Reference points, harvest control rules and management strategy evaluation in tuna Regional Fisheries Management Organisations : final report.
Date: 2020-08-25
Institutions: Executive Agency for Small and Medium-sized Enterprises
Subjects: authorised catch, catch by species, fishery management, fishery research, fishing controls, international organisation, sea fish

Reference points, harvest control 

rules and management strategy 

evaluation in tuna Regional Fisheries 
Management Organisations 

FINAL REPORT 

July 2018 

Authors: Robert Wakeford, Gorka Merino, Panayiota Apostolaki, Daniel Skerritt and 
Tim Davies. 

 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
EUROPEAN COMMISSION 

Executive Agency for Small and Medium-sized Enterprises (EASME) 
Unit A.3 — European Maritime and Fisheries Fund (EMFF) 

E-mail:  EASME-EMFF@ec.europa.eu  

European Commission 
B-1049 Brussels 

 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
Reference points, harvest control rules 
and management strategy evaluation in 
tuna Regional Fisheries Management 
Organisations 

EASME/EMFF/2016/008 Specific Contract No.06 

Final Report 

 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
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ISBN 978-92-9460-201-5 
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© European Union, 2020

 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
EASME/EMFF/2016/008 – Final Report 

CONTENTS 

LIST OF TABLES .......................................................................................................... III 

LIST OF FIGURES .......................................................................................................... V 

ACRONYMS ................................................................................................................ VII 

GLOSSARY OT TERMS ................................................................................................... IX 

EXECUTIVE SUMMARY ................................................................................................ XIII 

RESUME EXÉCUTIF ..................................................................................................... XIX 

RESUMEN EJECUTIVO ................................................................................................ XXV 

1 

INTRODUCTION .................................................................................................... 1 

1.1 
1.2 

Background ................................................................................................. 1 
Aims and objectives ...................................................................................... 2 

2 

3 

TASK 1: REFERENCE POINTS .................................................................................. 3 

TASK 2: HARVEST CONTROL RULES IN TUNA FISHERIES ........................................... 3 

3.1 
3.2 

3.3 

Sub-task 2.1: Inventory of harvest control rules in tuna RFMOs ......................... 3 
Sub-task 2.2: Strengths and weaknesses of harvest control rules for tuna 
stocks ......................................................................................................... 5 
3.2.1 
ICCAT North Atlantic albacore HCR .......................................... 5 
IOTC skipjack tuna harvest control rule ................................... 8 
3.2.2 
3.2.3  WCPFC Pacific Bluefin tuna rebuilding HCR .............................. 10 
3.2.4 
IATTC tropical tunas harvest control rule ................................ 12 
3.2.5  CCSBT southern bluefin management procedure ...................... 13 
Sub-task 2.3: Considerations for HCRs accounting for multispecies and 
mixed fisheries............................................................................................ 15 
3.3.1  Review of HCRs used for mixed fisheries in non-tuna 

management systems .......................................................... 15 

3.3.2  Overview of ICCAT tropical tuna fisheries as a paradigmatic 

example of multi-species management ................................... 16 

3.3.3  Options for Multispecies HCRs for tropical tunas (Catch, 

effort and fleet based managements) ..................................... 19 
3.3.4  Catch based management ..................................................... 19 
3.3.5 
Effort based management ..................................................... 20 
Fleet based management ...................................................... 21 
3.3.6 
3.3.7  Discussion ........................................................................... 22 

4 

TASK 3: MANAGEMENT STRATEGY EVALUATION (MSE) ............................................. 25 

4.1.1  Sub-task 3.1: Provide an analysis of management strategy 

evaluation in tuna RFMOs ...................................................... 25 

4.1.2  Sub-task 3.2: Provide an overview of operating models, 

HCRs (management procedures) and performance statistics 
used ................................................................................... 32 

4.1.3  Sub‐task 3.3: Analyze strengths and weaknesses of the 

process to develop HCRs and of the process to assess HCRs 
through MSE frameworks within tuna‐RFMOs taking into 
account different factors such as the capacity in third 
countries (information about the process), multispecies 
interactions and mixed nature of tuna fisheries ........................ 43 

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4.1.4  Sub‐task 3.4: Specify what could be defined as next steps to 

improve the current MSE framework in different tuna‐RFMOs..... 46 

5 

TASK 4: CASE STUDIES ........................................................................................ 51 

5.1 

5.2 

Sub-task 4.1: Harvesting strategies of the Western Central Pacific Fisheries 
Commission (WCPFC) .................................................................................. 51 
Sub-task 4.2: Development of mixed fisheries and single stock MSE for 
tropical tunas for International Commission for the Conservation of Atlantic 
Tunas (ICCAT) and Indian Ocean Tuna Commission (IOTC): Define options 
and preliminary models ................................................................................ 51 
5.2.1 
Introduction and review of current state ................................. 51 
5.2.2  Material and Methods ........................................................... 53 
5.2.3  Results ............................................................................... 57 
5.2.4  Discussion ........................................................................... 62 

6 

REFERENCES ....................................................................................................... 65 

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EASME/EMFF/2016/008 – Final Report 

LIST OF TABLES 

Table 1: Summary of harvest control rules that are currently being proposed, tested or 
applied in tuna RFMOs. HCRs/MPs currently established are shown in bold text.  3 

Table 2: Catch advice scenarios for multi-stock management of fisheries in ICES 

(WGMIXFISH).  15 

Table 3: Summary of the information on the models used and the main sources of 

uncertainty considered. 34 

Table 4: Roadmap towards adoption of MPs in IOTC. 

Table 5: Roadmap towards adoption of MPs in ICCAT. 

46 

48 

Table 6: Roadmap towards the adoption of MPs in the WCPFC (Santiago, 2018).

  48 

Table 7: Plan for adoption of a new MP for CCSBT (source: CCSBT, 2017b).  49 

Table 8: Scenarios simulated under MSE framework. 

54 

Table 9: Fleets considered in this simulation and the stocks they catch. 55 

Table 10: The reference points and control variables of the HCRs. 

56 

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EASME/EMFF/2016/008 – Final Report 

LIST OF FIGURES 

Figure 1: Extract from ICCAT Rec. 16-06 describing the HCR for North Atlantic 

albacore currently under consideration. It is noted that recent MSE has evaluated 
this as well as other 14 alternative HCR designs. (ICCAT Rec. 16-06). 

6 

Figure 2: Relationship between stock status and fishing intensity as described by the 

control parameters of the ICCAT HCR for North Atlantic Albacore. (ICCAT Rec. 17-
04). 

7 

Figure 3: Relationship between stock status and fishing intensity as described by the 

control parameters of the IOTC HCR for skipjack (IOTC Res. 16/02). 

9 

Figure 4: Yearly time series of the species catch composition with different operating 

fishing mode: a) purse seiners using FADs b) purse seiners fishing free swimming 
school and c) longliners. Data source: ICCAT Task II Catch and Effort statistics 
(T2CE) and CATDIS. 

17 

Figure 5: De Finetti triangles for: a) purse seiners using FADs b) purse seiners fishing 
free swimming schools and c) longline. Based on method described in Fonteneau 
et al., (2010).  17 

Figure 6: Geographical catch composition estimated with weighted mean (with the 

total landings). The size of the pie is defined with the historical total catch in each 
area: a) purse seiners using FADs b) purse seiners fishing free swimming schools 
and c) longline. Data source from ICCAT CATDIS.  18 

Figure 7: a) Relative size-frequency distribution (in numbers) for yellowfin, skipjack 
and bigeye tunas captured by purse seine fisheries on drifting FADs b) Relative 
size-frequency distributions of bigeye on longliners and DFAD (Fonteneau et al., 
2013).  18 

Figure 8: Harvest Control Rule adopted for North Atlantic albacore (ICCAT, 2017a).

  27 

Figure 9: HCR adopted for Indian Ocean skipjack (IOTC, 2016a). 

28 

Figure 10: Conceptual overview of the management strategy evaluation modelling 

process (source: Punt et al., 2016).  32 

Figure 11: Generic type of HCR evaluated for North Atlantic albacore (Merino et al., 

2016).  37 

Figure 12. Catch based 40:10 type Harvest Control Rule included in the IOTC albacore 

MSE. 

38 

Figure 13. Diagram of the CPUE-based HCR implemented for IOTC albacore (Kolody 

and Jumppanen, 2016). 

38 

Figure 14. Schematic representation of the PT 40:10 type MP category (Kolody and 

Jumppanen, 2016). 

39 

Figure 15: Performance indicators and associated statistics requested for the 

evaluation of HCRs for North Atlantic albacore (ICCAT, 2016a). 

41 

Figure 16: Candidate performance statistics and type of management objectives for 

the evaluation of management procedures (IOTC, 2016c).  41 

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Figure 17: ICCAT's management framework based on Rec. 11-13. 

51 

Figure 18: Conceptual representation of the main components modelled in FLBEIA 

(Garcia et al., 2013).  53 

Figure 19: Effort share of European purse seine fleets: Free school (FS) and Log 

school or FADs (LS). 

56 

Figure 20: Figure shows the historical and the estimated median values of bigeye 
(BET) in the projection with the MSE model of catch, recruitment, fishing 
mortality (f) and spawning stock biomass under different scenarios. The vertical 
discontinuous line is the year starts the projection 2013 and the horizontal 
discontinuous lines are Blim (red) and Btrigger (orange). 

57 

Figure 21: Historical and the estimated median, 5th and 95 quantiles, in the projection 

with the MSE model of bigeye (BET) catch, recruitment, fishing mortality (f) and 
spawning stock biomass under different scenarios. The vertical discontinuous line 
is the year starts the projection 2013 and the horizontal discontinuous lines are 
Blim (red) and Btrigger (orange).  58 

Figure 22: Historical and the estimated median values of yellowfin (YFT) in the 

projection with the MSE model of catch, recruitment, fishing mortality (f) and 
spawning stock biomass under different scenarios. The vertical discontinuous line 
is the year starts the projection 2013 and the horizontal discontinuous lines are 
Blim and Btrigger. 

59 

Figure 23: Historical and the estimated median values and the 5th and 95 quantile of 

yellowfin (YFT) in the projection with the MSE model of catch, recruitment, fishing 
mortality (f) and spawning stock biomass under different scenarios. The vertical 
discontinuous line is the year starts the projection 2013 and the horizontal 
discontinuous lines are Blim and Btrigger. 

59 

Figure 24: Historical and the estimated median values of skipjack (SKJ) in the 

projection with the MSE model of catch, recruitment, fishing mortality (f) and 
spawning stock biomass under different scenarios. The vertical discontinuous line 
is the year starts the projection 2013 and the horizontal discontinuous lines are 
Blim and Btrigger. 

60 

Figure 25: Historical and the estimated median values and the 5th and 95 quantile of 
skipjack (SKJ) in the projection with the MSE model of catch, recruitment, fishing 
mortality (f) and spawning stock biomass under different scenarios. The vertical 
discontinuous line is the year starts the projection 2013 and the horizontal 
discontinuous lines are Blim and Btrigger. 

61 

Figure 26: Historical and the estimated median values of total catches in the 

projection with the MSE model for each fleet. 62 

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ACRONYMS 

Term 

Description 

ALB 

B 

BET 

BFT 

Albacore tuna 

Total biomass 

Bigeye tuna 

Bluefin tuna 

CCSBT 

Commission for the Conservation of Southern Bluefin Tuna 

CITES 

CMM 

CMP 

Convention on International Trade in Endangered Species of Wild Fauna and 
Flora 

Conservation and Management Measure 

Candidate management procedure 

CPUE 

Catch-per-unit-effort 

DFAD 

Drifting fish aggregation device 

EASME 

Executive Agency for Small and Medium-sized Enterprises 

EMFF 

European Maritime and Fisheries Fund 

EPO 

ESC 

F 

FAD 

FAO 

FFA 

HCR 

Eastern Pacific Ocean 

Extended Scientific Committee (of CCSBT) 

Fishing mortality 

Fish aggregating device 

Fisheries and Agricultural Organisation of the United Nations 

Pacific Islands Forum Fisheries Agency 

Harvest control rule 

IATTC 

Inter-American Tropical Tuna Commission 

ICCAT 

International Commission for the Conservation of Atlantic Tunas 

ICES 

IOTC 

ISC 

International Council for the Exploration of the Sea 

Indian Ocean Tuna Commission 

International Scientific Committee (for Tuna and Tuna-like Species in the North 
Pacific Ocean) 

ISSF 

International Seafood Sustainability Foundation 

LRP 

MEY 

MP 

MSE 

MSY 

OM 

Limit reference point 

Maximum economic yield 

Management procedure 

Management strategy evaluation 

Maximum sustainable yield 

Operating model 

OMMP 

Operating Model and Management Procedure 

PBF 

Pacific bluefin tuna 

RFMO 

Regional Fisheries Management Organisation 

SAC 

SB 

Scientific Advisory Committee (of IATTC) 

Spawning biomass 

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Term 

Description 

SBT 

Southern bluefin tuna 

SCRS 

Standing Committee on Research and Statistics (of ICCAT) 

SKJ 

SPR 

SRR 

SSB 

Skipjack tuna 

Spawning potential per recruit 

Stock-recruitment relationship 

Spawning stock biomass 

SWO 

Swordfish 

TAC 

TRP 

Total allowable catch 

Target referent point 

UNCLOS 

United Nations Convention on the Law of the Sea 

UNFSA 

United Nations Fish Stocks Agreement 

WCPF 

Western and Central Pacific Fisheries 

WCPFC 

Western and Central Pacific Fisheries Commission 

WCPO 

Western and Central Pacific Ocean 

WPTT 

Working Party on Tropical Tuna 

YFT 

YPR 

Yellowfin tuna 

Yield per recruit 

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GLOSSARY OT TERMS 

Term 

Description 

Biomass (B) 

The total weight of all organisms in a population or a defined part of the 
population. 

Virgin Biomass 
(B0) 

BCURRENT 

BESCAPEMENT 

BLIM 

BMSY 

BTARGET 

BTHRESHOLD 

The theoretical carrying capacity of the recruited or vulnerable biomass of 
a fish stock. In some cases, it refers to the average biomass of the stock 
in the years before fishing started. More generally, it is the average over 
recent years of the biomass that theoretically would have occurred if the 
stock had never been fished. B0 is often estimated from stock modelling 
and various percentages of it (e.g. 40% B0) are used as biological 
reference points to assess the relative status of a stock. 

Current biomass (usually a mid-year biomass). 

For short-lived species, a deterministic biomass limit below which a stock 
is considered to have reduced reproductive capacity, including any 
identified additional biomass need. 

Reference point to indicate stock size below which the stock is in serious 
danger of collapse 

The long-term average biomass that is achieved by fishing at a constant 
fishing mortality rate equal to FMSY; in other words, the average biomass 
able to produce maximum sustainable yield (MSY). Since it is an average, 
the biomass at any particular time may be different from BMSY because of 
natural variability in productivity and breeding success, though the long-
term average is maintained.   

A target is a management objective based on a level of biomass (BTARGET) 
that should be achieved and maintained 

A threshold is a level of biomass (BTHRESHOLD) reflecting the precautionary 
approach that triggers pre-agreed management actions to reduce the risk 
of breaching the limits. Thresholds should be set sufficiently far away from 
limits so that there is low probability that the limits will be exceeded.  

BTRIGGER 

A trigger is a level of biomass (BTRIGGER) that triggers a specific 
management action. 

Catch-per-unit-
effort (CPUE) 

Fishing 
mortality (F) 

F0.1 

FCURRENT 

FLIM 

FLATEST 

The quantity of fish caught (in number or in weight) with one standard 
unit of fishing effort (e.g., number of fish taken per 1,000 hooks per day, 
or weight of fish taken per hour of trawling). CPUE is often considered an 
index of fish biomass (or abundance). Sometimes referred to as catch 
rate. 

The instantaneous fishing mortality rate. This is the fraction of the 
population (or year class or other defined group) that is expected to be 
caught at any single point in time. The annual fishing mortality rate is 
calculated using the formula 1-e-F, where “e” is the mathematical constant 
known as Euler’s number. For example, an F of 0.54 means that 0.417, or 
41.7 percent, of the population is caught each year.    

A biological reference point that is the fishing mortality rate at which the 
increase in equilibrium yield per recruit in weight per unit of effort is 10% 
of the yield per recruit produced by the first unit of effort on the 
unexploited stock (i.e. the slope of the yield per recruit curve for the F0.1 
rate is only 1/10th of the slope of the yield per recruit curve at its origin). 

An average fishing mortality value obtained from most recent few years 
and excluding the final year. 

The point above which the removal rate from the stock is too high. 

A single fishing mortality value obtained in the final year of the 
assessment, rather than an average of recent years (i.e. FRECENT). 

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Description 

Floss is usually defined as the fishing level F which will produce a long-
term spawning biomass per recruit (S/R) associated to BLOSS. 

A biological reference point. It is the fishing mortality rate that maximises 
equilibrium yield per recruit. FMAX is the fishing mortality level that defines 
growth overfishing. In general, FMAX is different from FMSY (the fishing 
mortality that maximises sustainable yield), and is always greater than or 
equal to FMSY, depending on the stock-recruitment relationship. 

A proxy for recruitment overfishing. FMED is the equivalent of the recruits 
per spawning stock biomass that have been above the replacement level 
in half the years. The usefulness of this reference point is dependent on 
the level of exploitation of the stock in question. It will result 
underestimation of FMED if the stock has only been lightly exploited. FMED 
is viewed as a limit reference point as fishing mortality rates higher than 
FMED lead to stock decline. 

The fishing mortality rate that corresponds to the maximum economic 
yield. 

At low biomass levels, the fishing mortality would be as close to zero as 
possible (FMIN) to rebuild within the maximum rebuilding time period. 

A fishing mortality rate that, if applied constantly, would result in BMSY  and 
maximum sustainable yield (MSY) on average over the long term 

A single fishing mortality value obtained in the final year of the 
assessment. 

A level of fishing mortality that reduces the spawning (biomass) per recruit 
to x% of the unfished spawner-per-recruit (SPR) level (e.g. F20%, F30%, 
F40%). 

Term 

FLOSS 

FMAX 

FMED 

FMEY 

FMIN 

FMSY 

FRECENT 

F%SPR 

FTARGET 

A target is a management objective based on a fishing mortality rate  

(FTARGET) that should be achieved and maintained 

FX% 

A fishing mortality rate that leads to X percent of the maximum spawning 
potential (e.g., egg production, recruits, spawners) that is obtained with 
no fishing. 

Harvest control 
rule (HCR) 

A pre-agreed rule that describes how the harvest is to be managed based 
on selected indicator(s) of stock status. Also known as a decision rule. 

KOBE Plot 

Limit reference 
point (LRP) 

Management 
Procedures (MP) 

A four-quadrant graphic that shows the status of a stock, the trajectory of 
the stock through time, or both. Stock abundance is on the horizontal axis, 
and fishing mortality is on the vertical axis. The axes are typically divided 
at B=BMSY and F=FMSY, respectively, and hence can graphically depict 
whether the stock is overfished and/or subject to overfishing. 

A benchmark for an indicator that defines an undesirable biological state of 
the stock. To keep the stock safe, the probability of violating an LRP 
should be very low. However, if an LRP is violated, immediate action—such 
as a suspension of fishing—should be taken to return the stock or fishery 
to the target level.   

A set of formal actions—usually consisting of a combination of monitoring 
data, analysis method, and harvest control rules—that are used to manage 
a fishery iteratively and adaptively. MPs are derived by simulation and 
chosen for their performance in meeting the specified management 
objectives and robustness to the presence of uncertainties. 

Maximum 
economic yield 
(MEY) 

The sustainable catch or effort level for a commercial fishery that allows 
net economic returns to be maximised. Note that for most practical 
discount rates and fishing costs MEY will imply that the equilibrium stock 
of fish is larger than that associated with MSY. In this sense MEY is more 
environmentally conservative than MSY and should in principle help 

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Term 

Description 

Management 
strategy 
evaluation 
(MSE) 

Maximum 
sustainable 
yield (MSY) 

Metiér 

Overfished 

protect the fishery from unfavourable environmental impacts that may 
diminish the fish population. 

A tool that scientists and managers can use to simulate the workings of a 
fisheries system and allow them to test whether potential harvest 
strategies or management procedures (MPs) can achieve pre-agreed 
management objectives. In so doing, MSE helps to determine the harvest 
strategy likely to perform best. That means the strategy would perform 
well, regardless of uncertainty, and balance trade-offs amid competing 
management objectives. Around the world, fisheries are moving toward 
management based on harvest strategies to increase long-term 
sustainability, stability and profitability. MSE must be an integral 
component of the process to ensure that the chosen strategy can achieve 
its objectives. 

The largest long-term average yield that can be taken from a stock under 
existing environmental conditions and a constant fishing mortality rate.    

A group of fishing operations targeting a specific assemblage of species, 
using a specific gear, during a precise period of the year and/or within the 
specific area. 

Stocks that are below a biomass limit, such as the soft limit, are frequently 
referred to as “overfished” (e.g. in the United States). However, the term 
“depleted” should generally be used in preference to “overfished” because 
stocks can become depleted through a combination of overfishing and 
environmental factors, and it is usually impossible to separate the two. 

Overfishing 

Overfishing is deemed to be occurring if FMSY (or relevant proxies) is 
exceeded on average. 

Precautionary 
approach 

Recruitment 

A management philosophy that requires consideration of risk reduction in 
decision-making, so that in the absence of full information, the decision 
taken results in the lowest risk to the stock. 

The amount of new fish that join a defined group of fish each year—due to 
growth and/or migration. The defined group may be the exploited part of a 
population, which is described as recruitment to the fishery. The defined 
group also may be the whole population (fished or unfished) older than a 
certain age (e.g., age 1 or the age at maturity). 

Recruitment 
overfishing 

Occurs when adults are depleted to the point that they cannot replenish 
themselves. Without remedy, this will lead to stock collapse. 

Reference 
points 

A benchmark against which the biomass or abundance of the stock or the 
fishing mortality rate (or exploitation rate), or catch itself can be measured 
in order to determine stock status. These reference points can be targets, 
thresholds or limits depending on their intended use. 

Selectivity 

Measures the relative vulnerability of different age (size) classes to being 
caught by a specific fishing gear or fleet. 

Spawning 
potential per 
recruit (SPR) 

The lifetime contribution of spawning output (e.g., eggs) that a recruit is 
expected to provide under the stated fishing mortality, relative to its 
lifetime production without fishing. Often expressed as a percentage. For 
example, SPR50% means that under the specified fishing mortality rate, a 
recruit will on average produce half the eggs in its lifetime that it would 
have produced without fishing. 

Stock 
recruitment 
relationship 
(SRR) 

The relationship between the parental fish stock (spawning biomass) and 
the resulting recruitment (usually the number of recruits to the exploitable 
phase). The SRR is used to predict the average number of recruits that 
would be produced at different population sizes. The most frequently used 
stock-recruitment relationship is the Beverton and Holt equation, in which 

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Term 

Description 

the expected number of recruits changes very slowly at high levels of 
spawning biomass. 

SB0.5R0 

Spawning biomass corresponding to that which produces a 50% reduction 
in recruitment as calculated in a Beverton-Holt spawner-recruit model with 
steepness (h) 

Spawning stock 
biomass (SSB) 

SSB0 

SSBCURRENT 

SSBF=0 

SSBLIM 

SSBMED 

SSBMSY 

SSBRECENT 

Steepness 

The total weight of the sexually mature part (i.e., adults) of a population. 

The virgin spawning stock biomass prior to fishing. SSB0 is calculated by 
reconstructing the population backwards to the point where fishing 
mortality was absent or negligible. This can be difficult to estimate due to 
uncertainty in historical catches. In addition, changing environmental 
conditions can affect recruitment patterns and result in differing values of 
SSB0. 

An average spawning stock biomass value obtained over the last few years 
rather than the latest point estimate. 

Spawning stock biomass in the absence of fishing. This is often estimated 
via models by projecting the population forwards over time in the absence 
of fishing mortality and under constant environmental conditions, or in 
practice at very low exploitation intensity. 

Spawning stock biomass (SSB) limit reference point. 

The median spawning stock biomass over a defined period. 

SSBMSY, also known as ‘spawning biomass at MSY’, is the biomass of 
spawners that would result on average if FMSY was applied constantly year 
after year. It is often measured by the biomass of female spawners only. 

Spawning stock biomass value obtained in the final year of the 
assessment. 

Steepness (h) is conventionally defined as the proportion of unfished 
recruitment (R0) that would be expected to be produced if the spawning 
biomass were reduced to 20% of unfished spawning stock biomass (SSB0). 
Stocks with high steepness produce many more births than deaths on 
average when the spawning stock is reduced to low levels by fishing. A 
greater excess of births over deaths means that a stock with high 
steepness enables a greater number of individuals to be taken from the 
stock sustainably, by fishing, than a comparable stock with lower 
steepness. The steepness of a stock is typically both very difficult to 
estimate and highly influential on harvest policy and stock assessment 
model outputs such as maximum sustainable yield and spawning stock 
biomass. It therefore represents a major source of uncertainty in most 
comprehensive stock assessments. 

Target reference 
point (TRP) 

A benchmark for an indicator that defines the target fishery state that 
should be achieved and maintained. Creates a buffer zone to ensure that 
the limit reference point (LRP) is not breached. Can be based on one or 
more biological, ecological, social or economic considerations. 

Yield per recruit 
(YPR) 

The expected yield (measured by numbers, biomass, etc.) that a new 
recruit will produce over its lifetime under a stated fishing mortality and 
selectivity. 

Sources: 
https://iss-foundation.org/knowledge-tools/issf-glossary/  
http://www.ices.dk/community/Documents/Advice/Acronyms_and_terminology.pdf 

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EXECUTIVE SUMMARY 

Background 

1.  Management  plans  developed  by  tuna  RFMOs  (t-RFMOs)  require  the  adoption  of 
management objectives and timeframes for achieving them. These can greatly benefit from 
using Reference Points (RP) to develop appropriate limits, targets or trigger points and help 
define the parameters of the management framework. Such reference points together with 
detailed rules on how to define allowable catches/exploitation (i.e. Harvest Control Rules, 
HCRs) can then be tested under different scenarios of state of nature and uncertainty to 
assess their effectiveness and trade-offs among different management strategies. 

2.  Management  Strategy  Evaluation  (MSE)  provides  a  platform  for  simulation-testing  such 
alternative management strategies explicitly accounting for uncertainty and has therefore 
been increasingly used in fisheries management to support management decisions. MSE is 
mainly used to test how well existing or proposed management strategies perform under 
different  scenarios  or  identify  the  most  effective  management  strategies  from  a  set  of 
candidate strategies and for a given set of objectives. 

Aims and objectives 

This study undertook the following four main tasks: 

3.  Task  1:  Reference  points.  Provide  an  inventory  of  RPs  for  all  tuna  stocks.  Use  of  RPs 
between  t-RFMOs  to  analyse  their  consistency  and  the  basis  for  their  establishment, 
including  the  strengths  and  weaknesses  of  each  individual  RP.  To  assess  the  relation 
between different types of RPs taking into account relevant factors such as the stock status 
and the exploitation patterns of different fisheries. Provide several case studies as examples 
of  different  types  of  RPs  for  the  same  tuna  stock  in  different  conservation  status  and 
harvested by different fisheries. 

4.  Task 2: Harvest control rules. Provide an inventory of what types of HCRs (management 
procedures) have been proposed, tested or applied in t-RFMOs. Analyse the strengths and 
weaknesses  of  different  types  of  HCR  (existing  and  under  development)  for  tuna  stocks 
taking into account factors  such as data availability, types  of fisheries and management 
systems.  Discuss  how  HCRs  could  be  developed  taking  into  account  multispecies 
interactions and mixed fisheries.  

5.  Task  3:  Management  Strategy  Evaluation.  Review  the  development  of  MSEs  across  t-
RFMOs,  including:  1)  evaluate  how  MSE  frameworks  have  been  planned  and  developed 
across  t-RFMOs;  2)  review  how  the  MSE  components  (operating  models,  Management 
Procedures (MP) and performance statistics) have been developed and  analyse how MSE 
has been used to support the adoption of HCRs; 3) identify strengths and weaknesses of 
the  process  to  develop  HCRs  and  MSE  frameworks  within  t-RFMOs;  and  4)  propose 
alternatives for improving MSE frameworks across t-RFMOs. 

6.  Task 4: Three t-RFMOs (i.e. WCPFC, ICCAT and IOTC) are used as case studies to provide 
a more detailed picture of the MSE process and its progress. The main objectives of the 
case  studies  are  to  understand  the  MSE  approaches  considered,  their  implications,  and 
progress so far but also consider additional options that can support the MSE process. 

Task 1: Review of reference points 

7.  Tuna RFMOs are in the process of establishing management objectives and defining target 
reference points (TRPs) and limit reference points (LRPs) as part of their Harvest Strategies 
(HS). Management objectives include sustainability, safety, production, employment and 
stability and RPs aim at guiding fisheries towards achieving these objectives. However, the 
approach towards establishing RPs is different across t-RFMOs and each approach has its 
own shortcomings for fisheries management practice. 

8.  Various  methods  are  available  to  calculate  RPs,  including  maximum  sustainable  yield 
(MSY)-based, depletion-based, spawning potential per-recruit (SPR) and yield-per-recruit 

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(YPR). Each method has its own particular strengths and weaknesses although both MSY- 
and depletion-based methods are the most commonly used by t-RFMOs.  

9.  Uncertainties  in  the  stock-recruitment  relationship  (SRR)  steepness  parameter  (h),  can 
significantly  weaken  the  ability  to  provide  robust  estimates  for  MSY-based  RPs  with  the 
stock assessment models currently in use. One major advantage of depletion-based RPs 
for management is that they remain relatively stable between each assessment and have 
provided  the  least  variation  in  the  results  across  a  range  of  steepness  values  and  stock 
assessment models. Where major uncertainties exist in model parameters such as the stock 
recruitment  steepness  (h)  value,  depletion-based  RPs  are  considered  to  provide  a  more 
robust approach to setting RPs. 

10.  A  review  of  LRPs  across  various  t-RFMOs  has  shown  a  lack  of  consistency  in  the  values 
used to support their Harvest Strategies. For example, IOTC has adopted an interim MSY-
based  LRP  for  yellowfin  tuna  of  40%SSBMSY  (which  is  equivalent  to  14%SSB0),  whereas 
WCPFC has adopted a depletion-based LRP of 20%SBCURRENT, F=0 (equivalent to 20%SSB0) 
for the same species. This would suggest that either IOTC is less precautionary or WCPFC 
is  more  conservative  in  setting  LRPs.  In  reality,  this  discrepancy  is  due  to  the  different 
nature  of  the  RPs  used  (MSY-  and  depletion-based).  Further  to  this  however,  stocks  in 
separate regions may have different levels of productivity, based on different biological or 
fishery characteristics. It is therefore not unexpected to observe dissimilar RPs for each t-
RFMO for the same species. 

11.  More recently, there has been a move towards adopting MSY as a LRP rather than a TRP. 
It  has  been  argued  that  given  the  uncertainties  in  calculating  MSY  and  the  adverse 
biological,  social  and  economic  consequences  of  exceeding  this,  some  t-RFMOs  such  as 
WCPFC now consider MSY as a LRP, in particular FMSY. This is based on the precautionary 
approach, UNFSA and other international instruments.  

12.  For  the  biological  status,  LRPs  have  increasingly  been  defined  as  20%  of  SSB0  using 
depletion-based methods, which is a precautionary RP for fisheries where the SRR remains 
uncertain.  Further to this, it has been suggested that FMSY represents an “upper bound” to 
fishing mortality rates, which is consistent with the definition of a LRP: “a state of a fishery 
and/or  a  resource  which  is  considered  to  be  undesirable  and  which  management  action 
should avoid”. 

13.  It has been shown that using typical SRR steepness values (h) for skipjack between 0.7-
0.9,    MSY-based  RPs  (e.g.  BMSY)  are  just  above  or  even  below  the  general  LRP  of 
20%SBCURRENT,F=0 adopted by WCPFC. Therefore under certain conditions, a reference point 
typically associated “to maintain or restore stocks at levels capable of producing maximum 
sustainable yield” would suddenly be viewed as “outside safe biological limits”. This paradox 
occurs specifically because the 20%SBCURRENT,F=0 as a single depletion-based LRP has been 
adopted across all main stocks, irrespective of the relative productivity of the population 
or selectivity of the fishery. Although calculating stock-specific LRPs and their associated 
levels of acceptable risk would help to overcome this issue, the current LRPs are biologically 
“precautionary”  and  therefore  in  line  with  the  requirements  of  WCPFC’s  Convention.  To 
date,  insufficient information is  available  to  establish  different  stock-specific  LRPs  within 
the region.  

14.  TRPs  may  be  set  to  achieve  management  objectives,  which  include  social  and  economic 
objectives. There is growing evidence to suggest that managing stock biomass above BMSY 
leads to larger fish, similar catch levels with greater economic benefit and lower ecological 
impact. This approach is consistent with the objectives of the CFP under article 2.2, which 
aims  to  “restore  and  maintain  populations  of  harvested  species  above  levels  which  can 
produce the maximum sustainable yield”. 

15.  Setting TRPs equivalent to 40%SSB0 or higher instead of MSY-based (BMSY) levels can bring 
notable differences (or underutilisation) in the level of catch opportunities and employment 
(fishing  effort).  To  date,  WCPFC  has  adopted  an  interim  TRP  for  skipjack  tuna  based  on 
50%SBCURRENT,F=0, which despite the many uncertainties, is well above the available SBMSY 

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estimates. While the interim TRP adopted by WCPFC might appear overly conservative, the 
assessment for skipjack is considered uncertain. 

16.  To  date,  the  probabilities  of  achieving  TRPs  and  avoiding  LRPs  and  the  timeframes  for 
achieving management objectives is currently under debate in all  t-RFMOs.  In particular 
there  is  no  clear  definition  of  what  constitutes  ‘high’,  ‘very  high’,  ‘low’  and  ‘very  low’ 
probabilities. 

Task 2: Harvest Control Rules in tuna fisheries 

17.  The use of HCRs has been increasingly favoured by t-RFMOs to enable them to implement 
good management practice of tuna stocks and also to simplify the negotiation process of 
establishing fishing limits and/or catch quotas and/or implementing technical measures. 

18.  An inventory has been provided summarising the status of HCRs in t-RFMOs for each stock. 
It  includes  HCRs  that  have  been  recommended  or  proposed  within  t-RFMOs,  as  well  as 
those that are tested or applied in some form.  

19.  Within ICCAT, HCRs have not been defined for skipjack, yellowfin, bigeye, southern Atlantic 
and Mediterranean albacore, and bluefin tuna although Recommendations 11-13 and 15-
07  provide  a  framework  for  establishing  them.  An  HCR  has  been  defined  for  Northern 
albacore in 2017 under Recommendation 17-04. Some of the strengths identified for the 
Northern albacore HCR include that it will be subject to peer review by SCRS in 2018 and 
should exceptional circumstances occur, the Commission will review and consider a possible 
revision of the HCR. Further to this, clear rules regarding the types of management action 
to be triggered at different reference points has been established, including reduction in 
Total Allowable Catch (TAC). The HCRs are subject to a Management Strategy Evaluation 
(MSE) that indicates that the HCR is robust to uncertainties in the stock. Conversely, some 
of the weaknesses identified show that it is not clear if probabilities relative to the RPs or 
the performance indicators will integrate model uncertainty, and also that the TAC is shared 
among many countries where there is less control over catches. 

20.  Since 2016, IOTC has established an HCR for skipjack tuna based on LRPs and TRPs under 
Resolution 16/02. IOTC has not yet established an HCR for bigeye, yellowfin or albacore. 
Some  of  the  major  strengths  of  the  IOTC  skipjack  HCR  include  management  objectives 
along with clear definitions for LRPs and TRPs, and setting of the TAC. Res. 16/02 requires 
the  HCR  and  control  parameters  to  be  evaluated  using  MSE  approach,  including  a  clear 
timeline  and  modification  of  the  HCR,  as  necessary.  A  number  of  weaknesses  were 
identified, including that the HCR is only recently agreed and that no meaningful evaluation 
can yet be made. Furthermore, the HCR does not explicitly make reference to acceptable 
probabilities for  exceeding RPs, nor is it clear how the role of subsistence fishing will be 
taken into account where thresholds have been exceeded. In addition, where the biomass 
is estimated to fall below the LRP there is no clear timeline within which a new HCR should 
be implemented, putting the status of the stock at higher risk of depletion. 

21.  WCPFC has not yet defined an HCR for skipjack, yellowfin or bigeye tuna. CMM 2014-06 
calls for WCPFC to develop and implement a Harvest Strategy approach that includes TRPs, 
HCRs  and  other  elements.  The  Northern  Committee  has  recommended  an  interim 
management framework for North Pacific albacore whereas in 2014 a Harvest Strategy for 
Pacific bluefin tuna has defined HCRs to achieve specific rebuilding targets. The rebuilding 
phase of the North Pacific albacore HCR is explicit how management action will be taken in 
relation to the rebuilding TRP, alongside an established timeline. There are also acceptable 
levels of risk specified, considered by WCPFC to be consistent with the UNFSA. Some of the 
potential weaknesses of this rebuilding HCR include that it has not yet been evaluated by 
MSE,  although  this  is  currently  under  development,  and  that  probability  of  the  stock 
declining below the LRP has not been clearly defined, as described only as ‘very low’. 

22.  In 2016, IATTC adopted an HCR for all tropical tuna under Resolution C-16-02 based on 
interim LRP and TRPs. With regards to North Pacific albacore, Resolution C-13-03 requires 
that IATTC staff shall review work undertaken by WCPFC towards the development of HCRs. 
With respect to the HCR for all tropical tuna, some of the strengths of Res. C-16-02 are 

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that  it  establishes  clear  definitions  for  interim  LRP  and  TRPs,  and  includes  pre-agreed 
management actions to be taken under various stock conditions, which allows management 
measures, such as a reduction in TAC to be implemented quickly, where required. A number 
of weaknesses in the HCR include that it is only considered on an interim basis until it has 
been  assessed,  as  no  MSE  process  has  yet  been  established  with  no  clear  probabilities 
related to exceeding RPs given. 

23.  CCSBT  developed  a  management  procedure  (MP)  in  2011  for  southern  bluefin  tuna, 
designed to achieve the recovery target. This MP, known as the ‘Bali Procedure’, sets clear 
probability-based  objectives  for  stock  rebuilding  using  an  interim  TRP  within  an  explicit 
time period. CCSBT tested a number of candidate MPs against a range of uncertainties to 
ensure a robust procedure was identified. The MP is also assessed regularly, including an 
annual review of implementation and regular evaluation of new data sources and operating 
models. One of the potential weaknesses of the MP is the complexity of the methods used, 
making it difficult to communicate to stakeholders and decision makers.  

24.  HCRs  accounting  for  multispecies  fisheries  management  can  be  applied  using  catch  and 
effort  limits.  In  general,  when  using  catch  limits,  a  real  time  monitoring  of  catch  is 
necessary but can be difficult. For example, in the IOTC there is a time lag between landings 
and  the  effective  sampling  of  catch.  This  can  cause  problems  of  non-compliance  if  the 
excess of catch is not detected or to premature closures if catch is overestimated. 

25.  In multispecies fisheries it is not possible to apply different levels of fishing effort to two or 
more species that are vulnerable to the same fishing gear and inhabit the same habitat. 
Provided that discarding is undesirable based on the Common Fishery Principles, when the 
catch  limit  for  one  stock,  (e.g.  yellowfin  in  IOTC  or  bigeye  in  ICCAT)  is  reached  (choke 
species) but not for the others, fleets will stop their fishing operations. In that case, the 
catch  limits  for  skipjack  for  example  will  not  be  reached  with  the  associated  loss  of 
opportunities for the fishing fleets and other undesirable socioeconomic consequences. The 
latter include loss of food production, shortages to canneries and potentially price increases 
due to a lower supply at international markets. 

26.  In general, TAC based management requires accurate estimates of stock status, RPs and 
recruitment  when  catch  limits  are  set.  Should  the  biomass  and  recruitment  be 
underestimated, catch limits will be reached sooner than expected and fishing opportunities 
would be wasted unless the choke species is discarded. On the contrary, if stock biomass 
is overestimated, when managing with fixed catch limits, biomass will continue to decline 
as fishing mortality will increase. In this regard, effort controls are a more flexible way to 
deal with multispecies fisheries since they can reconcile conservation objectives of two or 
more stocks when they are set for the most vulnerable stock, in this case bigeye.  

27.  Fishing effort limits are restrictions on the intensity of use of the fishing gears. These can 
include limits to the period of the fishing season, which is relatively easy to enforce through 
vessel monitoring systems (VMS), use of logbooks and other measures. Also, fishing effort 
control  reduces  the  need  for  a  real  time  monitoring  of  catch  which  is  often  difficult  and 
expensive. Under effort control systems, it is no longer necessary to estimate the fishable 
biomass  accurately  every  year,  as  the  level  of  fishing  mortality  is  restrained  directly, 
irrespective  of  the  continual  fluctuations  of  stock  size  by  controlling  the  level  of  fishing 
effort. In order to be effective, effort based management would require a tight control on 
fleets’ technological capacity and catchability.  In cases where fishing capacity increases, 
the fishing mortality produced with a given effort could be higher than expected and thus, 
compromise the sustainability of the stocks. 

28.  To date, only ICCAT uses TACs or overall catch limits for all the fleets involved in tropical 
tuna  fisheries.  IATTC  and  WCPFC  apply  output  controls  (TAC)  only  for  longline  fleets 
targeting bigeye tuna. In the Pacific, purse seine fleets activity is regulated through effort 
limits  (the  days  of  the  fishing  season).  The  IATTC  uses  an  effort  based  pseudo-HCR  to 
determine the number of fishing days that purse seines are permitted to fish in order to 
achieve MSY.  

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29.  In  2017,  IATTC  attempted  to  introduce  catch  limits  for  bigeye  and  yellowfin  catch  from 
purse  seine  fleets  operating  with  FADs  and  an  additional  catch  limit  for  yellowfin  from 
dolphin  associated  fisheries.  In  practice  this  proved  difficult  to  implement  as  the  purse 
seine fleet fishing on FADs had reached 80% of the total annual catch limit by mid-July. 
This  led  to  the  introduction  of  a  new  measure  (C-17-02)  after  only  5  months,  which 
prevented  the  FAD  fishery  from  closing  in  August  or  early  September,  with  dramatic 
consequences for purse seine fleets. 

Task 3: Management Strategy Evaluation 

30.  The  five  t-RFMOs  have  carried  out  some  type  of  MSE  work,  including  consultation  on 
management  objectives,  characterization  of  uncertainty  of  stocks’  dynamics  and 
observation, and evaluation of harvest strategies. Most of the MSE conducted to date has 
been  developed  by  the  RFMO  science  providers  with  seldom  direct  mandate  from  the 
Commissions. 

31.  The  study  provided  an  overview  of  operating  models  (OMs),  HCRs  and  performance 
statistics  used.  OMs  provide  mathematical  representations  of  the  system  that  is  being 
managed. The impact of fisheries management is evaluated before implementation in the 
OMs  when  using  MSE.  The  OMs  are  considered  alternative  representations  of  the  “true” 
dynamics of the stock and aim at covering all the uncertainties inherent to fish and fisheries’ 
dynamics. 

32.  Today, MSE is being developed for single species only, with objectives of maintaining stocks 
at healthy levels, promoting the successful recovery of overexploited stocks and to evaluate 
the economic benefits of precautionary management. In order to engage third countries in 
the MSE process across t-RFMOs, several initiatives (workshops, capacity building, courses 
and  projects)  are  being  organized.  This  will  help  developing  new  MSE  frameworks  that 
consider  alternative  approaches  such  as  multispecies  interactions  etc.  The  initiatives  to 
promote  the  engagement  of  third  countries  and  to  develop  alternative  MSE  approaches 
have been reviewed, including the impact of the Areas Beyond National Jurisdiction project 
on this process. 

33.  All five t-RFMOs have plans for evaluating MPs using MSE. In some RFMOs, the roadmap 
towards adopting MPs is clearly detailed and in others the process is only at an initial state.  

34.  The process in IOTC relies on the technical work and the interaction with the Commission. 
The IOTC aims at being able to adopt MPs for its most important stocks by 2020. In ICCAT, 
the  MSE  process  is  well  advanced  for  North  Atlantic  albacore  and  bluefin.  One  of  the 
differential aspects of ICCAT’s MSE process is that it will be independently evaluated, with 
the  evaluation  of  North  Atlantic  albacore  MSE  in  2018  that  will  contribute  to  the 
improvement of the process  for  other  stocks.  In addition, it will contemplate options for 
the  multispecies  management  instead  of  the  current  single  species  management 
framework.  In  the  WCPFC  the  feedback  process  is  advanced  and  has  made  substantial 
progress in defining management objectives thanks to a number of dialogue workshops. In 
the IATTC, the MSE work consists on identifying appropriate HCRs for bigeye and yellowfin 
but it is still in its early stages. There is a plan for MSE development that will be presented 
in the 2018 Scientific Advisory Committee. The CCSBT has decided to develop a new MP to 
guide the setting of TACs for 2021 and onwards.  The new MP will take into account changes 
in data availability, in particular changing the recruitment monitoring series from an aerial 
survey of juveniles to a juvenile gene tag/recapture program. 

Task 4: Case studies of select tuna RFMOs 

Harvest Strategies of WCPFC 

35.  WCPFC  has  progressed  in  developing  Harvest  Strategies  incorporating  the  maximum 
economic  yield  (MEY)  concept  as  well  as  socioeconomic  and  environmental  objectives. 
WCPFC  has  tried  to  operationalise  the  use  of  MEY  by  explicitly  accounting  for  economic 
yield (e.g. revenues) in their analysis despite concerns about completeness and viability of 
such work. This provides for an industry that is profitable and takes advantage of market 
trends and technological advances to achieve the best price and profit margins. However, 

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higher  fish  prices  mean  reduced  access  to  people  of  lower  economic  income  to  this 
important source of nutrients (e.g. developing countries, coastal communities that might 
rely on fish for their food). 

36.  There  are  options  other  than  those  currently  suggested  in  the  Scientific  Committee 
meetings and other working groups that could also lead to plausible Harvest Strategies that 
are discussed in this report. It is obvious that there is a diverse range of options that one 
can consider for the management of a fishery. However, it is not possible to say which of 
them  performs  better  until  it  is  clear  what  the  strategy  needs  to  achieve.  Therefore, 
agreeing  on  management  objectives  including  priorities  and  a  weight  assigned  to  each 
objective still remains a crucial step that, once completed, will add clarity to the process. 

Development of mixed fisheries and single stock MSE for tropical tunas for  IOTC and ICCAT: 
define options and preliminary models 

37.  This study represents a first step in the evaluation of management strategies for tropical 
tuna  stocks  in  a  mixed-fisheries  framework.  We  have  compared  three  different 
management  strategies  combined  with  different  fleet  dynamics.  The  effort-based 
management with a 25% reduction was translated into fleet dynamics reducing the effort 
of all the fleets by 25%. The other two HCRs used correspond to the HCRs proposed by 
ICES in the MSY framework and to a multi-stock HCR that uses  fishing mortality ranges 
around  MSY  targets.  These  two  HCRs  were  combined  with  two  different  fleet  dynamics 
which differed in the condition used to restrict the effort of the fleets, the minimum effort 
or the effort corresponding to the TAC of bigeye. 

38.  The  multi-stock  HCR  with  restricted  bigeye  TAC  produced  on  average  sustainable 
biomasses  for  the  three  stocks  but  the  probability  of  being  below  LRP  (BLIM)  was  higher 
than zero in some years. This type of management should be combined with strict control 
measures to ensure the fulfilment of the TAC advice.  

39.  The fleet dynamics used in this work were based on their historical behaviour. However, 
future work should focus first on the definition of the fleets and their métiers and afterwards 
identify the dynamics that better describe the fleet dynamics.  

40.  Simulations were based on an annual rather than quarterly time period that is used in stock 
assessment models. Future work should develop the simulation model in a seasonal fashion 
in  order  to  provide  a  more  accurate  representation  of  the  dynamic  of  the  fleet  and  a 
consistent approach between the stock assessment and the simulation model. 

*** 

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RÉSUMÉ EXÉCUTIF 

Background 

1.  Les plans de gestion développés par les ORGP thonières nécessitent l’adoption d’objectifs 
précis et de délais d’exécution. Ceux-ci peuvent être soutenus par des Points de Références 
(PR) visant à développer des limites appropriées, objectifs ou points de déclenchement, et 
à  définir  les  paramètres  du  cadre  de  gestion.  De  tels  PR,  ainsi  que  des  règles  détaillées 
précisant la manière dont les totaux autorisés de captures/exploitation (TAC) sont définis 
(Harvest  Control  Rules,  HCR),  peuvent  être  testés  sous  différents  scénarios  de  l’état  de 
nature et incertitude afin d’évaluer leur efficacité sous différentes stratégies de gestion. 

2.  L’Evaluation de la Stratégie de Gestion (« Management Strategy Evaluation », MSE) fournit 
un  outil  permettant  la  réalisation  de  tests  de  simulations.  Les  MSE  sont  de  plus  en  plus 
utilisés  en  gestion  des  pêcheries.  Elles  sont  principalement  utilisées  pour  mesurer  la 
performance de stratégies de gestion actuelles et proposées sous différents scénarios, ou 
pour  identifier  les  stratégies  les  plus  efficaces  parmi  une  série  de  potentielles  stratégies 
visant un ensemble d’objectifs en particulier. 

Objectifs principaux 

Les quatre tâches suivantes ont été entreprises durant l’étude : 

3.  Tâche 1 : Points de Référence (PR). Fournir un  inventaire de PR pour  tous les stocks de 
thon. Analyser la cohérence des PR entre ORGP et la base de leur définition, en précisant 
les forces et les faiblesses associées à chaque PR. Evaluer la relation entre différents types 
de  PR  en  tenant  compte  de  facteurs  pertinents  tels  que  l’état  des  stocks  et  le  mode 
d’exploitation pour différentes pêcheries. Fournir plusieurs études de cas comme exemples 
de  différents  types  de  PR  pour  un  même  stock  de  thon,  mais  dans  différents  états  de 
conservation et récolté par différentes pêcheries. 

4.  Tâche  2 :  Règles  de  Contrôle  de  Capture  (« Harvest  Control  Rules »,  HCR).  Fournir  un 
inventaire  du  type  de  HCR  qui  ont  été  proposés,  testés  ou  appliqués  dans  les  ORGP. 
Analyser les forces et les faiblesses de différents HCR (existants et en développement) pour 
les stocks de thon, en tenant compte de facteurs tels que la disponibilité des données, le 
type  de  pêcherie  et  le  système  de  gestion.  Examiner  comment  les  HCR  pourraient  être 
développés en tenant compte des interactions multi-espèces et des pêcheries mixtes.  

5.  Tâche  3 :  Evaluation  de  la  Stratégie  de  Gestion  (« Management  Strategy  Evaluation », 
MSE).  Examiner  le  développement  de  MSE  dans  les  différentes  ORGP  thonières,  en :  1) 
évaluant  comment  les  MSE  ont  été  planifiés  et  développés ;  2)  examinant  comment  les 
composantes  de  MSE  (modèles  d’opération,  procédures  de  gestion,  et  statistiques  de 
performance)  ont  été  développées  et  comment  les  MSE  ont  été  utilisés  pour  soutenir 
l’adoption de HCR ; 3) identifiant les forces et les faiblesses du processus de développement 
d’HCR  et  d’MSE  dans  les  ORGP  thonières ;  et  en  4)  proposant  des  alternatives  pour 
améliorer les MSE dans les ORGP thonières.  

6.  Tâche 4 : Fournir une image plus détaillée du processus de développement de MSE et de 
son  évolution  à  travers  trois  études  de  cas  d’ORGP  thonières  (WCFC,  CICTA  et  CTOI). 
L’objectif principal des études de cas est de comprendre les approches de MSE considérés, 
leurs  implications,  et  le  progrès  fait  jusqu’à  ce  jour,  mais  aussi  de  considérer  certaines 
options supplémentaires qui peuvent soutenir le processus de développement de MSE. 

Tâche 1 : Points de Référence  

7.  Les ORGP thonières sont en train d’établir des objectifs de gestion et de définir des Points 
de Référence  Cibles (PRC) et Limites de Points de Références (LPR)  dans le contexte de 
leurs  Stratégies  d’Exploitation  (SE).  Les  objectifs  de  gestion  incluent  la  durabilité,  la 
sécurité,  la  production,  l’emploi  et  la  stabilité  des  pêcheries.  Les  PR  visent  à  guider  les 
pêcheries vers l’atteinte de ces objectifs. 

8.  Plusieurs méthodes existent pour calculer les PR, par exemple des méthodes basées sur le 
rendement maximal durable (RMD, ou « Maximum Sustainable Yield », MSY), l’épuisement 
des stocks, le potentiel de reproduction par recrue,  et le  rendement  par  recrue. Chaque 

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méthode possède ses propres forces et faiblesses. Cependant, les méthodes basées sur le 
RMD et l’épuisement des stocks sont les méthodes les plus fréquemment utilisées par les 
ORGP. 

9.  Les incertitudes liées au paramètre de la pente de la relation stock-recrutement peuvent 
affaiblir  de  manière  considérable  l’exactitude  de  PR  basés  sur  le  RMD  en  utilisant  les 
modèles actuels d’évaluation des stocks. L’un des principaux avantages de PR basés sur 
l’épuisement  des  stocks  pour  la  gestion  des  pêcheries  réside  dans  leur  relative  stabilité 
d’une évaluation à l’autre. Ces PR ont montré les variations les moins importantes dans les 
résultats pour une série de pentes et modèles d’évaluation des stocks. Les PR basés sur 
l’épuisement des stocks sont considérés comme étant les plus fiables lorsque de grandes 
incertitudes  existent  autour  de  paramètres  tels  que  la  pente  de  la  relation  stock-
recrutement. 

10.  L’examen de LPR de différentes ORGP montre un manque de cohérence dans les valeurs 
utilisées pour appuyer leurs SE. Par exemple, la CTOI a adopté une LPR temporaire basée 
sur le RMD pour le thon Albacore de 40%SSBMSY (équivalent à 14%SSB0), tandis que la 
WCPFC  a  adopté  une  LPR  de  20%SBCURRENT,  F=0  (équivalent  à  20%SSB0)  pour  la  même 
espèce. Cela laisse à penser que soit la CTOI adopte une approche moins prudente, soit la 
WCPFC utilise une méthode plus conservative pour définir les LPR. En  réalité, ces écarts 
sont  dus  à  la  nature  différente  des  PR (basés  sur  le  RMD  ou  l’épuisement  des  stocks). 
Certains  stocks  dans  des  régions  différentes  peuvent  avoir  des  niveaux  de  productivité 
différents,  du  aux  différences  biologiques  ou  aux  caractéristiques  des  pêcheries.  Il  n’est 
donc pas étonnant d’observer des PR différents pour chaque ORGP thonière pour les mêmes 
espèces. 

11.  De plus en plus de LPR sont aujourd’hui définies sur base du RMD plutôt que sur base des 
PRC. Du aux incertitudes dans le calcul du RMD et aux conséquences biologiques, sociales 
et  économiques  engendrées  par  son  dépassement,  certaines  ORGP  telles  que  la  WCPFC 
définissent la LPR comme le RMD. Ceci est basé sur l’approche de précaution, l'Accord sur 
les stocks de poisson des Nations Unies, et d’autres outils internationaux.  

12.  Pour le statut biologique, les LPR sont de plus en plus établies à 20% SSB0 en utilisant des 
méthodes basées  sur l’épuisement des stocks, qui est un PR prudent  pour les pêcheries 
pour lesquelles le SSR reste incertain. De plus, il a été suggéré que FMSY représente une 
limite supérieure aux taux de mortalité par pêche, ce qui est cohérent avec la définition 
d’une LPR : « un état de pêcherie et/ou une ressource qui est considéré comme indésirable 
et que les mesures de gestion devraient éviter ». 

13.  Il a été démontré qu’en utilisant des valeurs typiques SRR de pentes pour le listao entre 
0.7-0.9, les PR basés sur le RMD (BMSY) sont juste au-dessus ou même en dessous de la 
LPR  générale  de  20%  SBCURRENT,F=0  adoptée  par  la  WCPFC.  Dès  lors,  sous  certaines 
conditions,  un  PR  typique  défini  « pour  maintenir  ou  restaurer  les  stocks  à  des  niveaux 
capables de produire le RMD » pourrait soudainement être  vu comme « hors des limites 
biologiques de sécurité ». Ce paradoxe apparait car les 20% SBCURRENT,F=0 comme seule LPR 
basée  sur  l’épuisement  des  stocks  a  été  adoptée  pour  tous  les  stocks  principaux, 
indépendamment  de  la  productivité  relative  de  la  population  ou  de  la  sélectivité  de  la 
pêcherie. Malgré que le calcul de LPR spécifiques à un stock et leurs niveaux associés de 
risque  acceptable  pourrait  aider  à  surmonter  le  problème,  les  LPR  actuels  sont 
biologiquement « prudentes » et ainsi en ligne avec les exigences de la Convention de la 
WCPFC.  A  ce  jour,  les  données  disponibles  sont  insuffisantes  pour  établir  des  LPR 
spécifiques à chaque stock dans la région. 

14.  Des  PRC  peuvent  être  définis  afin  d’atteindre  des  objectifs  de  gestion,  comprenant  des 
objectifs  sociaux  ou  économiques.  Il  est  de  plus  en  plus  suggéré  que  la  gestion  de  la 
biomasse du stock au-dessus de BMSY conduit à des poissons plus gros, à des niveaux de 
capture similaires avec un avantage économique plus important et un impact écologique 
moindre. Cette approche est cohérente avec les objectifs de la PCP en vertu de l'article 2.2, 
qui vise à « rétablir et maintenir les populations d'espèces exploitées au-dessus des niveaux 
qui peuvent produire le rendement maximal durable ». 

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15.  Définir  des  PRC  équivalents  à  40%SSB0  ou  plus  élevés  au  lieu  de  les  baser  sur  le  RMD 
(BMSY) peut apporter des différences notables (ou sous-utilisations) dans le niveau d’effort 
de pêche. A ce jour, la WCPFC a adopté un PRC  temporaire pour le thon listao basé sur 
50%  SBCURRENT,F=0,  qui,  malgré  les  nombreuses  incertitudes,  est  bien  au-dessus  des 
estimations disponibles de SBMSY. Même si le PRC adopté par la WCPFC peut paraître fort 
conservateur, l’évaluation pour le thon listao est considérée comme incertaine. 

16.  Aujourd’hui, les probabilités d'atteindre les PRC et les objectifs de gestion dans les délais 
définis, ainsi que d'éviter d’atteindre les LPR, font l'objet de débats dans toutes les ORGP 
thonières. Il n'existe notamment pas de définition claire de probabilités « élevées, « très 
élevées », « faibles » et « très faibles ». 

Tâche 2 : Règles de Contrôle de Capture (« Harvest Control Rules », HCR) 

17.  L'utilisation de HCR a été de plus en plus privilégiée par les ORGP thonières pour mettre 
en  œuvre  de  bonnes  pratiques  de  gestion  des  stocks  et  de  simplifier  le  processus  de 
négociation des limites de pêche et/ou de l’implémentation des mesures techniques. 

18.  Un inventaire a été fourni résumant l'état des HCR dans les ORGP thonières pour chaque 
stock. L’inventaire comprend les HCR qui ont été recommandés ou proposés dans les ORGP 
thonières, ainsi que ceux qui ont été testés ou appliqués. 

19.  Au sein de la CICTA, des HCR n'ont pas été définis pour le listao, l'albacore, le thon obèse, 
le  germon  de  l'Atlantique  sud  et  méditerranéen  et  le  thon  rouge,  bien  que  les 
Recommandations 11-13 et 15-07 fournissent un cadre pour leur établissement. Un HCR a 
été  défini  pour  le  germon  du  Nord  en  2017  en  vertu  de  la  Recommandation  17-04. 
Certaines des forces identifiées pour le HCR du germon du Nord comprennent le fait qu'il 
fera  l'objet  d'un  examen  par  le  SCRS  en  2018  et  que  dans  des  circonstances 
exceptionnelles, la Commission examinera et envisagera une éventuelle révision du HCR. 
De  plus,  des  règles  claires  concernant  les  types  d'actions  de  gestion  à  déclencher  pour 
différents PR ont été établies, y compris la réduction du total autorisé de capture (TAC). 
Les HCR sont soumis à des MSE qui indiquent que le HCR est robuste en cas d’incertitudes. 
Certaines des faiblesses identifiées montrent qu'il n'est pas clair si les probabilités relatives 
aux PR ou aux indicateurs de performance intégreront l'incertitude du modèle. De plus, le 
TAC est partagé entre de nombreux pays où le contrôle sur les captures est faible. 

20.  Depuis 2016, la CTOI a établi un HCR pour le thon listao sur base des LPR et des PRC en 
vertu de la Résolution 16/02. La CTOI n'a pas encore établi de HCR pour le thon obèse, 
l'albacore ou le germon. Parmi les principales forces du HCR de la CTOI, citons les objectifs 
de gestion ainsi que des définitions claires pour les LPR et PRC, et la définition du TAC. La 
Res.  16/02  exige  que  le  HCR  et  les  paramètres  de  contrôle  soient  évalués  par  MSE.  Un 
certain  nombre  de  faiblesses  ont  été  identifiées,  y  compris  le  fait  que  le  HCR  n'a  que 
récemment été accepté et qu'aucune évaluation significative n'a encore pu être réalisée. 
En  outre,  le  HCR  ne  fait  pas  explicitement  référence  aux  probabilités  acceptables  de 
dépassement des PR, et il n'est pas clair comment le rôle de la pêche de subsistance sera 
pris en compte lors de dépassements de seuils. Par ailleurs, lorsque la biomasse est estimée 
inférieure à la LPR, il n'existe pas de délais précis dans lesquels un nouveau HCR devrait 
être mis en œuvre, ce qui augmente le risque d'épuisement du stock. 

21.  La WCPFC n'a pas encore défini de HCR pour le listao, l'albacore ou le thon obèse. CMM 
2014-06 demande à la WCPFC d'élaborer et de mettre en œuvre une stratégie de capture 
qui  comprend  des  PRC,  HCR  et  autres  éléments.  Le  Comité  du  Nord  a  recommandé  un 
cadre  de  gestion  provisoire  pour  le  germon  du  Pacifique  Nord,  tandis  qu'en  2014,  une 
stratégie de capture pour le thon rouge du Pacifique a défini les HCR pour atteindre des 
objectifs de reconstitution spécifiques. La phase de reconstruction du HCR du germon du 
Pacifique Nord est explicite quant à la manière dont les mesures de gestion seront prises 
en relation avec le PRC de reconstruction, parallèlement à un calendrier établi. Des niveaux 
de  risques  acceptables  sont  également  précisés,  considérés  par  la  WCPFC  comme 
compatibles  avec  l'Accord  sur  les  stocks  de  poisson  des  Nations  Unies.  Certaines  des 
faiblesses potentielles de ce HCR incluent le fait qu'il n'a pas encore été évalué par MSE, 

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bien que cela soit en cours de développement, et que la probabilité que le stock baisse en 
dessous de la LPR n'a pas été clairement définie, autrement que « très basse ». 

22.  En 2016, la IATTC a adopté un HCR pour tous les thons tropicaux en vertu de la Résolution 
C-16-02 sur base de LPR et des PRC intérimaires. En ce qui concerne le germon du Pacifique 
Nord,  la  Résolution  C-13-03  exige  que  le  personnel  de  l'IATTC  examine  les  travaux 
entrepris par la WCPFC en vue de l'élaboration des HCR. Quant aux HCR pour tous les thons 
tropicaux, certaines des forces de la Res. C-16-02 sont qu’elle établit des définitions claires 
pour les LPR et PRC temporaires et qu’elle prévoit des mesures de gestion convenues au 
préalable  dans  diverses  conditions  de  stock,  ce  qui  permet  la  mise  en  œuvre  rapide  de 
mesures  de  gestion,  le  cas  échéant.  Certaines  faiblesses  du  HCR  incluent  qu'il  n'est 
considéré que provisoire jusqu'à ce qu'il soit évalué, car aucun MSE n'a encore été établie 
sans probabilités claires liées au dépassement des PR donnés. 

23.  La CCSBT a élaboré une procédure de gestion (PG) en 2011 pour le thon rouge du Sud, 
conçue dans le but d’atteindre l'objectif de reconstruction. Cette PG, connue sous le nom 
de « procédure de Bali », établit clairement des objectifs basés sur la probabilité pour la 
reconstitution des stocks en utilisant un PRC provisoire dans une période de temps explicite. 
La CCSBT a testé un certain nombre de PG liés à une série d'incertitudes afin de s'assurer 
qu'une  procédure  robuste  ai  été  identifiée.  La  PG  fait  également  l'objet  d'évaluations 
régulières, y compris un examen annuel de sa mise en œuvre et une évaluation régulière 
des  nouvelles  sources  de  données  et  des  modèles  d'exploitation.  L'une  des  faiblesses 
potentielles  de  la  PG  est  la  complexité  des  méthodes  utilisées,  ce  qui  rend  difficile  la 
communication aux parties prenantes et aux décideurs. 

24.  Les  HCR  prenant  en  compte  la  gestion  des  pêcheries  multispécifiques  peuvent  être 
appliquées  en utilisant des limites de capture  et d'effort.  En général,  pour les limites de 
capture, une surveillance en temps réel des captures est nécessaire mais peut être difficile. 
Par exemple, au sein de la CTOI il y a un décalage temporel entre les débarquements et 
l'échantillonnage effectif des captures. Cela peut causer des problèmes de non-conformité 
si  l'excès  de  capture  n'est  pas  détecté  ou  engendrer  des  fermetures  prématurées  si  les 
captures sont surestimées. 

25.  Dans  les  pêcheries  multispécifiques,  il  n'est  pas  possible  d'appliquer  différents  niveaux 
d'effort de pêche à deux espèces ou plus qui sont vulnérables au même engin de pêche et 
qui  habitent  le  même  habitat.  Sachant  que  les  rejets  sont  indésirables  sur  la  base  des 
Principes  Communs  de  Pêche,  lorsque  la  limite  de  capture  d'un  stock  (par  exemple 
l'albacore dans la CTOI ou le thon obèse dans la CICTA) est atteinte (« choke species ») 
mais pas pour les autres, les flottilles arrêteront leurs activités de pêche. Dans ce cas, les 
limites  de  capture  pour  le  listao,  par  exemple,  ne  seront  pas  atteintes,  avec  la  perte 
d'opportunités  associée  pour  les  flottes  de  pêche,  et  d'autres  conséquences  socio-
économiques indésirables. Ces dernières comprennent la perte de production alimentaire, 
des  pénuries  de  conserveries  et  des  augmentations  potentielles  de  prix  en  raison  d'une 
offre plus faible sur les marchés internationaux. 

26.  En général, la gestion basée sur les TAC nécessite des estimations précises de l'état des 
stocks, des PR et du taux de recrutement lorsque les limites de capture sont fixées. Si la 
biomasse et le recrutement sont sous-estimés, les limites de capture seront atteintes plus 
tôt que prévu et les possibilités de pêche seront gaspillées à moins que l'espèce « choke » 
ne soit rejetée. Au contraire, si la biomasse du stock est surestimée, la biomasse continuera 
à  diminuer  alors  que  la  mortalité  augmentera.  À  cet  égard,  les  contrôles  de  l'effort 
constituent  un  moyen  plus  souple  pour  gérer  les  pêcheries  multispécifiques  puisqu'ils 
peuvent concilier les objectifs de conservation de deux stocks ou plus lorsqu'ils sont fixés 
pour le stock le plus vulnérable. 

27.  Les limites de l'effort de pêche sont des restrictions sur l'intensité d'utilisation des engins 
de pêche. Ceux-ci peuvent inclure des limitations de la durée de la saison de pêche, qui 
sont relativement faciles à appliquer par le biais de systèmes de surveillance des navires 
(VMS), l'utilisation des journaux de bord, et autres mesures. De plus, le contrôle de l'effort 
de  pêche  réduit  la  nécessité  d'un  suivi  en  temps  réel  des  captures,  ce  qui  est  souvent 
difficile  et  coûteux.  Dans  les  systèmes  de  contrôle  de  l'effort,  il  n'est  plus  nécessaire 

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d'estimer  la  biomasse  exploitable  précisément  chaque  année,  puisque  le  niveau  de 
mortalité par pêche est directement limité, indépendamment des fluctuations continues de 
la  taille  du  stock.  Afin  d’être  efficace,  la  gestion  par  effort  exige  un  contrôle  strict  de  la 
capacité  technologique  et  du  potentiel  de  capture  des  flottes.  Dans  certains  cas  où  la 
capacité de pêche augmente, la mortalité par pêcherie due à un effort donné pourrait être 
plus élevée que prévu et pourrait dès lors compromettre la durabilité des stocks. 

28.  À ce jour, seule la CICTA utilise des TAC ou des limites de capture globales pour toutes les 
flottilles impliquées dans les pêcheries thonière tropicales. L’IATTC et la WCPFC appliquent 
des contrôles de captures (TAC) uniquement pour les flottilles palangrières ciblant le thon 
obèse. Dans le Pacifique, l'activité des flottilles de senneurs est réglementée par des limites 
d'effort  (durée  de  la  saison).  La  CICTA  utilise  un  pseudo-HCR  basé  sur  l'effort  pour 
déterminer le nombre de jours où les senneurs peuvent pêcher afin d'atteindre le RMD. 

29.  En  2017,  la  CICTA  a  tenté  d'introduire  des  limites  de  capture  pour  le  thon  obèse  et 
l'albacore pour les flottilles de senneurs opérant avec des dispositifs de concentration de 
poisson  (DCP)  et  une  limite  de  capture  supplémentaire  pour  l'albacore  provenant  des 
pêcheries associées aux dauphins. En pratique, cela s'est avéré difficile à mettre en œuvre 
car la flottille de senneurs pêchant sur les DCP avait atteint 80% de la limite de capture 
annuelle totale à la mi-juillet. Ceci a conduit à l'introduction d'une nouvelle mesure (C-17-
02) après seulement cinq mois, qui a empêché la fermeture de la pêcherie de DCP en août 
ou début septembre, avec des conséquences dramatiques pour les flottes de senneurs. 

Tâche 3: Evaluation des Stratégies de Gestion (« Management Strategy Evaluation », 
MSE) 

30.  Les cinq ORGP thonières ont réalisé un certain travail sur les MSE, y compris la consultation 
sur  les  objectifs  de  gestion,  la  caractérisation  de  l'incertitude  de  la  dynamique  et  de 
l'observation  des  stocks,  et  l'évaluation  des  stratégies  de  capture.  La  plupart  des  MSE 
réalisés à  ce jour  ont été élaborées par les  scientifiques recrutés par  des  ORGP avec un 
mandat rarement donné par les Commissions. 

31.  L'étude  a  donné  un  aperçu  des  modèles  d'exploitation  (« Operating  Models »,  OM),  des 
HCR, et des statistiques de performance utilisées. Les OM fournissent des représentations 
mathématiques du système géré. L'impact de la gestion des pêcheries est évalué avant sa 
mise en  œuvre dans les OM lors de l'utilisation de MSE. Les  OM sont considérés comme 
des représentations alternatives de la dynamique « réelle » du stock et visent à prendre 
en compte toutes les incertitudes inhérentes à la dynamique du poisson et de la pêche. 

32.  Aujourd'hui, les MSE sont développés pour des espèces individuelles, avec pour objectifs 
de  maintenir les  stocks  à  un  niveau  sain,  de  favoriser  le  succès  de  la  reconstitution  des 
stocks surexploités et d'évaluer les avantages économiques de la gestion préventive. Afin 
d'impliquer les pays tiers dans le processus d’MSE à travers les ORGP thonières, plusieurs 
initiatives (ateliers, renforcement des capacités, cours et projets) sont mises en place. Les 
initiatives  visant  à  promouvoir  l'engagement  des  pays  tiers  et  à  développer  d'autres 
approches MSE ont été examinées, y compris l'impact du projet « Areas Beyond National 
Jurisdiction » sur ce processus. 

33.  Les  cinq  ORGP  thonières  ont  des  plans  visant  à  évaluer  les  procédures  de  gestion 
(« Management Procedures », MP) en utilisant des MSE. Dans certaines ORGP, la feuille de 
route vers l'adoption des MP est clairement détaillée et dans d'autres, le processus  n’est 
qu’à ses débuts. 

34.  Le processus de la CTOI repose sur le travail technique et l'interaction avec la Commission. 
La CTOI vise à être en mesure d'adopter des MP pour ses stocks les plus importants d'ici 
2020. À la CICTA, le processus d’MSE est bien avancé pour le germon et le thon rouge de 
l'Atlantique Nord. L'un des aspects particuliers du processus de MSE de la CICTA est qu'il 
sera évalué de manière indépendante, avec l'évaluation de l'MSE du germon de l'Atlantique 
Nord en 2018 qui contribuera à l'amélioration du processus pour d'autres stocks. En outre, 
il envisagera des options pour la gestion multispécifique au lieu du cadre actuel de gestion 
d'une seule espèce. Au sein de la WCPFC, le processus de feedback est avancé et a fait des 
progrès importants dans la définition des objectifs de gestion grâce à un certain nombre 

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d'ateliers  de  concertation.  En  ce  qui  concerne  la  CICTA,  le  travail  de  MSE  consiste  à 
identifier  les  HCR  appropriés  pour  le  thon  obèse  et  l'albacore,  mais  il  n'en  est  qu'à  ses 
débuts.  Un  plan  pour  le  développement  de  MSE  sera  présenté  au  Comité  Consultatif 
Scientifique  de  2018.  La  CCSBT  a  décidé  de  développer  un  nouveau  MP  pour  guider 
l'établissement  des  TAC  pour  2021  et  au-delà.  Le  nouveau  MP  tiendra  compte  des 
changements  dans  la  disponibilité  des  données,  en  particulier  en  changeant  la  série  de 
surveillance du recrutement, d'une enquête aérienne sur les juvéniles à un programme de 
marquage génétique/recapture de juvéniles. 

Tâche 4 : Etudes de cas d’ORGP sélectionnées 

Stratégies de capture du WCPFC 

35.  La WCPFC a progressé dans l'élaboration de stratégies de capture intégrant le concept de 
rendement  économique  maximal  (« Maximum  Economic  Yield »,  MEY)  ainsi  que  des 
objectifs  socioéconomiques  et  environnementaux.  La  WCPFC  a  tenté  d'opérationnaliser 
l'utilisation  du  MEY  en  tenant  explicitement  compte  du  rendement  économique  (par 
exemple des revenus) dans son analyse, malgré certaines préoccupations sur l’intégralité 
et la viabilité de ce travail. Cela permet le développement d’une industrie rentable qui tire 
parti des tendances du marché et des progrès technologiques afin d’obtenir les meilleurs 
prix et marges bénéficiaires. Cependant, les prix plus élevés du poisson signifient un accès 
réduit à cette source importante nutriments pour les personnes à faibles revenus, dans les 
pays en développement ou dans les communautés côtières qui dépendent du poisson pour 
leur subsistance. 

36.  Le présent rapport examine d'autres options que celles actuellement suggérées dans les 
réunions  du  Comité  Scientifique  et  d'autres  groupes  de  travail  qui pourraient  également 
mener à des stratégies de capture plausibles. Il est évident qu'il existe un large éventail 
d'options que l'on peut envisager pour la gestion d'une pêcherie. Cependant, il n'est pas 
possible d’établir au préalable lesquelles d'entre elles fonctionneront  le mieux jusqu'à ce 
que les objectifs de la stratégie soient clairement définis. Par conséquent, s'entendre sur 
les objectifs de gestion, y compris les priorités et la pondération attribuée à chaque objectif, 
demeure une étape cruciale qui, une fois terminée, apportera plus de clarté au processus. 

Développement de MSE pour pêcheries multispécifiques et stocks uniques pour le thon tropical 
au sein de la CTOI et de la CICTA : définir des options et modèles préliminaires 

37.  Cette étude représente une première étape dans l'évaluation des stratégies de gestion des 
stocks de thons tropicaux dans un cadre de pêcheries mixtes. Nous avons comparé trois 
stratégies de gestion liées à différentes dynamiques de flotte. La gestion axée sur l'effort 
avec une réduction de 25% s'est traduite par une dynamique de la flotte réduisant de 25% 
l'effort de toutes les flottes. Les deux autres HCR utilisés correspondent aux HCR proposés 
par le CIEM dans le cadre du RMD, et à un HCR pour stocks multiples qui utilise des taux 
de mortalité par pêche rejoignant les objectifs de RMD. Ces deux HCR ont été combinés 
avec deux dynamiques de flottilles différentes de par la condition utilisée pour restreindre 
l'effort des flottilles, l'effort minimum, ou l'effort correspondant au TAC du thon obèse. 

38.  Le  HCR  à  stocks  multiples  avec  TAC  restreint  du  thon  obèse  a  produit  en  moyenne  des 
biomasses durables pour les trois stocks, mais la probabilité d'être inférieur au LPR (BLIM) 
était supérieure à zéro certaines années. Ce type de gestion doit être combiné avec des 
mesures de contrôle strictes pour s’assurer du respect du TAC. 

39.  Les dynamiques de flottilles utilisées dans ce travail étaient basées sur leur comportement 
historique.  Cependant,  à  l’avenir,  les  études  devraient  d'abord  se  concentrer  sur  la 
définition des flottilles et de leurs métiers, puis identifier les dynamiques qui décrivent le 
mieux la dynamique de ces flottilles. 

40.  Les simulations réalisées étaient basées sur une période annuelle plutôt que trimestrielle, 
qui est utilisée dans les modèles d'évaluation des stocks. A l’avenir, les études devraient 
développer  le  modèle  de  simulation  de  manière  saisonnière  afin  de  fournir  une 
représentation plus précise de la dynamique des flottilles et une approche cohérente entre 
l'évaluation des stocks et le modèle de simulation. 

*** 

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RESUMEN EJECUTIVO  

Fondo 

41.  Los  planes  de  manejo  desarrollados  por  las  OROP  del  atún  requieren  la  adopción  de 
objetivos y plazos específicos. Estos pueden ser apoyados por puntos de referencia (PR) 
para  desarrollar  límites  apropiados,  objetivos  o  puntos  de  disparo,  y  para  definir  los 
parámetros del marco de gestión. Estos PR, así como las reglas detalladas que especifican 
cómo  se  definen  los  Totales  Admisibles  de  Capturas  (TAC),  las  “Harvest  Control  Rules” 
(HCR),  se  pueden  probar  bajo  diferentes  escenarios  del  estado  de  la  naturaleza  y  la 
incertidumbre con el fin de evaluar su efectividad bajo diferentes estrategias de manejo. 

42.  La  evaluación  de  la  estrategia  de  gestión  (« Management  Strategy  Evaluation  »,  MSE) 
proporciona una herramienta para realizar pruebas de simulación. Las MPE se utilizan cada 
vez más en la gestión pesquera. Se utilizan principalmente para medir el rendimiento de 
las  estrategias  de  gestión  actuales  y  propuestas  bajo  diferentes  escenarios,  o  para 
identificar  las  estrategias  más  efectivas  entre  una  serie  de  estrategias  potenciales  para 
cumplir un conjunto particular de objetivos. 

Objetivos Principales 

Las siguientes cuatro tareas se llevaron a cabo durante el estudio: 

43.  Tarea  1:  Puntos  de  referencia  (PR).  Proporcionar  un  inventario  de  PR  para  todas  las 
poblaciones de atún. Analizar la coherencia de PR entre las OROP y la base de su definición, 
identificando las fortalezas y debilidades asociadas con cada PR. Evaluar la relación entre 
los diferentes tipos de PR teniendo en cuenta factores relevantes, como el estado del stock 
y los patrones de explotación para diferentes pesquerías. Proporcionar varios estudios de 
caso  como  ejemplos  de  diferentes  tipos  de  PR  para  el  mismo  stock  de  atún,  pero  en 
diferentes estados de conservación y cosechados por diferentes pesquerías. 

44.  Tarea 2: Reglas de Control de Capturas (« Harvest Control Rules », HCR). Proporcionar un 
inventario del tipo de HCR que se ha propuesto, probado o aplicado en OROP. Analizar las 
fortalezas y debilidades de diferentes HCR (existentes y en desarrollo) para las poblaciones 
de atún, teniendo en cuenta factores como la disponibilidad de datos, el tipo de pesca y el 
sistema de gestión. Examinar cómo se podrían desarrollar los HCR teniendo en cuenta las 
interacciones multiespecíficas y las pesquerías mixtas. 

45.  Tarea  3:  Evaluación  de  la  Estrategia  de  Gestión  (« Management  Strategy  Evaluation », 
MSE).  Examinar  el  desarrollo  de  MSE  en  las  diferentes  OROP  de  atún,  incluyendo:  1) 
evaluar cómo se han planificado y desarrollado los MSE; 2) examinar cómo se desarrollaron 
los componentes de MSE (modelos de operación, procedimientos de gestión y estadísticas 
de rendimiento) y cómo se utilizaron las MSE para apoyar la adopción del HCR; 3) identificar 
las fortalezas y debilidades del proceso de desarrollo de HCR y MSE en las OROP de atún; 
y 4) proponer alternativas para mejorar las MSE en las OROP de atún. 

46.  Tarea 4: Proporcionar una imagen más detallada del proceso de  desarrollo de  MSE y  su 
evolución a través de tres estudios de casos de OROP de atún (WCFC, ICCAT e IOTC). El 
objetivo  principal  de  los  estudios  de  casos  es  comprender  los  enfoques  de  MSE 
considerados, sus implicaciones y el progreso realizado hasta el momento, pero también 
considerar algunas opciones adicionales que pueden respaldar el proceso de desarrollo de 
MSE actual. 

Tarea 1: Puntos de Referencia 

47.  Las OROP de atún están en el proceso de establecer objetivos de gestión y definir puntos 
de referencia objetivo (PRO) y límites (PRL) en el contexto de sus estrategias de explotación 
(EE).  Los  objetivos  de  gestión  incluyen  la  sostenibilidad,  la  seguridad,  la  producción,  el 
empleo y la estabilidad de la pesca. Los PR están destinados a guiar a las pesquerías hacia 
estos objetivos. 

48.  Existen  varios  métodos  para  calcular  PR,  como  los  métodos  basados  en  el  rendimiento 
máximo sostenible (« Maximum Sustainable Yield », MSY), el agotamiento de existencias, 

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el potencial de reproducción por recluta y el rendimiento por recluta. Cada método tiene 
sus  propias  fortalezas  y  debilidades.  Sin  embargo,  los  métodos  basados  en  MSY  y  el 
agotamiento de existencias son los métodos más comunes utilizados por las OROP. 

49.  Las  incertidumbres  asociadas  con  el  parámetro  de  pendiente  de  la  relación  stock-
reclutamiento  pueden  disminuir  significativamente  la  precisión  de  PR  en  base  a  la  MSY 
utilizando los modelos de evaluación de stock actuales. Uno de los principales beneficios 
de  las  PR  basadas  en  el  agotamiento  de  las  poblaciones  para  la  gestión  pesquera  es  su 
estabilidad relativa de  una evaluación a otra.  Estos  PR mostraron las variaciones  menos 
significativas en los resultados para una serie de pendientes y modelos de evaluación de 
stocks. Los PR basados en el agotamiento de existencias se consideran los más confiables 
cuando existen grandes incertidumbres en torno a parámetros tales como la pendiente de 
la relación stock-reclutamiento. 

50.  La  revisión  de  PRL  de  diferentes  OROP  muestra  una  falta  de  consistencia  en  los  valores 
utilizados para respaldar sus EE. Por ejemplo, el IOTC adoptó un PRL temporal basado en 
MSY para atún aleta amarilla de 40% SSBMSY (equivalente a 14% SSB0), mientras que la 
WCPFC  adoptó  un  PRL  de  20%  SBCURRENT,  F  =  0  (equivalente  a  20%  SSB0)  para  la  misma 
especie.  Esto  sugiere  que,  o  bien  la  IOTC  adopta  un  enfoque  menos  conservador,  o  la 
WCPFC  utiliza  un  enfoque  más  conservador  para  definir  los  PRL.  En  realidad,  estas 
diferencias se deben a la naturaleza diferente de los PR (basados en el MSY o agotamiento 
de existencias). Algunas poblaciones en diferentes regiones pueden tener diferentes niveles 
de productividad debido a diferencias biológicas o características de la pesca. Por lo tanto, 
no es sorprendente observar diferentes PR para cada OROP de atún para la misma especie. 

51.  Cada vez más PRL se definen sobre la base de la MSY en lugar de sobre la base de los PRO. 
Debido a las incertidumbres en el cálculo del MSY y las consecuencias biológicas, sociales 
y económicas de  su superación, algunas OROP, como la WCPFC, definen el PRL como el 
MSY. Esto se basa en el enfoque precautorio, el Acuerdo sobre las poblaciones de peces de 
las Naciones Unidas y otras herramientas internacionales. 

52.  Para el estado biológico, los PRL se establecen cada vez más en un 20% de SSB0 utilizando 
métodos  de  agotamiento  del  stock,  que  es  un  PR  prudente  cuando  la  SSR  sigue  siendo 
incierta.  Además,  se  ha  sugerido  que  FMSY  representa  un  límite  superior  en  las  tasas  de 
mortalidad  por  pesca,  lo  que  es  consistente  con  la  definición  de  PRL:  "un  estado  de  la 
pesquería y / o un recurso que se considera indeseable y que las medidas de manejo deben 
evitarse". 

53.  Se ha demostrado que utilizando los valores típicos de pendiente SRR para atún barrilete 
entre 0,7-0,9, los valores de referencia basados en MSY (BMSY) están justo por encima o 
incluso por debajo del PRL general de 20% SBCURRENT,F = 0 adoptado por la WCPFC. Por lo 
tanto, bajo ciertas condiciones, un PR típico definido "para mantener o restaurar stocks a 
niveles  capaces  de  producir  MSY"  podría  verse  de  repente  como  "fuera  de  los  límites 
biológicos de seguridad". Esta paradoja aparece porque el 20% SBCURRENT,F = 0 como el único 
PRL  basado  en  el  agotamiento  de  existencias  se  adoptó  para  todas  las  poblaciones 
principales,  independientemente  de  la  productividad  relativa  de  la  población  o  la 
selectividad de la pesquería. Aunque el cálculo de  PRL específicos de stock y sus niveles 
asociados de riesgo aceptable pueden ayudar a superar el problema, los PRL actuales son 
biológicamente  "prudentes"  y,  por  lo  tanto,  están  en  línea  con  los  requisitos  de  la 
Convención WCPFC.  Hasta la fecha, no hay datos suficientes disponibles para establecer 
PRL específicos de stock en la región. 

54.  Los PRO se pueden definir para lograr objetivos de gestión, incluidos los objetivos sociales 
o económicos. Cada vez más se sugiere que el manejo de la biomasa de la población por 
encima  de  BMSY  conduce  a  peces  más  grandes  a  niveles  de  captura  similares  con  mayor 
beneficio  económico  y  menor  impacto  ecológico.  Este  enfoque  es  coherente  con  los 
objetivos de la PPC en virtud del párrafo 2 del artículo 2, que consiste en "restablecer y 
mantener  las  poblaciones  de  especies  explotadas  por  encima  de  los  niveles  que  pueden 
producir un rendimiento máximo sostenible". 

55.  Definir PRO equivalentes al 40% de SSB0 o más en vez de basarlas en el MSY (BMSY) puede 
traer diferencias significativas (o subutilización) en el nivel de esfuerzo de pesca. Hasta la 

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fecha, la WCPFC ha adoptado una PRO temporal para el atún barrilete basado en 50% de 
SBCURRENT,  F  =  0,  que,  a  pesar  de  las  muchas  incertidumbres,  está  muy  por  encima  de  las 
estimaciones disponibles de SBMSY. Aunque el PRO de la WCPFC puede parecer conservador, 
la evaluación para el atún barrilete se considera incierta. 

56.  Hoy,  la  posibilidad  de  alcanzar  los  PRO  y  los  objetivos  de  gestión  dentro  de  los  plazos 
definidos, así como la evitación de PRL, se están debatiendo en todas las OROP de atún. 
En particular, no hay una definición clara de probabilidades "altas", "muy altas", "bajas" y 
"muy bajas". 

Tarea 2: Reglas de Control de Capturas («Harvest Control Rules», HCR) 

57.  El uso de HCR ha sido cada vez más favorecido por las OROP de atún para implementar 
buenas prácticas de gestión de stocks y simplificar el proceso de negociación de límites de 
pesca y / o la implementación de medidas técnicas. 

58.  Se proporcionó un inventario que resume el estado de los HCR en las OROP de atún para 
cada stock. El inventario incluye los HCR que se recomendaron o propusieron en las OROP 
de atún, así como aquellos que se probaron o aplicaron. 

59.  Dentro de ICCAT, HCR no se han definidos para barrilete, atún aleta amarilla, patudo, atún 
blanco y atún rojo del Atlántico sur y Mediterráneo, aunque las Recomendaciones 11-13 y 
15-07 proporcionan un marco para su establecimiento. Se ha definido un HCR para el atún 
blanco  del  norte  en  2017  según  la  Recomendación  17-04.  Algunas  de  las  fortalezas 
identificadas para el atún blanco del norte incluyen el hecho de que será revisado por el 
SCRS en 2018 y que en circunstancias excepcionales la Comisión revisará  y considerará 
una posible revisión del HCR. Además, se han establecido reglas claras para los tipos de 
acciones de gestión para diferentes PR, incluida la reducción de la captura total admisible 
(TAC). El HCR está sujeto a MSE que indican que el HCR es sólido en caso de incertidumbre. 
Algunas de las debilidades identificadas indican que no está claro si las probabilidades de 
los PR o indicadores de rendimiento incorporarán la incertidumbre del modelo. Además, el 
TAC se comparte entre muchos países donde el control de captura es bajo. 

60.  Desde 2016, la IOTC ha establecido un HCR para el atún barrilete basado en PRL y PRO en 
virtud de la Resolución 16/02. La IOTC aún no ha establecido un HCR para el atún patudo, 
el rabil y el atún blanco. Las principales fortalezas del HCR de la IOTC incluyen objetivos 
de gestión, así como definiciones claras para PRL y PRO, y la definición de TAC. Res. 16/02 
requiere  que  el  HCR  y  los  parámetros  de  control  sean  evaluados  por  MSE.  Se  han 
identificado  varias  debilidades,  incluido  el  hecho  de  que  el  HCR  ha  sido  recientemente 
aceptado y aún no se ha completado una evaluación significativa. Además, el HCR no se 
refiere explícitamente a las probabilidades aceptables de superación, y no está claro cómo 
se  tendrá  en  cuenta  el  papel  de  la  pesquería  de  subsistencia  cuando  se  excedan  los 
umbrales. Además, cuando se estima que la biomasa está por debajo del PRL, no existen 
plazos específicos en los que se deba implementar un HCR nuevo, lo que aumenta el riesgo 
de agotamiento de existencias. 

61.  La WCPFC aún no ha definido un HCR para barrilete, rabil y atún patudo. La CMM 2014-06 
solicita  a  la  WCPFC  que  desarrolle  e  implemente  una  estrategia  de  captura  que  incluya 
PRO,  HCR  y  otros  elementos.  El  Comité  del  Norte  recomendó  un  marco  de  gestión 
provisional para el albacora del Pacífico Norte, mientras que, en 2014, una estrategia de 
captura  para  el  atún  rojo  del  Pacífico  definió  los  HCR  para  alcanzar  objetivos  de 
recuperación  específicos.  La  fase  de  reconstrucción  del  HCR  del  atún  blanco  del  Pacífico 
norte es explícita en cuanto a cómo se tomarán las medidas de gestión en relación con los 
PRO, en paralelo con un calendario establecido. También se especifican niveles aceptables 
de  riesgo  que  la  WCPFC  considera  compatibles  con  el  Acuerdo  sobre  las  poblaciones  de 
peces de las Naciones Unidas. Algunas de las debilidades potenciales de este HCR incluyen 
el hecho de que aún no ha sido evaluado por  MSE, aunque  esto  está  en desarrollo, y la 
probabilidad de que el stock caiga por debajo del PRL no ha sido claramente definido, que 
no sea "muy bajo". 

62.  En 2016, la IATTC adoptó un HCR para todos los atún tropicales en virtud de la Resolución 
C-16-02  basada  en  PRL  y  PRO  provisionales.  Para  el  albacora  del  Pacífico  Norte,  la 

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Resolución C-13-03 requiere que el personal de la CIAT revise el trabajo realizado por la 
WCPFC para el desarrollo del HCR. En cuanto al HCR para todos los atún tropicales, algunos 
de  los  puntos  fuertes  de  Res.  C-16-02  es  que  establece  definiciones  claras  para  PRL 
temporales  y  PRO  y  que  establece  medidas  de  gestión  previamente  acordadas  bajo  una 
variedad  de  condiciones  de  existencias,  lo  que  permite  la  rápida  implementación  de 
medidas de gestión, llegado el caso. Algunas de las debilidades del HCR incluyen que solo 
se considera provisional hasta que se evalúe, ya que aún no se ha establecido un MSE sin 
probabilidades claras de superar los PR dados. 

63.  La CCSBT desarrolló un procedimiento de gestión (PG) en 2011 para el atún rojo del sur, 
diseñado  para  lograr  el  objetivo  de  la  reconstrucción.  Este  PG,  conocido  como  el  "Bali 
Procedure", establece claramente los objetivos basados  en la probabilidad de reconstruir 
las poblaciones utilizando un PRO provisional dentro de un período de tiempo explícito. La 
CCSBT  ha  probado  una  serie  de  PG  vinculados  a  una  serie  de  incertidumbres  para 
garantizar que se haya identificado un procedimiento sólido. El PG también está sujeto a 
revisiones  periódicas,  incluida  una  revisión  anual  de  su  implementación  y  evaluación 
periódica  de  nuevas  fuentes  de  datos  y  modelos  comerciales.  Una  de  las  debilidades 
potenciales  del  PG  es  la  complejidad  de  los  métodos  utilizados,  lo  que  dificulta  la 
comunicación con las partes interesadas y los responsables de la toma de decisiones. 

64.  Los  HCR  teniendo  en  cuenta  la  gestión  de  las  pesquerías  de  especies  múltiples  pueden 
aplicarse utilizando límites de captura y esfuerzo. En general, para los límites de captura, 
el  monitoreo  en  tiempo  real  de  las  capturas  es  necesario,  pero  puede  ser  difícil.  Por 
ejemplo, dentro de la IOTC hay un desfase temporal entre los desembarques y el muestreo 
de captura real. Esto puede causar problemas de no conformidad si no se detecta un exceso 
de captura o si se cierran prematuramente si se sobreestiman las capturas. 

65.  En las pesquerías de especies múltiples, no es posible aplicar diferentes niveles de esfuerzo 
de pesca a dos o más especies que son vulnerables al mismo arte de pesca y que habitan 
en  el  mismo  hábitat.  Sabiendo  que  los  descartes  son  indeseables  sobre  la  base  de  los 
Principios de Pesca Común, cuando se alcanza el límite de captura de una población (por 
ejemplo, el atún aleta amarilla en la IOTC o patudo en la ICCAT) ("choke species") pero no 
para otros, las flotas dejarán de pescar. En este caso, los límites de captura para barrilete, 
por ejemplo, no se lograrán, con la consiguiente pérdida de oportunidades para las flotas 
pesqueras y otras consecuencias socioeconómicas indeseables. Estos incluyen pérdida de 
producción de alimentos, escasez de conservas y posibles aumentos de precios debido a 
una menor oferta en los mercados internacionales. 

66.  En general, la gestión basada en TAC requiere estimaciones precisas del estado del stock, 
PR y la tasa de reclutamiento cuando se establecen límites de captura. Si se subestiman la 
biomasa y el reclutamiento, los límites de captura se alcanzarán antes de lo esperado y las 
oportunidades de pesca se desperdiciarán a menos que se descarte la “choke species”. Por 
el contrario, si se sobreestima la biomasa del stock, la biomasa continuará disminuyendo 
mientras  que  la  mortalidad  aumentará.  A  este  respecto,  los  controles  de  esfuerzo 
proporcionan un medio más flexible para gestionar las pesquerías de especies múltiples ya 
que pueden conciliar los objetivos de conservación de dos  o más poblaciones cuando se 
establecen para el stock más vulnerable. 

67.  Los límites del esfuerzo de pesca son restricciones a la intensidad de uso de los artes de 
pesca. Estos pueden incluir limitaciones en la duración de la temporada de pesca, que son 
relativamente fáciles de aplicar a través de Sistemas de Localización de Buques (VMS), el 
uso  de  cuadernos  de  pesca  y  otras  medidas.  Además,  el  control  del  esfuerzo  pesquero 
reduce la necesidad de monitorear las capturas en tiempo real, lo que a menudo es difícil 
y costoso. En los sistemas de control del esfuerzo, ya no es necesario estimar la biomasa 
explotable  con  precisión  todos  los  años,  ya  que  el  nivel  de  mortalidad  por  pesca  está 
directamente  limitado,  independientemente  de  las  continuas  fluctuaciones  en  el  tamaño 
del  stock.  Para  ser  eficaz,  la  gestión  del  esfuerzo  requiere  un  control  estricto  sobre  la 
capacidad tecnológica y el potencial de captura de las flotas. En algunos casos en que la 
capacidad de pesca aumenta, la mortalidad por pesca debida a un esfuerzo dado puede ser 
mayor  de  lo  esperado  y,  por  lo  tanto,  podría  comprometer  la  sostenibilidad  de  las 
poblaciones. 

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68.  Hasta la fecha, solo la ICCAT utiliza TAC o límites de captura globales para todas las flotas 
involucradas en las pesquerías de atún tropicales. La CIAT y la WCPFC aplican controles de 
captura (TAC) solo para los palangreros que pescan patudo. En el Pacífico, la actividad de 
la flota de cerqueros está regulada por límites de esfuerzo (duración de la temporada). La 
ICCAT utiliza un pseudo-HCR basado en el esfuerzo para determinar el número de días que 
los cerqueros pueden pescar para alcanzar el MSY. 

69.  En 2017, la ICCAT intentó introducir límites de captura para el atún patudo y el rabil para 
las flotas de cerqueros que operan con dispositivos de concentración de peces (DCP) y un 
límite  de  captura  adicional  para  el  atún  aleta  amarilla  de  las  pesquerías  asociadas  con 
delfines. En la práctica, esto resultó difícil de implementar ya que la flota de cerqueros que 
pescaba con dispositivos de concentración de peces alcanzó el 80% del límite de captura 
anual total a mediados de julio. Esto condujo a la introducción de una nueva medida (C-
17-02)  después  de  solo  cinco  meses,  que  impidió  el  cierre  de  la  pesquería  con  DCP  en 
agosto  o  principios  de  septiembre,  con  consecuencias  dramáticas  para  las  flotas  de 
cerqueros.  

Tarea 3: Evaluación de Estrategias de Gestión («Management Strategy Evaluation», 
MSE) 

70.  Las cinco OROP de atún han trabajado en MSE, incluida la consulta sobre los objetivos de 
gestión,  la  caracterización  de  la  incertidumbre  de  la  dinámica  y  la  observación  de  las 
poblaciones  y  la  evaluación  de  las  estrategias  de  captura.  La  mayoría  de  los  MSE 
completados hasta la fecha han sido desarrollados por científicos reclutados por OROP con 
un mandato pocas veces otorgado por las Comisiones. 

71.  El estudio proporcionó una descripción general de los Modelos Operativos (MO), los HCR y 
las  estadísticas  de  rendimiento  utilizadas.  Los  MO  proporcionan  representaciones 
matemáticas del sistema gestionado. El impacto de la gestión pesquera se evalúa antes de 
la  implementación  de  MO  cuando  se  usa  MSE.  Los  MO  se  consideran  representaciones 
alternativas de la dinámica "real" del stock y tienen como objetivo tomar en cuenta todas 
las incertidumbres inherentes a la dinámica del pescado y la pesca. 

72.  Hoy  en  día,  se  están  desarrollando  MSE  para  especies  individuales,  con  el  objetivo  de 
mantener las existencias a un nivel saludable, promoviendo el éxito de la reconstrucción 
de  poblaciones  sobreexplotadas  y  evaluando  los  beneficios  económicos  de  la  gestión 
preventiva. Para involucrar a terceros países en el proceso de MSE a través de OROP de 
atún, se están implementando varias iniciativas (talleres, desarrollo de capacidades, cursos 
y proyectos). Se discutieron iniciativas para promover la participación de terceros países y 
desarrollar  otros  enfoques  de  MSE,  incluido  el  impacto  del  proyecto  Areas  Beyond 
Jurisdiction. 

73.  Las  cinco  OROP  de  atún  tienen  planes  para  evaluar  los  procedimientos  de  gestión  (PG) 
utilizando  MSY.  En  algunas  OROP,  la  hoja  de  ruta  para  la  adopción  de  los  PG  está 
claramente detallada y, en otros, el proceso está apenas en su infancia. 

74.  El proceso de la  IOTC se basa  en  el trabajo técnico y la interacción con la Comisión. La 
IOTC  pretende  poder  adoptar  PG  para  sus  mayores  stocks  para  2020.  En  la  ICCAT,  el 
proceso MSE está muy avanzado para el atún blanco y el atún rojo del Atlántico norte. Un 
aspecto particular del proceso MSE de la ICCAT es que se evaluará de forma independiente, 
con la evaluación de la MSE de atún blanco del Atlántico norte en 2018 que contribuirá a 
la mejora del proceso para otros stocks. Además, considerará opciones para el manejo de 
múltiples especies en lugar del actual marco de gestión de una sola especie. Dentro de la 
WCPFC, el proceso de feedback está avanzado y ha logrado un progreso significativo en la 
definición  de los  objetivos  de  gestión  a  través  de  una  serie  de  talleres  de  consulta.  Con 
respecto a la ICCAT, el trabajo de MSE es identificar los HCR apropiados para el patudo y 
el  atún  aleta  amarilla,  pero  todavía  está  en  su  infancia.  Se  presentará  un  plan  para  el 
desarrollo de MSE al Consejo Asesor Científico 2018. La CCSBT ha decidido desarrollar un 
nuevo PG para guiar el establecimiento de TAC para 2021 y más allá. El nuevo PG tendrá 
en cuenta los cambios en la disponibilidad de datos, en particular al cambiar las series de 

Page xxix 

 
 
 
EASME/EMFF/2016/008 – Final Report 

monitoreo de reclutamiento de una encuesta aérea de juveniles a un programa de genética 
/ recaptura de juveniles. 

Tarea 4: Estudios de casos de OROP seleccionadas 

Estrategia de captura de la WCPFC 

75.  La  WCPFC  ha  avanzado  en  el  desarrollo  de  estrategias  de  captura  que  incorporan  el 
concepto de máximo rendimiento económico («Maximum Economic Yield», MEY), así como 
objetivos socioeconómicos y ambientales. La WCPFC intentó operacionalizar el uso de MEY 
con una consideración explícita del desempeño económico (por ejemplo, los ingresos) en 
su  análisis,  a  pesar  de  algunas  preocupaciones  sobre  la  integridad  y  viabilidad  de  este 
trabajo. Esto permite el desarrollo de una industria rentable que aprovecha las tendencias 
del mercado y los avances tecnológicos para obtener los mejores precios y márgenes de 
ganancia. Sin embargo, los precios más altos del pescado significan un acceso reducido a 
esta importante fuente de nutrientes para las personas de bajos ingresos, en los países en 
desarrollo o en las comunidades costeras que dependen de los peces para su sustento. 

76.  Este informe analiza opciones distintas a las actualmente sugeridas en las reuniones del 
Comité Científico y otros grupos de trabajo que también podrían conducir a estrategias de 
captura  plausibles.  Está  claro  que  hay  una  amplia  gama  de  opciones  que  se  pueden 
considerar  para  la  gestión  de  una  pesquería.  Sin  embargo,  no  es  posible  establecer  de 
antemano  cuál  de  ellos  funcionará  mejor  hasta  que  los  objetivos  de  la  estrategia  estén 
claramente definidos. Por lo tanto, acordar los objetivos de gestión, incluidas las prioridades 
y  la  ponderación  asignada  a  cada  objetivo,  sigue  siendo  un  paso  crucial  que,  una  vez 
completado, aportará una mayor claridad al proceso. 

Desarrollo de MSE para pesquerías multi-especies y stocks únicos para atún tropical dentro de 
la IOTC y la ICCAT: identificar opciones y modelos preliminares 

77.  Este estudio representa un primer paso en la evaluación de las estrategias de gestión de 
poblaciones de atún tropical en un marco de pesca mixta. Comparamos tres estrategias de 
gestión relacionadas con diferentes dinámicas de flotas. La gestión basada en el esfuerzo 
con  una  reducción  del  25%  dio  como  resultado  una  dinámica  de  la  flota  que  redujo  el 
esfuerzo de todas las flotas en un 25%. Los otros dos HCR utilizados corresponden a los 
HCR propuestos por  ICES  en virtud del MSY,  y a un  HCR de stocks  múltiples que utiliza 
tasas  de  mortalidad  por  pesca  que  cumplen  los  objetivos  de  MSY.  Estos  dos  HCR  se 
combinaron  con  dos  dinámicas  de  flota  diferentes  debido  a  la  condición  utilizada  para 
restringir el esfuerzo de las flotas, el esfuerzo mínimo o el esfuerzo correspondiente al TAC 
de patudo. 

78.  La HCR multi-stock con un TAC pequeño para patudo producido biomasas sostenibles para 
las tres poblaciones, pero la probabilidad de estar por debajo del PRL (BLIM) fue superior a 
cero  en  algunos  años.  Este  tipo  de  gestión  debe  combinarse  con  estrictas  medidas  de 
control para garantizar el cumplimiento del TAC. 

79.  La dinámica de la flota utilizada en este trabajo se basó en su comportamiento histórico. 
Sin embargo, en el futuro, los estudios deberían centrarse primero en la definición de flotas 
y sus intercambios, y identificar las dinámicas que mejor describan la dinámica de estas 
flotas. 

80.  Las simulaciones realizadas se basaron en un período anual en lugar de trimestral, que se 
utiliza en los modelos de evaluación de stock. En el futuro, los estudios deberían desarrollar 
el  modelo  de  simulación  estacionalmente  para  proporcionar  una  representación  más 
precisa de la dinámica de la flota y un enfoque coherente entre la evaluación de stock y el 
modelo de simulación. 

*** 

Page xxx 

 
 
 
1  INTRODUCTION 

1.1  Background 

Management plans require the adoption of management objectives and timeframes for 
achieving  them  and  can  greatly  benefit  from  using  Reference  Points  (RP)  to  develop 
appropriate  limits,  targets  or  trigger  points  and  help  define  the  parameters  of  the 
management framework. Such reference points together with detailed rules on how to 
define  allowable  catches/exploitation  (i.e.  Harvest  Control  Rules,  HCRs)  can  then  be 
tested  under  different  scenarios  of  state  of  nature  and  uncertainty  to  assess  their 
effectiveness  and  trade-offs  among  different  management  strategies.  Management 
Strategy Evaluation (MSE) provides a platform for simulation-testing such alternative 
management  strategies  explicitly  accounting  for  uncertainty  and  has  therefore  been 
increasingly  used  in  fisheries  management  to  support  management  decisions.  MSE  is 
mainly used to test how well existing or proposed management strategies perform under 
different scenarios or identify the most effective management strategies from a set  of 
candidate strategies and for a given set of objectives. 

The MSE is a modelling-based process and its main components are (1) an  Operating 
Model (OM) to represent the ‘true’ underlying dynamics of the fishery resource and to 
generate simulated future data, (2) an estimation model (this varies in complexity) to 
assess the state of the stock relative to agreed targets and reference points based on 
the data  simulated using the  operating model,  and (3) one  or more decision rules to 
determine  what  management  actions  should  happen1,  i.e.  the  Management  Strategy. 
The MSE process ties well with the vision of the reformed EU Common Fisheries Policy 
(CFP)2  for  adopting  multi-annual  management  plans  for  fisheries  to  improve  stability 
and  robustness  of  management  approaches.    Additionally,  the  CFP  defines  that 
multiannual management plans should be developed for mixed fisheries when different 
stocks are caught jointly and that adds another layer of complexity. The latter makes 
the adoption of management and assessment processes that are robust to uncertainty 
even more important. 

Early adopters of HCRs and MSE includes the USA, where MSE is already being used to 
identify  management  strategies  that  meet  the  constraints/objectives  set  in  the 
Magnuson-Stevens  Act  and  associated  guidelines3,4,  Australia5,  and  international 
organizations  such  as  CCAMLR6.  The  joint  t-RFMOs  process  (Kobe  process)  also 
identified the developments of MSE as an important step to address the precautionary 
approach  and  that  has  also  led  to  the  development  of  the  Joint  tuna-RFMO  MSE 
Technical Working Group7 to advance work in this area.  

Although work on implementing MSE varies among the t-RFMOs, there are evidence of 
progress; For example the Working Party on Methods in IOTC has selected five species 
for  MSE  (albacore,  yellowfin,  bigeye,  skipjack  and  swordfish)  and  additional  work  to 

1 http://www.fao.org/fishery/eaf-net/eaftool/eaf_tool_50  

2 Regulation (EU) No 1380/2013 of the European Parliament and of the Council of 11 December 2013 on the 
Common Fisheries Policy, amending Council regulations (EC) No 1954/2003 and (EC) No 1224/2009 and 
repealing Council Regulations (EC) No 639/2004 and Council Decision 2004/585/EC.   

3 http://www.nmfs.noaa.gov/sfa/NSGtkgd.pdf  

4 http://www.westcoast.fisheries.noaa.gov/publications/fishery_management/groundfish/whiting/2014-

stock-assess.pdf  

5https://www.wcpfc.int/system/files/MOW3%20WP-07%20Australia%20-

%20Importance%20of%20harvest%20strategies%20and%20some%20examples.pdf  

6 Management Science in Fisheries: An Introduction to Simulation-based Methods, 2016. Edited by C.T.T 

Edwards and D.J Dankel. Published by Routledge. 

7 http://www.iccat.int/intermeetings/Performance_rev/ENG/PER_010_ENG.pdf 

Page 1 

 
 
 
                                           
Study on Circular Design of the Fishing Gear for Reduction of Environmental Impacts 

develop the yellowfin and bigeye tuna MSE is expected in 20188. Similarly, IATTC has 
already  trialled  MSE  for  Pacific  bluefin  tuna  but  just  as  an  exercise9  ICCAT  has  also 
developed an MSE to adopt a HCR for North Atlantic albacore in 2017 and is currently 
looking to develop an MSE for two BFT stocks.  

1.2  Aims and objectives 

This study undertook the following four main tasks: 

Task 1: Reference points. The study will provide an inventory of reference points for 
all  tuna  stocks.  Use  of  reference  points  between  t-RFMOs  will  be  analysed  for  their 
consistency  and  the  basis  for  their  establishment,  including  the  strengths  and 
weaknesses of each individual reference points. The relation between different types of 
reference points will be assessed taking into account relevant factors such as the stock 
status and the exploitation patterns of different fisheries. Several case studies will be 
given to provide examples of different types of reference points for the same tuna stock 
in different conservation status and harvested by different fisheries. 

Task 2: Harvest control rules (HCRs). The study will provide an inventory of what 
types of HCRs (management procedures) have been proposed, tested or applied in t-
RFMOs.  The  strengths  and  weaknesses  of  different  types  of  HCR  (existing  and  under 
development) for tuna stocks will be analysed taking into account factors such as data 
availability, types of fisheries and management systems.  Besides, it will be discussed 
how HCRs could be developed taking into account multispecies interactions and mixed 
fisheries.  

Task 3: Management Strategy Evaluation (MSE). A review of the development of 
MSEs  across  t-RFMOs  will  be  carried  out.  For  this,  we  will  1)  evaluate  how  MSE 
frameworks have been planned and developed across t-RFMOs; 2) review how the MSE 
components  (operating  models,  Management  Procedures  (MP)  and  performance 
statistics) have been developed and analysing how MSE has been used to support the 
adoption of HCRs; 3) identify strengths and weaknesses of the process to develop HCRs 
and MSE frameworks within t-RFMOs; and 4) propose alternatives for improving MSE 
frameworks across t-RFMOs. 

Task 4: Three tuna RFMOs will be used as case studies to provide a more detailed 
picture of the MSE process and its progress (e.g. WCPFC, ICCAT and IOTC). The main 
objectives of the case studies are to understand the MSE approaches considered, their 
implications, and progress so far but also consider additional options that can support 
the MSE process. 

8 www.iotc.org/sites/.../01/IOTC-2016-SC19-RE_-_FINAL_DO_NOT_MODIFY_0.pdf  

9 https://www.iattc.org/Meetings/Meetings2016/SAC-07/PDFs/Docs/_English/SAC-07-07h_Research-on-

Management-Strategy-Evaluation.pdf 

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2  TASK 1: REFERENCE POINTS 

As  specified  in  the  Terms  of  Reference,  a  separate  document  with  the  results  and 
conclusions has been written to address task 1 (see Wakeford et al., 2018). 

3  TASK 2: HARVEST CONTROL RULES IN TUNA FISHERIES 

3.1  Sub-task 2.1: Inventory of harvest control rules in tuna RFMOs 

A harvest control rule (HCR), in its broadest sense, is a set of well‐defined pre‐agreed 
rules or actions used for determining a management action in response to changes in 
indicators  of  stock  status  with  respect  to  reference  points.  A  well-designed  HCR 
encapsulates  good  management  of  the  target  stock  by  defining  clear  objectives, 
measures  of  performance  and  appropriate  management  actions  required  to  ensure 
fisheries meet their objectives. The use of HCRs has been increasingly favoured by tuna 
Regional Fisheries Management Organisations (t-RFMOs) to enable them to implement 
good management practice of tuna stocks and also to simplify the negotiation process 
of  establishing  fishing  limits  and/or  catch  quotas  and/or  implementing  technical 
measures. 

An inventory is provided below (Table 1) summarising the status of HCRs in t-RFMOs 
for  each  stock.  It  includes  HCRs  that  have  been  recommended  or  proposed  within  t-
RFMOs, as well as those that are tested or applied in some form. Further details of those 
HCRs that have been implemented or are under development by t-RFMOs are provided 
in the next section (3.2.2) where strengths and weaknesses are discussed.  

The term Management Procedure (MP) is a set of formal actions, usually consisting of a 
combination of monitoring data, analysis method and HCRs (synonymous with a harvest 
strategy), which are used to manage a fishery iteratively and adaptively.  

Table 1: Summary of harvest control rules that are currently being proposed, tested or 
applied in tuna RFMOs. HCRs/MPs currently established are shown in bold text.   

RFMO 

Skipjack 

Yellowfin 

Bigeye 

Albacore 

Bluefin 

ICCAT  HCRs are not yet defined for skipjack, 

yellowfin and bigeye tuna. However, Rec. 
11-1310 and Rec. 15-0711 provide a 
framework for establishing HCRs 

HCR has not yet 
been defined for 
eastern Atlantic 
& Mediterranean 
and western 
bluefin tuna. 

Rec. 11-13  and 
Rec. 15-07  
provide a 
framework for 
establishing 
HCRs 

HCRs have not 
yet been defined 
for southern and 
Mediterranean 
albacore 
although Rec. 
11-13 and Rec. 
15-07 provide a 
framework for 
establishing 
HCRs. 

An HCR has been 
defined for 
northern albacore 
in 
2017(Rec. 17-
0412)  

IOTC 

An HCR has 
been in place 
for skipjack 
tuna since 2016 

HCRs are not yet defined for bigeye, 
yellowfin or albacore 

n/a 

10 https://www.iccat.int/Documents/Recs/compendiopdf-e/2011-13-e.pdf  

11 https://www.iccat.int/Documents/Recs/compendiopdf-e/2015-07-e.pdf  

12 http://www.iccat.int/Documents/Recs/compendiopdf-e/2017-04-e.pdf 

Page 3 

 
 
 
                                           
Study on Circular Design of the Fishing Gear for Reduction of Environmental Impacts 

RFMO 

Skipjack 

Yellowfin 

Bigeye 

Albacore 

Bluefin 

(Res. 16/02)13, 
based on target 
and limit 
reference 
points14 

WCPFC  HCRs are not yet defined for skipjack, 

yellowfin or bigeye tuna. CMM 2014-0615 
calls for WCPFC to develop and implement a 
harvest strategy approach that includes 
target reference points (TRPs), HCRs and 
other elements 

IATTC 

IATTC adopted an HCR for tropical 
tunas in 2016, under Res. C-16-0219, 
based on interim target and limit 
reference points20  

The Northern 
Committee has 
recommended an 
interim 
management 
framework for 
the North Pacific 
albacore stock16, 
which includes a 
decision rule but 
falls short of a 
decision 
framework 

Res. C-13-0321 
requires that 
IATTC scientific 
staff shall review 
work undertaken 
by WCPFC 
towards the 
development of 
HCRs for North 
Pacific albacore, 
and make 
recommendations 
to the 
Commission 

CCSBT  n/a 

n/a 

n/a 

n/a 

A Harvest 
Strategy for 
Pacific Bluefin 
Tuna 
Fisheries17 
defined HCRs 
in 2014 to 
achieve 
rebuilding 
targets18  

Res. 16-0822 
requires that 
reference points 
and harvest 
control rules are 
developed for 
Pacific bluefin 
tuna by 2018, 
which should be 
comparable to 
those adopted by 
the WCPFC 

A management 
procedure has 
been in place 
for southern 
bluefin tuna 
since 2011, 

13 http://www.iotc.org/cmm/resolution-1602-harvest-control-rules-skipjack-tuna-iotc-area-competence 

14 Interim LRP of 0.2*SSB0 and 1.5*FMSY; Interim TRP of 0.4*SSB0 and FMSY 

15 https://www.wcpfc.int/doc/cmm-2014-06/conservation-and-management-measures-develop-and-

implement-harvest-strategy-approach  

16 https://www.wcpfc.int/node/29863  

17  Ibid. 

18 No limit reference point is defined; WCPFC (CMM 2016-04) has defined an initial rebuilding target 
reference point of 0.07SSB0. IATTC have put forward a proposal for a new rebuilding target 
20%SSBcurrent(F=0) by 2030 and a limit reference point 15%SSBcurrent,F=0. 
(https://www.wcpfc.int/system/files/WCPFC-NC13-IP-
08%20Refernce%20points%20and%20harvest%20control%20rules%20for%20Pacific%20bluefin%20tu
na%20-%20IATTC%20staff.pdf) 

19 https://www.iattc.org/PDFFiles/Resolutions/IATTC/_English/C-16-02-Harvest-control-rules.pdf  

20  LRP of 0.08*SSB0; TRP of SSBMSY and FMSY 

21 https://www.iattc.org/PDFFiles/Resolutions/IATTC/_English/C-13-03-North-Pacific-albacore.pdf  

22 https://www.iattc.org/PDFFiles/Resolutions/IATTC/_English/C-16-08-Conservation-and-management-of-

Pacific-bluefin-tuna.pdf  

Page 4 

 
 
                                           
RFMO 

Skipjack 

Yellowfin 

Bigeye 

Albacore 

Bluefin 

designed to 
achieve the 
recovery 
target23 

3.2  Sub-task  2.2:  Strengths  and  weaknesses  of  harvest  control  rules 

for tuna stocks 

This  sub-task  analyses  the  strengths  and  weaknesses  of  the  five  established  or  draft 
HCRs identified in sub-task 2.1, taking into account factors such as HCR specification, 
evaluation  procedures,  consideration  of  uncertainty  and  the  associated  management 
system. A non-exhaustive list of questions were developed to guide the assessment of 
HCR strengths and weaknesses was:  

1.  Have appropriate reference points been adopted, are they used appropriately in 
the  HCR  and  are  acceptable  levels  of  risk  of  exceeding  limit  reference  points 
defined? 

2.  Is  MSE  (Management  Strategy  Evaluation)  used  to  evaluate  the  HCR,  are  key 
uncertainties included in the MSE, and is the HCR robust to these uncertainties? 

3.  Have explicit management measures been identified and agreed, it is clear how 
these  will  be  triggered  in  the  HCR  and  are  these  likely  to  be  appropriate  for 
achieving management objectives?    

4.  Is  the  performance  of  the  HCR  reviewed  on  a  regular  basis,  or  has  a  timeline 

been established for its review?  

The  assessment  of  strengths  and  weaknesses  was  based  on  expert  judgement  using 
available  literature  on  the  HCR,  including  technical  working  party  reports  and  RFMO 
Commission meeting reports.   

3.2.1  ICCAT North Atlantic albacore HCR 

ICCAT has made significant progress in developing an HCR for North Atlantic albacore, 
with Recommendation 16-0624 and more recently Recommendation 17-0425. The former 
provided a generic HCR to be tested for the stock, along with candidate reference points. 
A description of the proposed rule is provided in Figure 1. 

23 The recovery target for southern bluefin tuna is to rebuild the stock to an interim building target reference 

point of 20% of the original spawning stock biomass by 2035. 
https://www.ccsbt.org/sites/ccsbt.org/files/userfiles/file/docs_english/operational_resolutions/Resolutio
n_Management_Procedure.pdf 

24 http://iccat.int/Documents/Recs/compendiopdf-e/2016-06-e.pdf  

25 Ibid.  

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Study on Circular Design of the Fishing Gear for Reduction of Environmental Impacts 

Figure 1: Extract from ICCAT Rec. 16-06 describing the HCR for North Atlantic 
albacore currently under consideration. It is noted that recent MSE has evaluated this 
as well as other 14 alternative HCR designs.26 (ICCAT Rec. 16-06). 

More  recently  a  well-defined  HCR  for  North  Atlantic  albacore  has  established  through 
Recommendation 17-04. The harvest control rule (HCR) sets a 3-year constant annual 
Total Allowable Catch (TAC) using the following three values estimated from each stock 
assessment27. For each value the median values, as reported in the summary table of 
the Standing Committee on Research and Statistics (SCRS) report, shall be used: 

a)  The estimate of current stock biomass (Bcurr) with respect to BMSY.  

b)  The estimate of the stock biomass at Maximum Sustainable Yield (BMSY).  

c)  The estimate of the fishing mortality at MSY (FMSY). 

A total of six control parameters are specified: 

a)  The biomass threshold level (BTHRESH) is equal to the biomass able to deliver the 

maximum sustainable yield (BTHRESH = BMSY).  

b)  A fishing mortality target corresponding to 80% of FMSY (FTAR = 0.8*FMSY) will be 
applied when the stock status is at, or above, the threshold level (BTHRESH). 

26 http://www.iccat.int/Documents/CVSP/CV074_2017/n_2/CV074020457.pdf 

27 It should be noted that the terminology referring to the stock biomass (B) has changed between Rec. 16-
06 and Rec. 17-04. In the former, the HCR referred specifically to the spawning stock biomass (SSB), 
whereas Rec. 17-04 refers to the stock biomass (B). This change is most likely due to the fact that the 
most recent stock assessment from which management decisions are made, is based on a biomass 
production model that does not specify spawning biomass. The HCR in Rec. 17-04 is therefore 
consistent with the latest stock assessment advice. 

Page 6 

 
 
 
                                           
c)  If  the  current  biomass  (BCURR)  is  estimated  to  be  below  the  threshold  level 
(BTHRESH) and higher  than  BLIM, then fishing  mortality  will  be  reduced  linearly  
for  the  next  multiannual management period (FNEXT). 

d)  If  the  current  biomass  (BCURR)  is  estimated  to  be  at,  or  below,  BLIM,  then  the 
fishing mortality shall be  set at FMIN with a view to  ensure a level of  catch for 
scientific monitoring. 

e)  The Maximum catch limits (Cmax) recommended are 50,000 t to avoid adverse 

effects of potentially inaccurate stock assessments 

f)  The  maximum  change  in  the  catch  limit  (Dmax)  shall  not  exceed  20%  of  the 
previous  recommended  catch  limit  when  BCURR≥BTHRESH.  The  HCR  described  by 
the control parameters produces a relationship between stock status (spawning 
biomass  relative  to  unfished  levels)  and  fishing  intensity  (exploitation  rate 
relative to target exploitation rate) as shown in Figure 2. 

Figure 2: Relationship between stock status and fishing intensity as described by the 
control parameters of the ICCAT HCR for North Atlantic Albacore. (ICCAT Rec. 17-04).  

Strengths 

  The HCR is formally adopted through Rec. 17-04 and will be subject to a peer 

review by SCRS in 2018. 

  Should  exceptional  circumstances  occur,  the  Commission  will  review  and 

consider a possible revision of the HCR.  

  The  proposed  HCR  as  set  out  in  Rec.  16-06  and  adopted  HCR  in  Rec.  17-04 
establishes  clear  rules  regarding  the  types  of  management  actions  to  be 
triggered at different reference points, including when such measures would be 
lifted.  This  transparency  is  important  as  it  allows  stakeholders  to  see  whether 
management is following its own agreed policies. 

  Both Rec. 16-06 and Rec. 17-04 requires that the HCR will include pre-agreed 
management actions to be taken under various stock conditions. Pre-agreement 
on management actions is key to the successful application of a HCR, as it allows 
management measures such as reduction in Total Allowable Catch (TAC) to be 
implemented rapidly when required, and avoiding the need for political decision 
making at the time.  

Page 7 

 
 
 
 
Study on Circular Design of the Fishing Gear for Reduction of Environmental Impacts 

  Both Rec. 16-06 and Rec. 17-04 explicitly requires evaluation of HCRs using  a 
management strategy evaluation (MSE), for both the evaluation of the proposed 
(and alternative) HCRs28 and testing of refined candidate reference points and 
associated  HCRs.  Furthermore,  and  related  to  MSE,  Rec. 16-06  notes  that  the 
introduction of the HCR will be an iterative process of adjustments on the basis 
of evaluation results and taking into account scientific advice. The use of MSE to 
evaluate HCRs, where this incorporates the main sources of uncertainty and the 
latest scientific advice, is generally considered best practice.   

  MSE indicates that candidate HCRs are robust to the uncertainties considered for 
this  stock29,  including  sources  of  information,  biological  parameters  (natural 
mortality and steepness) and fishery dynamics. Also, the HCRs are considered 
to be robust to a range of estimates of the stock's initial state of exploitation. 

  Rec.  17-04  introduces  a  maximum  catch  limit  to  avoid  adverse  effects  of 
potentially  inaccurate  stock  assessments  and  prevents  increasing  catches  to 
occur when information is uncertain.  

  Rec.  17-04  has  a  target  fishing  mortality  rate  less  than  FMSY  (FTAR  =  0.8*FMSY) 
that is used when the spawning stock biomass is above the threshold level. This 
helps ensure total fishing mortality is highly unlikely to exceed FMSY on the Kobe 
plot. 

Weaknesses 

  While Res. 16-06 determines that the HCR should maintain the stock in the green 
zone of the Kobe plot with at least a 60% probability, the accepted probability 
for  the  stock  being  in  the  red  quadrant  of  the  Kobe  plot  is  not  yet  defined  by 
ICCAT.  This  is  an  important  uncertainty  in  evaluating  and  selecting  harvest 
control  rules,  i.e.  ambiguity  on  whether  a  given  HCR  will  deliver  management 
outcomes.    

 

 

It  is  not  yet  clear  if  probabilities  relative  to  the  reference  points  or  the 
performance indicators will integrate model uncertainty.  

In  terms  of  available  management  measures,  the  TAC  is  shared  among  many 
countries and control is not precise, and allowing the carry-forward of uncaught 
allocations  effectively  decreases  the  control  over  fishing  mortality.  However, 
these weaknesses may be mitigated if incorporated in the HCR as uncertainties. 

3.2.2  IOTC skipjack tuna harvest control rule 

A well-defined HCR for skipjack tuna has recently been established through Resolution 
16/0230.  The  HCR  recommends  a  total  annual  catch  limit  based  on  spawning  stock 
biomass (referred to by IOTC as B31) using the following three values estimated from 
each skipjack stock assessment: 

a)  The estimate of current spawning stock biomass (Bcurr);  

b)  The estimate of the unfished spawning stock biomass (B0);  

c)  The estimate of the equilibrium exploitation rate (Etarg) associated with sustaining 

the stock at Btarg. 

28 Ibid.  

29 Ibid. 

30 http://www.iotc.org/cmm/resolution-1602-harvest-control-rules-skipjack-tuna-iotc-area-competence  

31   It should be noted that STECF advice for skipjack tuna HCR refer to spawning stock biomass as SSB (see 
section 5.6, STECF 2018): https://stecf.jrc.ec.europa.eu/documents/43805/2054982/STECF+PLEN+18-
01.pdf  

Page 8 

 
 
                                           
Five  control  parameters  are  specified:  (i)  a  threshold  level  that  will  trigger  fishing 
mortality  reductions  (target  reference  point=0.4B0);  (ii)  a  maximum  level  of  fishing 
intensity that will be applied when the stock is above the threshold level; (iii) a safety 
level, the percentage of B0 below which non-subsistence catch will be set to zero (0.1B0; 
note  that  this  is  below  the  limit  reference  point,  0.2B0);  (iv)  a  maximum  catch  limit 
(900,000 t); and (v) a maximum change in catch limit (30%).  The HCR described by 
the control parameters produces a relationship between stock status (spawning biomass 
relative  to  unfished  levels)  and  fishing  intensity  (exploitation  rate  relative  to  target 
exploitation rate) as shown in Figure 3.  

Figure 3: Relationship between stock status and fishing intensity as described by the 
control parameters of the IOTC HCR for skipjack (IOTC Res. 16/02).  

Resolution 16/02 further defines how the recommended total annual catch limit shall be 
set, depending on the current spawning biomass at a given time, rules on changes in 
catch limits between consecutive years, and a protocol for review of the HCR using MSE.  

Strengths 

  The  skipjack  tuna  HCR  described  in  Res.  16/02  sets  out  clear  management 
objectives  along  with  clear  definitions  for  target  and  limit  RPs.  These  RPs  are 
defined in relation to the level of biomass in the absence of fishing (B0) due to 
the difficulties in producing robust estimates of MSY-based reference points.  

  The relationship between the stock assessment, the HCR and the setting of total 
allowable catch (TAC) is clearly described. With regard to how the HCR will trigger 
management measures, explicit instructions are given on how total annual catch 
will be set according relative to different biomass-based threshold levels, with or 
without an allocation scheme in place32. This includes setting of a zero catch limit 
for non-subsistence fisheries at or below a safety level (Bcurr <= 0.1B0). No other 
technical measures are specified, e.g. area closures.  

  Res. 16/02 explicitly requires evaluation of the HCR and the control parameters 
using MSE, including a clear timeline for evaluation and modification of the HCR, 
as necessary, after several iterations (but no later than 2021). Furthermore, it 
requires  a  programme  of  work  to  further  refine  the  MSE  for  the  skipjack  tuna 
fishery.  This work will be important in refining the operating models used and 
reducing or better incorporating uncertainties.    

32 See setting of TAC for 2018 following the HCR: http://www.iotc.org/documents/calculation-skipjack-

catch-limit-period-2018-2020-using-hcr-adopted-resolution-1602  

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Study on Circular Design of the Fishing Gear for Reduction of Environmental Impacts 

  The  HCR  was  developed  and  tested  using  Management  Strategy  Evaluation 
(MSE)  that  ensured  that  the  long-term  median  spawning  biomass  (SB)  was 
maintained at a level equivalent to 0.61SB0 (i.e. 61% of the unfished spawning 
stock biomass) and a 90% probability of maintaining SB above 0.39SB0

33.  

Weaknesses 

  The HCR is only recently agreed, with the first implementation of the HCR to be 
based on the 2017 skipjack stock assessment. No meaningful evaluation can be 
made yet on whether the target fishing intensity is being achieved and the HCR 
is effective. 

  The  HCR  does  not  explicitly  make  reference  to  acceptable  probabilities  for 
exceeding  the  reference  points  (Bthresh,  Bsafety),  either  quantitatively  or 
qualitatively. This is a critical step in the harvest strategy development process, 
i.e. choosing the level of risk that will guide future fishery decisions. Typically, 
managers should set low levels of risk tolerance in cases of greater uncertainty. 
For  example,  where  there  is  a  greater  risk  of  the  stock  exceeding  a  reference 
point, the probability should be low (i.e. 10%). 

  There  remain  a  number  of  uncertainties  in  the  HCR,  including  the  role  of 
subsistence fishing if thresholds are exceeded and exactly how the target rates 
are to be implemented. 

 

In the case where the estimated spawning biomass falls below the LRP, the HCR 
will be reviewed and consideration given to replacing it with an alternative HCR 
specifically  designed  to  meet  a  rebuilding  plan.  There  is,  however,  no  clear 
indication of the timeframe within which a new HCR should be implemented and 
put the status of the stock at higher risk of depletion. 

3.2.3  WCPFC Pacific Bluefin tuna rebuilding HCR 

A  harvest  strategy  for  Pacific  bluefin  tuna  was  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 (CMM 
2014-06)34. Although the provisions of the harvest strategy are expressed in terms of a 
single stock, it is noted that they may be applied to multiple stocks as appropriate and 
as determined by the Northern Committee. The last stock assessment was conducted 
in 2016 and showed the status of Pacific bluefin tuna to be heavily overfished, with the 
spawning  stock  biomass  corresponded  2.6%  of  the  virgin  spawning  stock  biomass 
(SSB0) in the terminal year (2014) of the assessment35. A HCR, termed a decision rule, 
is described by WCPFC as follows:  

Harvest controls rules during initial rebuilding period (i.e. between 2015 and 2024): The 
interim  harvest  control  rules  below  will  be  applied  based  on  the  results  of  stock 
assessments and SSB projections36.  

33 http://www.iotc.org/documents/management-strategy-evaluation-indian-ocean-skipjack-tuna-fishery-0   

34 https://www.wcpfc.int/system/files/CMM%202014-

06%20Conservation%20and%20Management%20Measures%20to%20develop%20and%20implement
%20a%20harvest%20strategy%20approach%20for%20key%20fisheries%20and%20stocks%20in%20t
he%20WCPO.pdf   

35 http://isc.fra.go.jp/pdf/ISC16/ISC16_Annex_09_2016_Pacific_Bluefin_Tuna_Stock_Assessment.pdf  

36 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. 

Page 10 

 
 
                                           
a.  If  the  SSB  projection  indicates  that  the  probability  of  achieving  the  initial 
rebuilding  target  (i.e.  the  median  SSB  estimated  for  the  period  1952  through 
2014)  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 (‘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 (‘large fish’). For this purpose, the International Scientific Committee 
(ISC)  for  Tuna  and  Tuna-like  Species  in  the  North  Pacific  Ocean  (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  have  been  requested  to  provide 
relevant information on potential catch limit increases. 

Harvest  controls  rules  during  second  rebuilding  period:  Harvest  control  rules  to  be 
applied during the second rebuilding period are yet to be decided, taking into account 
the  implementation  of  the  interim  harvest  control  rules  applied  during  the  initial 
rebuilding period. 

Strengths 

  The  rebuilding  phase  HCR  described  by  WCPFC  is  explicit  how  management 
action will be taken in relation to the (rebuilding) interim target reference point, 
which  is  also  established  alongside  a  specific  timeline  for  this  target  being 
achieved.  The stock of Pacific bluefin is treated as a Level 2 stock37 under the 
Commission’s hierarchical approach for setting biological limit reference points. 
This is because steepness in the stock-recruitment relationship is not well known, 
although the key biological and fishery variables are reasonably well estimated. 
The  initial  rebuilding  target  for  the  stock  is  the  median  SSB  estimated  for  the 
period 1952 through 2014, to be reached by 2024 with at least 60% probability.  

  Acceptable levels of risk are specified explicitly in the HCR, and set at a level that 
the WCPFC have considered to be consistent with the UN Fish Stock Agreement.38 
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 the rebuilding targets.  

  Management  measures  to  be  enacted  by  the  HCR  are  clearly  described  by 
WCPFC,  and  consist  of  modifications  to  existing  catch  limits  which  have  a 
reasonable  expectation  of  being  implemented  effectively.  This  clarify  on  how 
management will respond to stock status relative to a reference point, in a pre-
agreed  manner,  is  fundamental  to  the  successful  functioning  of  an  HCR  as  it 
allows management action to be taken rapidly and free of political influence at 
the time.  

Weaknesses 

  The  HCR  is  not  yet  evaluated  using  MSE,  although  this  is  currently  under 
development. The ISC periodically evaluate stock size and exploitation rate with 

37 WCPFC has a 3-tier hierarchical approach (as outlined in SC7-MI-WP-03) to identify key LRPs for key 
target species in the WCPFC. Level 2 is defined for stocks where the stock-recruit relationship 
parameter for steepness (h) is not known well, if at all, but the key biological and fishery variables are 
reasonably well estimated (see https://www.wcpfc.int/harvest-strategy). 

38 

https://www.wcpfc.int/system/files/WCPFC13%20Summary%20Report%20final_issued%202%20March
%202017%20complete.pdf  

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Study on Circular Design of the Fishing Gear for Reduction of Environmental Impacts 

respect  to  the  established  reference  points  and  report  to  the  Scientific 
Committee. Until 2024, while the MSE is being developed, the ISC is requested 
to conduct stock assessments in 2018, 2020 and 2022. With the absence of an 
MSE  process,  there  remains  a  question  of  how  key  uncertainties  have  been 
considered  in  the  design  and  implementation  of  the  HCR,  with  a  risk  that  the 
HCR may ultimately be ineffective.  

  Once the stock is rebuilt, the Northern Committee will recommend conservation 
and management measures as needed to ensure that any target reference points 
are achieved on average in the long term, and ensure that the risk of the stock 
size  declining  below  the  limit  reference  point  (once  adopted)  is  ‘very  low’. 
However, this qualitative term is open to interpretation without clear guidelines 
on what ‘very low’ refers to in probabilistic terms.  

3.2.4  IATTC tropical tunas harvest control rule 

In  2016,  IATTC  adopted  HCR  for  tropical  tunas  based  on  the  interim target  and  limit 
reference  points  adopted  in  2014  (Resolution  C-16-02)39.  The  HCR  aims  to  prevent 
fishing  mortality  from  exceeding  the  MSY  level  for  the  tropical  tuna  stock  (bigeye, 
yellowfin  or  skipjack  that  requires  the  strictest  management.  If  fishing  mortality  or 
spawning biomass (for any of the three stocks) are approaching the corresponding limit 
reference  point  (i.e.  0.08*SSB0)  with  a  probability  of  10%  or  greater,  the  HCR  also 
triggers  the  establishment  of  additional  management  measures  to  reduce  fishing 
mortality and rebuild the stock. 

The  HCR  recommended  by  the  scientific  staff  for  the  purse  seine  fishery  for  tropical 
tunas was adopted in accordance with the following principles:  

a)  The  scientific  recommendations  for  establishing  management  measures  in  the 
fisheries  for  tropical  tunas,  such  as  closures,  which  can  be  established  for 
multiple  years,  shall  attempt  to  prevent  the  fishing  mortality  rate  (F)  from 
exceeding  the  best  estimate  of  the  rate  corresponding  to  the  maximum 
sustainable yield (FMSY) for the species that requires the strictest management. 

b)  If  the  probability  that  F  will  exceed  the  limit  reference  point  (FLIMIT)  is  greater 
than  10%,  management  measures  shall  be  established  as  soon  as  is  practical 
that have a probability of at least 50% of reducing F to the target level (FMSY) or 
less, and a probability of less than 10% that F will exceed FLIMIT. 

c)  If the probability that the spawning biomass (S) is below the limit reference point 
(SLIMIT) is greater than 10%, management measures shall be established as soon 
as  is  practical.  These  measures  shall  have  a  probability  of  at  least  50%  of 
restoring  S  to  the  target  level  (dynamic  SMSY)  or  greater.  In  addition,  the 
measures shall have a probability of less than 10% that S will descend to below 
SLIMIT in a period equivalent to either two generations of the stock or five years, 
whichever is greater.  

d)  For fisheries that use gears other than purse-seine nets, the recommendations 
by  the  IATTC  scientific  staff  on  additional  management  measures  shall  be  as 
consistent as possible with those adopted for the purse seine fishery, while taking 
account of the impact of those fisheries on the species compared to purse seine 
fishery. 

Strengths 

39 https://www.iattc.org/PDFFiles/Resolutions/_English/C-16-02-Harvest-control-rules.pdf  

Page 12 

 
 
 
                                           
  The HCR described in Res. C-16-02 establishes clear definitions for interim limit 
and  target  references  points,  using  both  fishing  mortality  and  biomass-based 
reference points.  

  Res.  C-16-02  requires  that  the  final  adopted  HCR  will  include  pre-agreed 
management actions to be taken under various stock conditions. Pre-agreement 
on  management  actions  is  key  to  successful  application  of  a  HCR.  It  allows 
management  measures,  such  as  reduction  in  TAC,  to  be  implemented  rapidly 
when required, and avoids the need for political decision making at the time. 

  The HCR sets out clear rules, with explicit probability thresholds, for triggering 
management action as the limit reference points (for F and S) are approached. 

Weaknesses 

  The HCR is currently established on an interim basis until it has been assessed. 
The scientific staff of the Commission shall carry out additional assessments of 
these HCRs and alternatives, which will be presented to the Scientific Advisory 
Committee  for  examination  in  order  to  allow  the  Commission  to  adopt  a 
permanent HCR. No timeline for this is given in Res. C-16-02.  

  No  MSE  process  has  been  established,  and  the  HCR  has  not  been  tested  for 
robustness  based  on  the  main  uncertainties  in  the  assessment,  such  as  the 
stock-recruitment relationship, or the ecological role of the stock. As such, there 
is uncertainty in how the HCR will perform in achieving management objectives, 
and any trade-offs between them.   

  While  the  specifications  of  the  HCR  state  that  the  management  measures 
levels  should  be  based  on  scientific 
triggered  by  exceeding  critical 
recommendations relating to the species that requires the strictest management, 
the measures to be used are not explicitly defined. 

  Not clear if probabilities relative to the RPs integrate model uncertainty. 

3.2.5  CCSBT southern bluefin management procedure 

Historically, southern bluefin tuna (SBT) stock has been heavily depleted. To assist in 
its rebuilding, CCSBT has developed a management procedure (MP), which can specify 
changes to the TAC for southern bluefin tuna (SBT) based on updated monitoring data. 
From 2002 to 2011, the CCSBT conducted extensive work to develop an MP in order to 
guide  its  global  TAC  setting  process  for  the  stock.  The  final  MP,  known  as  the  “Bali 
Procedure”, was recommended by the CCSBT’s Scientific Committee in July 2011. The 
procedure is a combination of two preferred MPs, and is a representation of all the work 
scientists had conducted in development. Parameters of the recommended rule can be 
adjusted  to  set  different  time  horizons  for  rebuilding,  and  to  constrain  the  maximum 
TAC changes allowed every time the TAC is updated. The parameters of the MP are as 
follows: 

a.  To rebuild the status of stock to an interim building target reference point of 20% 

of the original spawning stock biomass by 2035;  

b.  The MP shall ensure a 70% probability of achieving the interim rebuilding target;  

c.  The minimum increase or decrease TAC change shall be 100 tonnes;  

d.  The maximum increase or decrease TAC change shall be 3000 tonnes;  

e.  The TAC shall be set for three-year periods, subject to paragraph 7 Resolution 

on Adoption of a Management Procedure40; and  

40 

https://www.ccsbt.org/sites/ccsbt.org/files/userfiles/file/docs_english/operational_resolutions/Resolutio
n_Management_Procedure.pdf  

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Study on Circular Design of the Fishing Gear for Reduction of Environmental Impacts 

f.  The  national  allocation  of  the  TAC  within  each  three-year  period  will  be 
apportioned according to the Resolution on the Allocation of the Global TAC. 

Strengths 

  The “Bali Procedure” sets clear, probability-based objectives for stock rebuilding 
using  an  interim  rebuilding  target  reference  point  and  within  an  explicit  time 
period.  The  probability  of  achieving  the  interim  rebuilding  target  has  been  set 
high (i.e. above 50%) and reduces the risk of the stock not rebuilding within the 
timeframe. In this respect the MP is considered conservative. 

  The  MP  acts  on  a  combination  of  longline  CPUE41  and  scientific  aerial  survey 
data42,  which  covers  both  the  adult  and  juvenile  portions  of  the  stock 
respectively.  The  MP  includes  a  clearly  defined  meta-rule  process  that  pre-
specifies  what  should  happen  in  unlikely  exceptional  circumstances  when 
application of the TAC generated by the MP is considered to be highly risky or 
highly inappropriate. This provision effectively builds greater precaution into the 
MP.  

  The CCSBT tested a variety of candidate MPs with the aid of an operating model 
of the fishery that simulated the characteristics of the southern bluefin stock and 
fishery. The candidate MPs were tested against a range of uncertainties so that 
a robust procedure could be identified. 

  Performance of the MP is assessed regularly, including an annual review of the 
implementation  of  the  current  MP  and  regular  evaluation  of  new  data  sources 
and operating models. 

Weaknesses 

  The current Biomass Random Effects Model underpinning the “Bali Procedure" is 
complex,  potentially  making  it  difficult  to  communicate  to  stakeholders  and 
decision makers. 

41 CPUE data used in the MP is based on longline catch and effort data of Japanese, Australian (Real-Time 

Monitoring Program in the 1990s) and New Zealand (NZ) charter vessels at the shot-by shot resolution. 
Southern bluefin tuna aged 4 years or older are used in the CPUE dataset. 

42 The scientific aerial survey data are estimates of the biomass of SBT patches in the Great Australian Bight 
(GAB) as observed by experienced spotters. The aerial survey is conducted in January through March of 
each year, and consists of an aircraft flying along 15 north-south transect lines running from the coast 
to continental shelf (from 128E to 134E degrees longitude). The survey data consists of distance flown, 
location of sightings, biomass estimates of each school in a sighting, and environmental observations 
that might affect the number and size of sightings, such as sea surface temperature (SST), swell, haze, 
wind speed, and sea shadow. 

Page 14 

 
 
 
                                           
3.3  Sub-task 2.3: Considerations for HCRs accounting for multispecies 

and mixed fisheries 

Tropical  tunas  are  candidates  for  the  implementation  of  multi-species  management 
schemes  in  tuna  RFMOs.  This  sub-task  provides  a  discussion  on  how  HCRs  might  be 
developed considering multispecies interactions in mixed fisheries. For this, a review of 
HCRs used for mixed fisheries in International Council for the Exploration for the Seas 
(ICES) is provided. This review identifies and describes a number of HCRs that are of 
relevance  to  the  development  of  multispecies  HCRs  for  tuna  fisheries.  Also,  the 
information available for tuna fisheries management is reviewed and, finally, three types 
of multispecies HCRs are presented (Catch based, effort based and fleet based). 

3.3.1  Review  of  HCRs  used  for  mixed  fisheries  in  non-tuna  management 

systems 

The  ICES  Working  Group  on  Mixed  Fisheries  Advice  (WGMIXFISH)  produced  mixed 
fisheries  forecasts  for  the  North  Sea,  the  Celtic  Sea  and  the  Iberian  waters  in  2017 
(ICES, 2017a). All forecasts are based on the Fcube methodology (Iriondo et al., 2012) 
and  a  range  of  potential  management  scenarios  relevant  for  the  specific  regional 
fisheries. The model uses the output of the single stock assessments and evaluates the 
consequences  of  different  management  options  (e.g.  TACs  per  stock  and/or  effort 
allocations by fleet). The model uses catch information at métier and fleet levels. Fcube 
produces catch advice for multiple stocks following a series of rules or scenarios (Table 
2), including two types of multispecies HCR (Catch and effort based multispecies HCRs). 
These scenarios were analysed with the Fcube approach by the WGMIXFISH in different 
case studies: North Sea, Celtic Sea and Iberian waters. The main conclusion was that 
the most precautionary scenario impedes the maximization of fisheries potential while 
others cause overfishing. 

Table 2: Catch advice scenarios for multi-stock management of fisheries in ICES 
(WGMIXFISH). 

Scenarios 

Abbreviation 

Explanation 

Maximum  

max 

Minimum  

min 

For each fleet, fishing stops when all stocks have been 
caught up to the fleet’s stock shares†. This option 
causes overfishing of the single-stock advice 
possibilities for most stocks.  

For each fleet, fishing stops when the catch for any 
one of the stocks meets the fleet’s stock share. This 
option is the most precautionary option, causing 
underutilization of the single-stock advice possibilities 
of other stocks.  

Stock 

stock 

All fleets set their effort corresponding to their hake 
quota share, regardless of other catches.  

Status quo 
effort  

Economic 
value  

sq_E 

Val 

The effort is set equal to the effort in the most recently 
recorded year for which landings and discard data are 
available.  

The effort by fleet is equal to the average of the efforts 
required to catch the quota of each of the stocks, 
weighted by the historical catch value of that stock.  

† In WGMIXFISH, the term “fleet’s stock share” or “stock share” was used to describe the share of the 
fishing opportunities for each particular fleet, which was calculated based on the single-stock advice for 
2018 and the historical proportion of the stock landings taken by the fleet.  

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Study on Circular Design of the Fishing Gear for Reduction of Environmental Impacts 

When  fluctuating  around  MSY  catch  remains  in  a  relatively  low  range  and  this  is  the 
cornerstone of the concept of Pretty Good Yield (PGY) (Hilborn, 2010). PGY refers to a 
range of policies that provide good yield while also producing other desired outputs. The 
fraction of the single stocks’ MSY used to define the range of multispecies PGY is a trade-
off between the maximization of total catch from a variety of stocks and sustainability 
objectives. The most recent WGMIXFISH tested a series of multispecies HCRs combining 
a range of fishing mortality levels corresponding to MSY (FMSY) estimated by ICES for 
single stocks. For  example, a HCR that generates multispecies  TAC using the highest 
possible fishing mortalities for each stock was explored for demersal mixed fisheries off 
Iberian waters. Results show that the multispecies HCR makes a more adequate use of 
the  existing  fishing  opportunities  while  the  stocks  biomass  is  maintained  above 
reference levels.  

In the Faroe Plateau mixed fisheries, the management based on TAC failed to achieve 
the objective of an average annual fishing mortality for three gadoid stocks (Baudron et 
al.  2010;  ICES  2016).  Baudron  et  al.,  (2010)  developed  a  management  strategy 
evaluation  model  to  compare  an  effort-management  system  based  on  the  Faroese 
example with a TAC system as currently applied in EU fisheries. Results show that when 
the stocks are considered together in mixed fisheries, effort management seems to be 
appropriate,  and  inter-annual  flexibility  of  the  system  appears  to  be  the  best 
compromise  between  short-  and  long-term  objectives,  as  well  as  between  biological 
sustainability  and  economic  return.  Thus,  in  1996,  an  effort  based  regulation  system 
(days-at-sea)  was  established  aiming  at  reducing  discards  and  defining  a  simpler 
fisheries  management  administration.  However,  the  system  failed  at  adequately 
estimating  effort  and  fishing  mortality  for  the  target  stocks  (Nielsen  et  al.,  2006; 
Jákupsstovu  2007;  Christensen  et  al.,  2009;  Baudron  et  al.,  2010;  ACOM  2012; 
Búskaparráðið,  2010).  Nevertheless,  the  management  system  has  improved  in  the 
recent  years  towards  a  global  fisheries  management  plan  aiming  at  achieving  a 
multispecies MSY by modulating the overall fishing effort. 

3.3.2  Overview of ICCAT tropical tuna fisheries as a paradigmatic example of 

multi-species management 

The  information  available  in  the  ICCAT  website43  is  used  for  the  characterization  of 
Atlantic Ocean tropical tuna fisheries (bigeye, yellowfin and skipjack). The data explored 
include time series of catch per fishing operating mode and size distribution taken from 
the ICCAT website (Task II  Catch and Effort statistics (T2CE) and CATDIS).  The data 
using the fishing operating modes of Fish Aggregation Devices (FAD) or free school (FS) 
are  from  1991  to  2015,  stratified  in  time  and  space,  and  the  data  from  longliners 
correspond to the period between 1950 and 2015. The analyses of the time series of 
catch per gear are done by the working groups responsible of each stock’s assessments 
(Anon. 2015; Anon. 2016; Anon. 2017).  

The  annual  composition  of  nominal  catches  for  each  of  the  fishing  operating  modes 
targeting  tropical  tunas  is  shown  in  Figure  4.  Approximately  80%  of  the  catch  from 
purse  seines  using  FADs  corresponds  to  skipjack  tuna,  while  for  FS  more  than  75% 
corresponds  to  yellowfin.  With  regards  to  fleets  using  longlines,  the  proportion  of 
catches  has  shifted  since  1950s,  when  catch  consisted  mostly  on  yellowfin  to  more 
recent times where bigeye represents more than 75% of the total catch.  

43 www.iccat.int 

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Figure 4: Yearly time series of the species catch composition with different operating 
fishing mode: a) purse seiners using FADs b) purse seiners fishing free swimming 
school and c) longliners. Data source: ICCAT Task II Catch and Effort statistics (T2CE) 
and CATDIS. 

De Finetti triangles (Figure 5) show that for purse seines using FADs catch corresponds 
to skipjack (60-80%), bigeye (0-10%) and yellowfin (10-30%). The plots also show that 
free  school purse  seines and longlines are monospecific, i.e. different species  are not 
caught simultaneously. Longlines catch yellowfin or bigeye and purse seines operating 
over free schools catch yellowfin. 

Figure 5: De Finetti triangles for: a) purse seiners using FADs b) purse seiners fishing 
free swimming schools and c) longline. Based on method described in Fonteneau et 
al., (2010). 

Figure 6 show the differences on the spatial distribution of the main catches of Purse 
seiners and longliners. The main catches of purse seiners are closer to the coast than 
for longliners and their catch composition is also different as it is shown in Figure 5. 
The purse seiners catch composition is mainly skipjack when is fishing with FADs and 
yellowfin tuna when is fishing with free swimming schools, while for longliners most of 
the catches are bigeye tuna. 

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Study on Circular Design of the Fishing Gear for Reduction of Environmental Impacts 

Figure 6: Geographical catch composition estimated with weighted mean (with the 
total landings). The size of the pie is defined with the historical total catch in each 
area: a) purse seiners using FADs b) purse seiners fishing free swimming schools and 
c) longline. Data source from ICCAT CATDIS. 

Overall, purse seines using FADs catch smaller individuals of bigeye and yellowfin than 
purse seines targeting free schools (Fonteneau et al., 2013). The size distributions of 
the three  species caught using  Drifting FADs (DFAD) show a similar mode  around 45 
cm, with few individuals larger than 70 cm while individuals smaller than 40 cm observed 
only for skipjack (Figure 7). Longliners fish more mature bigeye than purse seiners being 
the mode at around 125 cm (Fonteneau et al., 2013). 

Figure 7: a) Relative size-frequency distribution (in numbers) for yellowfin, skipjack 
and bigeye tunas captured by purse seine fisheries on drifting FADs b) Relative size-
frequency distributions of bigeye on longliners and DFAD (Fonteneau et al., 2013).  

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3.3.3  Options for Multispecies HCRs for tropical tunas (Catch, effort and fleet 

based managements) 

World’s  tuna  stocks  are  currently  managed  in  single  stock  frameworks.  When  two  or 
more stocks are caught simultaneously, the mismatch between the catch profiles of the 
fleets  and  the  single  stock  advice  can  produce  an  incentive  to  generate  over-quota 
discards (Ulrich et al., 2011). However, the mismatch between single stocks’ TAC could 
be avoided by using multi-stock harvest control rules. In 2015 the European Commission 
(EC)  proposed  MSY  fishing  mortality  ranges  as  a  complement  to  the  MSY  fishing 
mortality  point  estimates  to  provide  flexibility  to  the  mixed-fisheries  management 
frameworks: the objective is to produce consistent TAC advice between stocks within 
the fishing mortality ranges, and to avoid the presence of choke or limiting species. The 
range of fishing mortalities compatible with an MSY approach were defined as the "range 
of fishing mortalities leading to no less than 95% of MSY and which were precautionary 
in the sense that the probability of spawning stock biomass (SSB) falling below the limit 
biomass reference point in a year in long-term simulations with fixed fishing mortality 
was less than 5% (ICES, 2016a)".  

3.3.4  Catch based management 

The framework of the fishing mortality ranges defined by the EC in 2015 is the starting 
point  for  the  definition  of  a  multi-stock  catch  based  HCR  (Garcia  et  al.,  2016).  The 
objective of the HCR is to avoid over-quota discards and to maximize the overall catch 
while ensuring the sustainability of the stocks.  

A multi-species HCR should fulfill the following properties: 

1.  Produce compatible catch advice among the stocks. 

2.  Take the most out of fishing opportunities (catch). 

3.  Result in fishing mortality levels compatible with the MSY ranges defined by the 

EC. 

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Study on Circular Design of the Fishing Gear for Reduction of Environmental Impacts 

1.  Compatible catch advice 

A linear relationship between fishing mortality and Effort is assumed, with catchability 
(q) as a proportionality parameter (F = q x Effort). For a compatible fishing mortality 
advice (Fadvst), the current fishing mortalities (Fsqst) are multiplied by a parameter (μ). 
Mathematically: 

Fadv𝑠𝑡 =  𝜇 ∙ Fsq𝑠𝑡 

where st denotes each of the stocks and 𝐹adv the fishing mortality that will correspond 
with the TAC advice. μ is defined so that the HCR fulfills the second and third properties. 

2.  Take the most out of fishing opportunities 

If the 𝐹adv of a given stock is equal or higher than the corresponding fishing mortality at 
MSY  (𝐹msy)  for  that  stock,  all  the  fishing  opportunities  corresponding  with  MSY 
framework will be used. Then, 𝜇0 will be used defined as: 

𝜇0 = max (

Fmsy𝑠𝑡
Fsq𝑠𝑡

) 

Fadv𝑠𝑡 =  𝜇0 ∙ Fsq𝑠𝑡   

And Fadvst will be equal to:  

3.  Compatible with MSY ranges 

In ICES Fmsy ranges are estimated for each of the stock defined as the range of 
fishing mortalities leading to no less than 95% of MSY and with a probability of 5 % of 
SSB falling below Blim in a year in long-term simulations with fixed. Thus, the F advice 
in the previous step could be higher than the upper bound of the fishing mortality 
range of some stocks. Hence, a second multiplier is applied to ensure that 𝐹adv falls 
within the ranges for all the stocks, i.e.: 
For any stock:  

 𝐹adv𝑠𝑡 = {

𝜇1 ∙ 𝜇0 ∙ Fsq𝑠𝑡 = min (

) ∙ 𝜇0 ∙ Fsq𝑠𝑡

Fadv0,𝑠𝑡 = 𝜇0 ∙ Fsq𝑠𝑡
Fupp𝑠𝑡
Fadv0,𝑠𝑡

if     𝜇0 ∙ Fsq𝑠𝑡 ≤ 𝐹upp𝑠𝑡 for all 𝑠𝑡,

if for any  𝑠𝑡     𝜇0 ∙ Fsq𝑠𝑡 > 𝐹upp𝑠𝑡

. 

where Fupp is the upper bound of fishing mortality range. 

In  a  TAC  management  system, 𝐹adv𝑠𝑡  is  translated  afterwards  in  catch  using  the 
corresponding catch production function (i.e. Baranov catch equation (Baranov, 1918)).  

4.  Stocks without analytical assessment. 

The stocks without analytical stock assessment, but subject to TAC and quota system, 
can be introduced in the framework of the multi-stock HCR if we assume mathematical 
relationship between the variation on the fishing mortality of the rest of the stocks and 
the  variation  on  the  catch  of  this  stock.  The  simplest  model  is  to  assume  that  the 
the 
variation 
decrease/increase of the fishing mortality of the rest of the stocks, i.e.: 

the  stock  decreases/increases 

the  catch  of 

linearly  with 

in 

𝐶𝑎𝑑𝑣𝑠𝑡 = 𝜇 ∙ 𝐶𝑠𝑞𝑠𝑡  

Then, the role of this stock in the equations in points 1, 2 and 3 is the equivalent to the 
role of the rest of the stocks but using catch instead of fishing mortality in status quo 
and target levels. Furthermore, to provide some flexibility to the system the advice of 
the stock should be accompanied by a catch range. 

3.3.5  Effort based management 

Effort based management is a potential alternative to TAC based management in mixed 
fisheries systems (Hauge and Wilson, 2009; Hegland and Hopkins, 2014). Effort based 

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management overcomes the problem of multi-stocks quota mismatch and hence, with 
over-quota discards. However, the correct implementation of this type of management 
requires a series of conditions: 

  The effort metric should be representative of the fishing capacity of the fleets.  

  Effort based management  incentives the increase of catchability, the so  called 
technological or effort creep and therefore, this will need to be taken into account 
when the relation between stock status and fishing effort is defined. 

The catch based HCR is also the foundation of the effort based management systems. 
In  this  case,  the  multiplier,  𝜇  in  the  formulation  of  the  multi-stock  HCR  should  be 
translated into effort using a pre-defined effort-fishing mortality relationship.  

3.3.6  Fleet based management 

Independently if the management is done in terms of effort or catch, the success of the 
harmonization of single stock TAC advices will depend on how homogeneous the fishery 
is  in  terms  of  fleet  specific  catch  profiles.  In  a  very  heterogeneous  fishery  with  very 
different catch profiles among fleets, consistent catch advice among stocks can only be 
obtained if the harmonization is performed at fleet or fishing mode level. Furthermore, 
when  the  harmonization  is  done  at  fishery  level,  there  could  be  cases  of  unjustified 
favors or penalties to individual fleets. For example, let’s take the case of a fishery with 
two fleets, one that catches only one stock and a second one that catches several stocks 
simultaneously. If the multi-stock HCR was applied and the TAC of the stock targeted 
by the single-stock fleet was decreased in order to harmonize the TACs, the catch-quota 
of the single-stock fleet would decrease automatically and the fleet would be penalized. 

The partial fishing mortality at fleet level, i.e. the fishing mortality applied by each fleet 
(or fishing mode), is defined as the product of the total fishing mortality and the ratio 
between fleet’s catch and total catch, that is: 

𝐹𝑓𝑙 =

𝐶𝑓𝑙
𝐶𝑡𝑜𝑡𝑎𝑙

∙ 𝐹 

The multi-stock catch based HCR can be applied at fleet level using the partial fishing 
mortalities of the stocks exploited by each of the fleets and dividing the target fishing 
mortality among fleets for each of the stocks.   

Fishing mortality is a function of fishing effort and catchability:  

𝐹𝑠𝑡,𝑓𝑙 = 𝜑(𝐸𝑓𝑙, 𝑞𝑠𝑡,𝑓𝑙) 

where  𝐸  denotes  effort  and  𝑞  catchability.  Therefore,  the  fishing  mortality  can  be 
modulated by both a variation of fishing effort or by a variation in catchability. Hence, 
a  target  fishing  mortality  could  be  achieved  by  varying  any  of  the  two  variables.  For 
example, in the case of the purse seiners operating on FADs, a reduction in the number 
of  FADs  is  expected  to  also  reduce  the  overall  catchability  of  the  fleet  if  the  other 
conditions  (e.g.  FAD  size,  effort)  remain  unchanged.  However,  depending  on  the 
definition of the effort (e.g. fishing days, fishing days*number of FADs) the number of 
FADs  could  be  part  of  the  effort  and  not  of  the  catchability.  In  this  case,  the  overall 
selectivity of the fleet on the stocks (the component of the catchability related with the 
size of the individual fishes) will change and therefore their MSY-based reference points 
will change too (Scott and Sampson, 2011).   

Fadv𝑠𝑡 =  𝜇 ∙ Fsq𝑠𝑡   = 𝜇 ∙ ∑ 𝜑(𝑞𝑠𝑞,𝑠𝑡,𝑓𝑙, 𝐸𝑠𝑞,𝑓𝑙)

𝑓𝑙

If a linear relationship is assumed between fishing mortality and effort, i.e.: 

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Study on Circular Design of the Fishing Gear for Reduction of Environmental Impacts 

Fadv𝑠𝑡 =  𝜇 ∙ Fsq𝑠𝑡   = 𝜇 ∙ ∑ 𝑞𝑠𝑞,𝑠𝑡,𝑓𝑙 ∙ 𝐸𝑠𝑞,𝑓𝑙

𝑓𝑙

where 𝑞, the catchability, is the proportionality parameter. In this case varying fishing 
mortality by  𝜇 is analogous to vary fishing effort, given that catchability 𝑞 is maintained 
constant. One of the problems of effort based management is the technological (Marchal 
et  al.,  2007)  creeping,  for  example  increases  in  catchability  through  increases  in  the 
number  of  FADs,    this  should  be  avoided  to  ensure  a  correct  implementation  of  the 
fishing mortality advice. If the relationship between fishing mortality and effort were not 
linear  and  different  depending  on  the  fleet,  in  that  case,  the  relationship  could  be 
described including a fleet dependent elasticity parameter on effort, 𝛼𝑓𝑙, in the model: 

𝛼𝑓𝑙
Fadv𝑠𝑡 =  𝜇 ∙ Fsq𝑠𝑡   = 𝜇 ∙ ∑ 𝑞𝑠𝑞,𝑠𝑡,𝑓𝑙 ∙ 𝐸𝑠𝑞,𝑓𝑙

𝑓𝑙

This means that the variation in effort would have different impact on fishing mortality 
depending on the fleet due to the 𝛼𝑓𝑙. For example if the alfa value for a given stock and 
fleet1  is  equal  to  1  (linear  fishing  mortality)  but  2  for  fleet2  (potential  relationship). 
Then  a  reduction  of  10%  of  in  the  Fadv  for  fleet1  would  mean  an  advice  in  effort  of 
0.9Esq, but for stock 2 it would mean an effort of sqrt(0.9)*Esq,fl2. 

However,  if  𝛼  depends  on  the  stock  the  formulation  of  the  multistock  HCR  could  be 
difficult to be implemented in an effort based management system because a common 
variation in fishing mortality for the stocks would not correspond to the same variation 
fishing effort at fleet level. 

Now if we think that at the same time we want simultaneously a reduction of 10% in 
effort for stock 2 where the alfa value of stock 2 is lineal, that would mean a reduction 
of effort of 10%, so 0.9Esq,fl1. So that would means two different advices on effort to 
the same fleet in order to have the same impact on the F of two stocks. 

3.3.7  Discussion 

Multispecies  fisheries  management  can  be  applied  using  catch  and  effort  limits.  Both 
types  feature benefits and shortcomings.  In this chapter we have focused  on tropical 
tuna fisheries, generally captured by European purse seiners with free school and FAD 
sets. For example, in the Indian Ocean, purse seiners mostly capture adult individuals 
of yellowfin on free schools and young individuals with FADs. The catch on free schools 
is almost entirely composed by yellowfin whereas the catch in FADs is mostly composed 
by skipjack and yellowfin juveniles. Currently, Indian Ocean yellowfin is considered to 
be overexploited and subject to overexploitation and skipjack is estimated to be at its 
target  RP  (40%  depletion).  In  the  Atlantic,  bigeye  is  overexploited  and  subject  to 
overexploitation and there are no signs of overexploitation for skipjack. 

In general, when using catch limits, a quasi real time monitoring of catch is necessary. 
This can be difficult however, as highlighted by IOTC’s Working Party on Data 
Collection and Statistics and Scientific Committee in 2017 (IOTC, 2017d). This is 
because there is a time lag between landings and the effective sampling of catch. The 
problem is that until catch is monitored there is no accurate accounting of the catch of 
each species and therefore the catch of yellowfin can only be estimated. This can 
cause problems of non-compliance if the excess of catch is not detected or to 
premature closures if catch is overestimated. In this case, alternative management 
measures would facilitate the control and monitoring of tropical tuna fisheries. The 
difficulties in monitoring catch will also worsen the catch statistics used in tropical tuna 
fisheries stock assessments. Improving the monitoring of catch is possible but would 
require the investment of additional human and technical resources. 

Page 22 

 
 
 
 
 
 
 
 
European purse seiners using FADs capture young individuals of yellowfin together with 
skipjack and, in some cases, with bigeye. However, the scientific advice in the form of 
stock  status,  reference  points  and  catch  projections  are  provided  in  a  single  species 
basis. In multispecies fisheries it is not possible to apply different levels of fishing effort 
to  two  or  more  species  that  are  vulnerable  to  the  same  fishing  gear  and  inhabit  the 
same habitat. According to the FAO Code of Conduct for Responsible Fisheries and other 
international agreements, discards are generally considered a waste of fish resources 
and inconsistent with responsible fisheries (FAO, 1995). ICCAT, in its ICCAT Information 
on  By-Catch  of  Tuna  Fisheries  (available  via  iccat.int)  also  calls  for  a  reduction  of 
discards.  Also,  specifically  in  ICCAT,  according  to  Recommendation  17-01,  it  is 
prohibited to discard any bigeye, yellowfin or skipjack captured in the Atlantic. In the 
IOTC, Resolution 17/04 also bans discards of bigeye tuna, skipjack tuna, yellowfin tuna, 
and non-targeted species caught by purse seine vessels in the IOTC area of competence. 
In tropical tunas, when the catch limit for one stock, (yellowfin in the IOTC or bigeye in 
ICCAT) is reached (choke species) but not for the others, fleets will stop their fishing 
operations. In that case, the catch limits for skipjack for example will not be reached 
with  the  associated  loss  of  opportunities  for  the  fishing  fleets  and  other  undesirable 
socioeconomic  consequences.  The  later  include  loss  of  food  production,  shortages  to 
canneries and potentially price increases due to a lower supply at international markets.  

Additionally,  species  like  tunas  feature  a  very  variable  recruitment.  In  general,  TAC 
based management requires accurate estimates of  stock status,  reference points and 
recruitment  when  catch  limits  are  set.  Should  the  biomass  and  recruitment  be 
underestimated,  catch  limits  will  be  reached  sooner  than  expected  and  fishing 
opportunities would be wasted unless the choke species is discarded. On the contrary, 
if stock biomass is overestimated, when managing with fixed catch limits, biomass will 
continue to decline as fishing mortality will increase. In this regard, effort controls are 
a  more  flexible  way  to  deal  with  multispecies  fisheries  since  they  can  reconcile 
conservation objectives of two or more stocks when they are set for the most vulnerable 
stock, in this case bigeye.  

Fishing effort limits are restrictions on the intensity of use of the fishing gears. These 
can include limits to the period of the fishing season, which is relatively easy to enforce 
through vessel monitoring systems (VMS), use of logbooks and other measures. Also, 
fishing effort control reduces the need for a real time monitoring of catch which is often 
difficult and expensive. Effort controls represent a flexible option to seek for achieving 
management objectives of multispecies fisheries. Effort control is particularly adequate 
for  stocks  which  assessments  remain  subject  to  uncertainty.  Under  effort  control 
systems,  it  is  no  longer  necessary  to  estimate  the  fishable  biomass  accurately  every 
year, as the level of fishing mortality is restrained directly, irrespective of the continual 
fluctuations of stock size by controlling the level of fishing effort. Effort will be adjusted 
periodically and progressively towards meeting the target reference points. With effort 
controls,  as  biomass  of  the  most  vulnerable  species  fluctuates  following  recruitment 
variability, the catch obtained when applying the effort limits will change proportionally, 
giving  automatic  feedback  control  and  allowing  for  meeting  management  objectives. 
Hence,  when  the  abundance  declines  or  increases,  the  catch  will  correspondingly 
decrease or increase. Also, the effort limits will facilitate the adequate management of 
the  less  vulnerable  stock.  For  an  effort  control  to  be  effective,  it  is  important  to 
understand  and  adequately  estimate  catchability  dynamics  of  the  fishing  gears.  It  is 
particularly important and critical to adequately incorporate the impact of effort creep 
as a result of technological improvement. In brief, in order to be effective, effort based 
management  would  require  a  tight  control  on  fleets’  technological  capacity  and 
catchability. In cases where fishing capacity increases, the fishing mortality produced 
with  a  given  effort  could  be  higher  than  expected  and  thus,  compromise  the 
sustainability of the stocks. 

History of TAC vs effort-based management in ICCAT, WCPFC and IATTC 

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Study on Circular Design of the Fishing Gear for Reduction of Environmental Impacts 

IATTC’s Resolution C-17-02 Conservation measures for tropical tunas in the Eastern 
Pacific Ocean during 2018-2020 and amendment to Resolution C-17-01, WCPFC CMM-
17-01: Conservation and Management Measure for bigeye, yellowfin and skipjack tuna 
in the Western and Central Pacific Ocean and ICCAT Recommendation 16-01: 
Recommendation by ICCAT  on a Multi-Annual Conservation and Management Program 
for Tropical Tunas.   

From the above, only ICCAT uses TACs or overall catch limits for all the fleets involved 
in tropical tuna fisheries. That is the case for Atlantic bigeye and yellowfin that 
together with Indian Ocean yellowfin and skipjack are the only tropical stocks 
managed through an overall TAC system. Last year both yellowfin and bigeye catch 
limits established in ICCAT were exceeded. In this way the approach followed in ICCAT 
and IOTC has not been able to reduce the fishing mortality to recommended levels 
due to lack of compliance to catch limits. IATTC and WCPFC apply output controls 
(TAC) only for longline fleets targeting bigeye tuna. In the Pacific, purse seine fleets 
activity is regulated through effort limits (the days of the fishing season). The IATTC 
uses an effort based pseudo-HCR to determine the number of fishing days that purse 
seines are permitted to fish in order to achieve MSY.  

In February 2017 the IATTC attempted to introduce catch limits for bigeye and 
yellowfin catch from purse seine fleets operating with FADs and an additional catch 
limit for yellowfin from dolphin associated fisheries. These measures aimed at 
mitigating the potential impact of the recent increase in capacity on the current status 
of bigeye and yellowfin stocks. The overall catch limit for 2017 corresponded to the 
average catch observed during 2013-2015 for both species combined. The attempt to 
introduce catch limits for the IATTC yellowfin and bigeye fisheries was shortly proven 
problematic and it had to be amended by a new measure, C-17-02, only 5 months 
after its entry into force. The reason for this was that, the purse seine fleet fishing on 
FADs had reached 80% of the total annual catch limit by mid-July, probably due to 
abnormally large recent recruitments that led to a higher than expected proportion of 
yellowfin and bigeye in FAD sets. If this measure hadn’t been amended, the FAD 
fishery would have been closed by August or early September, with dramatic 
consequences for purse seine fleets. The new measure, adopted in July 2017, 
eliminated the catch limits and incorporated 10 additional days of purse seine closure 
which resulted in a total of 72 days of closure. 

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4  TASK 3: MANAGEMENT STRATEGY EVALUATION (MSE) 

4.1.1  Sub-task 3.1: Provide an analysis of management strategy evaluation in 

tuna RFMOs 

Management Strategy Evaluation (MSE), i.e. the evaluation of management strategies 
using simulation, is considered to be the most appropriate way to evaluate the trade-
offs achieved by alternative management strategies and to assess the consequences of 
uncertainty for achieving management goals (Punt et al., 2016). 

MSE  involves  using  simulation  to  compare  the  relative  effectiveness  for  achieving 
management  objectives  of  different  combinations  of  (i)  data  collection  schemes,  (ii) 
methods of analysis and (iii) subsequent process leading management actions (Punt et 
al., 2016), i.e. different MPs. MSE requires developing a series of basic steps (Punt et 
al., 2016; Rademayer et al., 2007): 

1.  Identification  of  management  objectives  and  representation  of  these  using 

quantitative performance statistics. 

2.  Selection of hypotheses of system dynamics: a range of hypotheses concerning 
data, biological information, environmental impact or any other factor that may 
be considered a source of uncertainty in relation to system dynamics. 

3.  Constructing  Operating  Models  (OM): 

these  provide  a  mathematical 
representation  of  the  system  that  is  being  managed  (fish  and  fisheries).  The 
impact of the management measures decided through the HCRs in the MP will 
be  evaluated  in  the  OMs.  These  OMs  are  considered  to  be  alternative 
representations of the “true” dynamics of the stock. 

4.  Defining  Management  Procedures  (MP):  this  includes  data  used,  methods  of 

analysis and decision frameworks (e.g. Harvest Control Rules).  

5.  Simulation of the application of each management strategy or MP. 

6.  Summary  and  interpretation  of  performance  statistics:  this  may  lead  to 
refinement  of  the  relative  weighting  of  the  management  objectives  as  the 
simulation  process  develops  and  continues  to  provide  more  refined  (tuned) 
results to inform the quantitative trade-offs among competing goals. 

The five tuna RFMOs have carried out some type of MSE work, including consultation on 
management  objectives,  characterization  of  uncertainty  of  stocks’  dynamics  and 
observation, and evaluation of harvest strategies. Most of the MSE conducted  to date 
has been developed by the RFMO science providers with seldom direct mandate from 
the Commissions. However, in the recent times, all RFMOs have scheduled consultation 
and  dialogue  towards  addressing  the  different  steps  required  to  complete  the  MSE 
process.  In  this  section  we  review  the  steps  towards  the  development  of  MSE 
frameworks  and  the  adoption  of  MPs  (also  named  Harvest  Strategies,  HSs)  including 
HCRs in the five tuna RFMOs. Also, we review a series of recent global initiatives that 
are contributing to the MSE process across t-RFMOs.  

4.1.1.1  International Commission for the Conservation of Atlantic Tunas (ICCAT) 

SCRSs  Working  Group  on  Stock  Assessment  Methods  (WGSAM)  has  fostered  the 
development of MSE under the principles of the Precautionary Approach for tuna stocks 
in  the  Atlantic  since  2010  (ICCAT  2010).  This  development  has  been  followed  by 
successive recommendations by ICCAT Commission on which the development of MSE 
has been requested to evaluate HCRs consistent with ICCAT Commission objectives and 
decision  making  principles  (ICCAT  2015a).  To  date,  MSE  has  substantially  been 
developed for bluefin and North Atlantic albacore stocks.  

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ICCAT has placed a high priority on the completion of the MSE workplan for bluefin tuna. 
This includes  developing  new  and/or  improved  assessment  methods  for  this  stock  by 
the GBYP Core Modelling and MSE Group, which was created for this purpose in 2014 
(ICCAT,  2014).  This  group  has  structured  a  workplan  in  five  components:  1.  data 
collation,  management  and  synthesis;  2.  Review  and  selection  of  alternative  stock 
assessment models; 3. Development of MSE modeling platform; 4. Capacity building in 
Harvest Strategies, Reference Points and MSE; and 5. Consultation and engagement in 
design and evaluation of Harvest Strategies. 

Also in ICCAT, a specific Call for Tenders is supporting the MSE development for the two 
bluefin stocks. In the specific bluefin MSE meeting (Madrid, 16-20 April) different options 
for  Operating  Models  and  Management  Procedures  were  discussed.  The  current  MSE 
developed so far, considers a single stock of Atlantic bluefin with mixing between the 
Eastern and Western regions. With regards to the MPs, only empirical indicator based 
MPs were preliminary tested. Currently, there are ongoing discussions on the adequacy 
of the current OMs and further MP tests will be carried out in September 2018.  

With  regards  to  North  Atlantic  albacore  MSE,  this  has  been  developed  specifically  to 
allow  the  adoption  of  a  HCR  for  this  stock  in  2017  as  requested  by  the  Commission 
(ICCAT  2016b).  The  preliminary  and  draft  evaluations  of  HCRs  were  refined  in  2017 
using MSE (Merino  et al., 2017b). The technical group that has  carried out this work 
used  a  specifically  tailored  MSE  to  accommodate  a  Management  Procedure  that  is 
comparable  to  the  latest  assessment  of  this  stock  (ICCAT  2016c),  i.e.  simulating  the 
catch  data  and  CPUE  series  used  for  the  assessment  together  with  the  same  model 
(biomass dynamic model) and model specifications (same starting values (r = 0.2, K = 
10,000), shape of production function and bounds to parameter estimates). This work 
has  also  covered  the  uncertainty  inherent  to  this  fishery  through  a  range  of  age 
structured population dynamics, with options for natural mortality, steepness, dynamic 
catchability and available information as the Operating Models (Merino et al., 2017a). 

The technical work that has been produced under the SCRS has been communicated to 
stakeholders  through  the  Standing  Working  Group  on  Dialogue  between  Fisheries 
Scientists and Managers (SWGSM)(ICCAT 2015b; ICCAT 2017c) and the ICCAT’s Panel 
2 (Northern temperate tunas) (ICCAT 2016a). These meetings have helped defining the 
management objectives and the performance measures to evaluate the ability of MPs 
to  achieve  them.  For  example,  in  ICCAT’s  Recommendation  16-06  the  management 
objective for this stock is specified as to maintain the stock in the green quadrant of the 
Kobe plot with at least 60% of probability, while maximizing long‐term yield from the 
fishery  and  catch  and  effort  stability  (ICCAT  2016b).  Both  dialogue  platforms  have 
allowed  the  refinement  of  the  evaluation  of  HCRs  for  North  Atlantic  albacore  and 
discussing the development of bluefin MSE. Also, the SCRS has scheduled a workplan 
to complete the MSEs for North Atlantic albacore, swordfish, bluefin and tropical tunas 
(ICCAT 2017b) that has been endorsed by ICCAT’s Commission.   

In  November  2017,  based  upon  the  results  of  the  HCR  evaluation  for  North  Atlantic 
albacore, ICCAT adopted a model based HCR for this stock (Recommendation 17-04). 
The control parameters of the HCR  are the  following: a) BTHRESH=BMSY, BLIM=0.4*BMSY, 
FTAR=0.8*FMSY and FMIN=0.1*FMSY. In addition, the catch limits will not exceed the 50,000 
t to avoid adverse effects of potentially inaccurate stock assessments and the maximum 
change in the catch limit shall not exceed 20% of the previous recommended catch limit 
when  Bcurrent≥BTHRESH.  This  HCR  has  been  evaluated  to  achieve  the  management 
objective  of  maintaining  the  stock  in  the  green  quadrant  of  the  Kobe  plot  with  more 
than 60% probability. 

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Figure 8: Harvest Control Rule adopted for North Atlantic albacore (ICCAT, 2017a). 

4.1.1.2  Indian Ocean Tuna Commission (IOTC) 

The Working Party on Methods (WPM) of the IOTC started a workplan to evaluate MPs 
for albacore, bigeye, yellowfin and skipjack in 2012. Since then, a small ad-hoc working 
group  has  been  tasked  to  develop  MSE  works  and  to  report  the  IOTC  Commission 
through MP dialogue meetings specifically scheduled during IOTC Annual and Scientific 
Committee meetings. This ad-hoc or informal working group has annually reviewed the 
technical development of the MSE simulation frameworks developed in the IOTC. Also, 
the IOTC has established a dedicated Technical Committee of Management Procedures 
(TCMP)  as  a  formal  communication  channel  between  science  and  management  to 
enhance  decision-making  response  of  the  Commission  in  relation  to  Management 
Procedures  (MPs)  (IOTC,  2016b).  The  TCMP  met  in  May  2017  for  the  first  time  and 
provided a forum for discussion on the elements of MPs that require a decision by the 
Commission, and included the presentation of MSE results to facilitate the exchange of 
information and views between fishery scientists and managers. 

The  technical  work  carried  out  by  the  ad-hoc  working  group  includes  (IOTC  2017a; 
2018): 

A.  Progress on OMs and MPs of albacore, skipjack, bigeye and yellowfin:  

a.  The  grids  of  OMs  for  these  stocks  are  based  on  the  latest  stock 
assessments with alternatives for natural mortality, steepness, selectivity 
and dynamic catchability.  

b.  The MPs considered for these stocks include model based and empirical 
HCRs.  Overall,  the  skipjack  MSE  was  used  to  evaluate  only  a  series  of 
model based HCRs and did not evaluate a complete MP.  

c.  The  MSEs  for  albacore,  bigeye  and  yellowfin  are  scheduled  to  be 
completed in two or three years and they are including the current CPUE 
series  and  standardization  methods  used  in  the  assessments  of  these 
stocks.  

d.  The  management  objectives  are  relatively  generic:  i)  Maintain  the 
biomass  at  or  above  levels  required  to  produce  MSY  or  its  proxy,  and 
maintain the fishing mortality rate at or below FMSY or its proxy; and ii) 
avoid the biomass being below BLIM and the fishing mortality rate being 
above FLIM (Resolution 15-10). 

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e.  The  performance  measures  used  are  aligned  with  the  recommendation 
from IOTC’s Scientific Committee (IOTC 2015a). These include measures 
of stock status, safety, yield, abundance and stability. 

f.  The  MPs  evaluated  for  these  stocks  will  take  advantage  of  the  recent 
TCMP  meetings  in  May  201844  to  decide  on  tuning  parameters  for 
achieving management objectives. Fine tuning Management Procedures 
is basically adapting the coordinates of HCRs in order to exactly achieve 
the specific management objectives defined for each stock. For example, 
what HCR is estimated to exactly achieved the determined probabilities 
in the agreed timed. 

B.  Plan  for  developing  MSE  for  swordfish:  the  workplan  identified  by  the 
Commission  under  Res  15/10,  calls  for  MSE  on  swordfish  to  be  completed  by 
2017  and  presented  to  the  Commission  meeting  in  2018.  This  plan  has  been 
delayed but endorsed in the IOTC Commission meeting in 2018. 

C.  Visualization tools: The standardised figures and tables for presentation of MSE 

results that were agreed at WPM07 and SC19 in 2016 were reviewed. 

The  work  of  the  technical  working  group  has  been  the  basis  for  the  adoption  of 
Resolution  16-02  on  Harvest  Control  Rules  for  skipjack  tuna  in  the  IOTC  area  of 
competence. This resolution indicates the procedure to be followed to establish the catch 
limits for this fishery for each level of SSB estimated through a stock assessment agreed 
by  the  Working  Party  on  Tropical  Tunas  (WPTT)  and  endorsed  by  the  Scientific 
Committee  of  IOTC  (IOTC  2016a).  Resolution  16-02  specifies  a  relationship  between 
stock status (spawning biomass relative to unfished levels, %B0) and fishing intensity 
(exploitation rate relative to target exploitation rate) in Figure 9. 

Figure 9: HCR adopted for Indian Ocean skipjack (IOTC, 2016a).  

The  work  of  the  technical  working  group  has  also  been  the  cornerstone  for  the 
Recommendation 14-07 and Resolution 15-10 on target and limit reference points for 
albacore, bigeye, yellowfin, skipjack and swordfish and on a decision framework (IOTC 
2015b). It is important that this resolution is explicitly based on Resolution 12-01 on 
the  implementation  of  the  precautionary  approach.  Specifically,  Resolution  15-10 

44 TCMP (IOTC 2018) recommended that MSE tuning objectives for yellowfin (TY5) be retained and to revise 

a set of tuning objectives for bigeye (based on TB2; TB3 and TB4). See Appendix V for further details. 
www.iotc.org/sites/default/files/documents/2018/06/IOTC-2018-TCMP02-RE.pdf 

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recommends showing stock status results from stock assessments relative to limit and 
target  RPs  when  available.  It  is  also  important  to  note  that  currently,  despite  some 
agreement on the management objectives, there are no timeframe or probability levels 
agreed for none of these stocks. Along these lines, IOTC called the TCMP to define the 
overarching  management  objectives  to  guide  the  development  of  management 
procedures for the IOTC fisheries (IOTC 2016b). 

4.1.1.3  Western Central Pacific Fishery Commission (WCPFC) 

The  WCPFC's  science  provider,  the  Pacific  Community  (SPC)  has  developed  the  work 
towards implementing HSs or MPs. The technical work has been focused on estimating 
the impact of different management objectives (including specific timeframes, levels of 
risks  and  probabilities  of  overexploited  stocks)  on  fisheries  performance,  and  has 
included bio-economic analyses such as the estimation of the Maximum Economic Yield 
RP and historical catch rates for South Pacific albacore, bigeye, skipjack, yellowfin and 
southern  bluefin  tuna    (Preece  et  al.,  2011;  WCPFC,2015;  WCPFC,  2017a;  WCPFC, 
2017b;  WCPFC,  2017c;  WCPFC,  2017d;  WCPFC,  2017e;  WCPFC,  2017f).  For  that, 
alternative  parameter  sets  have  been  used  to  condition  operating  model  grids  and 
account for potential sources of uncertainty.  

The  technical  work  has  been  communicated  through  specific  Management  Objective 
Workshops (MoW) since 2012, where assistance has been provided to the Commission 
to understand the purpose and implications of management objectives, to understand 
both  the  role  of  appropriate  reference  points  and  the  process  of  evaluating  potential 
management measures in the achievement of management objectives; and to develop 
a list of recommended management objectives to guide the management of fisheries by 
the WCPFC (WCPFC 2012a; WCPFC 2012b; WCPFC 2013; WCPFC 2014).  

These  workshops  have  allowed  identifying  and  refining  potential  target  RPs  and 
proposing  Conservation  and  Management  Measures  (CMM)  on  establishing  harvest 
strategies  for  key  tuna  species.  Overall,  the  adopted  and  proposed  target  reference 
points in the WCPFC correspond to depletion levels notably above the estimated MSY 
reference points (e.g. 40% SB0). This is led by two different management objectives: 
1) Setting the TRP so that the probability of breaching the 20% SB0 LRP to a minimum 
and 2) recovering the stocks to abundance levels that will allow improving the economic 
efficiency of local fleets. The second management objective refers to leading the fishery 
to a biomass level that would allow longline fleets achieving the catch rates of 2008, 
when the fishery was at relatively acceptable levels. 

4.1.1.4  Inter-American Tropical Tuna Commission (IATTC) 

IATTC’s Scientific Advisory Council (SAC) has led the MSE process in this RFMO and has 
been responsible for the technical work that has guided the adoption of target and limit 
reference points and it is expected to guide the adoption of HCRs in the future. In 2003, 
SAC  organized  a  workshop  with  the  aim  of  describing  the  objectives  of  organizations 
and  their  use  of  reference  points,  and  those  describing  research  on  reference  points 
(IATTC,  2003).  After  a  number  of  consultations,  in  2014,  the  IATTC  adopted  interim 
target and limit reference points for tropical tuna stocks. The target reference points are 
the  biomass  and  fishing  mortality  rate  corresponding  to  the  MSY  (BMSY  and  FMSY, 
respectively), which have been the unofficial target RPs used in managing tuna in the 
eastern Pacific Ocean (EPO) through a pseudo HCR. The limit reference points are those 
associated with a 50% reduction in recruitment from pristine levels under a conservative 
assumption of the stock-recruitment relationship (steepness=0.75), which is based on 
biological  grounds  to  protect  a  stock  from  serious,  slowly  reversible,  or  irreversible 
fishing  impacts.  In  general,  this  is  interpreted  as  ensuring  that  recruitment  is  not 
substantially impacted, which aligns with Precautionary Approach principles.  

Following the adoption of the target and limit RPs, SAC has developed MSE frameworks 
for evaluating more elaborated HCRs for tropical and other tunas (IATTC 2015; IATTC 

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Study on Circular Design of the Fishing Gear for Reduction of Environmental Impacts 

2016a; IATTC 2016b; IATTC 2016c; IATTC 2017a; IATTC 2017b). In general, the OMs 
and the MPs for the MSEs are based on recent stock assessments carried out with the 
software Stock Synthesis (Methot Jr and Wetzel 2013), and are therefore conditioned 
to the available data. In particular, MSE efforts have been directed to the evaluation of 
the RPs adopted by IATTC on EPO bigeye and yellowfin tunas. SAC aims at continuing 
these  works  to  identify  additional  harvest  control  rules  for  the  management  of  these 
stocks (IATTC 2017a; IATTC 2017b). The HCR consider FMSY and BMSY as targets and aim 
at defining the length of the fishing season for tropical purse seiners (e.g. Resolution C-
17/02). 

4.1.1.5  Commission for the Conservation of Southern Bluefin Tuna (CCSBT) 

From 2002 to 2011, the CCSBT conducted extensive work to develop a MP, known as 
the  “Bali  procedure”  that  was  recommended  by  the  CCSBT’s  Extended  Scientific 
Committee (ESC) in order to guide its global TAC setting process for southern  bluefin 
tuna. The development of this work was initiated by a technical group of experts through 
specific workshops. The initial workshops (2002-2004) aimed at the development of a 
work plan to focus on the specification of OMs and the evaluation of simple  MPs. The 
results of the workshops were presented to the CCSBT through consultation  meetings 
and the candidate MP was refined until it was adopted in 2011. The technical working 
group was organized to develop the different components of the MSE in the following 
way (CCSBT, 2002): 

A.  Structure of the OMs: starting from an age structure dynamic population model, 
alternatives  for  stock  structure,  natural  mortality,  steepness,  growth,  stock 
recruitment  relationships,  weight-length  relations,  maturity  and  catchability 
were considered. 

B.  Fishery  model:  the  main  fisheries  catching  bluefin  tuna  were  identified,  their 

selectivity estimated and a component of unknown removal was included. 

C.  Conditioning on historical data and identification of data and error structure used 
for estimating model parameters: the data used to condition the OMs were total 
catch,  catch  and  age/length  and  three  abundance  indices  (CPUE,  tagging  and 
aerial surveys). Also, the methods for conditioning and other technical choices 
were discussed in this section. 

D.  Candidate MPs: this includes testing alternative sources of data to be used in the 
MP  and  the  proposal  of  decision  rules.  In  CCSBT,  since  the  beginning,  the 
decision rules have been based on empirical indicators such as indices of trends 
in  stock  status,  that  are  in  general  easily  understood  by  managers  and 
stakeholders  (ISSF,  2013).  In  particular,  the  CCSBT  technical  working  group 
focused on HCRs that use past catch and abundance indices to fix catch limits.  

E.  Testing of MPs:  this comprises modelling choices for evaluating MPs, including 

options for dealing with uncertainty and error. 

F.  Initial 

identification  of  objectives  and  related  performance  measures: 
management  objectives  and  performance  measures  need  to  be  agreed  in 
consultation with stakeholders, but the technical group defined three groups of 
management objectives including maximizing catch, safeguarding the resource 
(biomass, SSB, spawning potential and recruits) and stability of catch/effort.  

G.  Mechanics for conducting the evaluation tests: this included the organization of 
the  work  to  be  done  between  national  scientists,  computational  language  and 
share of files and scripts. 

The work plan and advances of the technical working group were periodically discussed 
with stakeholders  during workshops (2005) and CCSBT Commission meetings (2005-
2011).  In  these  consultations  the  management  objectives,  timeframes  and  tuning 
details were agreed before the adoption of the Bali procedure. This MP has been adopted 

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with the aim of leading southern bluefin tuna towards the agreed objectives (2011 and 
updated in 2013). The MP was tuned using the following specifications: 

•  a  70%  probability  of  rebuilding  the  stock  to  the  interim  rebuilding  target 

reference point of 20% of the original SSB by 2035; 

•  The minimum TAC change (increase or decrease) will be 100 tonnes; 

•  The maximum TAC change (increase or decrease) will be 3,000 tonnes; 

•  The TAC will be set for three-year periods; and 

  The  national  allocation  of  the  TAC  within  each  three-year  period  will  be 
apportioned according to CCSBT’s Resolution on the Allocation of the Global Total 
Allowable Catch. 

4.1.1.6  Global initiatives 

A series of global initiatives have also contributed to the development of MSE in tuna 
RFMOs. In particular, following international entities’ engagement with the MSE process, 
global partnerships have promoted the dialogue between managers and scientists, and 
facilitated the establishment of common frameworks for simulation tests and economic 
incentives  to  adopt  Harvest  Strategies,  the  precautionary  approach  and  sustainable 
fisheries management. 

a.  Joint Tuna RFMO Management Strategy Evaluation Working Group 
At  the  Third  Joint  Tuna  RFMOs  meeting  (La  Jolla,  California,  July  11-15,  2011)  it  was 
recognized  that  MSE  needs  to  be  widely  applied  to  implement  the  Precautionary 
Approach  for  tuna  fisheries  management.  Therefore,  a  Joint  MSE  Technical  Working 
Group was initially created to work electronically and a workshop was organized in 2016. 
This workshop comprised five themes: 1) Development of a dialogue with stakeholders; 
2) Conditioning of Operating Models; 3) Computational aspects; 4) Global albacore case 
study; and 5) Dissemination.  

b.  Capacity building workshops and dialogue initiatives 
The  Common  Oceans  ABNJ  Tuna  Project45,  in  collaboration  with  other  international 
organizations  (Food  and  Agriculture  Organization  of  the  United  Nations  (FAO),  World 
Wide  Fund  for  Nature  (WWF)  and  International  Seafood  Sustainability  Foundation 
(ISSF)), has  organized a series  of workshops to  improve the understanding of  better 
management  systems  for  the  shared  tuna  stocks.  These  workshops  have  specifically 
aimed at familiarising fisheries managers from developing States with the concepts of 
HSs  to  participate  more  fully  in  the  adoption  of  HSs  and  the  MSE  process.  These 
workshops  have  had  a  number  of  coincident  specific  objectives,  structure  and 
methodology. For example, all workshops have been inclusive and have requested the 
active participation of stakeholders in simulated management exercises and games. Five 
capacity building workshops have been held to date targeting officials from different t-
RFMOs  (ABNJ  2014;  ABNJ  2016):  2014,  Sri  Lanka  (IOTC);  2015,  Panama  (IATTC); 
2016, Ghana (ICCAT), 2017, Sri Lanka (IOTC); 2017, Bali (WCPFC), and January 2018 
in Senegal (ICCAT). 

c.  Marine Stewardship Council (MSC)  

The  MSC  is  an  international  non-profit  organization  addressing  the  problem  of 
unsustainable  fishing,  and  safeguarding  seafood  supplies  for  the  future  through 
certification  of  sustainable  fisheries.  MSC,  under  its  sustainable  fisheries  evaluation 
scheme (in its first principle of evaluation), explicitly requests the adoption of limit and 
target  reference points,  the  existence  of a  robust and precautionary  harvest strategy 
and  well  defined  and  effective  HCRs.  The  interpretation  of  these  criteria  has  been 

45 www.commonoceans.org/ 

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subjected to debate but it has  represented an  economic incentive for stakeholders to 
accelerate the implementation of HCRs and the development of MSE in tuna fisheries.  

4.1.2  Sub-task  3.2:  Provide  an  overview  of  operating  models,  HCRs 

(management procedures) and performance statistics used 

4.1.2.1  Sub-task 3.2.1. Operating Models (OMs)  

OMs  provide  mathematical  representations  of  the  system  that  is  being  managed 
(Rademayer  et  al.,  2007).  The  impact  of  fisheries  management  is  evaluated  before 
implementation  in  the  OMs  when  using  Management  Strategy  Evaluation  (MSE)  (see 
Figure 9; Punt et al., 2016). The OMs are considered alternative representations of the 
“true” dynamics of the stock and aim at covering all the uncertainties inherent to fish 
and  fisheries’  dynamics.  In  some  cases,  OMs  are  built  and  conditioned  from  stock 
assessment  models  which  are  modified  through  different  weighting  of  data  sources, 
model specifications and input parameters.  

The  design  of  an  OM  grid  aims  at  covering  the  most  uncertain  aspects  of  fish  and 
fisheries dynamics for the stock. In general, MSE developers identify the most uncertain 
parameters and processes and assign a range of values from very low to very high, thus 
building ranges for the most important parameters and when using in a factorial design, 
these contribute to building the called “uncertainty grid”. In general, there is agreement 
that  most  uncertain  parameters  in  tuna  stock  assessments  are  steepness,  natural 
mortality, migration, mixing, catchability dynamics and growth. Therefore, alternatives 
for these values are common to many MSE developments. In the next section we review 
which sources of uncertainty are considered in different stocks MSE across tuna RFMOs. 

Figure 10: Conceptual overview of the management strategy evaluation modelling 
process (source: Punt et al., 2016). 

In ICCAT, the MSE has made notable progress in the case of North Atlantic albacore 
and  East  Atlantic  bluefin  tuna.  For  the  first,  the  OMs  used  to  evaluate  HCRs  and  RPs 
consists  on  132  models  derived  from  the  2013  stock  assessment  using  the  fully 
structured  model  Multifan-CL  (ICCAT,  2013).  Using  10  scenarios  with  alternatives  on 
data sources and natural mortality from the 2013 stock assessment, a grid of 132 OMs 
was  built  exploring  additional  alternatives  for  natural  mortality  (3  options),  for  the 
steepness parameter (4 options) and temporal catchability for longline fleets (2 options) 
(Merino et al., 2017a). The 132 scenarios result from the 10 initial OMs multiplied by 3 

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mortality  options  and  4  steepness  options  plus  another  12  scenarios  agreed  by  the 
albacore working group with dynamic catchability.  

In the case of bluefin, several initiatives have developed OMs with alternative structures 
(Carruthers and Butterworth 2017; Kerr et al., 2017; Morse et al., 2017). In order to 
test  alternative  MPs  for  Atlantic  bluefin,  36  reference  case  and  4  sensitivity  test  OMs 
have been developed (Carruthers and Butterworth 2017). The grid of OMs is built using 
ranges  for  recruitment  dynamics  (high,  moderate  and  low),  recent  trajectory  of 
abundance (3 options), 2 mixing scenarios, 2 natural mortality rate scenarios and age 
at maturity (2  options). The  fitted reference  OMs  span a wide  range  of estimates for 
stock status and productivity (Carruthers and Butterworth, 2017). In the most recent 
developments, the Atlantic bluefin OMs consist on two regions with different options for 
biological parameters (including mixing). However, the final set of OMs for the bluefin 
MSE are yet to be agreed. 

In IOTC, MSE has progressed for albacore, bigeye, yellowfin and skipjack tunas.  The 
stock assessments for this stocks are carried out using Stok Synthesis (SS3) and the 
uncertainty grids considered in the assessments have been the basis to build the OMs 
of  the  four  stocks.  With  regards  to  albacore,  the  uncertainties  concerning  structural 
elements of the model formulation were considered key and they were used as the basis 
for the grid of OMs. The grid was built using feasible values for a number of assumptions 
and  fixed  parameters  in  the  population  model  (Mosqueira,  2016).  The  grid  of  Indian 
Ocean albacore incorporates the main sources uncertainty identified in the estimation 
of  population  trajectories  and  dynamics.  The  factors  considered  in  the  structural 
uncertainty grid are  seven: natural mortality (5 options), variance of  the recruitment 
deviates (2 options), steepness (3 options), coefficient of variation of CPUE indices (4 
options),  effective  sampling  size  of  each  length  data  point  (3  options),  catchability 
trends in the CPUE of longline fleets (3 options) and the form of the selectivity curve for 
longline fleets (2 options). The population models obtained from the complete grid of 
OMs included a high proportion of unrealistic estimates and plausibility criteria that were 
used for the final selection. The unrealistic values include estimates of MSY out of any 
realistic value, for example 3 orders of magnitude higher than historical maximum catch. 
After filtering, a total of 665 model runs were selected as part of the base case OM grid 
(Mosqueira, 2016). 

A simulation model of the Indian Ocean skipjack tuna fishery was developed for the 
evaluation of alternative fisheries management procedures (Bentley and Adam, 2015; 
Bentley and Adam, 2016). The model partitions the population by region (South-West, 
North-West, Maldives and East),  age  and  size  and  the  fishery  by  region  and  gear  (purse 
seine,  pole-and-line,  gill  net,  others).  Prior  probability  distributions  and  sensitivity 
ranges  are  defined  for  a  series  of  model  parameters  for  use  in  conditioning  and 
robustness testing. These parameters include weight-length coefficients, inflection point 
of  the  maturity  ogive,  steepness  of  the  maturity  ogive,  proportion  of  mature  fish 
spawning  by  quarter,  virgin  recruitment,  steepness  of  the  stock-recruitment 
relationship,  standard  deviation  of  stock-recruitment  deviations  from  the  stock 
recruitment relationship, proportion of total recruits by region, mean length of fish at 
the end of the first quarter, standard deviation of the length of fish at the end of the 
first  quarter,  instantaneous  rate  of  natural  mortality  at  a  weight  of  1kg,  exponent  of 
weight to natural mortality rate function, mean size of fish in their first quarter, standard 
deviation of fish in their first quarter, maximum growth rate, asymptotic length, growth 
variability and the proportion of fish moving between regions. 

The Indian Ocean yellowfin MSE has maintained a closed relationship between the 
stock  assessment  modelling  and  the  conditioning  of  OMs.  The  OMs  were  conditioned 
from  the  latest  stock  assessment  models  using  SS3.  The  reference  set  OM  is  an 
ensemble of assessment models that includes several alternative plausible assumptions. 
In  the  approach  to  uncertainty  quantification  emphasis  is  on  model  structural 
uncertainty and stochastic recruitment uncertainty. The reference set of OM consists of 
an  ensemble  of  216  models,  each  differing  from  the  base  case  conditioned  from  the 

Page 33 

 
 
 
Study on Circular Design of the Fishing Gear for Reduction of Environmental Impacts 

stock assessment in six modelling options. The reference set OM is built with alternatives 
for steepness (3 options), natural mortality (3 options), tag data weighting (3 options), 
catchability  dynamics  (2  options),  methods  for  CPUE  standardization  (2  options)  and 
tag-mixing periods (2 options) (Kolody and Jumppanen, 2017).   

IOTC  bigeye  MSE  followed  the  same  approach  used  with  yellowfin.  The  2013 
assessment of Indian Ocean bigeye using SS3 (Langley, 2013) was compatible with the 
development of an ensemble OM configuration because a grid-based approach was used 
to  explore  alternative  assumptions  and  their  interactions  (Kolody  and  Jumppanen, 
2016). The 18 SS models’ ensemble currently used for candidate MP evaluation include 
a factorial grid of three dimensions: steepness parameter (3 options), natural mortality 
(3 options) and temporal catchability trend (2 options).  

In the case of the CCSBT, a grid of 432 OMs is used to evaluate the performance of 
the  management  procedure  in  place  for  this  stock  (CCSBT  2017a).  The  model  is  a 
specifically tailored age structured model that considers two regions and is fitted using 
fishery  data  and  fishery  independent  abundance  series  and  genetic  information.  A 
weighted set of reference operating models represents the most important uncertainties 
in  the  model  structure,  parameters,  and  data.  These  include  alternative  values  for 
steepness (3 options), natural mortality rate at age 0 (4 options), natural mortality at 
age 10 (3 options), weighting of CPUE series (2 options), CPUE age range (2 options) 
and the power parameter on fecundity for allometric relationship between fecundity and 
reproductive success (3 options). 

The MSE for WCPFC is under development (WCPFC, 2017h) and is addressing issues 
generic  to  all  stocks.  The  OMs  rely  on  the  fully  integrated  stock  assessment  model 
Multifan-CL which is the model currently in use to provide scientific advice on tuna stocks 
status in the WCPFC. The current features available in Multifan-CL and the developments 
planned  for  the  future  (e.g.  the  generation  of  pseudo-data)  are  considered  to  be  an 
appropriate  tool  for  developing  the  OMs.  As  in  other  RFMOs,  the  approach  used  by 
WCPFC  to  capture  uncertainty  in  the  assessment  results  through  uncertainty  grids 
provide a starting point for capturing key uncertainties in the OMs. 

In  the  IATTC,  methods  to  conduct  MSE  using  the  SS3  general  stock  assessment 
program are being developed (Maunder 2014; IATTC 2016b; IATTC 2017b). MSE has 
supported  the  adoption  of  limit  and  target  reference  points  for  Eastern  Pacific  Ocean 
tropical tuna stocks (IATTC 2015;  IATTC 2016a; IATTC 2017a;  IATTC 2017b). In the 
case of bigeye, a MSE framework was built upon the results of the stock assessment 
made  using  SS3.  The  key  structural  sources  of  uncertainty  include  steepness  (3 
options), the average size of the oldest fish (3 options), natural mortality at age 0 (3 
options)  and  the  weighting  assigned  to  the  size  composition  data  (2  options)  (IATTC 
2017b).  

In the case of Pacific bluefin tuna, one MSE implementation has been developed using 
SS3  as  the  operating  model.  Samples  from  the  posterior  distribution  of  a  Bayesian 
application  of  SS  are  used  to  represent  the  possible  states  of  nature,  allowing  for 
uncertainty in parameters used in typical stock assessment models. Priors can be put 
on fixed model parameters as well as on estimated ones, to more accurately represent 
uncertainty. The analysis is the first step in developing a full MSE procedure to support 
management  advice  and  currently  considers  uncertainty  on  natural  mortality, 
steepness, growth and length composition data (Maunder 2014). 

A summary of the information on the models used and the main sources of uncertainty 
considered are shown in the table below. 

Table 3: Summary of the information on the models used and the main sources of 
uncertainty considered. 

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4.1.2.2  Sub-task 3.2.2. HCRs, MPs and performance statistics used.  

MPs represent the series of human actions undertaken to monitor the stock, assess its 
state,  make  management  decisions  and implement  the  management  advice.  In  MSE, 
the  MP  component  describes  how  the  true  dynamics  underlying  fisheries  exploitation 
fisheries 
are  represented  through  stock  assessment  and  controlled  through 
management. Related outputs are then fed into a HCR or decision framework to provide 
recommendations and management actions (Rademayer et al., 2007).  

Ideally, once the type of HCR is agreed, a fine tuning exercise is can help the election 
of a particular HCR in order to achieve a specific management objective, including exact 
probability  and  timeframes  of  achieving  this  probability.  However,  the  current 
management  objectives  (with  the  exception  of  CCSBT)  do  not  specifically  define  one 
probability and a timeframe. Most management objectives define a minimum level of 
probability  of  stock  status  and  not  a  specific  value.  For  example,  ICCAT  defines  the 
management  objective  for  North  Atlantic  albacore  as  of  achieving  at  least  a  60% 
probability  of  being  in  the  green  quadrant  of  the  Kobe  plot  and  not  a  specific  value. 

Page 35 

RFMOStockModelNº of OMSources of uncertaintyNorth Atlantic albacoreMultifan CL132Steepness, mortality, catchability, dataEast Altantic bluefinAd hoc36 (+4)Recruitment, abundance, mixing, mortality and age at maturitySkipjackAd hoc1weight-length, maturity, steepness, maturity, virgin recruitment,  standard deviation of stock-recruitment deviations, proportion of total recruits by region, mean length of fish, standard deviation of the length of fish at the end of the first quarter, instantaneous rate of natural mortality at a weight of 1kg, exponent of weight to natural mortality rate function, mean size of fish in their first quarter, standard deviation of fish in their first quarter, maximum growth rate, asymptotic length, growth variability and the proportion of fish moving between regions.BigeyeSS318steepness parameter (3 options), natural mortality (3 options) and temporal catchability trend YellowfinSS3216Steepness, mortality, tag data weighting, catchability dynamics, methods for CPUE standardization and tag-mixing periods AlbacoreSS3665Mortality, variance of rec deviates, steepness, CV of CPUE, sampling size, catchability, selectivityCCSBTSouthern bluefinAd hoc432Steepness,mortality,weightingofCPUEseries,CPUEagerangeandthepowerparameteronfecundityforallometricrelationshipWCPFCTropicals and albacoreMultifan CL-Under discussionIATTCTropicals and albacoreSS3Steepness, size of the oldest fish, mortality at age 0 and the weighting assigned to the size composition dataICCATIOTC 
 
 
 
Study on Circular Design of the Fishing Gear for Reduction of Environmental Impacts 

Therefore, the tuning of MP is a step that is currently not being fully developed across 
tuna RFMOs except for CCSBT.  

HCRs and MPs under investigation across tuna RFMOs 

In ICCAT, the MPs tested for North Atlantic albacore contain (i) an observation error 
model (OEM), (ii) a simple biomass production model and (iii) a model-based HCR. The 
OEM  reflects  the  uncertainties  between  the  actual  dynamics  of  the  resource  and 
perceptions  arising  from  observations  and  assumptions  by  modelling  the  differences 
between the measured value of a resource index and the actual value in the OM (Kell 
and  Mosqueira,  2016).  A  procedure  to  simulate  CPUE  from  the  OM  and  compare  the 
properties of the simulated to those used in the assessment was proposed for this stock 
(Merino et al., 2017b; Merino et al., 2017c). One of the options explored simulates fleet 
specific CPUE indices using each fleet’s selectivity pattern, catch and effort, and their 
properties are  compared with the abundance indices used in the 2016 assessment of 
this stock. The indices generated are used to fit the biomass dynamic model “mpb” (Kell, 
2016), which was used in the 2016 stock assessment of North Atlantic albacore. The fits 
are  made  using  the  same  specifications  and  modelling  choices  as  in  2016.  Harvest 
Control  Rules  describe  how  harvest  is  automatically  controlled  by  management  in 
relation to the state of some indicator of stock status (ISSF, 2013).  

In the case of North Atlantic albacore, when the stock level is above the precautionary 
threshold  (BTHRESH),  the  fishing  mortality  applied  to  the  stock  is  the  target  fishing 
mortality  (FTAR).  When  the  stock  falls  below  BTHRESH  but  above  the  LRP,  the  fishing 
mortality  will  be  lower  than  FTAR.  When  the  stock  falls  below  LRP,  the  remedial 
management action will be determined by FMIN, which for North Atlantic albacore was 
fixed at 0.1*FMSY As part of a HCR, threshold and LRPs are intended to restrict harvesting 
to  avoid  highly  undesirable  states  of  the  stock,  such  as  the  impairment  of  the 
recruitment, from which recovery could be irreversible or slowly reversible. The fishing 
mortality applied when the stock is evaluated to be above the BLIM but below BTHRESH is 
determined by the line that connects the coordinates (BLIM, FMIN) and (BTHRESH, FTAR), see 
Figure 11 for a generic linear model based HCR such as one of many tested for North 
Atlantic albacore and does not correspond to that adopted by ICCAT. In addition, options 
for  the  sequential  reduction  or  increase  of  catch  limits  above  certain  limits  was  also 
evaluated for this stock (ICCAT, 2017b).  

At  this  moment,  the  MPs  have  not  been  tuned  to  achieve  specific  management 
objectives. Tuning is the process on which the MP coordinates are specifically estimated 
to  achieve  management  goals.  In  ICCAT  albacore,  the  management  objective  is  to 
maintain the stock above certain level and not one level specifically. 

A range of FTAR from 0.6 to 1 FMSY and a range of BTHRESH of 0.6-1 of BMSY were evaluated 
for the North Atlantic albacore (ICCAT, 2017b). 

Page 36 

 
 
 
 
Figure 11: Generic type of HCR evaluated for North Atlantic albacore (Merino et al., 
2016). 

For Atlantic bluefin stocks, it was decided to initially explore management procedures 
that are based on empirical indicators of stock abundance rather than on model-based 
indicators of stock abundance as was the case for the northern albacore MSE. An initial 
set of relative abundance indices (three for the west and four for the east) were selected 
as  possible  candidates  to  be  examined  as  part  of  the  management  procedures  to  be 
tested for the setting of future TACs (ICCAT, 2017b). However, the initial set of MPs will 
be  extended  and  also  evaluated  over  the  course  of  2018  to  be  reported  in  the  2018 
Commission meeting (ICCAT, 2017b). In the 2018 ICCAT bluefin tuna and North Atlantic 
swordfish  MSE  meeting  (Madrid,  Spain),  the  MPs  considered  were  initially  evaluated. 
However, additional MPs are still to be designed, finalized and evaluated (ICCAT, 2018).  

In  IOTC,  empirical  and  model-based  MPs  are  being  evaluated.    For  example,  for 
albacore,  one  MP  is  based  on  a  stock  assessment  model,  and  another  is  driven  by 
changes in the CPUE series. The first MP uses the results of a biomass dynamic stock 
assessment to inform the harvest control rule on stock status. A decision is then made 
on changes to the total allowable catch levels from those set on the previous year of 
application  of  the  procedure.  Two  sources  of  information  are  generated  to  feed  the 
assessment  model:  total  catch  in  the  fishery  and  an  index  of  abundance.  A  Pella-
Tomlinson  biomass  dynamics  model  is  then  fit  to  the  data.  The  estimates  of  both 
depletion level, as the ratio of the spawning biomass in the last year of data to that in 
the first year, and of the F-at-MSY reference point, are then passed on to the harvest 
control rule (Figure 12, catch based 40:10 HCR where. 40:10 refers to the two biomass 
coordinates that delimit the HCR. At 40% of depletion catch (in  Figure 12)  or fishing 
mortality will start to be reduced. At 10% catch or fishing mortality will be reduced to a 
minimum. 

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Study on Circular Design of the Fishing Gear for Reduction of Environmental Impacts 

Figure 12. Catch based 40:10 type Harvest Control Rule included in the IOTC albacore 
MSE. 

For the CPUE-trend based indicator, the only source of information for the HCR is the 
index of abundance provided by the generated CPUE  series. The  HCR  takes the form 
TACt= TACt+1*(1+ƛ*b) where ƛ is a response multiplier and b is the slope of the linear 
model fit to the last ny years of data (Figure 13). 

Figure 13. Diagram of the CPUE-based HCR implemented for IOTC albacore (Kolody 
and Jumppanen, 2016). 

While the emphasis of the IOTC’s yellowfin and bigeye has been to develop OMs, four 
types  of  HCRs  have  also  been  tested  for  these  two  stocks  (Kolody  and  Jumppanen, 
2016;  Kolody  and  Jumppanen  2017).  These  include  a  catch  based  40:10  type  HCR 
coupled with a surplus production model, an F-based 40:10 type  HCR coupled with a 
surplus production model (Figure 14), a CPUE based HCR that aims for a desirable CPUE 
target by increasing or decreasing the TAC, depending whether CPUE is above or below 
the target and whether it is trending up or down (equal to the one tested for albacore, 
Figure 12), and a constant catch/effort. For all the four HCRs, the projection component 
of the OM simulates data that are consistent with the OM conditioning assumptions, and 
these data are interpreted by the MP to produce the Total Allowable Catch (TAC), subject 
to "realistic" data and analytical errors through the HCRs (Figure 14). 

Page 38 

 
 
 
 
Figure 14. Schematic representation of the PT 40:10 type MP category (Kolody and 
Jumppanen, 2016). 

The HCR shown in Figure 13 represents catch reductions relative to MSY as a response 
to  different  estimated  stock  levels.  Identical  HCRs  are  being  evaluated  that  consider 
fishing mortality reductions instead. 

Additional optional control parameters can be imposed on any MP in the MSE software 
developed for IOTC bigeye and yellowfin e.g., stability clauses, constrained catch/effort 
variations, total limits to catch. 

In  the  case  of  IOTC  skipjack,  a  series  of  additional  MP  were  developed  before  the 
adoption of a HCR in 2016 (Bentley and Adam, 2016; IOTC, 2016a). The classes of MP 
considered  for  this  stock  are  comparable  to  the  model  based  and  empirical  HCRs 
evaluated for bigeye and yellowfin. In the case of skipjack, one additional type of MP 
was evaluated: The FRange class. FRange class seeks to maintain the fishing mortality 
rate within a defined range. At periodic intervals the fishing mortality is estimated and 
compared  to  the  adopted  range  and  is  consequently  reduced  or  increased  if  it  is  not 
within the range.  

In the CCSBT, from 2002 to 2011 an MP that would determine the global catch limits 
was  developed.  In  that  time  the  CCSBT  tested  a  variety  of  candidate  MPs.  The  MPs 
tested  in  the  CCSBT  combine  model  based  stock  status  estimations  with  information 
from two abundance indices. The agreed MP, known as the “Bali procedure”, combines 
two MPs in one HCR. One of them uses CPUE and one aerial survey index while the other 
uses CPUE series and a Biomass Random Effect (BREM) stock assessment model. Also, 
the MP specifies the procedure to standardize the CPUE and other abundance indices. 
One important aspect of the MP developed in the CCSBT is that it is tuned to achieve 
very specific management objectives (70% of probability of achieving 20% SB0) and in 
the constraints to the catch limit variation and allocation (CCSBT, 2013). 

The CCSBT is currently in the process of developing a new MP to guide setting quotas 
for 2021 and onwards. The new MP will take into account changes in data availability: 
in  particular,  changing  the  recruitment  monitoring  series  from  an  aerial  survey  of 
juveniles  to  a  juvenile  gene  tag/recapture  program.  Besides,  consideration  is  being 
given  to  the  inclusion  of  additional  data  sources  while  maintaining  the  conceptual 
underpinning  of  the  “Bali  procedure”,  i.e.  the  combination  of  an  index  of  recruitment 
and  the  harvested  component  or  fish  stock.  However,  a  wider  range  of  MPs  can 
eventually be explored, including the use of a biomass production model instead of the 
currently used BREM (CCSBT, 2017a). 

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Study on Circular Design of the Fishing Gear for Reduction of Environmental Impacts 

In the IATTC, the MSE research has used estimates from the OMs with error to evaluate 
the performance of a linear model based HCR with FTAR=FMSY (Maunder, 2014; IATTC, 
2016b; IATTC, 2016a). IATTC has designed a roadmap to develop MSE that considers 
further identifying candidate management strategies and coding these as management 
procedures (See IATTC document SAC-07-07h).  

In  the  WCPFC,  the  consultation  has  consisted  on  alternative  proposals  to  establish 
target and limit RPs towards designing HCR (WCPFC, 2017a; WCPFC, 2017d; WCPFC, 
2017f;  and  WCPFC,  2017g).  The  technical  development  of  MPs  has  consisted  on 
developing the methodology to estimate stock status and defining a decision framework 
(WCPFC, 2017g). The MP can be based on empirical and model based methods. After 
consultation  and  using  the  skipjack  stock  status  as  example,  it  was  decided  that 
empirical estimation methods (CPUE trends) would be unlikely to work well in instances 
where purse seine fisheries account for a large proportion of catch because purse seine 
CPUE  is  difficult  to  interpret  and  unlikely  to  provide  a  reliable  signal  to  the  HCR. 
Therefore,  for  skipjack,  research  has  focused  on  a  model-based  approach.  Two 
alternative  modelling  platforms  are  being  used  to  estimating  stock  status  for  WCPO 
skipjack.  The  first  is  based  on  the  stock  assessment  software  a4a  that  has  been 
developed as part of the FLR project46, to which an age-specific CPUE and a tag based 
index  have  been  fitted.  The  second  approach  attempted  to  trim  down  the  current 
MULTIFAN-CL assessment model to produce a simplified and faster running model.  

In  the  case  of  North  Pacific  albacore,  common  efforts  between  WCPFC  and  IATTC 
scientific bodies have attempted to compare the current stock assessment with an MP 
comprised of simple harvest rates applied to two CPUE-based indices of abundance, one 
for  spawners  and  one  for  recruits  and  a  simple  catch  based  MP  (IATTC,  2016b). 
However,  the  MSE  for  North  Pacific  albacore  is  still  very  preliminary  and  further 
developments are scheduled including empirical and model based MPs (WCPFC, 2015b; 
IATTC, 2016b). 

Performance statistics used to evaluate MPs across tuna RFMOs 

In  MSE,  performance  statistics  are  used  to  represent  management  objectives  and  to 
summarize the ability of MPs to achieve them. As the MSE process evolves, performance 
statistics can help refining the relative weighting of management objectives (Punt et al., 
2016). Management objectives are often generic (e.g. catch as much as possible in a 
stable manner, reduce risks and ensure sustainability), and these need to be converted 
into operational objectives  expressed in terms of the  values of performance statistics 
(Punt et al, 2016). The conversion of conceptual objectives into operational objectives 
is    discussed  between  RFMOs  scientific  providers  and  stakeholders  (including  policy 
makers)  through  specific  meetings  and  dedicated  workshops  (e.g.  ICCAT’s  Panel  2, 
Standing  Working  Group  between  Scientists  and  Managers  (SWGSM);  IOTC’s 
Management Procedure Dialogue (MPD) and the Technical Committee for Management 
Procedures  (TCMP);  WCPFC  Management  Objective  and  Harvest  Strategy  workshops 
(MOW and HSW) and CCSBT Management Procedure Workshop (MPW)). 

ICCAT Commission through its Panel 2 and the SWGSM, have established very specific 
performance  statistics  for  the  evaluation  of  HCRs  of  North  Atlantic  albacore.  These 
consist on 15 stock status, safety, catch and stability indicators and guidelines for their 
specific calculation (Figure 15). 

46 http://flr-project.org 

Page 40 

 
 
 
 
 
                                           
Figure 15: Performance indicators and associated statistics requested for the 
evaluation of HCRs for North Atlantic albacore (ICCAT, 2016a). 

Currently, ICCAT has requested the development of comparable performance statistics 
for  the  evaluation  of  MPs  for  East  Atlantic  and  Mediterranean  bluefin  stock  (ICCAT, 
2017b; ICCAT, 2017c; ICCAT, 2017d). 

In IOTC, the SC has developed a series of candidate performance statistics and types 
of management objectives for the evaluation of MPs for all stocks (IOTC, 2015a; IOTC, 
2016c), which include status, safety, yield, abundance and stability indicators (Figure 
16). 

Figure 16: Candidate performance statistics and type of management objectives for 
the evaluation of management procedures (IOTC, 2016c). 

In the IATTC, the Scientific Advisory Council has evaluated RPs and HCRs using a series 
of  quantities  to  determine  MP  performance  (IATTC,  2015).  These  include:  (1)  the 
frequency  with  which  the  fishing  mortality  drops  below  F50%R0  (being  SSB50%R0,  a 

Page 41 

Candidate performance statistics Performance measure/s Summary statistic Status: maximize probability of maintaining stock in the Kobe green zone Mean spawner biomass relative to unfished SB/SB0 Geometric mean over years Minimum spawner biomass relative to unfished SB/SB0 Minimum over years Mean spawner biomass relative to BMSY SB/SBMSY Geometric mean over years Mean fishing mortality relative to target F/Ftarg Geometric mean over years Mean fishing mortality relative to FMSY F/FMSY Geometric mean over years Probability of being in Kobe green quadrant SB, F Proportion of years that SB ≥ SBtarg & F ≤ Ftarg Probability of being in Kobe red quadrant SB, F Proportion of years that SB < SBtarg & F > Ftarg Safety: maximize the probability of the stock remaining above the biomass limit Probability that spawner biomass is above 20% of SB0 SB Proportion of years that SB > 0.2SB0 Yield: maximize catches across regions and gears Mean catch C Mean over years Mean catch by region and/or gear C Mean over years Mean proportion of MSY C/MSY Mean over years Abundance: maximize catch rates to enhance fishery profitability Mean catch rates by region and gear A Geometric mean over years Stability: maximise stability in catches to reduce commercial uncertainty Mean absolute proportional change in catch C Mean over years of absolute (Ct / Ct−1) Variance in catch C Variance over years Variance in fishing mortality F Variance over years Probability of fishery shutdown C Proportion of years that C = 0   
 
 
 
 
Study on Circular Design of the Fishing Gear for Reduction of Environmental Impacts 

proposed criterion to establish LRPs, where R0 is the recruitment at pristine level) (2) 
the frequency with which the spawning biomass depletion level drops below the LRP of 
SB50%R0 (3) the probability (uses frequency as proxy) that recruitment drops below 50% 
R0 and (4) the average catch and coefficient of variation (CV) of catch from the multiple 
simulations. In the particular case of dolphinfish (Coryphaena hippurus), the SAC used 
total  catch  during  the  projected  years  (2015-2019)  and  the  spawning  biomass  ratio 
(SBR; the ratio of the spawning biomass at that time to that of the unfished stock) for 
the last year in the projection (2019), as the performance statistics (IATTC, 2016c). 

In  the  CCSBT,  the  new  MP  for  SBT  is  currently  being  evaluated  using  the  same 
performance  statistics  used  in  the  2011  evaluation  (Davies  et  al.,  2018).  The 
performance measures include: 

  Catch performance measures: 

o  Average short term (10 year) and long term catch 
o  Measure  of  TAC  smoothness:  average  annual  catch  variability  over  25 

years 

o  Maximum TAC decrease 
o  Proportion  of  occurrence  where  initial  2  TAC  changes  are  up  and  then 

down 

o  Proportion of occurrence where initial 4 TAC changes are set up then down 
o  Proportion of runs with TAC above the current catch at the tuning year. 
o  Lower 10th percentile in year t, e.g. in 10 years 

  SSB performance: 

o  SSB in medium term relative to SSB0 
o  Spawning biomass in short term relative to current 
o  Spawning biomass in medium term relative to current 
o  Minimum spawning biomass relative to current 
o  Proportion of runs above the current biomass at the tuning year 
o  Appearance that catch continues to increase while SSB stays low (ratio of 
catch/SSB in 2030 for a) lower 10th, b) median, c) upper 90th percentile) 
o  SSB lower (10th) percentile continuing to increase (no decline in period 

2013-2035) 

o  Lower 10th SSB percentile in year t, e.g. in 10 years 

  CPUE performance: 

o  CPUE relative to CPUE in the short term. 

In the WCPFC, during its 2nd Management Objectives Workshops (MOW) (WCPFC, 2013), 
a  “strawman”  was  considered,  i.e.  a  list  of  candidate  management  objectives  and 
performance  indicators  for  each  major  fishery.  Four  types  of  candidate  indicators 
suggested to measure progress towards achieving the management objectives for five 
fisheries/stocks: 

  Biological  indicators  such  as  fishing  mortality  and  biomass  are  used  at  the 
Commission  as  an  expression  of  stock  status  to  inform  decision‐making  and 
assess  progress  towards  objectives  such  as  optimum  utilization.  Biological 
indicators  may  be  used  to  measure  performance  relative  to  an  ‘economic’ 
objective –  e.g. biomass as an indicator of economic yield. These are  likely to 
provide  the  indicators  (and  basis  of  reference  points)  that  will  inform  harvest 
control rules. 

  Economic  indicators  can  be  used  to  monitor  the  economic  performance  of  a 
fishery. For example, they can track progress towards the maximum economic 
yield,  or  measure  whether  domestic  development  is  occurring  at  the  rate 
required  for  employment  and  economic  development  in  developing  States  in 
accordance  with  Article  30  2(a).  Useful  indicators  include  resource  rent  or 
economic profits, CPUE, and contributions from fisheries to the Gross Domestic 
Product (GDP). 

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  Social  indicators  are  of  considerable  importance  to  coastal  communities,  but 
setting  operational  social  objectives  and  indicators  is  challenging.  Indicators 
include  employment  in  the  fisheries  and  associated  sectors,  human  capacity 
development, the maintenance of artisanal fisheries and consumption of pelagic 
fish by coastal communities. These indicators will be useful for monitoring, and 
where possible, considering the impacts of management decisions.  

  Ecosystem indicators are at an early stage of development, as are the associated 
operational  management  objectives.  Trends  in  bycatch  rates  and/or  ecological 
community indicators derived from catches, and the biological characteristics of 
the species (e.g. trophic level) show promise in providing indicators of use for 
fisheries management. 

4.1.3  Sub‐task  3.3:  Analyze  strengths  and  weaknesses  of  the  process  to 
develop  HCRs  and  of  the  process  to  assess  HCRs  through  MSE 
frameworks  within  tuna‐RFMOs  taking  into  account  different  factors 
such as the capacity in third countries (information about the process), 
multispecies interactions and mixed nature of tuna fisheries 

Today, MSE is being developed for single species only, with objectives of maintaining 
stocks at healthy levels, promoting the successful recovery of overexploited stocks and 
to  evaluate  the  economic  benefits  of  precautionary  management.  In  order  to  engage 
third countries in the MSE process across tuna RFMOs, several initiatives (workshops, 
capacity building, courses and projects) are being organized. This will help developing 
new  MSE  frameworks  that  consider  alternative  approaches  such  as  multispecies 
interactions etc. This section reviews the initiatives used to promote the engagement of 
third countries and to develop alternative MSE approaches.  

All five tuna RFMOs have  committed to a path of adopting HS  or MP  to achieve their 
general  management  objectives  of  high  long-term  yields  whilst  maintaining  stocks 
within sustainable limits with high probability, consistent with the PA. The PA seeks to 
protect  fish  stocks  from  fishing  practices  that  may  put  their  long-term  viability  in 
jeopardy  despite  the  many  unknowns  on  stocks  biology,  response  to  fishing  or  exact 
state of exploitation (Garcia, 1996). In practice, the PA requires fisheries management 
bodies to determine the status of fish stocks relative to target reference points and limit 
reference  points,  to  predict  outcomes  of  management  alternatives  for  reaching  the 
targets while avoiding the limits, and to characterize the uncertainty in both cases. 

In the tuna RFMOs, the MSE process has represented an opportunity to engage scientists 
and managers view on tuna fisheries stock assessment and management. The adoption 
of Harvest Strategies has been one condition for the certification of tuna fisheries by the 
Marine Stewardship Council and this has speeded up the process of setting management 
objectives, characterizing the uncertainty inherent to fisheries, developing performance 
measures and evaluating alternative harvest strategies, including harvest control rules. 

In general, the MSE process has been led by small team of scientists within each RFMO 
science providers. However, one key component of the MSE process is the engagement 
with  third  countries  of  the  contracting  parties,  in  particular  developing  ones,  within 
RFMOs. One way to do this have been through specific, manager-orientated workshops. 
The Common Oceans ABNJ Tuna Project47 and other organizations (see sub-task 3.1), 
has  organized  a  series  of  workshops  to  improve  the  understanding  of  better 
management  systems  for  the  shared  tuna  stocks.  These  workshops  have  specifically 
aimed at familiarising fisheries managers from developing States with the concepts of 
harvest  strategies  in  order  to  allow  their  full  participation  in  the  adoption  of  harvest 
strategies  and  in  the  whole  MSE  process.  In  this  section  we  will  briefly  review  the 
objectives and outcomes of the ABNJ workshops towards building capacity on MSE in 

47 www.commonoceans.org/ 

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Study on Circular Design of the Fishing Gear for Reduction of Environmental Impacts 

developing countries. Note that the objectives and outcomes of the workshops are very 
similar. 

1) ABNJ: First Indian Ocean Tuna Management Workshop on Implementation 
of the Precautionary Approach and Rights-Based Management (22nd – 24th 
April 2014, Beruwala, Sri Lanka)  

The first tuna RFMO capacity building was held in Sri Lanka (Indian Ocean, IOTC) in 
2014 (ABNJ, 2014). The medium-term goal of these workshops was to improve the 
capacity of developing coastal states to engage in dialogue and negotiations for the 
implementation of sustainable tuna management through the Indian Ocean Tuna 
Commission (IOTC). In particular, the first workshop was designed to increase the 
capacity of Indian Ocean developing coastal states to engage in: 

Development of Harvest Strategies for Conservation Measures; 
Evaluation of their performance against management objectives; and 

i) 
ii) 
iii)  Understanding their sensitivity and robustness to major sources of uncertainty. 

The workshop was positively evaluated by organizers and participants. However, 
the participants identified a series of topics for improvement that could allow 
achieving the objectives of these workshops and which include:  

i) 

ii) 

iii) 

iv) 

v) 
vi) 

further development and annotation of material for circulation to participants 
prior to the workshops;  
incorporation of gaming with simple computer simulations to demonstrate key 
concepts;  
greater use of “worked examples” from other RFMOs/fisheries to demonstrate 
concepts and issues associated with development and implementation;  
an increased focus on the policy, management and socio-economic associated 
with the process of development and implementation. 
follow up dialogue on HCR, reference points and MSE;  
further explanation of the Kobe Matrix and its role in management advice; and 

vii) 

further dialogue on the modelling approach and process for MSE in IOTC. 

2) ABNJ:  Workshop  on  tuna  management  of  Eastern  Pacific  Ocean  coastal 

states (24th – 25th February 2015, Panama) 

The main objective of this workshop  was to create a better understanding of Eastern 
Pacific Ocean coastal states on the PA, the HCR and MSE for the sustainability of tuna 
fisheries (ABNJ, 2015). The workshop also aimed at fostering the development of HCR 
for the EPO tuna fisheries considering the key elements of management for the coastal 
states pertaining to the G-77 group.  

The workshop was organized in two days and covered the following specific topics: 

i) 

International management of fisheries, origins of the precautionary approach, 
harvest control rules and MSE 
Precautionary approach, harvest control rules and MSE 

ii) 
iii)  General background to Harvest Strategies and MSE in tuna RFMOs 
iv)  State of the art of Harvest Strategies in the IATTC 

3) ABNJ: Atlantic Tuna Harvest Strategies Capacity Building (30th-31st August, 

Accra, Ghana) 

This workshop had the main goal to create a better understanding among Atlantic 
Ocean States of the PA, HS and MSE for sustainable tuna fisheries (ABNJ 2016). 
The participants represented a diverse range of roles and experience in ICCAT. The 
workshop featured an agenda of interaction and dialogue among participants, 
aimed at providing hands on opportunities to learn harvest strategy concepts and 
run mock simulations of management strategy evaluations of harvest control rules. 
Attendees gained an increased understanding of the importance of HSs and 
significantly increased both their knowledge of HS principles and concepts. 
Participants expressed: 

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i) 

ii) 

iii) 

a strong need for  Commission assistance for  additional resources to  enhance 
in-country training and engagement of managers, fishers and stakeholders,  

a strong need to develop national level science expertise to support Commission 
level HS processes.  

the  support  to  a  sustainable  tuna  management  enabled  by  deliberate 
management  strategy  evaluation  of  trade-offs  among  potentially  competing 
management objectives. 

iv)  Some concerns relative to the use of English language, which is often a barrier 

for a number of native French and Spanish speakers, as well as Portuguese. 

4) ABNJ:  Indian  Ocean  Tuna  Harvest  Strategies  Capacity  Building  (22nd  -23rd 

March, 2017, Colombo, Sri Lanka) 

Similar to previous workshops, the main goal was to create a better understanding 
among Indian Ocean States of the precautionary approach, HSs and MSE for 
sustainable tuna fisheries (ABNJ 2017a). The structure of this workshop was very 
similar to the previous edition of the workshop in Ghana for ICCAT countries. This 
was also aimed at fostering the interaction and dialogue among participants and 
aimed at providing hands on opportunities to learn HS concepts and to run 
simulations of MSE and HCR. 

5) ABNJ: Western and Central Pacific Ocean Tuna Harvest Strategies Capacity 

Building (1st -2nd August, 2017, Bali, Indonesia) 

The main objective of this workshop was also to create a better understanding 
among Western and Central Pacific Ocean States of the precautionary approach, 
HSs and MSE for sustainable tuna fisheries (ABNJ 2017b). The workshop was 
designed to complement and support the capacity building that has already been 
delivered to WCPFC members, including through the Management Options 
Workshop (MOW) (WCPFC, 2015c) process and the work that the Pacific 
Community (SPC) is about to initiate for the countries in the region. It was 
specifically aimed at East and Southeast Asian countries but open to all Members, 
Participating Territories and Cooperating Non-member(s) the WCPFC.  

During the workshop attendees gained an increased understanding of the 
importance of HSs and significantly increased both their knowledge of HS principles 
and concepts and also their confidence in being able to apply them in the 
Commission and in-country settings. Participants expressed a desire to learn 
negotiation skills applicable to use during Commission meetings, and desired more 
case study examples on how other RFMOs and countries are collecting data and 
implementing harvest strategies. There was strong support among workshop 
participants for the use of MSE to consider trade-offs between potentially competing 
management objectives and facilitate the negotiation of tuna management 
arrangements. 

6) ABNJ: Atlantic Ocean Tuna Management Workshop (30th -31st January 2018, 

Dakar, Senegal) 

Another capacity building workshop was held in Dakar, Senegal on 30-31 February 
2018 with a goal to create a better understanding among Atlantic Ocean States of 
the precautionary approach, HSs and MSE for sustainable tuna fisheries (ABNJ 
2018a). The workshop was designed to complement and support the capacity 
building that has already been delivered to ICCAT members in previous workshops 
and dialogue meetings, as well as upcoming efforts the ICCAT Scientific Committee 
is about to initiate for countries in the region. Following recommendations from the 
August 2016 ABNJ workshop in Ghana, it was specifically aimed at Francophile 
Contracting Party and Cooperator countries of ICCAT. 

Attendees learned about the importance of HSs, significantly increasing both their 
knowledge of HS principles and concepts as well as their confidence in being able to 

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Study on Circular Design of the Fishing Gear for Reduction of Environmental Impacts 

apply them in the Commission and in country settings. Participants expressed a 
desire for more fishery-specific examples in the workshop content and an additional 
day of training for both the content and practical exercises. They also desired to 
learn more about the fundamentals of the Harvest Strategy process. 

7) ABNJ:  Western  and  Central  Pacific  Ocean  Tuna  Management  (20th-  21st 

February, 2018, Nadi, Fiji) 

Another similar capacity building workshop was held in Nadi, Fiji on 20-21 February 
2018 with the same goal of contributing to the understanding among Western and 
Central Pacific Ocean States of the precautionary approach, HSs and MSE for 
sustainable tuna fisheries (ABNJ, 2018b). 

The workshop was designed to complement and support the capacity building that 
has already been delivered to WCPFC members, including through the Management 
Options Workshop (MOW) process and the work that the Pacific Community (SPC) 
is about to initiate for the countries in the region. It was open to all Members, 
Participating Territories and Cooperating Non-member(s) of the WCPFC. 

Attendees gained understanding of the importance of HSs and significantly 
increased both their knowledge of HS principles and concepts and also their 
confidence in being able to apply them in Commission and in-country settings. 
Participants expressed a desire to learn more about the fundamentals of the 
Harvest Strategy process, particularly MSE. They also desired more fishery-specific 
examples in the workshop content and a training link to the national level as 
national interests dictate how countries behave at a regional level.  

4.1.4  Sub‐task 3.4: Specify what could be defined as next steps to improve the 

current MSE framework in different tuna‐RFMOs 

All  five  tuna  RFMOs  have  plans  for  evaluating  MPs  using  MSE.  In  some  RFMOs,  the 
roadmap towards adopting MPs is well detailed and in others the process is at its initial 
states. In this section we briefly review the work plans and provide a short comparison 
of the process in all tuna RFMOs. 

The  roadmap of  IOTC towards the adoption of MPs for the  main Indian Ocean  stocks 
(IOTC,  2017b)  is  specific  to  the  roles  of  the  scientific  working  groups,  the  Technical 
Committee  on  Management  Procedures  (TCMP)  and  the  Commission.  The  feedback 
between the three key players of the MSE process is well established and scheduled in 
yearly meetings of the WG and Scientific Committee, annual meetings of the TCMP and 
Commission  (Table  4).  The  process  in  IOTC  relies  on  the  technical  work  and  the 
interaction with the Commission. The IOTC aims at being able to adopt MPs for its most 
important stocks by 2020. 

Table 4: Roadmap towards adoption of MPs in IOTC. 

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The  roadmap  for  ICCAT  stocks  (Die,  2018)  clearly  lists  the  steps  that  the  scientific 
working  groups  will  undertake  to  provide  the  evaluations  of  candidate  MPs  to  the 
Commission.  However,  it  is  not  as  specific  as  the  IOTC  in  the  interactions  between 
managers and scientists (Table 5). In ICCAT, Panels and the Standing Working Group 
between Scientists and Managers (SWGSM) are the groups responsible of the feedback 
between the Commission and MSE developers. One of the differential aspects of ICCAT’s 
MSE process is that it will be independently evaluated. This evaluation will start in 2018 
with  the  evaluation  of  North  Atlantic  albacore  MSE  and  will  contribute  to  the 

Page 47 

Albacore201820192020Undertake MSEEvaluate candidate MPAdvice to Com on MPs elements that need decision from COMConsider work from subsidiary bodiesDecision and adoption of MP or recommend further MSERefine HCR with MSEApply HCR to calculate TACAdvice to COM on the application of the HCRProvide direction to refine HCR and MSEConsider work from subsidiary bodiesUndertake MSEEvaluate candidate MPAdvice to Com on MPs elements that need decision from COMConsider work from subsidiary bodiesDecision and adoption of MP or recommend further MSEUndertake MSEEvaluate candidate MPAdvice to Com on MPs elements that need decision from COMCommissionConsider work from subsidiary bodiesDecision and adoption of MP or recommend further MSEDevelop OM and MSE (preliminary analyses)Consider recommendations from Com to develop MSEEvaluate candidate MPConsider work from subsidiary bodiesDecision and adoption of MP or recommend further MSETCMPCommissionWP and SCTCMPCommissionWP and SCTCMPWP and SCYellowfinSkipjackBigeyeSwordfishTCMPWP and SCCommissionWP and SCTCMPCommission 
 
 
 
 
Study on Circular Design of the Fishing Gear for Reduction of Environmental Impacts 

improvement of the process for other stocks. This independent review is not foreseen 
in other tuna RFMOs where the internal working groups and parties are the “reviewers” 
of the technical work and the process. In ICCAT, the MSE process is well advanced for 
North  Atlantic  albacore  and  bluefin.  In  addition,  specific  calls  for  tenders  are  being 
launched  in  2018  to  support  the  development  of  MSE  for  swordfish  and  tropical  tuna 
stocks. A key novel aspect of the tropical tunas MSE is that it will contemplate options 
for  the  multispecies  management  instead  of  the  current  single  species  management 
framework.  

Table 5: Roadmap towards adoption of MPs in ICCAT. 

In the WCPFC the feedback process is advanced and has made substantial progress in 
defining management objectives thanks to a number  of dialogue workshops  (WCPFC, 
2012a; WCPFC, 2013; WCPFC, 2014; WCPFC, 2015b; WCPFC, 2015c; WCPFC, 2017g; 
WCPFC 2017f). The technical work that will support the adoption of MPs in the WCPFC 
is being developed by its science provide SPC. The plans for developing the technical 
work and agreeing on the necessary steps towards the adoption of MPs is shown in Table 
6. 

Table 6: Roadmap towards the adoption of MPs in the WCPFC (Santiago, 2018). 

Page 48 

North A. albacore2018201920202021Finalization of diagnostics and improvement of MPRe-evaluation of performance of MPs and exceptional circumstancesDevelopment of MPsEvaluation of MPsIndependent review of MSE processDevelopment of MPsEvaluation of MPsIndependent review of MSE processDocumentation for stakeholdersNorth A. swordfishDevelopment of OMDevelopment of OM alternativesDevelopment of MPsEvaluation of MPsIndependent review of MSE processDocumentation for stakeholdersDevelopment of OMConditioning of OMDevelopment of OM alternativesRe-evaluation of performance of MPs and exceptional circumstancesDevelopment of MPsEvaluation of MPsIndependent review of MSE processDocumentation for stakeholdersBluefin tuna (E-W)Tropical tunas 
 
 
In  the  IATTC,  the  MSE  work  consists  on  identifying  appropriate  HCRs  for  bigeye  and 
yellowfin but it is still in its early stages. There is a plan for MSE development that will 
be presented in the 2018 Scientific Advisory Committee (SAC). 

The CCSBT has decided to develop a new MP to guide the setting of TACs for 2021 and 
onwards.  The new MP will take into account changes in data availability, in particular, 
changing  the  recruitment  monitoring  series  from  an  aerial  survey  of  juveniles  to  a 
juvenile gene tag/recapture program.  In the 2017 meeting of the  Extended Scientific 
Committee (ESC), a work plan was agreed (Table 7) towards the adoption of the new 
MP  in  2020  by  the  Extended  Commission  (EC).  This  work  plan  foresees  annual 
consultations while the candidate MP (CMPs) are evaluated by the Operating Model and 
Management Procedure technical group (OMMP). The  ESC  acknowledged the  value of 
having multiple groups tabling CMPs for an iterative process that refines and improves 
these  before  the  final  selection.  For  this  reason,  all  members  are  encouraged  to 
contribute to the MP development process.  

Table 7: Plan for adoption of a new MP for CCSBT (source: CCSBT, 2017b). 

Page 49 

South Pacific albacore2018201920202021Agree Target RPDevelop HCRs and MSEAdopt HCRDevelop HCRs and MSEAdopt HCRAgree Target RPPerformance indicators and monitoring strategyDevelop HCRs and MSEAdopt HCRAgree Target RPPerformance indicators and monitoring strategyDevelop HCRs and MSEAdopt HCRBigeyeSkipjackYellowfin 
 
 
 
 
Study on Circular Design of the Fishing Gear for Reduction of Environmental Impacts 

Comparative of work plans across tuna RFMO 

The  MSE  process  is  being  developed  across  tuna  RFMOs  through  specific  work  plans. 
Each  RFMO  features  steps  that  can  contribute  to  the  developments  elsewhere.  For 
example: 

1)  Independent  expert  evaluations:  ICCAT’s  MSE  process  and  the  MSE  simulation 
framework  used  to  evaluate  HCRs  for  North  Atlantic  albacore  will  be  reviewed  by 
independent  experts.    The  review  will  be  extended  to  all  the  Atlantic  species  MSE  as 
they progress. This external review process is not foreseen in other RFMOs: however 
they all would benefit from that.  

2) Periodical revision of the technical work at Working Groups: In the IOTC, the technical 
work to evaluate MPs is being developed by MSE experts under specific contracts. This 
work  is  periodically  presented  to  the  Working  Party  on  Methods  and  each  species 
working party. In ICCAT, this is carried out by scientists from the CPCs (albacore) but 
also  by  external  experts  through  dedicated  contracts  (bluefin,  swordfish  and  tropical 
stocks). In the WCPFC, IATTC and CCSBT, the MSE work and the evaluation of MPs is 
carried out by their scientific bodies. In IOTC and ICCAT the technical work is periodically 
presented and reviewed by the different working groups of the SCRS and SC. This is not 
the case elsewhere where the work is presented directly in the SC meetings. In terms 
of the validation of the technical work, the periodical reviews within the working groups 
of the RFMO could improve (but also delay) the process. 

3)  The  feedback:  In  ICCAT  and  CCSBT  the  feedback  between  Commission  and  the 
technical  works  has  been  more  productive  than  elsewhere.  In  particular,  ICCAT’s 
SWDSM and Panel 2 proved very effective in refining the HCRs to be evaluated (ICCAT, 
2015b; ICCAT, 2016a; ICCAT, 2017c) for bluefin and North Atlantic albacore. The level 
of the concepts discussed in these forums is probably more advanced than in the other 
RFMOs where the dedicated dialogue meetings and workshops are used to define and 
clarify the MSE concepts to Commissioners. The recently established working groups in 
IOTC and WCPFC aims at feedbacks that will allow refining the MPs and advancing the 
process. 

4)  Multispecies  options  for  tropical  stocks:  To  date,  there  is  no  multispecies  HCR 
evaluated within tuna RFMOs, even though ICCAT foresees the development of this type 
of  HCR.  Tropical  tunas  represent  an  opportunity  to  explore  options  for  multi-species 

Page 50 

yearmonthMeetingObjectiveJuneOMMP9First presentation of CMPs using new OmsSeptemberESC+1day OMMPEvaluation of refined CMPsOctoberECResults on CMP to EC. Consultation with stakeholders. EC confirm or amend recovery objectivesJune/JulyOMMP10Recondition the OM and review initial updated versions of CMPs to develop a limited set to put forward to the ESCSeptemberESC+1day OMMPReview and advice on set of CMPs and interaction with stakeholdersOctoberECAim to select and adopt MPJuneSpecial ESC/EC meetingContingency placeholder in case more time is needed to complete evaluationSeptemberESCImplementation of adopted MP to provide TAC advice for 2021Updated assessments including projections with adopted MPOctoberECAgree TAC for TAC 2021-2023201820192020 
 
 
 
management  measures,  such  as  limitations  on  effort  or  fishing  gears.  Tropical  tuna 
stocks  are  often  captured  together,  especially  by  purse  seine  fleets  using  Fish 
Aggregation Devices (FADs). The use and regulation of FADs is currently been discussed 
in all tuna RFMOs (ICCAT, 2017c). The MSE that will be developed across tuna RFMOs 
would allow evaluating options for FAD management, including reductions in number or 
usage by purse seine fleets.  

5  TASK 4: CASE STUDIES 

5.1  Sub-task 4.1: Harvesting strategies of the Western Central Pacific 

Fisheries Commission (WCPFC) 

As specified in the Terms of Reference, a separate document has been written to address 
task 4.1 (see Apostolaki et al., 2018). 

5.2  Sub-task 4.2: Development of mixed fisheries and single stock MSE 
for 
the 
Conservation  of  Atlantic  Tunas  (ICCAT)  and  Indian  Ocean  Tuna 
Commission (IOTC): Define options and preliminary models 

for  International  Commission 

tropical 

tunas 

for 

5.2.1  Introduction and review of current state 

ICCAT  has  committed  to  adopt  harvest  strategies  or  MP  to  achieve  its  management 
objectives of high long-term yields whilst maintaining stocks within sustainable limits 
with high probability, consistent with the PA. The PA seeks to protect fish stocks from 
fishing  practices  that  may  put  their  long-term  viability  in  jeopardy  despite  the  many 
unknowns on stocks biology, response to fishing or exact state of exploitation (Garcia, 
1996).  

The  current  management  framework  of  ICCAT’s  tropical  tuna  stocks  is  based  on 
Recommendation  11-13,  which  recommends  management  actions  for  the  different 
states of exploitation of the stocks, expressed in biomass and harvest rates relative to 
their  corresponding  Maximum  Sustainable  Yield  RPs.  The  implicit  target  of  this 
recommendation is to maintain the stocks in the green area (B>BMSY and F<FMSY) with 
high probability, which adds to the traditional objective of achieving MSY. However, this 
recommendation relies on the interpretation of what is considered ‘high probability’ and 
‘as short a period as possible’ (Figure 17). 

Figure 17: ICCAT's management framework based on Rec. 11-13. 

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Study on Circular Design of the Fishing Gear for Reduction of Environmental Impacts 

ICCAT’s  Working  Group  to  Enhance  the  Dialogue  between  Fisheries  Scientists  and 
Managers  recommended  ways  to  further  define  the  current  management  framework 
building  on  Recommendation  11-13,  in  particular  in  relation  to  RPs,  associated 
probabilities and timeframes (Rec. 15-07). Also, one of the main goals of ICCAT’s SCRS 
Science Strategic Plan (2015-2020) is to evaluate precautionary management RPs and 
MPs  that  are  robust  to  the  many  uncertainties  inherent  to  fisheries.  In  this  context, 
ICCAT also aims at adopting HCRs, i.e. a set of pre-agreed (and specific) management 
decisions that are used to set limits to catch or effort  according to the state  of some 
indicators of stock status with respect to reference points. Therefore, ICCAT is moving 
towards  a  scientifically  sound  and  specific  decision-making  scheme  that  needs  to  be 
evaluated before adoption.  

Bigeye tuna (BET), yellowfin tuna (YFT) and skipjack (SKJ) are the three tropical tuna 
stocks  fished  in  the  Atlantic.  These  stocks  are  often  caught  simultaneously,  but  are 
assessed independently:  this might lead to undesired effects in the implementation of 
the single stock TAC. For example, the mismatch between the catch profiles of the fleets 
and the single stock advice can produce an incentive to generate over-quota discards 
of  one  of the stocks if its catch limits are exceeded but not the others’  (Ulrich et al., 
2011).  According  to  the  FAO  Code  of  Conduct  for  Responsible  Fisheries  and  other 
international agreements, discards are generally considered a waste of fish resources 
and inconsistent with responsible fisheries (FAO, 1995). ICCAT, in its ICCAT Information 
on  By-Catch  of  Tuna  Fisheries  (available  via  iccat.int)  also  calls  for  a  reduction  of 
discards. Therefore, a responsible management of tuna stocks would avoid discards. 

The  mismatch  between  single  stocks’  TAC  could  be  avoided  using  a  multi-stock 
management framework, e.g. multi-stock harvest control rules. ICCAT foresees to adopt 
a specific management plan for tropical tunas by 2019 and for this it needs support to 
evaluate  multi-species  management  measures.  MSE  with  simulation  tests  can  be  a 
valuable  tool  to  estimate  different  levels  of  probability  of  achieving  management 
objectives  through  different  management  options.  To  support  the  development  of  a 
robust advice framework for tropical tuna stocks, we used a preliminary MSE framework 
to test a series of multi-stock harvest control rules. 

In those lines, ICCAT has just funded a Call for Tenders to support the development of 
a  robust  advice  framework  consistent  with  the  Precautionary  Approach  (PA)  for  the 
Atlantic tropical tuna stocks. The objectives of this initiative include developing a MSE 
framework  composed by a series of  OMs and  MPs for tropical tuna stocks. As a main 
novelty, this project foresees to evaluate multispecies HCRs similar to the ones describe 
in  this  section.  Therefore,  the  results  presented  here  are  a  first  step  towards  the 
evaluation of multispecies MPs in the tuna RFMO context. For now,  except for  fishing 
effort limitations, there is no MSE develop for more than one stock in any tuna RFMO.  

At this moment, in IOTC there is no plans for considering multispecies MP for tropical 
tunas or any other stock. 

According  to  the  most  recent  assessments  of  these  stocks  bigeye  is  overfished  and 
subject to overfishing, yellowfin is overfished but not subject to overfishing and the East 
and West skipjack stocks are most likely not overfished nor subject to overfishing. In 
this study we use MSE to explore the potential capacity of different multispecies HCRs 
to achieve ICCAT’s management objectives. In brief, we have evaluated three types of 
HCR: 1) A constant TAC strategy (referred as E75 in the scenarios), 2) The ICES MSY 
framework HCR and, 3) A multi-stock HCR aiming at MSY ranges for the three tropical 
tuna stocks. 

The HCRs have been evaluated under different scenarios for fleet dynamics or strategies 
on effort allocation, which determine how much effort is applied to each stock and how 
this is allocated between different métiers within a fleet. In this case, the métiers refer 
to the two modalities of purse seine fishing (free school and FADs). In particular, the 
E75 HCR assumes a 75% of the status quo effort with the current share of effort (i.e. 
fishing mortality reduction of 25%) between FADs and free school; the ICES multi-stock 
HCRs  calculate  effort  and  TAC  for  two  different  levels  of  effort  allocation  between 

Page 52 

 
 
métiers. This approach is based on the Fcube method presented in Ulrich et al., (2011) 
and  Iriondo  et  al.,  (2012).  The  basis  of  the  model  is  to  estimate  the  potential  future 
levels of effort by fleet corresponding to the fishing opportunities (TACs by stock and/or 
effort allocations by fleet) available to that fleet, based on how the fleet distributes its 
effort across its métiers, and the catchability of each of these métiers. This level of effort 
is in return used to estimate landings and catches by fleet and stock,  using standard 
forecasting procedures. The inputs required to perform the forecast are: mean weight 
at  age,  the  mean  selectivity  at  age,  discard  ratio  (3  year  averages)  and  recruitment 
(geometric mean).  

5.2.2  Material and Methods 

We  developed  the  MSE  using  the  modelling  platform  FLBEIA,  a  bio-economic  impact 
assessment model based on the MSE approach (Jardim et al., 2013; Garcia et al., 2017). 
This model is written in R and requires the use of FLR libraries48. Figure 18 shows the 
structure  of  the  MSE  built  with  FLBEIA  which  includes  operating  and  management 
Procedure  models.  The  OM  is  composed  by  stock,  fleet  and  OM  covariates 
(environmental variables, prey, predators  etc.), and the  MP is  composed by the data 
collection, stock assessment and decision making. 

Figure 18: Conceptual representation of the main components modelled in FLBEIA 
(Garcia et al., 2013). 

In  general,  MSE  involves  using  simulation  to  compare  the  relative  effectiveness  for 
achieving  management  objectives  of  different  combinations  of  (i)  data  collection 
schemes,  (ii)  methods  of  stock  assessment  and  (iii)  subsequent  process  leading 
management actions (Punt et al., 2016), i.e. different MPs. In this document we show 
preliminary results on the performance of a multi-stock HCRs which makes use of fishing 
mortality ranges to generate multi-stock TAC advice. To carry out this MSE, guidelines 
and best practices summarized in Rademeyer et al. (2007) and Punt et al. (2016) were 
followed. 

5.2.2.1  Management objectives 

The overall management intention in ICCAT is to assure the long term sustainability of 
the  stock  as  well  as  of  the  fisheries,  which  in  operational  terms  is  translated  as  the 
highest long-term average catch with a high probability of being in the green quadrant  
(the  target)  and  a  low  probability  of  being  outside  biological  limits  (the  limit)  (ISSF 
2013).  

48 www.flr-project.org  

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Study on Circular Design of the Fishing Gear for Reduction of Environmental Impacts 

5.2.2.2  Selection of hypotheses 

We condition the MSE with the reference case of the latest  SS3 stock assessments of 
bigeye  and  yellowfin.  For  the  eastern  skipjack  tuna  the  results  of  a  preliminary  SS3 
model are used (Quang, in preparation). 

5.2.2.3  Operating Models 

For the purposes of this study, the OMs are age structured population dynamic models 
conditioned  from  the  outputs  of  the  SS3  models  available  for  bigeye,  yellowfin  and 
Eastern skipjack. Western skipjack was not considered in the study because there is not 
an  age  structured  assessment  model  available  actually  for  this  stock.  Biological 
parameters such as maturity, and natural mortality at age are taken directly from the 
SS3  models.  A  deterministic  segmented  regression  model  is  assumed  for  the  stock-
recruitment  relationships  and  its  parameters  are  calculated  from  the  data  series 
produced by the assessment models (SS3) assuming a steepness of 0.8 for the three 
stocks, however, in the interpretation of the results, it must be taken into consideration 
that  in  the  assessment  of  bigeye  and  yellowfin  tuna,  different  steepness  value  are 
considered between 0.7-0.9 and 0.75-0.95 respectively, and the reproductive potential 
of SKJ could be higher than for the other two stocks. A degree of statistical uncertainty 
is  considered  in  the  S-R  relationship  assuming  a  lognormal  variability  distribution 
(CV=30%). 

5.2.2.4  Management Procedure 

In the current set up, the MSE does not include any data collection, assessment model 
or  implementation  process.  Therefore,  the  simulations  shown  here  assume  that  the 
information on stock status is perfect and that management measures are implemented 
without error. In the future, this MSE will be developed to include observation errors, 
the assessment models and a detailed decision-making framework.  

Fmsy ranges for each of the stock were estimated following the ICES MSY framework 
(ICES  2017c).  The  range  of  fishing  mortalities  compatible  with  an  MSY  approach  to 
fishing were de-fined as the range of fishing mortalities leading to no less than 95% of 
MSY and which were precautionary in the sense that the probability of SSB falling below 
Blim  in  a  year  in  long-term  simulations  with  fixed  F  was  ≤5%.  Eqsim  (stochastic 
equilibrium reference point software) function defined in the msy R package was used 
to  provide  MSY  reference  points  based  on  the  equilibrium  distribution  of  stochastic 
projections. Productivity parameters (i.e. year vectors for natural mortality, weights-at-
age, maturities, and selectivity) are resampled at random from between 2005 and 2014 
for the three stocks. Recruitments are resampled from their predictive distribution which 
is based on parametric models fitted to the full time-series provided in this case, Ricker, 
segmented regression and Beverton and Holt were assumed for the three stocks. 

The MP of this MSE is composed by three types of HCRs: 1) A fixed advice of constant 
TAC  (E75)  (based  on  effort),  2)  The  ICES  MSY  framework  HCR  with  two  options 
(ices_Emin and ices_Ebet) (based on catch) and, 3) A multi-stock HCR aiming at MSY 
ranges for the three tropical tuna stocks (multi_Emin and multi_Ebet) (based on catch), 
see Table 8 and sub-task 2.3 (section 3.3 of this report). 

Table 8: Scenarios simulated under MSE framework. 

HCR 

Fleet dynamics  Abreviation 

Description 

Fixed advice 

25%  
reduction in 
effort 

E75 

E75, a constant Total Allowable Catch TAC 
strategy based on their latest scientific 
advice: TACBET=65000, TACYFT=110000 t, 
TACSKJ=163000t†. The Reduction of 25% of 
the last 3 years average effort. 

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ICES 

Fcube:min 

ices_Emin 

ICES 

Fcube:BET 

ices_Ebet 

MULTISTOCK  Fcube:min 

multi_Emin 

MULTISTOCK  Fcube:BET 

multi_Ebet 

Seeks for single FMSY for all stocks but fishing 
stops when fleet’s allocated quota is reached 
for any stock. 

Seeks for single FMSY for all stocks but fishing 
stops when fleet’s allocated quota of bigeye 
is reached. 

Aims at maintaining fishing mortality at 
overall MSY ranges and maximizing total 
catch. Fishing stops when fleet’s allocated 
quota is reached for any stock. 

Aims at maintaining fishing mortality at 
overall MSY ranges and maximizing total 
catch. All fleets set their effort corresponding 
to their bigeye tuna quota share, regardless 
of other catches. 

†Based on their latest scientific advice and for western Atlantic skipjack the most recent catch estimates 

2012 

5.2.2.5  First set-up of the bigeye simulation model and scenarios 

For  the  projection  of  the  three  stocks  we  use  an  age  structured  population  dynamic 
model and fleet specific fishing mortality, effort and performance indicators. The Cobb 
Douglas  production  model  (Cobb  and  Douglas,  1928)  is  used  to  estimate  the  catch 
production  per  fleet.  Effort  and  elasticity  parameters  are  assumed  equal  to  one,  so 
catches per fleet depend only on the fleets’ catchability and exploitable biomass. The 
fleets and their codes considered for this preliminary set up are shown in Table 9. 

Table 9: Fleets considered in this simulation and the stocks they catch. 

FLEETS 

METIERS 

STOCKS 

Description 

PS_SPFR 

PS_SPFR_FS 
PS_SPFR_LS 

YFT, BET,SKJ  Spanish and French purse seiners 

PS_GH 

PS_GH 

YFT, BET,SKJ  Baitboat and Purse seiners Ghana 

BB 

BB 

YFT, BET,SKJ  BET: Baitboat Portugal, Spain and Others 

YFT: Baitboat area2 and Dakar 

SKJ: Baitboat Azores, Canary and Others 

LL_JP 

LL_JP 

YFT, BET  

Japanese longliners 

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Study on Circular Design of the Fishing Gear for Reduction of Environmental Impacts 

LL_Other 

LL_Other 

YFT, BET  

Other longliners 

Others_YFT  Others_YFT 

YFT 

Rod and Reel from US and Others 

Others_SKJ  Others_SKJ 

SKJ 

Longline and others 

Figure 19 shows the effort share of European purse seines. The effort share is estimated 
as the mean of the ratio of catches per species by each métier.   

Figure 19: Effort share of European purse seine fleets: Free school (FS) and Log 
school or FADs (LS). 

The reference points of each stock following the single stock and the multi-stock HCR 
are estimated following the ICES guidelines (ICES,2016b; ICES, 2017b) and are shown 
in Table 10. 

Table 10: The reference points and control variables of the HCRs. 

REFERENCE POINT (RP) 

YFT 

BET 

SKJ 

HCR 

Biomass limit RP 

BLIM 

2.60e+05 

3.20e+05 

2.20e+05 

ICES/MULTI 

Trigger biomass RP 

Btrigger  3.64e+05 

4.48e+05 

3.08e+05 

ICES/MULTI 

FMSY 

1.10e-01 

8.00e-02 

6.80e-01 

ICES/MULTI 

Fupp 

1.30e-01 

1.00e-01 

9.9e-01 

MULTI 

Flow 

8.00e-02 

6.00e-02 

4.20e-01 

MULTI 

FIshing mortality at 
MSY 

Upper bound of 
fishing mortality rate 

Lower bound of 
fishing mortality rate 

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5.2.3  Results 

The results suggest that when the effort is reduced by 25% and the advice is set fixed 
in the projection (E75), then the estimated median catch is higher than the TAC set in 
the  projection  for  bigeye  tuna  in  the  projection,  65,000  t.  This  means  that  the 
differences  between  the  TAC  and  catches  are  discarded  for  this  stock  (Figure  20).  In 
this scenario the median fishing mortality is constant at 0.12 with a slight increase in 
recruitment and SSB, which is above the estimated Btrigger.  

In the other scenarios, in the first years of the projection the catches and the fishing 
mortality decrease with different intensities, because the SSB for bigeye is below the 
Btrigger  and  therefore  the  effort  is  reduced.  After  that,  catches  and  fishing  mortality 
increase back to higher levels, but still remain lower than the values estimated for the 
E75 rule; in particular, F sets at 0.08 in the ICES HCRs, which is also the estimated FMSY 
for bigeye, while it increases up to 0.1, which is the Fupp value for bigeye. The simulations 
are very similar when Emin or Ebet are used in both single and multispecies HCRs, because 
the  minimum  effort  corresponds  to  the  effort  necessary  to  catch  the  quota  share  of 
bigeye tuna.  

With both HCRs (ICES and multi-stock) the increase in SSB is higher than with the fixed 
TAC  (E75).  The  estimated  median  catches  in  the  projection  are  higher  when  the 
multistock HCR is used compare to the values obtained with the ICES approach. When 
the E75  HCR is applied, the probability of SSB falling below Btrigger is higher than 0 
(Figure  21)  (Table  10),  while  it  is  equal  to  0  when  the  ICES  and  multistock  HCR  are 
applied.  In  light  of  these  considerations,  the  multistock  HCR  emerges  as  the  most 
effective, as it provides the highest catches with no risk of falling below Btrigger. 

Figure 20: Figure shows the historical and the estimated median values of bigeye 
(BET) in the projection with the MSE model of catch, recruitment, fishing mortality (f) 
and spawning stock biomass under different scenarios. The vertical discontinuous line 
is the year starts the projection 2013 and the horizontal discontinuous lines are Blim 
(red) and Btrigger (orange). 

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Study on Circular Design of the Fishing Gear for Reduction of Environmental Impacts 

Figure 21: Historical and the estimated median, 5th and 95 quantiles, in the projection 
with the MSE model of bigeye (BET) catch, recruitment, fishing mortality (f) and 
spawning stock biomass under different scenarios. The vertical discontinuous line is 
the year starts the projection 2013 and the horizontal discontinuous lines are Blim 
(red) and Btrigger (orange). 

Table 10: the probability of ssb of BET being below Btrigger of Blim in each of the 
scenarios.  

P(ssb2020<Btri)  

P(ssb2020<Blim) 

P(ssb2029<Btri)  

P(ssb2029<Blim) 

BET 

scenario 

E75 

ICES_Emin 

ICES_Ebet 

Multi_Emin 

0.32 

0 

0 

0 

0 

0 

0 

0 

0 

0.21 

0 

0 

0 

0 

0 

0 

0 

0 

0 

Multi_Ebet 

0.01 

In the case of yellowfin, the highest median catch is also estimated when the E75 HCR 
is applied, but the catches are lower than the TAC of 110,000 t, and the fishing mortality 
is around 0.14, i.e. higher than the FMSY, which is 0.11. The recruitment is stable around 
the mean and the SSB decreases in the first years of the projection, but remains stable 
after 2020 at levels below Btrigger (Figure 22).  

The  estimated  median catches  with  both  HCRs  (ICES  and  Multistock)  fall  to  very  low 
values at the start of the projection. This is because the SSB values of bigeye are below 
its Btrigger, therefore the fishing mortality of BET is reduced and  consequently also the 
fishing mortality on yellowfin. The fishing mortality of multi_Ebet is the second highest 
and its values are close to the FMSY value of 0.11; the median SSB remains stable above 
Btrigger. In the other scenarios, fishing mortality is lower than 0.1 but higher than Flow, 
and the SSB of all of them is higher and stable. Due to the uncertainty considered some 
of the iterations show that SSB can fall below Btrigger and -on a minor extent- below Blim 
with some probability (Table 11). 

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Figure 22: Historical and the estimated median values of yellowfin (YFT) in the 
projection with the MSE model of catch, recruitment, fishing mortality (f) and 
spawning stock biomass under different scenarios. The vertical discontinuous line is 
the year starts the projection 2013 and the horizontal discontinuous lines are Blim 
and Btrigger. 

Figure 23: Historical and the estimated median values and the 5th and 95 quantile of 
yellowfin (YFT) in the projection with the MSE model of catch, recruitment, fishing 
mortality (f) and spawning stock biomass under different scenarios. The vertical 
discontinuous line is the year starts the projection 2013 and the horizontal 
discontinuous lines are Blim and Btrigger. 

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Study on Circular Design of the Fishing Gear for Reduction of Environmental Impacts 

Table 11: the probability of ssb of YFT being below Btrigger of Blim in each of the 
scenarios  

P(ssb2020<Btri)   P(ssb2020<Blim) 

P(ssb2029<Btri)   P(ssb2029<Blim) 

YFT 

scenario 

E75 

0.88 

ICES_Emin 

0.47 

ICES_Ebet 

0.47 

Multi_Emin 

0.59 

Multi_Ebet 

0.74 

0.38 

0.05 

0.05 

0.03 

0.17 

0.9 

0.62 

0.62 

0.66 

0.74 

0.38 

0.05 

0.05 

0.03 

0.17 

In  the  case  of  skipjack,  the  estimated  median  catch  with  the  E75  scenario  are  lower 
than the advice of 163,000 t (Figure 24). The fishing mortality is around 0.14, which is 
much lower than the estimated FMSY value of 0.6. The SSB decreases in the first years 
of the projection but it stabilizes above Btrigger after some years. The recruitment is also 
stable throughout the projection. The second highest fishing mortality is estimated in 
the scenario multi_Ebet (0.3), which is lower than Flow=0.42. Figure 25 shows that the 
uncertainty in this stock is higher than on the others and all the scenarios show that 
there  is  some  risk  of  falling  below  Btrigger.  Furthermore,  the  multi_bet  scenario  shows 
that with some probability biomass can fall below BLIM (Table 12). 

Figure 24: Historical and the estimated median values of skipjack (SKJ) in the 
projection with the MSE model of catch, recruitment, fishing mortality (f) and 
spawning stock biomass under different scenarios. The vertical discontinuous line is 
the year starts the projection 2013 and the horizontal discontinuous lines are Blim 
and Btrigger. 

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Figure 25: Historical and the estimated median values and the 5th and 95 quantile of 
skipjack (SKJ) in the projection with the MSE model of catch, recruitment, fishing 
mortality (f) and spawning stock biomass under different scenarios. The vertical 
discontinuous line is the year starts the projection 2013 and the horizontal 
discontinuous lines are Blim and Btrigger. 

Table 12: the probability of ssb of SKJ being below Btrigger of Blim in each of the 
scenarios.  

SKJ 

scenario 

P(ssb2020<Btri)   P(ssb2020<Blim) 

P(ssb2029<Btri)   P(ssb2029<Blim) 

E75 

0.89 

ices_min 

0.88 

ices_Ebet 

0.88 

multi_Emin 

0.89 

multi_Ebet 

0.92 

0.61 

0.41 

0.41 

0.4 

0.64 

0.9 

0.88 

0.88 

0.88 

0.92 

0.61 

0.41 

0.41 

0.4 

0.64 

Figure 26 shows the impact of the different HCRs and fleet dynamics on the catch. The 
estimated  median  catches  with  the  E75  scenario  reach  the  highest  values  for  all  the 
fleets except for the Others_SKJ, which only capture skipjack. For this fleet, the highest 
catches are estimated in the scenario with ICES HCRs based on single stock advice. For 
the rest of the fleets the highest difference between the scenarios is at the start of the 
projection period when the SSB of bigeye tuna is lower than Btrigger. Afterwards, following 
the SSB increase of bigeye, the differences  in catches between the  various scenarios 
decrease. For all of the fleets, except Others_YFT and Others_SKJ, the second highest 
catches are estimated with the multi-HCR type. 

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Study on Circular Design of the Fishing Gear for Reduction of Environmental Impacts 

Figure 26: Historical and the estimated median values of total catches in the 
projection with the MSE model for each fleet. 

5.2.4  Discussion 

This study represents a first step in the evaluation of management strategies for tropical 
tuna  stocks  in  a  mixed-fisheries  framework.  We  have  compared  three  different 
management  strategies  combined  with  different  fleet  dynamics.  The  effort-based 
management  with  a  25%  reduction  was  translated  into  fleet  dynamics  reducing  the 
effort of all the fleets by 25%. The other 2 HCRs used correspond to the HCRs proposed 
by  ICES  in  the  MSY  framework  and  to  a  multi-stock  HCR  that  uses  fishing  mortality 
ranges  around  MSY  targets.  These  two  HCRs  were  combined  with  two  different  fleet 
dynamics  which  differed  in  the  condition  used  to  restrict  the  effort  of  the  fleets,  the 
minimum effort or the effort corresponding to the TAC of bigeye. 

The SSB of bigeye is the only one that increased significantly in all the scenarios reaching 
MSY  level  in  the  long  term,  although  the  MSY  level  is  below  the  historical  maximum 
catch record.  

The  scenario  with  25%  reduction  in  effort  produced  the  highest  fishing  mortality  and 
the lowest SSB for all the stocks and years. In the ICES scenarios the “min” and “bet” 
options  produced  similar  results  because  for  most  of  the  fleets  bigeye  is  the  most 
restrictive  stock.  The  multi-stock  scenario  did  not  produce  the  same  behavior:  the 
reason  is  that  when  using  the  upper  limit  of  the  fishing  mortality  range  bigeye  is  no 
longer the most restrictive stock.  

The  multi-stock  HCR  restricted  with  bigeye  TAC  produced  on  average  sustainable 
biomasses for the three stocks  but the probability of being below BLIM was higher than 
zero in some years.  This type  of management  should be combined with strict control 
measures  to  ensure  the  fulfillment  of  the  TAC  advice.  In  fact,  this  HCR  and  the 
introduction  of  fishing  mortality  ranges  were  defined  in  the  light  of  the  new  landing 
obligation policy (Garcia et al., 2016) which forces the fleets to stop fishing when the 
first of the quotas has been reached; such behavior corresponds with the ‘min’ option. 
In the long term the multi-stock HCR scenario combined with ‘min’ behavior is similar 
to  the  ICES  scenarios,  but  in  the  short  term  the  catches  were  higher  with  the  multi-
stock HCR.   

The fleet dynamics used in this work were based on the historical behavior. However, 
future  work  should  focus  first  on  the  definition  of  the  fleets  and  their  métiers  and 
afterwards identify the dynamics that better describe the fleet dynamics.  

The assessment models of the stocks are quarterly based, however the simulation was 
run in yearly basis and this produces some inconsistencies between the models: future 
work should develop the simulation model in a seasonal  fashion in order to provide a 

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more  accurate  representation  of  the  dynamic  of  the  fleet  and  a  consistent  approach 
between the assessment and the simulation model. In the future, the development of a 
MSE model including the seasonal dimension is recommended in order to compare the 
results of both models and understand the impact of the seasonal effect in the dynamic 
of the stock and the fishery.  

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Page 64 

 
 
 
 
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