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The 2018 Joint tuna RFMO Management Strategy Evaluation Working Group Meeting in Seattle, USA – 13-15 June 2018

Glossary of terms for harvest strategies, management procedures and

management strategy evaluation

Terms commonly used in Management Strategy Evaluation or Management Procedure literature

Term

Definition

Abbreviation/Symbol

Average Annual Variation

(in catch/TAC)

The absolute value of the proportional TAC change each

year, averaged over the projection period.

AAV

Biomass Stock biomass, which may refer to various components

of the stock. Often spawning stock biomass (SSB) of

females is used, as the greatest conservation concern is

to maintain the reproductive component of the

resource.

Candidate Management

Procedure

An MP (defined below) that has been proposed, but not

yet adopted.

CMP

Conditioning

The process of fitting an Operating Model (OM) of the

resource dynamics to the available data on the basis of

some statistical criterion, such as a Maximum

Likelihood. The aim of conditioning is to select those

OMs consistent with the data and reject OMs that do

not fit these data satisfactorily and, as such, are

considered implausible.

Error Differences, primarily reflecting uncertainties in the

relationship between the actual dynamics of the

resource (described by the OMs) and observations. Four

types of error may be distinguished, and simulation

trials may take account of one or more of these:

 Estimation error: differences between the

actual values of the parameters of the OM and

those provided by the estimator when fitting a

model to the available data;

 Implementation error: differences between

intended management actions (as output by an

MP) and those actually achieved (e.g. reflecting

over-catch);

 Observation error (or measurement error):

differences between the measured value of

some resource index and the corresponding

value calculated by the OM;

 Process error: natural variations in resource

dynamics (e.g., fluctuations about a stock-

recruitment curve or variation in fishery or

survey selectivity /catchability).

Estimator The statistical estimation process within a population

model (assessment or OM); in a Management Strategy

Evaluation (MSE) context, the component that provides

information on resource status and productivity from

past and generated future resource-monitoring data for

input to the Harvest Control Rule (HCR) component of

an MP in projections.

The 2018 Joint tuna RFMO Management Strategy Evaluation Working Group Meeting in Seattle, USA – 13-15 June 2018

Term Definition Abbreviation/Symbol

Exceptional circumstances Specifications of circumstances (primarily related to

future monitoring data falling outside the range covered

by simulation testing) where overriding of the output

from a Management Procedure should be considered,

together with broad principles to govern the action to

take in such an event.

Feedback Control Rules or algorithms based, directly or indirectly, on

trends in observations of resource indices, which adjust

the management actions (such as a TAC change) in

directions that will change resource abundance

towards a level consistent with decision makers’

objectives.

Harvest Control Rule

(also Decision Rule)

A pre-agreed and well-defined rule or action(s) that

describes how management should adjust management

measures in response to the state of specified

indicator(s) of stock status. This is described by a

mathematical formula.

HCR

Harvest Strategy

Some combination of monitoring, assessment, harvest

control rule and management action designed to meet

the stated objectives of a fishery. Sometimes referred to

as a Management Strategy (see below). A fully specified

harvest strategy that has been simulation tested for

performance and adequate robustness to uncertainties

is often referred to as a Management Procedure.

Implementation The practical application of a Harvest Strategy to

provide a resource management recommendation.

Kobe Plot A plot that shows the current stock status, or a

trajectory over time for a fished population, with

abundance on the horizontal axis and fishing mortality

on the vertical axis. These are often shown relative to

MSY

and to F

MSY

, respectively. A Kobe plot is often

divided into four quadrants by a vertical line at B=B

MSY

and a horizontal line at F=F

MSY

Limit Reference Point A level of biomass below, or fishing mortality above,

which an actual value would be considered undesirable,

and which management action should seek to avoid.

LRP

Management Objectives

The social, economic, biological, ecosystem, and

political (or other) goals for a given management unit

(i.e. stock). These typically conflict, and include concepts

such as maximising catches over time, minimising the

chance of unintended stock depletion, and enhancing

industry stability through low inter-annual variability in

catches. For the purposes of Management Strategy

Evaluation (MSE) these objective need to be quantified

in the form of Performance statistics (see below).

Objectives, MOs

The 2018 Joint tuna RFMO Management Strategy Evaluation Working Group Meeting in Seattle, USA – 13-15 June 2018

Term Definition Abbreviation/Symbol

Management Plan In a broad fisheries governance context, a Management

Plan is the combination of policies, regulations and

management approaches adopted by the management

authority to reach established societal objectives. The

management plan generally includes the combination of

policy principles and forms of management measures,

monitoring and compliance that will be used to regulate

the fishery, such as the nature of access rights,

allocation of resources to stakeholders, controls on

inputs (e.g. fishing capacity, gear regulations), outputs

(e.g. quotas, minimum size at landing), and fishing

operations restrictions (e.g. closed areas and seasons).

Ideally, the Management Plan will also include the

Harvest Strategy for the fishery or a set of principles and

guidelines for the specification, implementation and

review of a formal Management Procedure for target

and non-target species.

Management Procedure

A management procedure has the same components as

a harvest strategy. The distinction is that each

component of a Management Procedure is formally

specified, and the combination of monitoring data,

analysis method, harvest control rule and management

measure has been simulation tested to demonstrate

adequately robust performance in the face of plausible

uncertainties about stock and fishery dynamics.

Management Strategy Synonymous with harvest strategy. (But note that this is

also used with a broader meaning in a range of other

contexts.)

Management Strategy

Evaluation

A process whereby the performances of alternative

harvest strategies are tested and compared using

stochastic simulations of stock and fishery dynamics

against a set of performance statistics developed to

quantify the attainment of management objectives.

MSE

Maximum Economic Yield The (typically annual) yield that can be taken

continuously from a stock sustainably (i.e. without

reducing its size) that maximizes the economic yield of a

fishery in equilibrium. This yield occurs at the effort level

that creates the largest positive difference between

total revenues and total costs of fishing (including the

cost of labor, capital, management and research etc.),

thus maximizing profits.

MEY

Maximum Sustainable Yield The largest (typically annual) yield that can be taken

continuously from a stock sustainably (i.e. without

reducing its size). In real, and consequently stochastic

situations, this is usually estimated as the largest

average long-term yield that can be obtained by

applying a constant fishing mortality F, where that F is

denoted as F

MSY

Observation Model The component of the OM that generates fishery-

dependent and/or fishery-independent resource

monitoring data from the underling true status of the

resource provided by the OM, for input to an MP.

The 2018 Joint tuna RFMO Management Strategy Evaluation Working Group Meeting in Seattle, USA – 13-15 June 2018

Term Definition Abbreviation/Symbol

Operating Model(s)

A mathematical–statistical model (usually models) used

to describe the fishery dynamics in simulation trials,

including the specifications for generating simulated

resource monitoring data when projecting forward in

time. Multiple models will usually be considered to

reflect the uncertainties about the dynamics of the

resource and fishery.

OM(s)

Performance

statistics/measures

A set of statistics used to evaluate the performance of

Candidate MPs (CMPs) against specified management

objectives, and the robustness of these MPs to

important uncertainties in resource and fishery

dynamics.

Plausibility (weights) The likelihood of a scenario considered in simulation

trials representing reality, relative to other scenarios

also under consideration. Plausibility may be estimated

formally based on some statistical approach, or

specified based on expert judgement, and can be used

to weight performance statistics when integrating over

results for different scenarios (OMs).

Precautionary Approach

An approach to resource management in which, where

there are threats of serious irreversible environmental

damage, lack of full scientific certainty is not used as a

reason for postponing cost-effective measures to

prevent environmental degradation.

Reference case

(also termed reference

scenario or base case)

A single, typically central, conditioned OM for evaluating

Candidate MPs (CMPs) that provides a pragmatic basis

for comparison of performance statistics of the CMPs.

RC (or BC)

Reference set

(also termed base-case or

evaluation scenarios)

A limited set of scenarios, with their associated

conditioned OMs, which include the most important

uncertainties in the model structure, parameters, and

data (i.e. alternative scenarios which have both high

plausibility and major impacts on performance statistics

of Candidate MPs).

Research-conditional option Temporary application of an MP that does not satisfy

conservation performance criteria, accompanied by

both a research programme to check the plausibility of

the scenarios that gave rise to this poor performance

and an agreed subsequent reduction in catches should

the research prove unable to demonstrate

implausibility.

Robustness tests Tests to examine the performance of an MP across a full

range (i.e. beyond the range of the Reference Set of

models alone) of plausible scenarios. While plausible,

robustness test OMs are typically considered to be less

likely than the reference set OMs, and often focus on

particularly challenging circumstances with potentially

negative consequences to be avoided.

Scenario A hypothesis concerning resource status and dynamics

or fishery operations, represented mathematically as an

OM.

The 2018 Joint tuna RFMO Management Strategy Evaluation Working Group Meeting in Seattle, USA – 13-15 June 2018

Term Definition Abbreviation/Symbol

Simulation trial/test

A computer simulation to project stock and fishery

dynamics for a particular scenario forward for a

specified period, under controls specified by a HS or MP,

to ascertain the performance of that HS or MP. Such

projections will typically be repeated a large number of

times to capture stochasticity.

Spawning Biomass, initial Initial spawning biomass prior to fishing as estimated

from a stock assessment.

SSB

Spawning Biomass, current Spawning biomass (SSB) in the last year(s) of the stock

assessment.

SSB

current

Spawning Biomass at MSY The equilibrium spawning biomass that results from

fishing at F

MSY

. In the presence of recruitment variability,

fishing a stock at F

MSY

will result in a biomass that

fluctuates above and below SSB

MSY

SSB

MSY

Stationarity The assumption that population parameter values are

fixed (at least in expectation), and not varying

systematically, over time. This is a standard assumption

for many aspects of stock assessments, OMs and

management plans.

Stock assessment

The process of estimating stock abundance and the

impact of fishing on the stock, similar in many respects

to the process of conditioning OMs.

Target Reference Point

The point which corresponds to a state of a fishery

and/or resource which is considered desirable and

which management aims to achieve.

TRP

Trade-offs

A balance, or compromise, achieved between desirable

but conflicting objectives when evaluating alternative

MPs. Trade-offs arise because of the multiple objectives

in fisheries management and the fact that some

objectives conflict (e.g. maximizing catch vs minimizing

risk of unintended depletion).

Tuning

The process of adjusting values of control parameters of

the Harvest Control Rule in a Management Procedure to

achieve a single, precisely-defined performance statistic

in a specified simulation test. This reduces confounding

effects to allow the performance of different candidate

MPs to be compared more readily with respect to other

management objectives. For example, in the case of

evaluating rebuilding plans, all candidate MPs might be

tuned to meet the rebuilding objective for a specified

simulation trial; then the focus of comparisons among

MPs is performance and behaviour with respect to catch

and CPUE dimensions.

Weight(s) Either qualitative (e.g. high, medium, low) or

quantitative measures of relative plausibility accorded

across a set of scenarios.

Worm plot Time series plots showing a number of possible

realizations of simulated projections of, for example,

catch or spawning biomass under the application of an

MP for a specific OM or weighted set of OMs.