Manual on sample-based data collection for fisheries assessment

Examples from Viet Nam

Per Johan Sparre
Danish Institute for Fisheries Research
Charlottenlund, Denmark


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ISBN 92-5-104526-7

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To Thuy, Huong and Ngoc, three hardworking data collectors of Viet Nam.


The assignment to prepare the present manual was given at the “Regional Workshop on Routine Capture Fishery Data Collection” held 25–28 May 1998 in Bangkok, at the FAO Regional Office for Asia and the Pacific. The Workshop was organized and funded by the FAO/DANIDA Project GCP/INT/575/DEN, “Training in Fish Stock Assessment and Fishery Research Planning”. It developed the “Guidelines for the routine collection of capture fishery data” (FAO Fisheries Technical Paper 382), which forms part of a series supporting the “Code of Conduct for Responsible Fishing”.

The present manual aims at providing more details on the mechanics of implementing a routine data collection system. The structure of the manual follows that of the Guidelines, but emphasis is placed on providing practical information and detailed examples. The document draws heavily on experience gained in setting up a data collection system in Viet Nam with the assistance of a DANIDA-funded national project “Assessment of the Living Marine Resources in Viet Nam”, Phase 1, 1 Mar 1996 – 31 Oct 1997.

The first drafts were prepared shortly after the Workshop. However, in order to bring the manual in line with the Guidelines, a thorough revision was undertaken in 2000 by the author and Paul Medley as editor, using funds of the FAO/Norway FISHCODE Project GCP/INT/648/NOR.

The manual should be considered as one of the major outputs of the FAO/DANIDA Project “Training in Fish Stock Assessment and Fishery Research Planning”. It is expected to contribute to better data collection for fisheries management and fish stock assessment and eventually to an improvement of fisheries management.

Siebren C. Venema

Project Manager


Participants in FAO/DANIDA Workshop on data collection
Regional Fisheries Management Bodies and Research Councils
All FAO Members and Associate Members
All FAO Offices
FAO Fisheries Department
Directors of Fisheries
Fisheries Research Institutes
Other interested Nations, International Organizations, Universities and NGOs

Sparre, P.J.
Manual on sample-based data collection for fisheries assessment. Examples from Viet Nam.
FAO Fisheries Technical Paper. No. 398. Rome, FAO. 2000. 171p.


This manual deals with the practical implementation of a routine data collection programme. The data collection programme is developed through a top-down approach, from the identification of the objectives down to the practical recording and management of data obtained from the fishery. The issues are dealt with both through detailed discussion and by using simple examples. The examples are mostly based on situations in tropical fisheries, and in particular, experience has been drawn from developing a data collection programme in Viet Nam. The main questions addressed in the manual are which fisheries data to collect, where and when to collect them.

Only data collected from commercial marine capture fisheries are considered (data from freshwater fisheries, cultured fish and experimental fishery are excluded). The methodologies used are mainly appropriate for a tropical, developing country, with many small (artisanal) vessels and a few large (industrial) vessels.

The methodology is the “sample-based approach” - the manual does not deal with a methodology which assumes complete enumeration. The data collection methodology presented attempts to utilize whatever information can be obtained in practice in a developing country.

Processing and storing of data (fisheries databases) and staff training are partly covered.

Food and Agriculture Organization of the United Nations
Rome, © FAO 2000

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This electronic document has been scanned using optical character recognition (OCR) software. FAO declines all responsibility for any discrepancies that may exist between the present document and its original printed version.



1   Introduction

1.1   Scope

1.1.1   Data Collection Topics Covered
1.1.2   Data Collection Topics Not Covered

1.2   Organisation of the Manual
1.3   Who Should Read this Manual

2   Objectives of Data Collection

2.1   Overall Objectives
2.2   Responsibilities

2.2.1   Directorate of Fisheries
2.2.2   Fisheries Research Institute
2.2.3   Other Agencies

2.3   Management Units And Reference Points

3   Indicators and Data Variables

3.1   Fisheries Activity Data

3.1.1   Catch, Landings and Discards
3.1.2   Fishing Effort and Activity
3.1.3   The Fleet Concept

3.2   Biological Information

3.2.1   Species Composition of Commercial Groups
3.2.2   Fish Stock Assessment, Virtual Population Analysis
3.2.3   Fish Stock Assessment Forecast
3.2.4   Data Requirements for Fish Stock Assessment

3.3   Bio-Economic Information

3.3.1   Fish Prices
3.3.2   Costs of Fish Harvesting
3.3.3   Investments, Foreign Exchange Costs, Taxes and Subsidies

3.4   AN Example FROM A Tropical Fishery

3.4.1   Data Types Collected
3.4.2   Methodology for Estimation of Total Catches
3.4.3   Estimation of Discards from Limited Data

4   Data Collection Strategy: Sampling

4.1   Sample-Based Estimation Versus Complete Enumeration
4.2   Geographical and Seasonal Division of Populations
4.3   Stratification

4.3.1   Criteria for Strata Selection
4.3.2   Designing Strata

4.4   Raising Samples to Totals

4.4.1   Principles of Raising
4.4.2   Raising to Trip Total
4.4.3   Raising to Total of a Province (Geographical Stratum)
4.4.4   Raising to Total Country
4.4.5   Example to Illustrate the Raising Procedures

5   Data Collection Methods

5.1   The Basic Record: “The Fishing Trip”
5.2   Fishing Vessels

5.2.1   Vessel Registration
5.2.2   Frame Survey

5.3   Commercial (Species) Groups
5.4   Data From Processing Plants
5.5   Data From Other Sources
5.6   Log Books / Sales Slips Filled in by Fishers / Buyers
5.7   The Skipper / Merchant Interview at the Landing Place
5.8   Data Collection Forms

5.8.1   Common Features of All Forms
5.8.2   Form 1: Trip Interview
5.8.3   Form 2: Species Composition of Commercial Group
5.8.4   Form 3: Length Frequency
5.8.5   Form 4: Extension of Form 1: Variable Costs & Earnings Per Trip
5.8.6   Form 5: Fishing Activity In Base Port
5.8.7   Form 6: Frame Survey
5.8.8   Form 7: Fixed (Annual) Costs By Vessel
5.8.9   Form 8: Vessel Registration
5.8.10   Forms 1 to 8.

6   Databases and Data Management

6.1   Tables, Relations And Queries
6.2   Forms of Database
6.3   The Use of Codes

6.3.1   The Use of Unique Keys
6.3.2   Codes for International Exchange of Data
6.3.3   Codes for National Fisheries Data Collection
6.3.4   Example of a Code for Species: “NAN-SIS Species Code”
6.3.5   Code for Gears
6.3.6   Code for Fishing Fleets
6.3.7   Code for Commercial Groups (Species/Size/Treatment-Quality)

6.4   Use of Look-Up Tables
6.5   Reports from the Data Base
6.6   SQL (Structured Query Language)
6.7   Data Validation
6.8   Design of Fisheries Reports
6.9   Design of Fisheries Sector Profiles
6.10   An Example Fisheries Database

6.10.1   Tables of FDDB
6.10.2   Forms of FDDB

7   Implementation of Sampling Programme

7.1   Pilot Sampling Programme
7.2   Budget of Sampling Programme
7.3   Training

7.3.1   Training of Data Manager and Supervisors
7.3.2   Training of Enumerators, Encoders and Support Staff

7.4   Consultation

7.4.1   Consultations with Fisheries Administrators
7.4.2   Consultations with Fisheries Managers and the Fishing Industry
7.4.3   Exchange of Experiences with Other Countries or International Organisations

7.5   Documentation of the Programme
7.6   The Iterative Process of Implementing a Data Collection Programme

8   References


ACCESSThe database component of Microsoft Office
ACFM / ICESAdvisory Committee for Fisheries Management / International Council for the Exploration of the Sea.
Activity levelMeasure for fishing effort per time unit (say, fishing days per month).
Administrative unitDivision of country, for example, province (or state), districts, communes etc.
Base portThe port that is used as base for fishing trips.
CAlgebraic term for the number of individuals caught (by fishery).
CatchFish caught, either measured as “number of individuals” or as “weight of biomass” (yield). Catch = Landings + Discards
Cohort analysisIn this manual used as synonym for “Virtual Population Analysis” (a standard method for fish stock assessment).
ControlThe basic component of a form. A control appears on the computer screen, for example, as a “box” for entry of data, or a “button”, which starts an operation when clicked on by the mouse.
CPUECatch Per Unit of Effort
DANIDADanish International Development Agency
DatabaseA computerised object composed of Tables, Forms and Reports
DiscardThe part of the catch that encountered the gear but was not landed.
EEZExclusive Economic Zone
EffortMeasure for fishing activity (say, number of fishing days)
EXCELThe spreadsheet program of Microsoft Office
F (Fpa)Fishing mortality (Fishing mortality of the “Precautionary Approach”)
FieldThe basic component of a record (a row) in table. A field is the smallest unit in the database.
Fishing mortalityInstantaneous rate of fishing mortality. A measure for the rate of death caused by fishing.
Fishing powerTwo fishing vessels are said to have the same “fishing power” if they can catch the same amounts and qualities of fish under similar conditions.
Fishing tripIn the simple case, a fishing vessel leaves the port, steams to the fishing grounds, fishes for a while and steams back to the port where it lands all the catch. This set of events is called a “fishing trip”. For more details, see Section 5.
Fixed costs of harvestingThe costs depend on the number of vessels, for example, depreciation of hull, engine and gear, insurance, interest, etc.
FleetA group of fairly uniform vessels that have approximately the same size and approximately the same construction. They use the same type of gears and fishing techniques and most often they also share fishing grounds.
FormThe screen displays by which the user interacts with the database (soft form).
Frame surveyInventory list of fishing units at a specific time, sometimes combined with an indication of their activity levels (for example number of active fishing days per month). A frame survey is usually a complete enumeration as far as the number of units is concerned, whereas the activity data are often are sampled.
GISGeographical Information System
Gross Value Added (GVA)The total income generated by the production: (Private profit) + (Wages + salaries) + (Interest) + (Licence fee) + (Depreciation) + (Taxes and duties minus subsidies)
Home portThe place of registration of a fishing vessel
HPHorse Power
ICESInternational Council for the Exploration of the Sea
Input TablesThe basic database tables containing the observations collected by interviews of skippers, merchants etc., and by recording experimental fishing.
LANLocal Area (computer) Network
LandingsThe part of the catch that is actually brought back to land.
Look-Up-TableTable with options for filling the fields in the input tables.
Management UnitA “management unit” is the same as a stock whenever the stock has been identified. When the stock cannot be identified, “Management unit” replaces the concept. A management unit is something for which it is possible to make predictions, under various assumptions on the future fishing regime.
MBALMinimum Biological Acceptable Level
Merchant / BuyerPerson who buys the landings for re-sale to next chain in the market. They often have additional relationship to the fishers, for example they may lend them money, pay for medical expenses etc.
MPAModal Progression Analysis Method for the analysis of a time series of size frequency data.
MSYMaximum Sustainable Yield
NStock Numbers (Number of survivors)
NAN-SISSoftware for fishery survey data logging and analysis (FAO Computerised Information Series, Fisheries, No. 4), developed for the NORAD-funded Nansen Programme.
Net Value AddedNVA = (Gross value added) - (Depreciation)
Neyman's CriteriaCriteria for optimum allocation of data collection resources
NORADNorwegian Agency for Development Co-operation
Opportunity costThe benefit foregone by using a scarce resource for one purpose instead of its next best alternative.
PAlgebraic term for the price per kg
PopulationThe set of “data-units” from which data are collected
Private profit(Ex-vessel value of catch) - (Costs of fishing)
Private Profitability (%)100*(Private profit) / (Investments)
Provisional reference pointWhen information for determining reference points for a fishery is poor or absent, provisional reference points shall be set. Provisional reference points may be established by analogy to similar and better-known stocks.
QueryA request to the database to perform some operations on the tables (say, merging, filtering and sorting records).
Recruit, RecruitmentA “recruit” is a juvenile fish entering the exploited part of the stock. “Recruitment” is the number of recruits per spawning season.
Reference points (precautionary reference points)There are two types of precautionary reference points: Conservation or limit reference points and management or target reference points. Limit reference points set boundaries which are intended to constrain harvesting within safe biological limits. Target reference points are intended to meet management objectives.
StockA “stock” can be defined as a group of animals from one species, which share a common gene pool. There are many other definitions of the “stock” concept.
StratificationDivision of the population into strata, and allocation of sampling intensity to strata.
SSBSpawning Stock Biomass, the biomass of adult fish that contribute to spawning.
Variable costs of harvestingThere are two types of variable costs: (1) Costs linearly related to fishing effort, for example fuel and lubrication, repairs and maintenance, ice, crew wages (independent of yield in value), etc. (2) costs, which depend on the ex-vessel value of the landings; for example: crew remuneration and fish auctioning/marketing fees.
Vessel registerDatabase containing a set of parameters for each vessel, such as a unique registration code, the dimensions of the hull and the engine etc. The vessel register is used for the purposes of taxation, payment of subsidies, issuing license, payment of licence fee, monitoring, control and surveillance, enforcement of fisheries regulations, inspection, etc. The vessel register is also used for processing of catch and activity information.