THE FISHERIES ECOLOGY OF AFRICAN FLOODPLAINS CONTENTS

by

R.L.Welcomme
Fishery Resources Officer
Aquatic Resources Surveys and Evaluation Service
Fishery Resources Division

COMMITTEE FOR INLAND FISHERIES OF AFRICA (CIFA)

CIFA documents are issued in three series:

CIFA Report

Report of each session, in English and French.

CIFA Technical Paper

Selected scientific and technical papers, including some of those contributed as working documents to sessions of the Committee and reports of subcommittees, working parties, study groups and correspondence networks. Published in English and French.

CIFA Occasional Papers

Papers of general interest to the Committee. Published in the language submitted, either in English or French.

Copies of these documents can be obtained from:

Secretary
Committee for inland Fisheries of Africa
Department of Fisheries
FAO
Via delle Terme di Caracalla
00100 Rome, Italy

PREPARATION OF THIS DOCUMENT

At the First Session of the Committee for Inland Fisheries of Africa (N'Djamena, Chad, 1972) it was recommended: Recommendation CIFA/72/9 that a Correspondence Working Group be established for the collection of existing data on floodplain fisheries and for the stimulation of research on these areas and that members of the group should subsequently meet in order to prepare a technical publication on the subject (CIFA, 1973). This technical Paper is intended to partially fulfil the first part of the recommendation. Based on a review of the literature, personal observations and unpublished information supplied by various African fishery workers, it summarizes what is known of the fisheries ecology of the floodplain systems of the African continent. Some observations are necessarily speculative, or based on circumstantial evidence, but it is hoped that these will stimulate interest and discussion and serve as a basis for future work on this area.

FOOD AND AGRICULTURE ORGANIZATION OF THE UNITED NATIONS
Rome, May 1975

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CONTENTS

ACKNOWLEDGEMENTS

SUMMARY

1. INTRODUCTION

2. THE MORPHOLOGY OF FLOODPLAINS

2.1 General Morphology

2.2 Classification of Floodplains

2.3 Distribution and Area

3. DRY SEASON USES OF FLOODPLAIN

4. LIMNOLOGICAL FACTORS

4.1 Flood Regimes

4.2 Physical and Chemical Factors

4.3 Phytoplankton and Other Organisms

4.4 Summary

5. FISH BIOLOGY

5.1 Distribution of Fish within the System

5.2 Migration

5.3 Reproduction

5.4 Feeding

5.5 Growth

5.6 Mortality

5.7 Summary

6. METHODS OF FISHING

6.1 Seasonality of Fishing

6.2 Fishing by Confining Fish

6.3 Fishing for Migrating Fish

7. CATCH AND PRODUCTIVITY

7.1 Productivity

7.2 Standing Stocks

7.3 Catch

7.4 Fluctuations in Catch between Years

7.5 Summary

8. MODELS OF FLOODPLAIN FISHERIES

8.1 A Simple Computer Model of a Floodplain and Its Fish Populations

9. MANAGEMENT OF FLOODPLAINS

9.1 Effects on Fisheries of Other Uses of the Floodplain

9.2 Integrated Management of Floodplain Systems

9.3 Management of the Fishery

9.4 Manipulation of Hydrological Regime

REFERENCES

ACKNOWLEDGEMENTS

I wish to thank the many fishery workers in Africa who made this survey possible by providing data on the morphology and fisheries of their national floodplains and in particular the members of the CIFA Correspondence Working Group on Floodplain Fisheries, Messrs. A. Catchy-Ngakoudou, J.R. Durand, R.E. Hastings, J.M. Kapetsky, A. Konare, A. Mabaye, J. Okedi, C. Reizer, V.O. Sagua.

Especial thanks are also due to Mr. D. Hagborg who prepared the computer programme from the arguments presented in Section 8.1 Dr. J. Kapetsky for many discussions and ideas, and for permitting me to plunder much of his invaluable unpublished material and all my other colleagues in Headquarters and the Field who have participated in exchanges of views resulting in this summary.

SUMMARY

Floodplains are defined as those low lying areas, bordering rivers, which are seasonally inundated by overspill from the main river channel.

During the dry season there is an accumulation of nutrients on the plain in the form of animal dung, rotting vegetation and ash from the fires which sweep them towards the end of the dry period. These nutrients rapidly enter into solution during the earlier stages of flooding, and combined with the river borne silt, support a rapid growth of plants, insects and other forms of aquatic life.

This outburst of productivity provides the essential conditions for the reproduction, feeding and growth of the many species of fish which migrate onto the floodplain from the river channel with the rising waters. The flood cycle is vital to the continued survival of these fish species, and any alterations in the intensity or duration of the floods can produce changes in the fish population in following years.

Because of the great concentrations of fish occurring during migrations onto and off of the floodplain, and in floodplain pools during the dry season, the fisheries of some African floodplains are among the most important of the continent.

Rivers and their floodplains are much sought after for a variety of uses other than fisheries. Many of these uses may conflict with the maintenance of the fish communities. Dam, irrigation and drainage schemes may alter or suppress flood cycles to the detriment of fish stocks, and in many areas of Africa complete fisheries have been lost downstream of major dams. Industrial and agricultural activity can, through the discharge of toxic wastes or the use of insecticides, so pollute the environment that many species are unable to complete their life cycle. This effect, which is most marked in Europe and North America, has not yet appeared as a major problem in Africa, although it remains a potential threat.

Because of the number of competing functions rivers and their floodplains have to be treated as a multi-purpose resource. This implies management so that the sum of the yields from the component uses is maximal. To maximalize yields in this way implies considerable knowledge of the way the resource behaves under different patterns of exploitation. Unfortunately the biology and ecology of river and floodplain fisheries in Africa have been little studied and the basic information necessary for the type of decisions required for management is lacking. Due to this lack the fisheries component of river-floodplain management has been largely overlooked, and a valuable source of animal protein is in many areas threatened by projects aimed at developing an alternative aspect of the resource.

It is therefore proposed that intensified studies are necessary both on the theoretical basis of floodplain fisheries productivity, and on the practical ways in which fisheries may be integrated in the general development of such areas.