MSE updates
• Atlantic Bluefin Tuna MSE Shiny App: Interactive demo where users can select different set of operating models to compare performance among candidate harvest strategies

Management Objectives:

Conceptual Management Objectives:

• Greater than [___]% probability of occurring in the green quadrant of the Kobe matrix
• Less than [___]% probability of the stock falling below B_LIM
• Maximize overall catch levels
• Any increase or decrease in TAC between management periods should be less than [___]%.

Reference Points:

• Interim Limit Reference Point: 0.4B_MSY
• Interim Target Reference Point: B_MSY based on convention objective

Candidate Harvest Strategies:

Using MSE to evaluate both constant and threshold model-based harvest strategies.

Progress Update & Workplan:

MSE process began in 2018, currently developing MSE framework and operating models

• 2021-2022: Adopt reference set of OMs, adopt operational management objectives, and test candidate harvest strategies
• 2023: Finalize MSE and adopt final harvest strategy

Link to relevant policy document or update:

• Resolution 19-14: Initial Management Objectives
• Report of the 2022 ICCAT Atlantic Swordfish Data Preparatory Session: Navigate to item 6 ‘MSE Matters’ to read a summary of the MSE work and recent 2022 updates

Management Objectives:

General: Maintain the stock biomass in the green zone of the Kobe plot (not overfished and not subject to overfishing) while maximizing the average catch from the fishery and reducing the variation in the total allowable catch (TAC) between management periods.

• The bigeye tuna spawning stock has a 60% probability of achieving the target reference point of SB_MSY by 2034-2038;
• The bigeye tuna spawning stock biomass avoids breaching the interim limit reference point of 50%B_MSY with a high probability

Reference Points:

• Interim Limit Reference Point: 50% B_MSY and 130% F_MSY
• Interim Target Reference Point: B_MSY and F_MSY

Harvest Strategy:

Adopted in 2022, IOTC adopted a fully specified harvest strategy. An exceptional circumstances protocol still needs to be specified.

Specifications:

• Type: Model-based
• Management cycle: 3 years
• Data inputs: Total catches of bigeye tuna, longline CPUE data
• Management output: Quota
• Harvest control rule:
  The MP uses a hockey-stick HCR that constructs a harvest rate based on biomass depletion (measured relative to carrying capacity) from a simple biomass dynamic model. The pivot points are at 40% and 10% of carrying capacity, with the HCR multiplier linearly decreasing from 1 to almost zero between those pivot points.
• Other:
  Maximum quota change: +/- 15%

Outcome:

The harvest strategy-derived TAC will first be implemented in 2024. A mechanism to control catch will be developed in 2025 if an allocation scheme has not yet been agreed.

Link to relevant policy document or update:

• Resolution 22/03 on a Management Procedure for Bigeye Tuna in the IOTC Area of Competence

Management Objectives:

Tuning Objectives (for MSE purposes):

• Pr(Kobe green zone 2030:2034) = 0.5. The stock status is in the Kobe green quadrant over the period 2030:2034 exactly 50% of the time (averaged over all simulations)
• Pr(Kobe green zone 2030:2034) = 0.6. The stock status is in the Kobe green quadrant over the period 2030:2034 exactly 60% of the time (averaged over all simulations)
• Pr(Kobe green zone 2030:2034) = 0.7. The stock status is in the Kobe green quadrant over the period 2030:2034 exactly 70% of the time (averaged over all simulations)

Reference Points:

• Interim Limit Reference Point: 40% B_MSY and 140% F_MSY
• Interim Target Reference Point: B_MSY and F_MSY

Candidate Harvest Strategies:

Both model-based and empirical, CPUE-based harvest strategies are being tested via MSE. Harvest control rules are being tested with the following constraints:

• TAC setting every 3 years
• 15% TAC change limits
• 3 year lag between data and TAC implementation

Progress Update & Workplan:

Evaluation of candidate harvest strategies underway via MSE

• 2022: Refine and further develop MSE and candidate harvest strategies
• 2023 or 2024: Adopt final harvest strategy

Link to relevant policy document or update:

• Swordfish Management Strategy Evaluation Update: Updates to the MSE framework as of 2022
• Resolution 15/10 on Target and Limit Reference Points and a Decision Framework

Management Objectives:

Tuning Objectives (for MSE purposes):

• Pr(mean(SB(2019:2038)>=SB(MSY)) = 0.5. Average SB over the period 2030-2034 exceeds SB_MSYin exactly 50% of the simulations)
• Pr(Kobe green zone 2019:2038) = 0.5. The stock status is in the Kobe green quadrant over the period 2019-2038 exactly 50% of the time (averaged over all simulations)
• Pr(Kobe green zone 2019:2038) = 0.6. The stock status is in the Kobe green quadrant over the period 2019-2038 exactly 60% of the time (averaged over all simulations)
• Pr(Kobe green zone 2019:2038) = 0.7. The stock status is in the Kobe green quadrant over the period 2019-2038 exactly 70% of the time (averaged over all simulations)

Reference Points:

Interim Limit Reference Point: 40% B_MSY and 140% F_MSY
Interim Target Reference Point: B_MSY and F_MSY

Candidate Harvest Strategies:

Both model-based and empirical, CPUE-based harvest strategies are being tested via MSE. Harvest control rules are being tested with the following constraints:

• Total Allowable Catch (TAC) to be set every 3 years (and held constant between settings)
• A maximum of 15% change to the TAC (increase or decrease) relative to the previous TAC

Progress Update & Workplan:

Evaluation of candidate harvest strategies underway via MSE.

• 2022: Refine and further develop MSE and candidate harvest strategies
• 2023 or 2024: Adopt final harvest strategy

Link to relevant policy document or update:

• Albacore Management Strategy Evaluation Update: Updates to the MSE framework as of 2022
• Resolution 15/10 on Target and Limit Reference Points and a Decision Framework

Management Objectives:

Tuning Objectives (for MSE purposes):

• Pr(B(2029)>=B(MSY) ) = 0.5 (SB in 2029 exceeds SB_MSY in exactly 50% of the simulations)
• Pr(B(2034)>=B(MSY) ) = 0.6 (SB in 2034 exceeds SB_MSY in exactly 50% of the simulations)

Reference Points:

• Interim Limit Reference Point: 40% B_MSY and 140% F_MSY
• Interim Target Reference Point: B_MSY and F_MSY

Candidate Harvest Strategies:

Comprehensive harvest strategy proposed by Australia. MSE evaluating model-based HCRs with these candidate constraints:

• Total Allowable Catch (TAC) to be set every 3 years (and held constant between settings)
• A maximum of 15% change to the TAC (increase or decrease) relative to the previous TAC

Progress Update & Workplan:

Evaluation of candidate harvest strategies underway via MSE. Reference set of operating models were revised in 2021 due to concerns about uncertainty in the stock assessment on which the operating models are based, strengthening the MSE.

• 2022: Refine and further develop MSE and candidate harvest strategies
• 2023: Adopt final harvest strategy

Link to relevant policy document or update:

• IOTC Yellowfin Tuna Management Procedure (MP) Evaluation Update June 2021
• Resolution 15/10 on Target and Limit Reference Points and a Decision Framework
• Proposal on a Management Procedure for Yellowfin Tuna in the IOTC Area of Competence: Proposed by Australia

Management Objectives:

WCPFC Interim Management Objective:

• 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
• Maintain an equitable balance of fishing privileges among countries
• 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).

Reference Points:

• Initial Rebuilding Target: historical median biomass (equivalent to 6.4%SSB₀) by 2024
• Second Rebuilding Target: 20% SSB_F=0by 2034
• Candidate Limit Reference Points: 5%SSB_F=0, 7.7%SSB_F=0, 15%SSB_F=0, 20%SSBF=0
• Candidate Threshold Reference Points: 15%SSB_F=0, 20%SSB_F=0, 25%SSB_F=0
• Candidate Target Reference Points: 10%F_SPR, 15%F_SPR, 20%F_SPR, 30%F_SPR, 40%F_SPR
• Candidate F_min: 5%F_target, 10%F_target

^{*SSBF=0 = spawning stock size that would exist in the absence of fishing}

^{*SPR = Spawning Potential Ratio, or the lifetime spawning output that a young fish is expected to produce under current fishing mortality compared to what it would produce in the absence of fishing.}

Candidate Harvest Strategies:

Model-based, sliding HCRs are being explored in the initial MSE work, with a view to develop a comprehensive harvest strategy.

Progress Update & Workplan:

2022-2023: Operationalize management objectives, develop MSE
2024: Provide feedback on MSE, adopt harvest strategy

Link to relevant policy document or update:

• WCPFC Harvest Strategies: Navigate to Pacific bluefin tuna to read an overview of each element of the untested harvest strategy and work going towards the MSE
• Terms of Reference for Pacific Bluefin MSE/ Candidate Reference Points and Harvest Control Rules: Navigate to Attachment F and G

Management Objectives:

• Maintain Spawning Stock Biomass (SSB) above the Limit Reference Point, with a probability of at least 80% over the next 10 years.
• Maintain depletion of total biomass around historical (2006-2015) average depletion over the next 10 years.
• Maintain fishing intensity (F) at or below the target reference point with a probability of at least 50% over the next 10 years.
• To the extent practicable, management changes (e.g., catch and/or effort) should be relatively gradual between years.

Reference Points:

• Target reference point (TRP) = F45_%, which is the fishing intensity (F) level that results in the stock producing 45% of spawning potential ratio (SPR).
• Threshold reference point (SSB_threshold) = 30%SSB_current,F=0, which is 30% of the dynamic unfished spawning stock biomass.
• Limit reference point (LRP) = 14%SSB_current,F=0, which is 14% of the dynamic unfished spawning stock biomass.

WCPFC:

• Limit Reference Point: 20%SSB_{current F=0}
• Target Reference Point: To be determined based upon socioeconomic factors

Ranges for proposed reference points for new harvest strategy:

• Target Reference Point: F₄₀-F₅₀
• Threshold Reference Point: 14-30% SSB₀
• Limit Reference Point: 7%-20% SSB₀ 

^{*SSBcurrent F=0 = stock size that would exist in absence of fishing}

Candidate Harvest Strategies:

Developed by the IATTC and WCPFC Joint Working Group, the harvest strategy was adopted by IATTC in 2023.  It is scheduled for adoption by WCPFC in December 2023, having been endorsed by WCPFC’s Northern Committee in July 2023.

Specifications

• Type: Model-based
• Management cycle: Regular stock assessments every 3 years with a review of the performance completed by 2030 and 2033.
• Data inputs: Stock assessment estimates
• Management output: Fishing intensity
• Harvest control rule:
  • If SSB_current/SSB_current,F=0 is above or equal to SSB_threshold with a probability of at least 50%, fishing intensity shall be maintained at or below the TRP on average over 10 years.
  • If SSB_current/SSB_current,F=0 is below SSB_threshold with a probability greater than 50%, and is above the LRP with a probability of at least 50%, fishing intensity shall be reduced to a level in accordance with the formula:

F = (TRP – F_min/SSB_threshold – LRP) * (SSB_current/SSB_current,F=0 – LRP) + F_min

• If SSB_current/SSB_current,F=0 is at or below the LRP with a probability of greater than 50%, the IATTC shall, in collaboration with the ISC and in coordination with the WCPFC, adopt rebuilding measures that will rebuild SSB to levels of at least the SSB_threshold with a probability of at least 65% within 10 years of SSB_current/SSB_current,F=0 having been identified to be at or below the LRP with a probability greater than 50%. In the absence of such rebuilding measures, fishing intensity shall be set at F_min.

• Other:
  • If SSB_current/SSB_current,F=0 is above the LRP and below SSB_threshold the maximum increase or decrease in catch or effort between the three-year management periods shall be 20% relative to the catch and effort levels specified for the previous year.
  • The IATTC scientific staff in 2024 shall collaborate with the ISC to advise how fishing intensity should be interpreted to actual management under this harvest strategy.

Progress Update & Workplan:

Pending adoption from WCPFC in December 2023, the stock has the potential to have the first trans-Pacific harvest strategy in history.  The first full review of its performance will be in 2030.

Link to relevant policy document or update:

• IATTC: Resolution C-23-02 – Amendment to Harvest Strategy for North Pacific Albacore in the Eastern Pacific Ocean
• Report of the North Pacific Albacore Tuna Management Strategy Evaluation
• Presentation of the above report
• Resolution HS 2022-01: Adopts management objectives, reference points, acceptable levels of risk, and other provisions, with provisions to identify and adopt harvest control rules and exceptional circumstances in 2023.

Management Objectives:

• SSB/SSB_MSY = 100%, with an acceptable level as low as 85%;
• Variation in annual yield is <10%, with an acceptable level as high as 25%;
• Probability of overfished 0%, with an acceptable level as high as 25%;
• Probability of herring fishery closure between 0-10%.

Reference Points:

Upper biomass parameter (overfished threshold): 50%SSB_MSY
Lower biomass parameter (closes fishery): 10%SSB_MSY
Maximum fishing mortality: 80%F_MSY

Harvest Strategy:

Measure includes only a harvest control rule as opposed to a full harvest strategy.

Specifications:

• Type: Model-based
• Management cycle: 3 years, but quota may be different each year
• Data inputs: Recruitment estimates derived from 1995 VPA, mean weights at age, surplus production model
• Management output: Quota
• Harvest control rule: When biomass is greater than 50% of SSB/SSB_MSY, the maximum
  fishing mortality allowed is 80% of F_MSY, so 20% of F_MSY is left for herring predators. As biomass declines further, fishing mortality declines linearly, and if biomass falls below 10% of SSB/SSB_MSY, the fishery closes.

Outcome:

The MSE-tested HCR was implemented for the first time in 2019. Following accounting of the 2020 catches, catch limits decreased for 2022 and 2023 due to overages in 2020.

Link to relevant policy document or update:

Atlantic Herring Fishery Management Plan: Management Strategy Evaluation Debrief Final Report

Atlantic Herring Fishery Management Plan- Ammendment 8

Management Objectives:

Per New Zealand’s Harvest Strategy Standard:

• Achieve the MSY-compatible target or better with at least 50% likelihood
• Limit the risk of breaching the soft limit to no more than 10%
• Limit the risk of breaching the hard limit to no more than 2%

Reference Points:

• Target Reference Point: B_MSYor B_REFa historical stock size proxy from when the stock had” good productivity and was demonstrably safe”; B_REFis always ≥ B_MSY
• Soft Limit:20%SSB₀or 50%B_REF
• Hard Limit:10%SSB₀or 25%B_REF

^{*SSB0 = spawning stock size that would exist in the absence of fishing}

Harvest Strategy:

• Type: Empirical
• Management cycle: 5 years
• Data inputs: CPUE
• Management output: Quota
• Harvest control rule: There are 4 different rock lobster stocks that have an HCR, and each is slightly different. They include step and sliding rules.
• Other: Varies by stock, but most set a minimum quota change.

Outcome:

All but one of the ten lobster stocks in New Zealand are above the target. The single stock considered overfished is still above both the soft and hard limits, according to a 2018 assessment. While the 2022 assessment has yet to be completed for the stock, initial information suggests abundance may be increasing for the stock under current management controls. In 2019, the MPs for two management areas recommended increases in TAC. Two management areas are no longer managed by harvest strategies due to a loss of some of the catch/ effort data, which had been used as the basis for the harvest strategies.

Link to relevant policy document or update:

Operational management procedures of New Zealand rock lobster stocks for 2020–21: Describes performance of harvest strategies and recommendations

Management Objectives:

• Maintain female spawning stock biomass above the LRP of 0.4B_MSY in 95% of years measured over two sablefish generations (36 years)
• When in the Cautious Zone (i.e., 0.4B_MSY<B<0.8B_MSY), limit the probability of decline over the next 10 years to very low (5%) at the LRP, increasing linearly to moderate (50%) at the TRP
• Maintain the female spawning biomass above B_MSY, or 0.8B_MSY when rebuilding from the Cautious Zone, in the year 2052 with 50% probability
• Minimize probability that annual TAC levels are below 1,992 tonnes measured over two Sablefish generations
• Maximize the average annual catch over 10 years, subject to meeting the four objectives above

Reference Points:

• Upper Stock Reference Point: 0.8B_MSY
• Limit Reference Point: 0.4B_MSY
• Target Reference Point: B_MSY or 0.8B_MSY (when rebuilding from the Cautious Zone)

Harvest Strategy:

A fully specified harvest strategy that has been tested via MSE. Operating models for the MSE continue to be updated, most recently in 2019, to account for new data.

Specifications:

• Type: Model-based
• Management cycle: Annual
• Data inputs: Stock assessment using a surplus production model
• Management output: Quota
• Harvest Control Rule: A harvest control rule in which the harvest rate on legal-sized sablefish is reduced linearly from U_MSY (maximum sustainable yield), when the estimated stock is above 0.6B_MSY, to zero when the estimated stock size is less than 0.4B_MSY

Outcome:

A 2019 update found that sablefish have now recovered to or above 0.8B_MSY with 50% probability, so are now outside of the Cautious Zone. The 2019-2020 TAC was the highest TAC recommenced thus far by the HCR.

Link to relevant policy document or update:

• Integrated fisheries management plan summary: Groundfish – Pacific Region, 2022
• Evaluating the robustness of management procedures for the Sablefish (Anoplopoma fimbria) fishery in British Columbia, Canada for 2017-18

Management Objectives:

Maintain both stocks about B_MSY and balance trade-offs between catch, effort and inter-annual variability in TAC

Reference Points:

Target Reference Point: B_MSY

Harvest Strategy:

A fully specified harvest strategy that has been tested via MSE. It includes rules for Exceptional Circumstances for when certain key indices drop below pre-determined threshold values, or when further observations fall outside the range tested within the MSE. Operating models for the MSE continue to be updated, most recently in 2021, to account for new data.

Specifications:

• Type: Empirical
• Management cycle: Annual
• Data inputs: Commercial CPUE and survey abundance indices.
• Management output: Quota
• Harvest Control Rule: TAC recommendations are based on the output of the harvest strategy formula

Outcome:

The 2021 assessment showed both hake stocks above the B-based target reference points. While the TAC trend has been downwards since 2020, the harvest strategy is responding properly to some recent recruitments lower than average to ensure the stocks are maintained near or above B_MSY. The harvest strategy will be revised in 2022.

Link to relevant policy document or update:

• The 2018 Operational Management Procedure for the South African Merluccius paradoxusand capensis
• Update to the Reference Case model incorporating the 2020 commerical and 2021 survey data

Management Objectives:

Biological

• To maintain stocks at (on average), or return to, a target biomass point B_TARG or equivalent proxy (e.g. F_TARG or CPUE_TARG) equal to the stock size that aims to maximise net economic returns for the fishery as a whole
• To maintain stocks above the limit biomass level, or an appropriate proxy, at least 90% of the time
• A reduced level of fishing if a stock is below B_TARG but above B_LIM (or an appropriate proxy)
• To implement rebuilding strategies, no-targeting and incidental bycatch TACs if a stock moves below B_LIM (or an appropriate proxy)
• To ensure the sustainability of fisheries resources, including consideration of the individual fishery circumstances and individual species or stock characteristics, when developing a management approach

Socio-economic

• To maintain stocks at (on average), or return to, a target biomass point B_TARG equal to the stock size that aims to maximise net economic returns for the fishery as a whole
• To maximise the profitability of the fishing industry and the net economic returns to the Australian community
• To minimise costs to the fishing industry, including consideration of the impacts on the industry of large or small changes in TACs and the appropriateness of multi-year TACs

Ecosystem

• To be consistent with the principles of ecologically sustainable development, including the conservation of biological diversity, and the adoption of a precautionary risk approach

Reference Points:

• Limit Reference Point: 20%B₀
• Trigger Reference Point: 35%B₀
• Target Reference Point: 120%B_MSYand 48%B₀

^{*B0 = stock size that would exist in the absence of fishing
*120%BMSY is a proxy for BMEY, the biomass that will produce maximum economic yield}

Harvest Strategy:

This fully specified, MSE-tested harvest strategy framework applies to the Southern and Eastern scalefish and shark fishery, with each stock applying one of four different HCRs included in the harvest strategy.

Specifications:

• Type: Empirical
• Management cycle: 3 years
• Data inputs: CPUE, indices of abundance, size and age data
• Management output: Quota
• Harvest control rule: If B is below limit, no targeted fishing and a rebuilding strategy will be developed; if below trigger, TAC declines linearly toward the target to allow stock to rebuild to target level; if above target, fish at F that produces target biomass (i.e., F₄₈); if between trigger and target, also fish at F₄₈to account for uncertainty in status

Outcome:

According to the most recent 2019 assessment, the stock is considered sustainable at 34% of unfished spawning stock biomass, above Bmsy but below the TRP. The current level of fishing pressure under the HCR is unlikely to deplete the stock or impair recruitment.

Link to relevant policy document or update:

• Harvest Strategy Framework: for the Southern and Eastern Scalefish and Shark fishery: See page 12 for a description of the Tier 1 harvest strategy that the stock falls under
• The effects of implementing a ‘dynamic B₀’ harvest control rule in Australia’s Southern and Eastern Scalefish and Shark Fishery
• Tiger Flathead: Overview of the fishery provided by the Australian government

Management Objectives:

• Maintain stock at levels that can produce MSY, as qualified by relevant environmental and economic factors
• Use HCR to maintain stock at or above the target and well above the limit

Reference Points:

• Target/Threshold Reference Point: 40%B₀
• Limit Reference Point: 20%B₀
• Safety Reference Point: 10%B₀

^{*B0 = stock size that would exist in the absence of fishing}

Harvest Strategy:

The current HCR is slated to be expanded to a fully specified harvest strategy in 2023 or 2024.

• Type: Model-based
• Management cycle: 3 years
• Data inputs: Stock assessment estimates of current spawning stock biomass (B_curr); unfished stock biomass (B₀); equilibrium exploitation rate (E_targ) associated with sustaining the stock at Btarg
• Management output: Quota
• Harvest control rule: Reduces catch linearly from the threshold level (0.4B₀) to the safety level (0.1B₀); zero catch below safety level, except for subsistence fisheries
• Other:
  Maximum catch limit: 900,000t
  Maximum quota change: +/- 30%

Outcome:

Based on the 2020 stock assessment, the stock is currently not overfished or experiencing overfishing. Current spawning stock biomass is estimated to be at 0.45B₀, above the target reference point. However, because there is no allocation key, the HCR-associated TAC has been exceeded by up to 30% in every year since adoption. Overages are expected to continue until the quota is allocated. Regardless, the TAC was increased by almost 10% to 513,572 t for the 2021-2023 period as the skipjack stock continues to be productive regardless of these overages, likely due to favorable environmental conditions.

Link to relevant policy document or update:

Resolution 16/02 on Harvest Control Rules for Skipjack Tuna in the IOTC Area of Competence

Management Objectives:

• Restore to within a prescribed period of time or maintain at B_MSY (chance of B₂₀₃₇<B_MSY is ≤ 50%)
• The risk of failure to meet the B_MSY target and interim biomass targets within a prescribed period of time should be kept moderately low
• Low risk (<30% chance) of exceeding F_MSY
• Very low risk (<10%) of going below an established threshold [e.g. B_lim or B_lim proxy]
• Maximize yield in the short, medium and long term (5,10, 20 years, respectively)
• The risk of steep decline of stock biomass should be kept moderately low
• Keep inter annual TAC variation below “an established threshold” (i.e., 15%)

Reference Points:

• Target reference point: B_MSY
• Proxy limit reference point: 30%B_MSY

Harvest Strategy:

The original HCR adopted in 2010 proved unsuccessful and was modified in 2017. The current harvest strategy will be implemented until 2024, so a new one will be adopted in 2023. If circumstances occur outside the ranges tested by the MSE, the exceptional circumstances protocol will be triggered, possibly changing the HCR.

Specifications:

• Type: Empirical
• Management cycle: 3 years
• Data inputs: Five survey-based abundance indices
• Management output: Quota
• Harvest control rule: Combination of a target-based and slope-based rule that increases or decreases quota depending on the current TAC and recent trends in survey biomass
• Other:
  Maximum quota change: +/- 10%

Outcome:

Greenland halibut are considered overfished. The initial HCR adopted in 2010 had to be revised in 2017 as the exceptional circumstance protocol was triggered in 4 out of 6 years, likely due to annual catch estimates far exceeding the TAC. The TAC based on the current HCR increased in 2019 to 16521 t but decreased for 2022 to 15,864 t.

Link to relevant policy document or update:

• Report of the NAFO Joint Commission-Scientific Council Working Group on Risk-Based Management Strategies (WG-RBMS) Meeting: See item 5 on page 5 for harvest strategy specifications
• Report of the NAFO Joint Commission-Scientific Council Working Group on Risk- Based Management Strategies (WG-RBMS) Meeting: See item 4 on page 3 for an update on the harvest strategy

Management Objectives:

• Maintain stock in green quadrant of Kobe plot with at least 60% probability while maximizing long-term yield
• Rebuild to or above SSB_MSY with at least 60% probability within as short a time as possible, while maximizing average catch and minimizing TAC changes

Reference Points:

• B-Threshold Reference Point (interim): B_MSY
• B-Limit Reference Point (interim): 40% B_MSY
• F-Target Reference Point (interim): 80% F_MSY
• F- Minimum Reference Point (interim): 10% F_MSY

Harvest Strategy:

Adopted in 2021, ICCAT successfully converted the HCR into a full harvest strategy through the addition of an exceptional circumstances protocol and the specification of the data collection and assessment methods needed to apply the HCR.

Specifications:

• Type: Model-based
• Management cycle: 3 years
• Data inputs: Stock assessment estimates of current stock biomass (B_curr) with respect to B_MSY, stock biomass at maximum sustainable yield (B_MSY), fishing mortality at MSY (F_MSY)
• Management output: Quota
• Harvest control rule:
  If B>B_THRESHOLD (B_MSY), fish at F_TARGET (80%F_MSY)
  If B_LIM<B<B_THRESHOLD, reduce F linearly as specified in HCR
  If B<B_LIM, suspend fishery and initiate scientific monitoring at F_MIN (10% F_MSY)
• Other:
  Maximum catch limit: 50,000t
  Maximum quota change: +25%/-20% if current biomass is above B_THRESHOLD

Outcome:

The stock was declared recovered in 2016, a year before the HCR was adopted. The 2018-20 quota set by the HCR was limited by the 20% maximum change clause included in the original HCR. Using the 2020 stock assessment, the HCR recommended a TAC increase for the 2021-23 management period which was agreed to by all parties without controversy, despite the virtual meeting necessitated by COVID-19.

Link to relevant policy document or update:

Recommendation by ICCAT on Conservation and Management Measures, Including a Management Procedure and Exceptional Circumstances Protocol, for North Atlantic Albacore

Management Objectives:

• Convention objective: “Ensure, through appropriate management, the conservation and optimum utilization of southern bluefin tuna”
• Harvest strategy objectives: See target reference points below

Reference Points:

• Limit Reference Point: 24% SSB₀
• Target Reference Point (long-term): 30% SSB₀ by 2035, with a 50% chance of success

^{*SSB0 = spawning stock size that would exist in the absence of fishing}

Harvest Strategy:

Fully-specified ‘Cape Town Procedure’ adopted in 2019 was tested through comprehensive MSE process.

Specifications:

• Type:Empirical
• Management cycle: 3 years
• Data inputs: Longline catch per unit effort index, gene tagging, close-kin genetics
• Management output: Quota
• Harvest control rule: Hybrid rule that increases or decreases quota using model-based log-linear trend in adult biomass inferred by an age-structured model using genetic data and an empirical-based-staged response to CPUE.
• Other:
  Maximum quota change = 3000 t (~15-20%)
  Minimum quota change = 100 t

Outcome:

Quotas have increased each management cycle since the harvest strategy was adopted (an 87% increase between 2011 and 2020). The number of adult fish increased from 5% SSB₀ in 2010 to 20% SSB₀ in 2020.

Link to relevant policy document or update:

• Management Procedure: Overview and history of the harvest strategy
• A scientific alternative to moratoria for rebuilding depleted international tuna stocks