Marine Fisheries Ecology

Preface ix

Acknowledgements xii

1 Marine fisheries ecology: an introduction 1

1.1 Introduction 1

1.2 Fisheries of the world 1

1.2.1 History of fisheries 1

1.2.2 Fishery science 6

1.2.3 Diversity of fisheries 7

1.3 Patterns of exploitation 9

1.3.1 Boom and bust 9

1.3.2 Conservation and ecosystem concerns 14

1.4 Why manage fisheries? 14

1.5 Objectives of management 15

1.5.1 Range of objectives 15

1.5.2 Balancing objectives 16

1.5.3 From objective to action 17

1.6 Meeting management objectives 17

1.7 Structure of this book 18

Summary 20

2 Marine ecology and production processes 21

2.1 Introduction 21

2.2 Primary production: sources and magnitude 21

2.3 Phytoplanktonic production 22

2.3.1 Links between production and physical processes 22

2.3.2 Upwellings and fronts 24

2.3.3 Rates of phytoplanktonic production 25

2.4 Non-phytoplanktonic production 28

2.4.1 Macroalgae 28

2.4.2 Mangroves 29

2.4.3 Coral reef algae 29

2.4.4 Seagrasses and marsh plants 30

2.4.5 Microphytobenthos 31

2.5 Heterotrophic production 31

2.5.1 The fate of primary production 31

2.5.2 Transfer along the food chain 32

2.5.3 Production of fished species 34

2.5.4 Linking primary production and landings 37

Summary 38

3 Fished species life histories and distribution 39

3.1 Introduction 39

3.2 Fishes 39

3.3 Invertebrates 41

3.4 Life histories 55

3.4.1 Sex sex reversal and sex ratios 55

3.4.2 Growth maturity and longevity 56

3.4.3 Egg size fecundity and reproduction 59

3.5 Distribution in space and time 62

3.5.1 Geographical ranges and stock structures 62

3.5.2 Migration 62

3.5.3 Larval transport retention and dispersal 65

3.5.4 Metapopulations 68

Summary 69

4 Population structure in space and time 70

4.1 Introduction 70

4.2 Recruitment 70

4.2.1 Spawner and recruit relationships 71

4.2.2 Mortality during the early life history 78

4.2.3 Depensation 83

4.2.4 Regulation in fish populations 85

4.3 Density-dependent habitat use 86

Summary 88

5 Fishing gears and techniques 90

5.1 Introduction 90

5.2 From shoreline gathering to satellites 90

5.3 Modern commercial fishing gears 94

5.3.1 Towed fishing gear 95

5.3.2 Static fishing gear 103

5.4 Other fishing techniques 106

5.5 Conservation methods 108

Summary 111

6 Fishers: socioeconomics and human ecology 112

6.1 Introduction 112

6.2 Motivations for fishing 112

6.2.1 Food 112

6.2.2 Income 113

6.3 Modifications to fishing behaviour 115

6.3.1 Social 115

6.3.2 Religion 117

6.4 Conflicts and conflict resolution 118

6.4.1 Competing for fish 118

6.4.2 Fish wars 121

6.4.3 Fishers in the political process 122

6.4.4 Traditional management systems 123

6.4.5 Customary marine tenure 124

6.4.6 Co-management 125

Summary 126

7 Single-species stock assessment 127

7.1 Introduction 127

7.2 Balancing birth and death 127

7.3 Surplus production models 128

7.3.1 Stability 128

7.3.2 Models of population growth 130

7.3.3 Fitting models to data 130

7.3.4 Surplus production models in action 132

7.4 Delay–difference models 135

7.4.1 Delay–difference models in action 137

7.5 Virtual population analysis 138

7.5.1 Age-based cohort analysis 140

7.5.2 Length-based cohort analysis 143

7.6 Statistical catch-at-age methods 144

7.7 Yield-per-recruit models 145

7.7.1 Yield-per-recruit models in action 146

7.8 Incorporating recruitment 149

7.8.1 Replacement lines 149

7.8.2 Replacement lines in action 150

7.9 Confronting risk and uncertainty 152

7.9.1 Bayesian analysis 153

7.9.2 Resampling methods 154

7.10 Biological reference points 155

Summary 157

8 Multispecies assessment and ecosystem modelling 159

8.1 Introduction 159

8.2 Multispecies surplus production 159

8.2.1 Multispecies surplus production in action 160

8.3 Multispecies yield per recruit 162

8.3.1 Multispecies yield per recruit in action 162

8.4 Multispecies virtual population analysis 162

8.4.1 Multispecies VPA in action 164

8.4.2 Applying MSVPA data to single-species model 169

8.5 Predators prey and competitors 169

8.5.1 Predator–prey dynamics 169

8.5.2 Competition an unexpected result 170

8.5.3 Management implications 171

8.6 Size spectra 171

8.7 Ecosystem models 173

8.7.1 Ecosystem models in action 174

Summary 177

9 Getting the data: stock identity and dynamics 178

9.1 Introduction 178

9.2 Stock identification 178

9.2.1 The stock concept 178

9.2.2 Methods of stock identification 178

9.3 Stock dynamics 184

9.3.1 Sampling 184

9.3.2 Length weight and age 189

9.3.3 Growth 195

9.3.4 Maturity 199

9.3.5 Fecundity 199

9.3.6 Mortality 201

9.4 The impact of errors 203

Summary 204

10 Getting the data: abundance catch and effort 205

10.1 Introduction 205

10.2 Abundance 205

10.2.1 Survey design 205

10.2.2 Visual census methods 206

10.2.3 Acoustic methods 209

10.2.4 Trawl surveys 210

10.2.5 Depletion methods 213

10.2.6 Mark–recapture methods 214

10.2.7 Egg production methods 214

10.3 The fishery 219

Summary 221

11 Bioeconomics 223

11.1 Introduction 223

11.2 The value of fisheries 223

11.2.1 Trade in fished species 223

11.2.2 Catch values and employment 224

11.3 Bioeconomic models 225

11.3.1 Descriptive bioeconomics 226

11.3.2 Optimal fishing strategies 230

11.3.3 Bayesian methods 235

11.4 Economic vs. social management objectives 237

11.4.1 Subsidies 237

11.4.2 The case for economic efficiency 237

Summary 238

12 Fishing effects on populations and communities 239

12.1 Introduction 239

12.2 Vulnerability to fishing 239

12.2.1 Behaviour 239

12.2.2 Life histories 241

12.3 Intraspecific effects 242

12.3.1 Age and size structure 242

12.3.2 Reproduction 243

12.3.3 Genetic structure 244

12.4 Community effects 245

12.4.1 Diversity 245

12.4.2 Community structure 250

12.4.3 Size structure 251

12.4.4 Competition and trophic interactions 252

Summary 256

13 Bycatches and discards 258

13.1 Introduction 258

13.2 Catches discards and bycatches 258

13.2.1 Definitions 258

13.2.2 Reasons for discarding 258

13.3 Alternatives to discarding 260

13.4 Fisheries and bycatches 260

13.5 Incidental captures 262

13.5.1 Seabirds 262

13.5.2 Sea turtles 264

13.5.3 Sea snakes 265

13.5.4 Marine mammals 265

13.6 Methods to reduce bycatches 267

13.7 Ghost fishing 267

13.8 Sociocultural differences 270

Summary 271

14 Impacts on benthic communities habitats and coral reefs 272

14.1 Introduction 272

14.2 Fishing disturbance 272

14.2.1 Fishing vs. natural disturbance 272

14.2.2 Distribution of fishing disturbance 273

14.3 Direct effects of fishing gear on the seabed 276

14.3.1 Towed fishing gear 276

14.3.2 Direct effects on the substratum 277

14.3.3 Effects on infauna 277

14.3.4 Effects on epifauna 281

14.3.5 Meta-analysis 284

14.4 Effects of static fishing gears 284

14.5 Long-term effects 285

14.6 Fishing as a source of energy subsidies 288

14.6.1 Have population changes occurred? 290

14.7 Indirect effects on habitats 290

14.7.1 Loose seabeds 290

14.7.2 Coral reefs 291

Summary 293

15 Fishery interactions with birds and mammals 294

15.1 Introduction 294

15.2 Birds 294

15.2.1 Competition between birds and fisheries 296

15.2.2 Benefits of discarding 300

15.2.3 Waders and shellfish 301

15.3 Mammals 303

15.3.1 Competition between mammals and fisheries 304

15.3.2 Prey release 307

Summary 309

16 A role for aquaculture? 310

16.1 Introduction 310

16.2 Aquaculture past and present 310

16.3 What is cultivated? 312

16.4 Production systems 313

16.5 Feeding constraints 314

16.6 Prospects for expansion 314

16.6.1 Cage cultivation 316

16.6.2 Stock enhancement and ranching 318

16.7 Case studies 319

16.7.1 Shrimp farming 319

16.7.2 Bivalve mariculture 322

Summary 326

17 Management and conservation options 327

17.1 Introduction 327

17.2 Management objectives strategies and actions 327

17.2.1 From objective to action 327

17.2.2 Catch control 328

17.2.3 Effort control 331

17.2.4 Technical measures 331

17.2.5 Management in action 332

17.3 Improving management 335

17.3.1 Enforcement and compliance 335

17.3.2 Co-management 337

17.3.3 Ownership of resources and harvesting rights 338

17.3.4 Uncertainty and the precautionary approach 338

17.3.5 Role of science 339

17.4 Multispecies and ecosystem-based management 341

17.4.1 What are the objectives? 341

17.4.2 What can be achieved? 341

17.5 Managing fisheries for conservation 342

17.5.1 Endangered species 342

17.5.2 Habitats 343

17.5.3 Protected areas and no-take zones 344

17.6 Future trends 346

17.6.1 Fisheries science 346

17.6.2 Fisheries management 346

Summary 347

References 348

Appendices

1 List of symbols 380

2 Fisheries websites 385

3 Geographic index 389

Index 393