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Part I Introduction and Overview Sharks of the Open Ocean: Biology, Fisheries and Conservation. Edited by M. D. Camhi, E. K. Pikitch and E. A. Babcock © 2008 Blackwell Publishing Ltd. ISBN: 978-0632-05995-9

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Page 1: Sharks of the Open Ocean || Introduction to Sharks of the Open Ocean

Part I

Introduction and Overview

Sharks of the Open Ocean: Biology, Fisheries and Conservation. Edited by M. D. Camhi, E. K. Pikitch and E. A. Babcock

© 2008 Blackwell Publishing Ltd. ISBN: 978-0632-05995-9

Page 2: Sharks of the Open Ocean || Introduction to Sharks of the Open Ocean

Chapter 1

Introduction to Sharks of the Open Ocean

Ellen K. Pikitch, Merry D. Camhi and Elizabeth A. Babcock

Introduction

The chondrichthyans, or cartilaginous fi shes, are among the oldest extant taxa of verte-brates, having survived for more than 400 million years. Fishes that were morphologically similar to modern sharks swam in the seas when dinosaurs walked on land (Grogan and Lund, 2004). Cartilaginous fi shes range from planktivores to apex predators, and exhibit every reproductive mode known in vertebrates, from egg laying to placental vivipar-ity (Snelson et al., 2008). They are found throughout the world’s oceans – from coastal waters to the open ocean, from the surface to depths of 3,000 m (Priede et al., 2006).

Of the roughly 1,160 extant species of cartilaginous fi shes, 26–31 species (about 2.5%) are oceanic (Compagno, 2008), spending much of their life in open ocean waters away from continental landmasses. Oceanic waters are generally less productive and contain less biomass and less diversity than coastal waters. Nevertheless, there are also hot spots of relatively high productivity and biodiversity in the open ocean, generally associated with nearby structures such as seamounts, as well as areas where eddies frequently form (Worm et al., 2003). Areas of high productivity can vary seasonally, or shift with oceano-graphic conditions, so that it is necessary for tuna, billfi shes, sharks, turtles, seabirds, and other large animals of the high seas to migrate long distances (Block et al., 2001). The open ocean sharks are particularly well adapted to this changing environment, possessing the ability to migrate across ocean basins. For example, blue sharks (Prionace glauca, Carcharhinidae) routinely cross the Atlantic (Kohler and Turner, 2008), and white sharks (Carcharodon carcharias, Lamnidae) tagged off the Pacifi c Coast of North America have traveled to the Hawaiian Islands (Boustany et al., 2002, 2008) and from South Africa to Western Australia (Bonfi l, 2005). The oceanic species also tend to produce larger litter sizes than related coastal species, which Snelson et al. (2008) suggest may be an adapta-tion to the scarce and patchy food resources in the open ocean. These large litter sizes do not make them more productive than other sharks; rather, the oceanic species fall into the middle of the range of shark productivities (Smith et al., 2008a).

While there are far fewer species of elasmobranchs (sharks and rays) in the open ocean than in coastal waters, these species are wide-ranging and relatively numerous, and play an important role in the food webs of the high seas. Sharks are the apex predators of the open

Sharks of the Open Ocean: Biology, Fisheries and Conservation. Edited by M. D. Camhi, E. K. Pikitch and E. A. Babcock

© 2008 Blackwell Publishing Ltd. ISBN: 978-0632-05995-9

Page 3: Sharks of the Open Ocean || Introduction to Sharks of the Open Ocean

4 Sharks of the Open Ocean

ocean, feeding on tunas, other fi shes, and squid. Historically, they were quite common in the high seas and were caught in most fi shing operations. In high-seas fi sheries for tunas and swordfi sh, the most common bycatch species are sharks – often blue and silky (Carcharhinus falciformis, Carcharhinidae) sharks (Williams, 1999; Beerkircher et al., 2008; Hazin et al., 2008). Many recent studies have demonstrated declines in the biomass of top predators, including sharks, throughout the world’s oceans (Friedlander and DeMartini, 2002; Myers and Worm, 2003; Hutchings and Reynolds, 2004). Given the potential importance of apex predators in structuring marine food webs (Estes et al., 1998), there is a critical need for increased understanding of the biology, current status, and ecological role of oceanic sharks. These species have received less research attention than their coastal relatives, in part because of the diffi culty of studying wide-ranging ani-mals that spend most of their lives far from land.

The need for oceanic shark research and management

In 2000, the editors of this book and the Ocean Wildlife Campaign convened a symposium on open ocean sharks, called the International Pelagic Shark Workshop, in Pacifi c Grove, California. At that time, large and expanding high-seas fi sheries (Fig. 1.1) were killing hundreds of thousands of sharks a year as both directed catch and bycatch, yet few studies had been conducted on the biology of oceanic sharks or their capacity to sustain these fi sh-eries. Although the ranges of oceanic sharks often overlap the 200-nautical-mile exclusive economic zones of coastal nations, where there is some potential for management, many of these sharks are also caught in international waters, where shark fi shing is generally not regulated. Open ocean sharks are apex predators and, like virtually all chondrichthyans, have a limited ability to sustain fi sheries.

Other fishes and invertebrates

Sharks and rays

Tuna and billfishes

16

14

12

10

18

Cat

ches

(x1

,000

,000

t)

1950

1955

1960

1965

1970

1975

Year

1980

1985

1990

1995

2000

6

4

2

0

Fig. 1.1 Total fi sh catches in the high seas, defi ned as all areas not included in the exclusive economic zones (i.e., within 200 nautical miles of the coast) of any country, from 1950 to 2001 (Watson et al., 2004; Pauly, 2005).

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Introduction to Sharks of the Open Ocean 5

One of the few well-studied populations of oceanic sharks was that of the Northwest Atlantic porbeagle (Lamna nasus, Lamnidae). This population had collapsed in the 1960s from severe overfi shing, and had recovered somewhat during the 1980s. Since the 1990s, the porbeagle population has declined to the lowest levels on record, despite the fi shery being strictly controlled under a management plan that is intended to be precautionary (Campana et al., 2008). We were concerned that other pelagic sharks with similar life histories might also be experiencing unsustainable fi shing pressure, and decided a symposium would help highlight the research and management needs for these species.

The International Pelagic Shark Workshop brought together 130 fi shery scientists, man-agers, and conservationists from 12 countries. The Workshop objectives were to collate all available biological and fi shery data for oceanic sharks subject to fi sheries and to identify additional data and analyses required for assessment and for the purposes of fi shery manage-ment. We focused on 12 oceanic pelagic and coastal/outer-shelf pelagic species of special management concern from four families: Alopiidae – pelagic thresher (Alopias pelagicus), bigeye thresher (A. superciliosus), and common thresher (A. vulpinus); Lamnidae – shortfi n mako (Isurus oxyrinchus), longfi n mako (I. paucus), salmon shark (Lamna ditropis), and porbeagle (L. nasus); Carcharhinidae – silky (Carcharhinus falciformis), oceanic whitetip (C. longimanus), and blue shark (P. glauca); and Dasyatidae – pelagic stingray (Pteroplatytrygon violacea) (Table 1.1). The white shark (Carcharodon carcharias, Lamnidae) was added later when evidence of its oceanic migrations was published (Boustany et al., 2002, 2008).

The Workshop raised awareness of the conservation status and management gaps for these high-seas oceanic species. It also served to focus and accelerate research and conser-vation measures by scientists, fi shing nations, and regional fi sheries management organiza-tions, whose subsequent fi ndings and actions are refl ected in the chapters in this volume.

Sharks of the Open Ocean is organized into fi ve parts: (1) Introduction and Overview; (2) Life History and Status of Pelagic Elasmobranchs; (3) Trends in Catches and Abundance of Pelagic Sharks; (4) Methods to Improve Understanding of Pelagic Sharks: Demographics, Assessment, and Stock Structure; and (5) Conservation and Management Outlook for Pelagic Sharks. Each part begins with an introduction written by the editors. Some

Table 1.1 Elasmobranch species addressed in Sharks of the Open Ocean.

Common name Scientifi c name

Pelagic thresher Alopias pelagicusBigeye thresher Alopias superciliosusCommon thresher Alopias vulpinusWhite shark Carcharodon carchariasShortfi n mako Isurus oxyrinchusLongfi n mako Isurus paucusSalmon shark Lamna ditropisPorbeagle Lamna nasusSilky shark Carcharhinus falciformisOceanic whitetip shark Carcharhinus longimanusBlue shark Prionace glaucaPelagic stingray Pteroplatytrygon violacea

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6 Sharks of the Open Ocean

commercially important coastal species (e.g., dusky, Carcharhinus obscurus; hammerheads, Sphyrna spp.; and tiger sharks, Galeocerdo cuvier) move offshore and are taken regularly in pelagic fi sheries. These species, however, as well as other noncommercial pelagic and semipelagic elasmobranchs (Compagno, 2008), are not addressed in this volume, except in a comparative demographic study (Smith et al., 2008a) and in a chapter describing an assessment of school sharks (Galeorhinus galeus, Triakidae; Walker et al., 2008), which was included as a demonstration of a spatially explicit stock assessment method that would be useful for oceanic sharks. It should also be noted that we have not been strict in the use of the terms “oceanic” and “pelagic” in reference to open ocean sharks, allowing authors to use these terms interchangeably (although see Compagno, 2008, for defi nitions of the terms).

Evaluating the conservation status of open ocean sharks

Compared to the coastal sharks, and to the tunas caught in high-seas fi sheries, the oceanic sharks have not been well studied: Data on catches, abundance trends, and life history are quite limited. These data are necessary to determine whether current fi shing levels are sus-tainable and to develop a strategy to conserve and manage oceanic shark populations. Most importantly, we need to know how many sharks of each species are being killed in fi sher-ies, at least in recent years, but preferably over the entire history of the fi shery. In general, once catches are known, there are several ways to determine whether they are sustainable. An index of abundance, such as a survey or the catch rates in a fi shery (which can be pro-portional to abundance), can be used to assess whether the historical catches caused a given population to decline, and if so, by how much. A population dynamics model fi tted to the abundance and catch data can be used to ascertain what level of catch is sustainable, and whether catches need to be reduced to allow the population to rebuild to a healthy level. This is the method most commonly used in fi sheries stock assessment and management (Campana et al., 2008; McAllister et al., 2008; Walker et al., 2008). It is also common to use demographic methods, which use age-specifi c estimates of fecundity, natural mortality, and fi shing mortality (Au et al., 2008; Cortés, 2008; Smith et al., 2008a), to evaluate a population’s vulnerability to fi shing pressure. Such methods can determine the relative vul-nerability of different species, and can determine which life stages need the greatest pro-tection. Methods that combine abundance indices and demographic data can also be used to evaluate the sustainability of fi sheries (McAllister et al., 2008).

Our ability to apply these fi shery assessment methods to oceanic sharks, however, is sty-mied by data limitations, particularly on total landings and discards. Although sharks are commonly caught in high-seas fi sheries, they are often caught incidentally in fi sheries tar-geting tunas or swordfi sh. Because of this, shark catches have generally not been reported, or have been reported as “unidentifi ed sharks” instead of by species (Camhi et al., 2008a; Smale, 2008). A recent study of the shark fi n trade found that the current catches of some species, such as blue and shortfi n mako, are much higher than the landings reported to the Food and Agriculture Organization (FAO) and the regional fi shery management organizations (Clarke, 2003; Clarke et al., 2006). Of the shark fi ns traded in Hong Kong, 17% (by weight) were from blue sharks; fi ns from silky, shortfi n mako, threshers, and oceanic whitetip were

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Introduction to Sharks of the Open Ocean 7

also common. The estimated numbers of pelagic sharks killed annually to support this trade were 4.6–15.8 million blue sharks, 400,000–2,000,000 silky, 200,000–1,200,000 oceanic whitetip, 300,000–1,000,000 shortfi n mako, and 400,000–3,900,000 threshers (Clarke et al., 2006). The shark catches reported to regional fi shery management organi-zations have been increasing over the last decade, although it is not clear how much of the increase represents an actual increase in catches and how much is simply due to better reporting (Babcock and Nakano, 2008; Smale, 2008). In any case, these large catches may or may not be sustainable for species with life histories more similar to those of marine mammals than to the bony fi shes that are caught in high-seas fi sheries (Camhi et al., 1998).

Despite the lack of reliable catch data, several recent studies have evaluated changes in oceanic shark abundance over time to determine whether fi sheries have caused their deple-tion. Survey data have shown declines in male blue sharks in the Northwest Atlantic (Hueter and Simpfendorfer, 2008). Studies of shark catch rates from commercial fi sheries have found declines of thresher, blue, mako, and oceanic whitetip sharks in the Northwest Atlantic (Baum et al., 2003), although Nakano (1996) found that blue shark catch rates were stable in the Atlantic, as well as in the Pacifi c and Indian Oceans. Assessments of shark status based on fi shery catch rates as well as catch data have shown some decline of short-fi n mako sharks, but no clear trend for blue sharks in the Atlantic (Babcock and Nakano, 2008). There is evidence of a decline in an eastern Pacifi c population of common threshers followed by some rebuilding (Smith et al., 2008b). Studies comparing shark catch rates in historical surveys to catch rates from modern commercial fi sheries (from observer data) have estimated declines in abundance of more than 90% for oceanic whitetip and silky sharks in the Gulf of Mexico (Baum and Myers, 2004) and 87% for blue sharks in the cen-tral Pacifi c Ocean (Ward and Myers, 2005). For many populations of oceanic sharks, there are no data on trends in abundance or the available data are patchy, unreliable, or con-tradictory; however, for populations that have been studied, most have shown a declining trend (Camhi, 2008; Camhi et al., 2008a). Thus, the concern that some of the many popu-lations that have never been studied may be depleted seems warranted (Camhi, 2008).

One reason for concern about population declines of pelagic sharks is that, because of their life history, sharks are particularly at risk for extinction (Pikitch, 2005). Of 133 marine vertebrate, invertebrate, and algae populations that have gone locally, regionally, or globally extinct within the last 300 years (Dulvy et al., 2003), 64 were marine fi shes, of which 32 were sharks and rays. Considering that sharks and rays represent only about 5% of all marine fi shes (Nelson, 1994), the fact that half of the extinct populations of fi shes were sharks and rays implies that they may be particularly vulnerable. It is also worth noting that habitat loss or ecological impacts of invasive species were the cause (at least in part) of extinction for 25 of the 32 extinct fi nfi sh populations, whereas exploitation was the cause of extinction for all 32 of the sharks and rays (Dulvy et al., 2003). Extinction risk was correlated strongly with large body size, and less strongly with small geographic range and habitat specialization. Oceanic sharks are wide-ranging and are not habitat specialists, but they are all large-bodied animals and are heavily exploited, implying that they may indeed be at increased risk.

Removal of apex predators has been demonstrated to profoundly impact some marine ecosystems (Estes et al., 1998). As the apex predators of the high seas, pelagic sharks are likely to strongly infl uence food web structure (Bascompte et al., 2005). The understand-ing that alterations in food web processes could undermine the sustainability of fi sheries

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8 Sharks of the Open Ocean

and cause undesirable changes in ecosystem structure and function (Bakun and Weeks, 2004) has recently led to a paradigm shift in fi sheries management, from a focus on man-aging each species individually to ecosystem-based fi shery management (Pikitch et al., 2004). The large-scale removal of oceanic sharks could have far-ranging negative eco-system effects. For example, Stevens et al. (2000) used the dynamic mass balance model Ecosim to predict the impacts of shark removals from three ecosystems. In all three sys-tems, the biomass of some prey species increased two- to threefold after shark removal, but other prey species decreased or remained stable and the biomass dynamics were com-plex and diffi cult to predict. Similarly, the food web model of Bascompte et al. (2005) implied that sharks strongly infl uence the functioning of food webs, so that the overfi sh-ing of sharks may have contributed to the degradation of Caribbean coral reefs. Thus, overexploitation of oceanic sharks may have consequences for marine ecosystems that are diffi cult to predict and even more diffi cult to reverse.

The future of oceanic sharks

Oceanic sharks remain among the least studied and least managed of the elasmobranchs, although they are among the most heavily impacted by fi shing. Over the past decade, progress has been made in improving our understanding of the biology, status, and trends of oceanic sharks, and in documenting the catches. Management has also improved, but it may be too little and too late. The 1999 FAO International Plan of Action for the Conservation and Management of Sharks (IPOA-Sharks) called on states and regional fi sh-ery management organizations to assess the status of shark populations and develop plans for their management. As of this writing, only 22 of 113 shark-fi shing states have accom-plished either of these tasks (Cavanagh et al., 2008). A more encouraging development is that measures to ban or limit “fi nning” – the practice of retaining the fi ns of a shark and discarding the carcass (Meliane, 2003; Camhi et al., 2008b) – have been enacted to varying degrees by Australia, Brazil, Canada, Costa Rica, Ecuador, Egypt, the European Union, Israel, Namibia, Nicaragua, Oman, Palau, Seychelles, South Africa, Spain, and the United States (Fig. 1.2). In 2004, the International Commission on the Conservation of Atlantic Tunas (ICCAT) passed a resolution banning fi nning by ICCAT member nations in the Atlantic, which was the fi rst fi nning ban in international waters. Similar resolu-tions were passed in 2005 by the General Fisheries Commission of the Mediterranean (GFCM), the Inter-American Tropical Tuna Commission (IATTC), the Indian Ocean Tuna Commission (IOTC), and the Northwest Atlantic Fisheries Organization (NAFO), and in 2006 by the Southeast Atlantic Fisheries Organization (SEAFO) (Camhi et al., 2008b). Because oceanic sharks are a major component of the fi n trade, these conservation meas-ures may help reduce the mortality of oceanic sharks, and may improve the quality of the data on oceanic shark catches, but only if these measures are adequately enforced.

This book provides new information on the biology and ecology of oceanic sharks, their fi sheries, and their management, and also serves as a compilation of the current state of knowledge. In gathering this information, we were struck by the many gaps in our knowledge of the oceanic sharks. Although many papers have been published on pelagic sharks, they tend to focus on only a few populations. For example, while many individual

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Introduction to Sharks of the O

pen Ocean

9

United States

Brazil

Ecuador

Costa Rica

South Africa

Australia

Oman

European Union

IATTC ICCAT

NAFO

Seychelles

Palau

SEAFO

IOTC

GFCM

Canada (Atlantic)

Nicaragua

EgyptIsrael

Namibia

Fig. 1.2 Countries and regional fi sheries management organizations that have taken measures to ban or limit fi nning (Meliane, 2003; Camhi et al., 2008b).

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10 Sharks of the Open Ocean

oceanic sharks have been tagged, the vast majority have been blue sharks in the Northwest Atlantic (Kohler and Turner, 2008). Sharks that are farther offshore and are not caught in recreational fi sheries are not as likely to be tagged. Clearly, there is a pressing need for research to assess the status of understudied species like the threshers and silky sharks. Recent improvements in the quality of catch statistics and efforts to infer catches from trade data are laudable, and should be continued. The research presented in this volume, as well as in other studies published in the last several years, makes it clear that oceanic sharks are at risk from high-seas fi shing, and that some populations are depleted and per-haps even threatened with extinction. We call on all fi shing nations, as well as the regional fi shery management organizations, to begin or intensify their efforts to assess the status of these species and to develop and implement effective management plans to ensure sus-tainable populations of oceanic sharks, before it is too late to stem and reverse the decline of the sharks of the open ocean.

References

Au, D. W., Smith, S. E. and Show, C. (2008) Shark productivity and reproductive protection, and a comparison with teleosts. In: Sharks of the Open Ocean: Biology, Fisheries and Conservation (eds. M. D. Camhi, E. K. Pikitch and E. A. Babcock). Blackwell Publishing, Oxford, UK.

Babcock, E. A. and Nakano, H. (2008) Data collection, research, and assessment efforts for pelagic sharks by the International Commission for the Conservation of Atlantic Tunas. In: Sharks of the Open Ocean: Biology, Fisheries and Conservation (eds. M. D. Camhi, E. K. Pikitch and E. A. Babcock). Blackwell Publishing, Oxford, UK.

Bakun, A. and Weeks, S. J. (2004) Greenhouse gas buildup, sardines, submarine eruptions and the possibility of abrupt degradation of intense marine upwelling ecosystems. Ecology Letters 7, 1015–1023.

Bascompte, J., Melián, C. J. and Sala, E. (2005) Interaction strength combinations and the overfi shing of a marine food web. Proceedings of the National Academy of Sciences 102, 5443–5447.

Baum, J. K. and Myers, R. A. (2004) Shifting baselines and the decline of pelagic sharks in the Gulf of Mexico. Ecology Letters 7, 135–145.

Baum, J. K., Myers, R. A., Keller, D. G., Worm, B., Harley, S. J. and Doherty, P. A. (2003) Collapse and conservation of shark populations in the Northwest Atlantic. Science 299, 389–391.

Beerkircher, L. R., Cortés, E. and Shivji, M. S. (2008) Case study: Elasmobranch bycatch in the pelagic longline fi shery off the southeastern United States, 1992–1997. In: Sharks of the Open Ocean: Biology, Fisheries and Conservation (eds. M. D. Camhi, E. K. Pikitch and E. A. Babcock). Blackwell Publishing, Oxford, UK.

Block, B. A., Dewar, H., Blackwell, S. B., Williams, T. D., Prince, E. D., Farwell, C. J., Boustany, A., Teo, S. L. H., Seitz, A., Walli, A. and Fudge, D. (2001) Migratory movements, depth preferences and thermal biology of Atlantic bluefi n tuna. Science 293, 1310–1314.

Bonfi l, R., Meyer, M., Scholl, M. C., Johnson, R., O’Brien, S., Oosthuizen, H., Swanson, S., Kotze, D. and Paterson, M. (2005) Transoceanic migration, spatial dynamics, and population linkages of white sharks. Science 310, 100–103.

Boustany, A. M., Davis, S. F., Pyle, P., Anderson, S. D., Le Boeuf, B. J. and Block, B. A. (2002) Expanded niche for white sharks. Nature 415, 35–36.

Boustany, A. M., Weng, K. C. M., Anderson, S. D., Pyle, P. and Block, B. A. (2008) Case study: White shark movements in the North Pacifi c pelagic ecosystem. In: Sharks of the Open Ocean: Biology,

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Introduction to Sharks of the Open Ocean 11

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Camhi, M., Fowler, S., Musick, J., Bräutigam, A. and Fordham, S. (1998) Sharks and Their Relatives: Ecology and Conservation. IUCN/SSC Shark Specialist Group. IUCN, Gland, Switzerland and Cambridge, UK, 39 pp.

Camhi, M. D., Lauck, E., Pikitch, E. K. and Babcock, E. A. (2008a) A global overview of commercial fi sheries for open ocean sharks. In: Sharks of the Open Ocean: Biology, Fisheries and Conservation (eds. M. D. Camhi, E. K. Pikitch and E. A. Babcock). Blackwell Publishing, Oxford, UK.

Camhi, M. D., Fordham, S. V. and Fowler, S. L. (2008b) Domestic and international management for pelagic sharks. In: Sharks of the Open Ocean: Biology, Fisheries and Conservation (eds. M. D. Camhi, E. K. Pikitch and E. A. Babcock). Blackwell Publishing, Oxford, UK.

Campana, S. E., Joyce, W., Marks, L., Hurley, P., Natanson, L. J., Kohler, N. E., Jensen, C. F., Mello, J. J., Pratt Jr., H. L., Myklevoll, S. and Harley, S. (2008) The rise and fall (again) of the porbeagle shark population in the Northwest Atlantic. In: Sharks of the Open Ocean: Biology, Fisheries and Con servation (eds. M. D. Camhi, E. K. Pikitch and E. A. Babcock). Blackwell Publishing, Oxford, UK.

Cavanagh, R. D., Fowler, S. L. and Camhi, M. D. (2008) Pelagic sharks and the FAO International Plan of Action for the Conservation and Management of Sharks. In: Sharks of the Open Ocean: Biology, Fisheries and Conservation (eds. M. D. Camhi, E. K. Pikitch and E. A. Babcock). Blackwell Publishing, Oxford, UK.

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Clarke, S., Magnusson, J. E., Abercrombie, D. L., McAllister, M. and Shivji, M. S. (2006) Identi-fi cation of shark species composition and proportion in the Hong Kong shark fi n market using molecular genetics and trade records. Conservation Biology 20(1), 201–211.

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Cortés, E. (2008) Comparative life history and demography of pelagic sharks. In: Sharks of the Open Ocean: Biology, Fisheries and Conservation (eds. M. D. Camhi, E. K. Pikitch and E. A. Babcock). Blackwell Publishing, Oxford, UK.

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12 Sharks of the Open Ocean

Hueter, R. E. and Simpfendorfer, C. A. (2008) Case study: Trends in blue shark abundance in the western North Atlantic as determined by a fi shery-independent survey. In: Sharks of the Open Ocean: Biology, Fisheries and Conservation (eds. M. D. Camhi, E. K. Pikitch and E. A. Babcock). Blackwell Publishing, Oxford, UK.

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