Fisheries Acoustics: Theory and Practice (Fish and Aquatic Resources)

Fisheries Acoustics......Page 2
Contents......Page 8
Series Foreword......Page 14
Preface......Page 17
Acknowledgements......Page 19
1 Introduction......Page 21
1.1 A brief history......Page 22
1.2 Synopsis......Page 26
1.3 Acoustic terminologyand symbols......Page 29
2.1 Introduction......Page 40
2.2 Sound waves......Page 41
2.2.1 Pressure and displacement......Page 42
2.2.2 Energy and intensity......Page 43
2.2.4 The decibel......Page 44
2.3 Transducers and beams......Page 46
2.3.1 The equivalent beam angle......Page 52
2.3.2 Controlling the beam shape......Page 53
2.3.4 Limits to power transmission in water......Page 55
2.4.1 Beam spreading......Page 58
2.4.2 Absorption......Page 60
2.4.3 The sound speed......Page 62
2.4.4 Pulses and ranging......Page 66
2.5 Acoustic scattering......Page 67
2.5.1 Targets large and small......Page 68
2.5.2 Target strength......Page 71
2.5.3 Standard targets......Page 73
2.5.4 Target shape and orientation......Page 76
2.5.5 Multiple targets......Page 78
2.5.6 Volume/area scattering coefficients......Page 79
2.5.7 Radiation pressure on targets......Page 80
2.6 Echo detection......Page 81
2.6.2 Noise......Page 83
2.7 The operating frequency......Page 85
Appendix 2A:Calculation of the acoustic absorption coefficient......Page 87
Appendix 2B:Calculation of the speed of sound in water......Page 88
3.1 Introduction......Page 90
3.2 Echosounders......Page 91
3.2.2 The echo-integrator......Page 94
3.2.3 The basic netsonde......Page 96
3.2.4 The scanning netsonde......Page 97
3.3 Instruments for measuring the target strength......Page 99
3.3.1 The dual-beam echosounder......Page 100
3.3.2 The split-beam echosounder......Page 102
3.4 Sonars......Page 104
3.4.2 Side-scan sonar......Page 105
3.4.3 Sector scanners......Page 108
3.4.4 Three-dimensional sonar systems......Page 113
3.4.5 The Doppler effect......Page 117
3.5 Wideband systems......Page 118
3.6 Sound source location:pingers,transponders and hydrophone arrays......Page 120
3.7.1 Transducers on or near the vessel......Page 122
3.7.2 Deep-towed bodies......Page 124
3.7.3 Vessel noise performance......Page 127
3.8 Calibration......Page 128
3.8.1 The on-axis sensitivity......Page 131
3.8.2 Experimental procedure......Page 133
3.8.3 The TVG function......Page 138
3.8.4 The equivalent beam angle......Page 139
3.8.5 Overall sensitivity and the sound speed......Page 140
3.8.6 Direction-sensing echosounders......Page 141
3.8.7 Calibration of multi-beam sonars......Page 144
3.8.8 Good calibration practice......Page 146
4.1 Introduction......Page 147
4.2 Biological sounds......Page 148
4.3 Hearing......Page 149
4.3.1 Auditory detection capability......Page 150
4.3.2 Masking and the critical bandwidth......Page 153
4.3.3 Ultrasound and infrasound......Page 157
4.4 Biological sonar......Page 159
4.5.1 High-energy sound sources......Page 165
4.5.2 Noise pollution......Page 174
4.5.3 Limiting the damage......Page 177
4.6 The swimbladder......Page 178
5.1 Introduction......Page 183
5.2.1 Interpreting the echogram......Page 184
5.2.2 Echosounder mapping......Page 186
5.2.3 Side-scan sonar......Page 191
5.2.4 Multi-beam sonar......Page 194
5.3 Echo-counting......Page 196
5.3.1 Single-target echoes......Page 197
5.3.2 Range compensation......Page 200
5.3.3 Single-beam echosounders......Page 201
5.3.4 Direction-sensing echosounders......Page 204
5.3.5 Thresholding and the sampled volume......Page 205
5.3.6 Applications......Page 206
5.4 Echo-integration......Page 207
5.4.1 Range compensation......Page 208
5.4.2 The echo-integrator equation......Page 209
5.4.3 The linearity principle......Page 211
5.4.4 Non-linear effects......Page 214
5.4.5 Integration near the seabed......Page 218
5.4.6 The threshold problem......Page 221
5.4.7 Applications......Page 222
5.5.1 Fixed sonar installations......Page 223
5.5.2 Horizontal sonar for shallow water applications......Page 225
5.5.3 Target tracking......Page 229
5.5.4 Doppler sonar......Page 230
5.5.5 Forward scattering......Page 231
Appendix 5A:The true size distribution of fish schools......Page 232
Appendix 5B:Calculation of the TVG error......Page 235
6.1 Introduction......Page 237
6.2 Target strength measurement techniques......Page 238
6.2.1 Immobile fish......Page 239
6.2.2 Live fish in cages......Page 240
6.2.3 Wild fish......Page 245
6.2.4 Modelling......Page 249
6.3.1 Immobile fish......Page 253
6.3.2 Live fish in cages......Page 255
6.3.3 Wild fish......Page 275
6.3.4 Size-dependence of target strength......Page 278
6.3.5 Modelling......Page 280
6.4 Discussion......Page 281
6.4.1 Comparison of target strength measurement techniques......Page 282
6.4.2 Classification of fish targets......Page 283
6.4.3 Variation with fish size......Page 285
6.4.4 Behaviour and physiology......Page 288
6.5 Collected target strength data for survey applications......Page 290
7.1 Introduction......Page 297
7.2 Acoustic classification of plankton......Page 299
7.3 Scattering models......Page 301
7.3.1 FL class (soft fluid-like tissues)......Page 303
7.3.2 ES class (elastic shell)......Page 306
7.3.3 GB class (gas bearing)......Page 308
7.3.4 Acoustic properties of fluid-like bodies......Page 309
7.4 Target strength......Page 311
7.5.1 Abundance estimation......Page 315
7.5.2 Size determination–the inverse problem......Page 319
7.5.3 Species identification......Page 325
7.5.4 Other methods of in situ observation......Page 328
8.1 Introduction......Page 329
8.2 Survey strategic decisions......Page 330
8.2.1 The geographical area......Page 331
8.2.2 Working time......Page 332
8.3.1 Survey objectives......Page 334
8.3.2 Stratification of effort......Page 335
8.3.3 Proportions of time allocated to transects and trawls......Page 336
8.3.4 Pre-planned track options:systematic or random designs......Page 338
8.3.5 Pre-planned track options:parallel or triangular designs......Page 344
8.3.7 Transect direction......Page 346
8.3.8 Mapping the cruise track......Page 347
8.4 Riverine surveys......Page 349
8.5.1 The outline survey......Page 353
8.5.3 Increased transect density......Page 354
8.5.4 Randomized extra transects......Page 355
8.6 Multi-ship surveys......Page 357
8.8 More specialized surveys......Page 359
8.9.1 Live-fish calibration......Page 360
8.9.2 Inter-ship comparison......Page 361
9.1 Introduction......Page 364
9.2.1 Classifying or partitioning the echo-integrals......Page 366
9.2.2 Quality control of echogram data......Page 371
9.3 Species composition......Page 372
9.3.1 Analysis of fishing samples......Page 373
9.3.2 Length-frequency distributions......Page 374
9.3.3 Proportions by species......Page 375
9.3.4 Selection of homogeneous regions......Page 376
9.4 The echo-integrator conversion factor......Page 378
9.4.1 Single species......Page 379
9.4.3 Number–weight relationships......Page 380
9.5 Abundance estimation......Page 381
9.5.1 Spatial estimates and statistical concepts......Page 382
9.5.2 Contour and distribution maps......Page 384
9.5.3 Estimation with a rectangular grid......Page 386
9.5.4 Transform methods......Page 387
9.5.5 Geostatistics......Page 389
9.6 Precision of the abundance estimate......Page 390
9.6.1 Repeated surveys......Page 391
9.6.2 Stratified random transects......Page 392
9.6.3 Geostatistical variance......Page 393
9.6.4 The degree of coverage......Page 394
9.6.5 Bootstrap or resampling methods......Page 396
9.6.6 Relative importance of various random errors......Page 397
9.7.2 Transducer motion......Page 398
9.7.3 The surface bubble layer......Page 400
9.7.4 Hydrographic conditions......Page 402
9.7.5 Fish migration......Page 403
9.7.6 Diurnal behaviour rhythms......Page 405
9.7.7 Avoidance reactions......Page 406
9.7.8 Precision of the estimated species proportions......Page 408
9.8 Accuracyof the abundance estimate......Page 409
9.8.1 Intrinsic error analysis......Page 410
9.8.2 Comparison with other methods......Page 412
References......Page 415
Species Index......Page 452
Author Index......Page 455
Subject Index......Page 464