Sharks of the Open Ocean

i III iimi mil mm B/83010 Sharks of the Open Ocean Biology, Fisheries and Conservation Edited by Merry D. Camhi Conservation Consultant, USA Ellen K. Pikitch Pew Institute for Ocean Science, Rosenstiel School of Marine and Atmospheric Science, University of Miami, USA Elizabeth A. Babcock Pew Institute for Ocean Science, Rosenstiel School of Marine and Atmospheric Science, University of Miami, USA Blackwell Science Contents List of Contributors Series Foreword Foreword Acknowledgments xxi xxix xxxii xxxiv Part I Introduction and Overview 1 Introduction to Sharks of the Open Ocean Ellen K. Pikitch, Merry D. Camhi and Elizabeth A. Babcock 1 3 Introduction The need for oceanic shark research and management Evaluating the conservation status of open ocean sharks The future of oceanic sharks References 3 4 6 8 10 Pelagic Elasmobranch Diversity Leonard J. V. Compagno 14 Introduction Pelagic shark diversity Pelagic sharks in perspective Acknowledgments References 14 15 20 22 22 The Reproductive Biology of Pelagic Elasmobranchs Franklin F. Snelson Jr., Brenda L. Roman and George H. Burgess 24 Introduction Methods and definitions Modes of reproduction Reproductive trends in pelagic elasmobranchs Reproduction in lamniform sharks Litter size Birth size Gestation period Reproductive periodicity 24 25 25 27 28 28 30 31 32 2 3 viii Contents Age and size at maturity Development Reproduction in requiem sharks Litter size Birth size Gestation period Reproductive periodicity Age and size at maturity Development Reproduction in the pelagic stingray Litter size Birth size Gestation period Reproductive periodicity Age and size at maturity Development Discussion References Part II 4 5 Life History and Status of Pelagic Elasmobranchs Introduction Biology and ecology Fisheries and status Conclusion 34 36 37 37 38 39 39 39 40 41 41 41 41 42 42 42 43 45 55 57 57 58 59 The Biology and Ecology of Thresher Sharks (Alopiidae) Susan E. Smith, Randall C. Rasmussen, DarleneA. Ramon and Gregor M. Cailliet 60 Introduction Distribution and movements Biology and ecology Age and growth Reproduction Diet Threats and status Acknowledgments References 60 60 62 62 64 64 65 66 66 The Biology and Ecology of the White Shark, Carcharodon carcharias Barry D. Bruce 69 Introduction Distribution, movements, and stock structure Geographic distribution Tagging studies and in situ observations 69 70 70 71 Contents Seasonal movements Effects of temperature Stock structure Biology and ecology Age and growth Mortality Reproduction Diet Threats and status Acknowledgments References Case Study: White Shark Movements in the North Pacific Pelagic Ecosystem Andre M. Boustany, Kevin C. M. Weng, Scot D. Anderson, Peter Pyle and Barbara A. Block 7 ix 71 71 72 72 72 74 74 75 75 76 76 82 Introduction Methods and Results References 82 83 85 The Biology and Ecology of the Shortfin Mako Shark, Isurus oxyrinchus John D. Stevens 87 Introduction Biology and ecology Age and growth Reproduction Diet Distribution and movements Distribution Migration and movements Threats and status Fisheries Stock structure and status References 87 88 88 89 89 89 89 89 90 90 91 91 The Biology and Ecology of the Salmon Shark, Lamna ditropis Kenneth I Goldman and John A. Musick 95 Introduction Biology and ecology Distribution and movements Threats and status 95 96 98 100 Contents 9 10 11 Acknowledgments References 101 102 The Biology and Ecology of the Porbeagle Shark, Lamna nasus Malcolm P. Francis, Lisa J. Natanson and Steven E. Campana 105 Introduction Distribution, movements, and stock structure Biology and ecology Length-length and length-weight relationships Length at birth and maturity Growth, maturity, and recruitment Maximum length, longevity, and natural mortality Length, age, and sex composition Reproduction Diet Threats and status Fisheries Stock status Acknowledgments References 105 106 107 107 107 107 109 109 110 110 110 110 111 111 111 The Biology and Ecology of the Silky Shark, Carcharhinus falciformis Ramon Bonfil 114 Introduction Distribution, movements, and stock structure Geographic, depth, and age-related distribution Movements and migrations Stock structure and genetic studies Biology and ecology Reproduction Age and growth Diet Threats and status Silky sharks in tropical fisheries Stock assessment and fisheries management Conservation of silky sharks References 114 115 115 117 117 119 119 121 122 122 122 123 124 125 The Biology and Ecology of the Oceanic Whitetip Shark, Carcharhinus longimanus Ramon Bonfil, Shelley Clarke and Hideki Nakano 128 Introduction Distribution and movements 128 129 Contents 12 13 Biology and ecology Diet Reproduction Age and growth Demographic analyses Fisheries Catch and catch-rate data Utilization Management and conservation Acknowledgments References 131 131 131 132 133 134 134 135 136 137 137 The Biology and Ecology of the Blue Shark, Prionace glauca Hideki Nakano and John D. Stevens 140 Introduction Biology and ecology Age and growth Reproduction Diet Distribution and movements Distribution Migration and movements Threats and status Fisheries Population status Acknowledgments References 140 141 141 141 142 143 143 143 145 145 147 148 148 The Biology and Ecology of the Pelagic Stingray, Pteroplatytrygon violacea (Bonaparte, 1832) Julie A. Neer 152 Introduction Biology and ecology Distribution and movements Threats and status Conclusions Acknowledgments References 152 153 155 157 157 158 158 Part III Trends in Catches and Abundance of Pelagic Sharks Introduction Description of fisheries and catch data 161 163 163 Contents Abundance trends from catch-rate data Recommendations References 14 15 16 164 165 165 A Global Overview of Commercial Fisheries for Open Ocean Sharks Merry D. Camhi, Elizabeth Lauck, Ellen K. Pikitch and Elizabeth A. Babcock 166 Introduction Data limitations and collection efforts Global elasmobranch catches Pelagic sharks in Atlantic Ocean fisheries Pelagic sharks in Pacific Ocean fisheries Pelagic sharks in Indian Ocean fisheries A catalog of pelagic-shark-fishing nations Major pelagic-shark-fishing nations Moderate pelagic-shark-fishing nations Discussion Acknowledgments References 166 167 170 172 174 175 176 179 182 185 186 186 Recreational Fishing for Pelagic Sharks Worldwide Elizabeth A. Babcock 193 Introduction Information sources Recreational fishing by country Australia New Zealand United States United Kingdom Ireland Canada South Africa Italy Other countries Conclusions Acknowledgments References 193 194 194 194 197 198 200 200 200 201 201 201 201 202 202 Case Study: Blue and Mako Shark Catch Rates in US Atlantic Recreational Fisheries As Potential Indices of Abundance Gregory Skomal, Elizabeth A. Babcock and Ellen K. Pikitch 205 Introduction Methods 205 206 Contents Results Discussion Acknowledgments References 17 Catches of Pelagic Sharks by Subsurface Longline Fisheries in the South Atlantic Ocean during the Last Century: A Review of Available Data with Emphasis on Uruguay and Brazil 213 Fabio H. V. Hazin, Matt K. Broadhurst, Alberto F. Amorim, Carlos A. Arfelli and Andres Domingo Introduction Catches of pelagic sharks by distant-water longline fleets Japan China Taiwan Korea Spain Catches of pelagic sharks by longline fleets from coastal nations Uruguay Brazil Factors influencing small-scale temporal and spatial trends in catches of blue shark Management of pelagic sharks and directions for future research Conclusions Acknowledgments References 18 19 207 209 211 211 214 215 215 215 215 216 216 216 217 219 223 225 226 226 227 Case Study: Blue Shark Catch-Rate Patterns from the Portuguese Swordfish Longline Fishery in the Azores Alexandre Aires-da-Silva, Rogerio Lopes Ferreira andJoao Gil Pereira 230 Introduction Fishing seasons Standardized catch rates Length-frequency samples Conclusions Acknowledgments References 230 231 232 233 233 234 234 Case Study: Trends in Blue Shark Abundance in the Western North Atlantic As Determined by a Fishery-Independent Survey Robert E. Hueter and Colin A. Simpfendorfer 236 Introduction Survey catch records 236 237 Contents Trends in abundance Acknowledgments References 238 240 241 Case Study: Elasmobranch Bycatch in the Pelagic Longline Fishery off the Southeastern United States, 1992-1997 Lawrence R. Beerkircher, Enric Cortes and Mahmood S. Shivji 242 Introduction Methods and Results Acknowledgments References 242 242 246 246 Pelagic Shark Fisheries in the Indian Ocean Malcolm J. Smale 247 Introduction Shark catches Commonly caught species Lamnidae Alopiidae Carcharhinidae Management and conservation Acknowledgments References 247 248 252 252 253 253 254 255 255 Case Study: The Bycatch of Pelagic Sharks in Australia's Tuna Longline Fisheries John D. Stevens and Sally E. Wayte 260 Introduction Species composition Catch rates and catch Length and sex composition Stock status Acknowledgments References 260 261 262 265 267 267 267 Case Study: Catch and Management of Pelagic Sharks in Hawaii and the US Western Pacific Region Paul J. Dalzell, R. Michael Laws and Wayne R. Haight 268 Introduction Catches and catch rates Stock status Economics and management Conclusions Acknowledgments References 268 269 271 272 273 273 273 Contents 24 25 26 xv Case Study: Pelagic Shark Fisheries along the West Coast of Mexico Oscar Sosa-Nishizaki, J. Fernando Marquez-Farias and Carlos J. Villavicencio-Garayzar 275 Introduction Artisanal fishery Pelagic longline fishery Gill-net fisheries Shrimp trawl bycatch Fisheries interactions and stock assessment Regulations Conclusions References 275 276 277 277 278 278 279 280 281 V Methods to Improve Understanding of Pelagic Sharks: Demographics, Assessment, and Stock Structure Introduction Demography Stock structure and movement Stock assessment Conclusion 283 285 285 286 286 287 Intrinsic Rates of Increase in Pelagic Elasmobranchs Susan E. Smith, David W.Au and Christina Show 288 Introduction Methods Estimating the intrinsic rate of increase rz(MSY) or rebound potential Choosing and applying life-history parameters Precision Results Discussion Acknowledgments References 288 290 290 291 292 292 292 294 294 Shark Productivity and Reproductive Protection, and a Comparison with Teleosts David W.Au, Susan E. Smith and Christina Show 298 Introduction Methods Estimating productivity Parameters of rebound potential Reproductive protection against collapse and time for recovery Results The mortality corresponding to MSY 298 299 299 299 302 303 303 xvi Contents Productivities: sharks and teleosts 303 Reproductive protection against collapse and recovery times from depletion 304 Discussion 306 Acknowledgments 306 References 306 27 28 29 Comparative Life History and Demography of Pelagic Sharks Enric Cortes 309 Introduction Methods Analysis of differences in life-history traits among species Estimation of population parameters and elasticities The simulation and projection process Results Differences in life-history traits among pelagic shark species Simulation of population parameters and elasticities, and position of the inflection point of population growth curves Discussion Links between life-history traits and population statistics of pelagic sharks: conservation and management implications Interpretation of rates of increase and the position of the inflection point of population growth curves Acknowledgments References 309 310 310 311 313 314 314 Molecular Markers and Genetic Population Structure of Pelagic Sharks Edward J. Heist 323 Introduction Molecular markers Genetic stock structure of pelagic sharks Conclusions Acknowledgments References 323 325 328 329 330 330 Case Study: Rapid Species Identification of Pelagic Shark Tissues Using Genetic Approaches Mahmood S. Shivji, Melissa Pank, Lisa J. Natanson, Nancy E. Kohler and Michael J. Stanhope Introduction General methods Case studies Conclusions 314 316 316 318 320 320 334 334 335 335 337 Contents 30 31 xvii Acknowledgments References 337 338 Stock Structure of the Blue Shark (Prionace glauca) in the North Atlantic Ocean Based on Tagging Data Nancy E. Kohler and Patricia A. Turner 339 Introduction Methods Results and discussion Distribution of sizes and sex ratios Transregional movements Summary Acknowledgments References 339 341 341 342 342 347 348 348 Why Are Bayesian Methods Useful for the Stock Assessment of Sharks? Murdoch K. McAllister, Ellen K. Pikitch and Elizabeth A. Babcock 351 Introduction What should be the main goal of stock assessment for sharks? How has advice been provided for shark fishery management? Demographic analysis Fitting surplus production models to times-series of observations on relative abundance Age-structured, length-structured, or stage-structured modeling Some problems encountered with conventional assessment methods Compiling basic biological and fishery data Integrating different types of data and results Reconciling contradictory data, information, and results Thoroughly accounting for uncertainty Conveying uncertainty in a meaningful way to decision makers How should uncertainty be dealt with in stock assessment? Identify alternative plausible hypotheses Evaluate the weight of evidence in support of each hypothesis Use decision tables without mathematical probabilities Bayesian methods Bayes' theorem Example: National Marine Fisheries Service assessment of Atlantic coastal sharks A Bayesian stock assessment of Atlantic large coastal sharks Recommendations for learning Bayesian stock assessment methods Conclusions Acknowledgments References 351 352 352 352 354 355 355 355 356 356 356 357 357 358 358 358 359 359 361 361 363 364 364 364 Contents 32 Embracing Movement and Stock Structure for Assessment of Galeorhinus galeus Harvested off Southern Australia Terence I. Walker, Bruce L. Taylor, Lauren P. Brown and Andre E. Punt 369 Introduction Stock structure and movement patterns Spatially aggregated stock assessment Stock assessment incorporating movement rates and stock structure Movement simulation model Spatially structured stock assessment model Movement estimation within an integrated tag model Conclusions Appendix: movement estimation within an integrated tag model Model parameters Likelihood function Movement and survival Mortality Growth Acknowledgments References 369 373 374 375 376 377 377 384 385 385 386 386 387 388 388 389 Part V 33 34 Conservation and Management Outlook for Pelagic Sharks Introduction Data collection and assessment Shark fishery management New technologies Conclusion 393 395 395 395 396 396 Conservation Status of Pelagic Elasmobranchs Merry D. Camhi 397 Introduction Threats Conservation status Discussion Acknowledgments References 397 398 400 410 412 412 Domestic and International Management for Pelagic Sharks Merry D. Camhi, Sonja V. Fordham and Sarah L. Fowler 418 Introduction Management tools available for pelagic sharks Fishing restrictions 418 419 420 Contents Prohibitions on finning Species protections International and regional management action Fisheries agreements Wildlife conservation agreements Domestic management action Conclusions Recommendations Acknowledgments References 35 36 • The Rise and Fall (Again) of the Porbeagle Shark Population in the Northwest Atlantic Steven E. Campana, Warren Joyce, Linda Marks, Peter Hurley, Lisa J. Natanson, Nancy E. Kohler, Christopher F. Jensen, Joseph J. Mello, Harold L. Pratt Jr., Sigmund Myklevoll and Shelton Harley 420 423 425 425 430 433 437 438 439 439 445 Introduction Fishery and population dynamics The fishery Trends in length and age composition Commercial catch rates Estimation of rates of natural and total mortality Recent mortality rates based on Paloheimo Z's Petersen calculations of abundance and exploitation rate Yield per recruit Age- and sex-structured population model Discussion Acknowledgments References 445 446 446 449 450 450 453 453 454 455 455 459 460 Methods to Reduce Bycatch Mortality in Longline Fisheries Daniel L. Erickson and Steven A. Berkeley 462 Introduction Methods Gulf of Mexico pelagic longline experiment Gulf of Alaska demersal longline experiment Results Gulf of Mexico pelagic longline experiment Gulf of Alaska demersal longline experiment Discussion Acknowledgments References 462 463 463 464 465 465 467 468 470 470 xx 37 38 Index Contents Data Collection, Research, and Assessment Efforts for Pelagic Sharks by the International Commission for the Conservation of Atlantic Tunas Elizabeth A. Babcock and Hideki Nakano 472 Introduction Assessment of blue and shortfin mako sharks Conclusions References 472 474 476 477 Pelagic Sharks and the FAO International Plan of Action for the Conservation and Management of Sharks Rachel D. Cavanagh, Sarah L. Fowler and Merry D. Camhi 478 Introduction Progress Discussion Lack of political will Lack of technical capacity Lack of resources Pelagic sharks and the IPOA Summary Acknowledgments References 478 481 485 485 486 486 487 488 489 489 493