ALCOM Field Document No.38

TAG-RECAPTURE STUDY ON TWO SELECTED SMALL WATER BODIES IN MALAWI TABLE OF CONTENTS

By

Emmanuel Kaunda

Funding Agencies:

SWEDISH INTERNATIONAL DEVELOPMENT AUTHORITY BELGIAN ADMINISTRATION FOR DEVELOPMENT CO-OPERATION

Executing Agency:

FOOD AND AGRICULTURE ORGANIZATION OF THE UNITED NATIONS
Harare, Zimbabwe, December 1995

PREFACE

ALCOM, in collaboration with the Government of Malawi has carried out studies in two small water bodies of Malawi; Mikolongwe and Mbvoniha.

The objectives of the study were to develop empirical models which use easily measurable parameters like morphometrics and limnological characteristics of small water bodies to estimate fish yields or biomass.

ALCOM is a regional aquaculture and fisheries programme of the FAO (Food and Agriculture Organization of the United Nations). Based in Harare, Zimbabwe, it covers all the member-countries of SADC (Southern African Development Community) - Angola, Botswana, Lesotho, Malawi, Mauritius, Mozambique, Namibia, South Africa, Swaziland, Tanzania, Zambia and Zimbabwe.

The aim of ALCOM is to assist member-countries improve the living standards of rural populations through the practice of aquaculture. Toward this end, pilot activities are conducted in member-countries to demonstrate new techniques, technologies or methodologies. Successes achieved, ideas derived, lessons learnt, are applied on a wider scale by member-governments.

ALCOM is funded by Sweden and Belgium. Its preparatory phase began in 1986, and its first implementation phase in 1990.

Address:

The designations employed and te presentations of material in this publications do not imply the impression of any opinion whatsoever on the part of the Food and Agriculture Organization of the United Nations.

ABSTRACT

A one year study was carried out in two small water bodies in Malawi, southern Africa by ALCOM in collaboration with the Government of Malawi to test length-based, tag-recapture and empirical methods to estimate growth, mortality rates and fish production.

Almost the same estimates of growth performance indicators were obtained using length frequency analysis and multiple tag recapture analysis. Different estimates were found on biomass and production using the methods including empirical models.

While use of length frequency methods (using non selective gears) and tag recapture are recommended for estimating growth parameters, length frequency methods (using non selective gears) have advantage over the latter because of their low input requirement in manhours. Single catch tag-recapture method is recommended for estimating fish standing biomass. It is recommended that studies be carried out to develop empirical models which use easily measurable parameters like morphometrics and limnological characteristics of small water bodies to estimate fish yields/production or biomass. Such models can replace the recommended single catch tag-recapture because they require low inputs of time and manhours.

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TABLE OF CONTENTS

Preface

Abstract

1.0   Introduction

2.0   Methodology

3.0   Data Analysis

3.1   Length Based Methods

3.1.1   Growth parameters

3.1.2   Mortality rates

3.1.3   Fish Production

3.2   Tag-Recapture Data

3.2.1   Growth parameters(L∞ & K)

3.2.2   Mortality rates and fish production

3.3   Empirical Models

4.0   Results

4.1   Growth Parameters

4.2   Fish Production and Mortality/Survival Rates

4.3   Inputs Required to Collect Data for Different Methods

5.0   Discussion

5.1   Growth Parameters

5.2   Mortality Rates and Fish Production

6.0   Conclusions And Recommendations

7.0   References

Appendix I

Appendix II