Women engaged in artisanal fishing of the clam Venus antiqua in southern Chile, illustration by Emanuela D'Antoni

FAO Fisheries Technical Paper 448

Enhancing or restoring the productivity of natural populations of shellfish and other marine invertebrate resources


J.F. Caddy
Laboratorio Biología Pesquera
CINVESTAV Unidad Mérida
Mérida, Yucatán, México
and
O. Defeo
Laboratorio Biología Pesquera
CINVESTAV Unidad Mérida
Mérida, Yucatán, México
and Facultad de Ciencias - DINARA
Montevideo, Uruguay

FOOD AND AGRICULTURE ORGANIZATION OF THE UNITED NATIONS
Rome, 2003

Table of Contents


The designations employed and the presentation of material in this publication do not imply the expression of any opinion whatsoever on the part of the Food and Agriculture Organization of the United Nations concerning the legal status of any country, territory, city or area or of its authorities, or concerning the delimitation of its frontiers or boundaries.

ISBN 92-5-105017-1
ISSN 0429-9345

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© FAO 2003

Caddy, J.F.; Defeo, O.
Enhancing or restoring the productivity of natural populations of shellfish and other marine invertebrate resources.
FAO Fisheries Technical Paper. No. 448. Rome, FAO. 2003. 159p.

ABSTRACT

A broad review is provided of factors relevant to enhancing populations of invertebrate resources and methods promoting their recovery by natural recruitment, restocking or habitat restoration. The review focuses on the biological, technical, environmental, economic and biological factors affecting the feasibility of restoring or enhancing productivity of commercially valuable local invertebrate populations. Three categories of enhancement activity are recognized: restoring or enhancing stocks by conventional management methods, transplanting or seeding, and the use of juveniles produced from collectors in the wild or from hatcheries. Some guidelines are provided on issues related to enhancing recruitment, site selection, experimental closures, ecosystem considerations including predator control, as part of a stock management and enhancement programme. Ownership and co-management issues, and the necessary decisional rules for successful management are discussed, as well as how to reconcile the enhancement programme with other uses of the coastline. Spatial and geographical considerations are addressed, including allocation of areas for enhancement, rotational harvest schemes, use of refugia for protecting juveniles and the spawning stock, and the impact of the use of coastal zones for other human activities.


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TABLE OF CONTENTS


CONTENTS

PREPARATION OF THIS DOCUMENT

ACKNOWLEDGEMENTS

INTRODUCTION

1. THE CONTEXT FOR ENHANCEMENT OF INVERTEBRATE STOCKS

1.1. Functional categories of invertebrate marine resources
1.2. The context for shellfish enhancement and restoration
1.3. Possible approaches to resource manipulation: some working definitions

2. ASSESSING THE STATE OF INVERTEBRATE RESOURCES

2.1. Stock assessment methods applied to sedentary and semi-sedentary resources

2.1.1. Biomass estimates and distribution
2.1.2. Growth
2.1.3. Mortality
2.1.4. Merging growth and mortality for stock enhancement: cohort projections
2.1.5. Production/area estimates
2.1.6. Production modelling

2.2. Settlement dynamics and the stock-recruitment relationship

2.2.1. Settlement
2.2.2. The stock-recruitment relationship
2.2.3. Compensation or depensation?

2.3. Information requirements for monitoring stock condition and recovery
2.4. Management advice and organizational requirements for managing invertebrates
2.5. The use of indicators and reference points

2.5.1. The management context for indicators and reference points
2.5.2. Fishing indicators, recruitment success and reference points
2.5.3. Fecundity-based reference points
2.5.4. Other empirical reference points

2.6. Harvest control laws and indicators of productivity for managing and restoring invertebrate fisheries

3. METAPOPULATIONS, NATURAL STOCK REGENERATION AND SPATIALLY EXPLICIT MANAGEMENT TOOLS

3.1. Metapopulations
3.2. Source and sinks and their practical implications
3.3. Linking natural restocking and spatially explicit management tools

3.3.1. MPAs and ad hoc area closures
3.3.2. The source-sink hypothesis for stock replenishment and the siting of MPAs
3.3.3. Rotational harvesting schemes
3.3.4. Average meat count regulations

3.4. Controlled field experimentation and natural stock regeneration

4. EXPERIMENTAL CULTIVATION AND SEEDING

4.1. A brief historical overview of shellfish hatcheries
4.2. Viability of stocked organisms
4.3. Transplanting and thinning
4.4. Recruitment enhancement and population seeding
4.5. Field identification in the wild of stocked invertebrates introduced from hatcheries
4.6. The use of collectors
4.7. Effects of stocking on natural populations
4.8. Production under controlled conditions
4.9. Genetic factors

5. ECOSYSTEM ISSUES

5.1. Trophic cascades
5.2. Predators, competitors and their control
5.3. Interspecific interactions and side effects of fishing on the ecosystem
5.4. Invasions, species introductions, massive mortalities and diseases
5.5. Techno-ecological interdependencies

6. THE ROLE OF HABITAT IN STOCK ENHANCEMENT AND RESTORATION

6.1. Habitat requirements
6.2. Bottlenecks in production
6.3. Stock replacement, habitat rehabilitation or mitigation?
6.4. Choosing a site for enhancement activities

6.4.1. Sediment properties
6.4.2. Hydrodynamic factors
6.4.3. Carrying capacity and habitat suitability

7. GUIDELINES FOR CONDUCTING AND EVALUATING STOCK ENHANCEMENT PROGRAMMES

7.1. Experimental design

7.1.1. Local scale
7.1.2. Large scale

7.2. Technical feasibility
7.3. Economic feasibility
7.4. Evaluating the success of enhancement exercises

8. MANAGEMENT OF ENHANCEMENT AND USER RIGHTS

8.1. The social context of stock enhancement
8.2. Legislation and ownership
8.3. Co-management

REFERENCES

ANNEX I. A BRIEF OUTLINE OF THE TRAFFIC LIGHT METHOD

BACK COVER


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