1 Habitat partitioning and vulnerability of sharks in the Great Barrier Reef Marine Park 1 2 3 4 2 5 6 3 Daniela M. Ceccarelli1*, Ashley J. Frisch2, Nicholas A. J. Graham2, Anthony M. Ayling3, Maria Beger4 7 8 9 4 10 11 12 5 1PO Box 215, Magnetic Island, QLD 4819, Australia 13 14 15 6 2ARC Centre of Excellence for Coral Reef Studies, James Cook University, Townsville QLD 4811, Australia 16 17 18 7 3Sea Research, 20 Rattray Ave, Hideaway Bay, QLD 4800, Australia 19 20 21 8 4 ARC Centre of Excellence for Environmental Decisions, School of Biological Sciences, The University of 22 23 9 Queensland, Brisbane, QLD 4072, Australia 24 25 26 10 27 28 29 11 *Corresponding author: Tel/Fax: +61 (0)7 4758 1866; email: [email protected] 30 31 32 12 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 1 60 61 62 63 64 65 13 Abstract 1 2 3 14 Sharks present a critical conservation challenge, but little is known about their spatial distribution and 4 5 15 vulnerability, particularly in complex seascapes such as Australia’s Great Barrier Reef Marine Park (GBRMP). 6 7 16 We review (1) the distribution of shark species among the primary habitats of the GBRMP (coral reefs, 8 9 17 inshore/shelf, pelagic and deep-water habitats), (2) the relative exploitation of each species by fisheries, and (3) 10 11 18 how current catch rates interact with their vulnerability and trophic index. Excluding rays and chimaeras, we 12 13 19 identify a total of 82 shark species in the GBRMP. We find that shark research in the GBRMP has yielded little 14 15 20 quantitative information on most species. Reef sharks are largely site-fidelic, but can move large distances and 16 17 21 some regularly use non-reef habitats. Inshore and shelf sharks use coastal habitats either exclusively or during 18 19 22 specific times in their life cycle (e.g. as nurseries). Virtually nothing is known about the distribution and habitat 20 21 23 use of the GBRMP’s pelagic and deep-water sharks. At least 46 species (53.5%) are caught in one or more 22 23 24 fisheries, but stock assessments are lacking for most. At least 17 of the sharks caught are considered highly 24 25 25 vulnerable to exploitation. We argue that users of shark resources should be responsible for demonstrating that a 26 27 26 fishery is sustainable before exploitation is allowed to commence or continue. This fundamental change in 28 29 27 management principle will safeguard against stock collapses that have characterised many shark fisheries. 30 31 32 28 33 34 35 29 Key words: elasmobranchs, Great Barrier Reef, shark fisheries, food webs, top-down control, apex predators 36 37 38 30 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 2 60 61 62 63 64 65 31 Introduction 1 2 3 32 Top predators are typically the first to disappear from impacted marine ecosystems (Friedlander and DeMartini 4 5 33 2002; Sandin et al. 2008; Graham et al. 2010). In some habitats, anthropogenic impacts have reduced the 6 7 34 abundance of apex predators by 90% or more, and some species are now considered to be functionally extinct 8 9 35 (Myers and Worm 2003; Ferretti et al. 2008; Estes et al. 2011). Their high commercial value combined with 10 11 36 their K-selected life-history (slow growth, late maturity, low fecundity) reduces productivity of these apex 12 13 37 predators and inhibits recovery of exploited populations (Pauly et al. 1998; Stevens et al. 2000a; Collette et al. 14 15 38 2011). Sharks are one of the groups that occupy the top trophic level of marine food chains, and shark 16 17 39 populations worldwide are under increasing pressure from fisheries (Stevens et al. 2000a; Friedlander and 18 19 40 DeMartini 2002; Pauly and Palomares 2005; Heithaus et al. 2008). The reported worldwide shark catch is 20 21 41 between 700,000 and 850,000 tonnes per year, with an estimated annual increase in landings of 2%; this 22 23 42 excludes the illegal and unreported shark catch driven by the high demand for shark fins in Asian markets 24 25 43 (Rabehagasoa et al. 2012). These high exploitation rates highlight the need for greater knowledge and better 26 27 44 management of sharks across the globe (Herndon et al. 2010; White et al. 2012), both of which are hampered by 28 29 45 the lack of life history information for most species (Tobin et al. 2010). 30 31 32 46 Gathering biological and ecological information is a crucial first step to understanding the importance and 33 34 47 vulnerability of species and species groups within the ecosystems they occupy. Life history traits that indicate 35 36 48 productivity should be known before a species is deemed sustainably exploitable (Dulvy and Forrest 2010). 37 38 49 Unfortunately, most species have already suffered some degree of fishing pressure, which can alter some life 39 40 50 history parameters such as maximum size, reproductive age and lifespan, therefore distorting estimates of 41 42 51 productivity (Forrest and Walters 2010; Field et al. 2012). Furthermore, the collection of these data is rarely 43 44 52 fishery-independent, and samples are therefore subject to the inherent size, sex and species selectivity of the 45 46 53 fishing gear (Harry et al. 2011b). Even more difficult is the study of distribution and abundance; such data are 47 48 54 also almost always only available through fishery catches (DEEDI 2011a). Where fishery-independent research 49 50 55 has examined the role of predation in marine ecosystems, results are seldom spatially uniform. Our 51 52 56 understanding of the ecological role of marine top predators in general, and sharks in particular, is confounded 53 54 57 by differences between methods and gears, and tends to be focused on relative changes in catch rates (Ferretti et 55 56 58 al. 2010). 57 58 59 3 60 61 62 63 64 65 59 The removal of apex predators may result in trophic cascades whereby changes occur throughout the food web, 1 2 60 sometimes down to primary producers (Pinnegar et al. 2000; Myers et al. 2007; Baum and Worm 2009; Estes et 3 4 61 al. 2011). Evidence of predator release following shark exploitation has been shown in North Carolina (U.S.A.), 5 6 62 South Africa, Queensland (Australia) and Western Australia (Myers et al. 2007; Heithaus et al. 2008; Ferretti et 7 8 63 al. 2010). However, such effects have yet to be measured more broadly, as very little information exists for non- 9 10 64 commercial species or for complex habitats such as coral reefs (Field et al. 2009). The understanding of the 11 12 65 ecological role of sharks is hampered by the “shifting baseline” syndrome (Jackson and Jacquet 2011), whereby 13 14 66 research began in a system that had already been exploited by humans, sometimes for hundreds of years (Ward- 15 16 67 Paige et al. 2012). If our investigations are taking place in a re-stabilised system where trophic cascades have 17 18 68 already occurred, then even our best “unfished” control areas are not representative of baseline or pristine 19 20 69 conditions. 21 22 23 70 The Great Barrier Reef (GBR), which extends for 2,300 km along the northeastern coast of Australia, is the 24 25 71 largest and one of the most intensely managed coral reef systems in the world (McCook et al. 2010). The GBR 26 27 72 Marine Park (GBRMP), which is also listed as a World Heritage Area, encompasses not only coral reefs, but 28 29 73 includes a diversity of inter-connected non-reef habitats such as mangrove estuaries, sandy bays, seagrass beds, 30 31 74 rocky shoals, soft-sediment habitats, continental shelf and slope, and deep oceanic waters (up to ~ 3,000 m 32 33 75 deep). The elasmobranch fauna of the GBRMP is equally diverse: 134 species from 41 families have been 34 35 76 recorded, which includes large predatory sharks, smaller benthic carnivores, plankton feeders and rays (Last and 36 37 77 Stevens 2009; Last and White 2011). The GBR has been identified as one of the world’s hotspots of shark 38 39 78 species richness, endemicity and functional diversity (Lucifora et al. 2011). Despite the intensity of local 40 41 79 management (McCook et al. 2010), and targeted research on fisheries effects (e.g. Harry et al. 2011b) and 42 43 80 commercially important species (e.g. Knip et al. 2012c; Morgan et al. 2012), relatively little is known about the 44 45 81 GBRMP’s shark community. For most species, their ecological parameters, life-history traits and population 46 47 82 status in the GBRMP are yet to be determined (Last and Stevens 2009; Tobin et al. 2010). The populations of a 48 49 83 few species have already shown dramatic declines (e.g. tiger shark Galeocerdo cuvier, grey reef shark 50 51 84 Carcharhinus amblyrhynchos; Robbins et al. 2006; Ferretti et al. 2010; Hisano et al. 2011). Due to the lack of 52 53 85 stock assessments and population size estimates for most species, population declines are unlikely to be 54 55 86 detected, and the risk of unsustainable exploitation is likely to be high. The management of the GBRMP 56 57 87 provides a potential vehicle to target certain species for conservation, or curtail fisheries activities to achieve 58 59 4 60 61 62 63 64 65 88 sustainability, but this needs to be underpinned by ecological information. Here we approach this question by 1 2 89 considering shark distributions relative to habitat types and vulnerability of sharks based on their known life 3 4 90 history parameters, and seek answers to the following questions: 5 6 7 91 1) How are the GBRMP’s shark species distributed between its primary habitat types? 8 9 10 92 2) Which species are exploited in the GBRMP, and by which fisheries? 11 12 93 3) How does the intrinsic vulnerability of these species relate to their catch rates by the different fisheries and 13 14 15 94 their potential ecological importance in the system? 16 17 95 Literature and data review - methods 18 19 20 96 The species list of sharks known to exist within the GBRMP was obtained from Chin and Kyne (2007) and Last 21 22 97 and Stevens (2009). All searches for data and literature were based on this species list, with the exclusion of the 23 24 98 rays (superorder Batoidea) and chimaeras, resulting in 82 species of sharks (Table 1). Peer-reviewed literature 25 26 99 and grey literature were reviewed to seek information on the distribution, abundance, vulnerability and 27 28 100 ecological role of sharks within the GBRMP. When such literature or data were unavailable for the GBRMP, we 29 30 101 drew on literature on the same species within similar habitats of other regions. 31 32 33 102 Information on the distribution, abundance, vulnerability and ecological role of each species was organised into 34 35 103 sections pertaining to three primary habitat categories: (1) coral reefs, (2) inshore and GBR shelf, (3) deep slope 36 37 104 and pelagic (outside the GBR shelf edge, but still within the GBRMP boundary), and the depth range was added 38 39 105 for each species (from Last and Stevens 2009). Data on the proportional catch of each species were obtained 40 41 42 106 from the Queensland Shark Control Program (QSCP), the East Coast Inshore Finfish Fishery (ECIFF), the Coral 43 44 107 Reef Finfish Fishery (CRFF) and the Eastern Tuna and Billfish Fishery (ETBF), either directly or from the 45 46 108 literature (e.g. Evans 2007; Heupel et al. 2009). QSCP data from beaches south of the GBRMP were not used 47 48 109 for this review. Although these are the best available data, there is almost certainly selective bias in catch data 49 50 110 with regard to size, species and sex. Further, the QSCP catch is probably biased toward large species and 51 52 111 individuals, even though sharks less than 2 m in length still comprise approximately half of the catch (Sumpton 53 54 112 et al. 2011). 55 56 57 58 59 5 60 61 62 63 64 65 113 Shark research in the GBRMP 1 2 3 114 A comprehensive literature search of the 82 shark species identified for GBRMP yielded 116 documents, 4 5 115 including 93 papers from peer-reviewed journals and 23 reports from the ‘grey’ literature, dating back to 1951. 6 7 116 Species recorded most often were C. amblyrhynchos, the blacktip reef shark Carcharhinus melanopterus and the 8 9 117 scalloped hammerhead Sphyrna lewini (appearing in 29, 26 and 26 documents respectively, Fig. 1). Of the 82 10 11 118 species, 30 appeared in 1-10 documents, and no literature of any kind from within the GBRMP was available for 12 13 119 28 species. Most studies were of a descriptive nature (60% of studies), detailing neurological, physiological, 14 15 120 behavioural, phylogenetic and life history characteristics. Approximately 40% of documents yielded some 16 17 121 information on the abundance, distribution and ecology of sharks in the GBRMP. Only 19 (16.2%) documents 18 19 122 provided specific data and information relating to the distribution and abundance of sharks in the GBRMP. 20 21 22 123 Distribution of shark species between primary habitat types 23 24 25 124 Coral reefs 26 27 125 Coral reefs comprise only 5-6% of the GBRMP (Pitcher et al. 2009), but tend to attract the greatest attention 28 29 126 because of their disproportionate biodiversity and relative ease of access to researchers. Currently, 14 species of 30 31 127 GBRMP sharks are considered coral reef specialists (Chin et al. 2012). Of these, eight are site-attached 32 33 128 mesopredators that feed mostly on worms and crustaceans, and include Orectolobidae, Hemiscylliidae (Heupel 34 35 129 and Bennett 1998), tawny nurse sharks Nebrius ferrugineus and zebra sharks Stegostoma fasciatum. These less 36 37 130 mobile species may display specific habitat preferences, such as an attraction to areas of high structural 38 39 131 complexity (Carraro and Gladstone 2006). 40 41 42 132 More mobile coral reefs shark species include C. amblyrhynchos, C. melanopterus, lemon shark Negaprion 43 44 133 acutidens and whitetip reef shark Triaenodon obesus. The silvertip shark Carcharhinus albimarginatus is also 45 46 134 frequently associated with reefs (Fig. 2). The grey nurse shark Carcharias taurus, which may occur at the 47 48 135 southern end of the GBRMP, feeds primarily on fast-moving piscivorous fish and other elasmobranchs (Ferrara 49 50 136 et al. 2011; Froese and Pauly 2012). Many of these species are shallow-water specialists (e.g. C. melanopterus, 51 52 137 T. obesus), but some have been found below 100 m (C. amblyrhynchos at ~280 m, C. albimarginatus at ~800 53 54 138 m). In Palau, C. amblyrhynchos undertakes vertical movements associated with daily, lunar and seasonal cycles 55 56 139 in temperature and ambient light (Vianna et al. 2013). Wider-ranging species known to visit coral reefs of the 57 58 59 6 60 61 62 63 64 65 140 GBRMP include tiger shark G. cuvier, S. lewini, bull shark Carcharhinus leucas, great hammerhead Sphyrna 1 2 141 mokarran, and pigeye shark Carcharhinus amboinensis. Most studies on the role of coral reef predators consider 3 4 142 only the two most commonly found species (given their abundance, conspicuousness and presence in fisheries 5 6 143 catches), C. amblyrhynchos and T. obesus. This means that knowledge of the predation “footprint” of reef- 7 8 144 associated sharks is generally restricted to the effects of generalist top predators. 9 10 11 145 Resident coral reef sharks are more abundant, and therefore potentially more important trophically, at a local 12 13 146 scale than rarer and more transient larger predators (Gaston and Fuller 2008). However, transient predators may 14 15 147 have a greater regulating role overall through predation on resident sharks - for instance, both C. albimarginatus 16 17 148 and S. mokarran are known to prey on C. amblyrhynchos (Randall 1977; Mourier et al. 2012). Resident sharks 18 19 149 are also likely to affect the density and behaviour of smaller predators (including teleosts such as groupers), 20 21 150 which in turn influence recruitment, abundance and behaviour of smaller fish at lower trophic levels (e.g. 22 23 151 Stallings 2008). Therefore, the removal of a resident shark by a transient apex predator may result in top-down 24 25 152 effects on prey communities. 26 27 28 153 In the GBRMP, sharks associated with coral reefs may frequently also be found in other habitats, such as coastal 29 30 154 habitats and inshore nursery areas (Chin et al. 2012). Acoustic telemetry has recently revealed complex 31 32 155 movement dynamics and the use of various habitats in reef-associated species such as C. melanopterus (Fig. 2, 33 34 156 Chin et al. 2012), and tagging and genetic studies have found that C. amblyrhynchos is capable of long-range 35 36 157 (>100 km) movement between the Coral Sea and the GBRMP (Heupel et al. 2010). There may be greater 37 38 158 connectivity between distant reefs, and between reef and non-reef habitats, than previously thought, but the 39 40 159 frequency of large-scale movements (> 100 km) is unknown (Whitney et al. 2012). 41 42 43 160 Coastal, inshore and inter-reef shelf habitats 44 45 161 Non-reef habitats of the GBR tend to be generally summarised as “GBR lagoon”, and include a wide range of 46 47 162 inshore and offshore habitats with soft-sediment substrates, from mangrove estuaries to deep areas towards the 48 49 163 edge of the continental shelf (Pitcher et al. 2009). The majority of the GBRMP’s sharks are associated with this 50 51 164 habitat; thirty-four species have at least a partial association with coastal or shelf habitats. Of these, nine can be 52 53 54 165 considered inshore specialists (Table 1). Shark species commonly found in GBR lagoon habitats include outer- 55 56 166 shelf deepwater sharks such as sawtail sharks, spurdogs and gummy sharks, and small carcharhinids such as the 57 58 167 Australian sharpnose shark Rhizoprionodon taylori and the sliteye shark Loxodon macrorhinus (Fig. 2). Most 59 7 60 61 62 63 64 65 168 small coastal shark species are relatively sedentary, with home ranges of 100 km2 or less (Speed et al. 2010). 1 2 169 Larger, more mobile predators that are likely to be most abundant in coastal, inshore and inter-reefal habitats are 3 4 170 Australian blacktip shark Carcharhinus tilstoni, common blacktip shark Carcharhinus limbatus, graceful shark 5 6 171 Carcharhinus amblyrhynchoides, spinner shark Carcharhinus brevipinna, spot-tail shark Carcharhinus sorrah 7 8 172 and C. melanopterus (Fig. 3 & 4). Sphyrna lewini and C. leucas are the largest sharks commonly present in 9 10 173 nearshore coastal habitats (Chin and Kyne 2007), although research in northern Australian waters suggest that 11 12 174 adult S. lewini females may be preferentially found offshore (Stevens and Lyle 1989), and can dive to 964 m 13 14 175 during diel vertical movements in the Gulf of Mexico (Hoffmayer et al. 2013). Both species are apex predators 15 16 176 with broad diets that include teleosts, elasmobranchs, benthic crustaceans and, for C. leucas, the occasional 17 18 177 terrestrial mammal (Last and Stevens 2009). Carcharhinus leucas is perhaps the most specialised inshore shark 19 20 178 among the large apex predators; it has been known to venture far upstream in estuarine environments (but has 21 22 179 been recorded on reefs and reef bases, and as deep as 150 m, Last and Stevens 2009). Estuaries are used by 23 24 180 juveniles of this species (Heupel and Simpfendorfer 2008), whilst adults use coastal habitats, thereby effectively 25 26 181 linking estuarine and coastal food webs (Matich et al. 2011). Galeocerdo cuvier is widely distributed across 27 28 182 inshore and inter-reef habitats (Cappo et al. 2007; Sumpton et al. 2011). In Shark Bay, Western Australia, G. 29 30 183 cuvier has a major role in regulating the behaviour and survivorship of turtles, cetaceans and dugongs (Heithaus 31 32 184 and Dill 2006; Wirsing et al. 2007; Heithaus et al. 2008). G. cuvier may have a similar role in inshore and inter- 33 34 185 reef areas of the GBRMP, especially shallow embayments that host large populations of marine mammals and 35 36 186 turtles; however, these effects have yet to be demonstrated on Australia’s tropical east coast. On the northern 37 38 187 GBR at Raine Island, the highest-density green turtle Chelonia mydas rookey in the world attracts G. cuvier 39 40 188 throughout the year. Recent tracking research suggests that G. cuvier feeds on diverse prey throughout the year 41 42 189 and targets C. mydas during the nesting season, and may have a significant impact on the C. mydas nesting 43 44 190 population (Fitzpatrick et al. 2012). 45 46 47 191 Some inshore areas along the GBR coast have been identified as providing a successful refuge for a number of 48 49 192 coexisting species, with favourable conditions such as sufficient resources coupled with a degree of protection 50 51 193 from fishing (Knip et al. 2012b). This is especially true of species that exhibit reproductive philopatry, returning 52 53 194 to specific areas to mate or give birth, such as C. leucas in northern Australian estuaries (Tillett et al. 2012). 54 55 195 When multiple species use the same area, habitat partitioning can occur even within single embayments (Yates 56 57 196 et al. 2012). Spatial segregation according to sex and age is common (Speed et al. 2010). Younger sharks are 58 59 8 60 61 62 63 64 65 197 usually found preferentially in shallower, turbid waters, whilst adults tend to inhabit slightly deeper waters 1 2 198 (Tillett et al. 2011; Knip et al. 2011). Habitat partitioning is probably driven by a combination of prey 3 4 199 abundance, competition, predator avoidance and habitat preference (Speed et al. 2010; Yates et al. 2012). Depth 5 6 200 partitioning among coastal and shelf shark species remains to be explored, but is likely to be significant, as some 7 8 201 species are found exclusively in shallow water (e.g. C. brevipinna, 0-75 m; C. amblyrhynchoides, 0-50 m) or 9 10 202 deeper shelf waters (e.g. pencil shark Hypogaleus hyugaensis, 40-230 m), while others have a wider depth range 11 12 203 (e.g. dusky shark Carcharhinus obscurus, 0-400 m). Among sharks with a broad depth range, some species are 13 14 204 found preferentially at the deeper or shallower end of the range; for instance, C. tilstoni, C. sorrah, C. 15 16 205 amblyrhynchoides and the milk shark Rhizoprionodon acutus tend to be most common near the surface, while 17 18 206 the hardnose shark Carcharhinus macloti is often caught in deeper areas (Fig. 2, Stevens 1999). 19 20 21 207 Site fidelity in non-reef sharks is not well understood, but has been demonstrated for a number of species, both 22 23 208 in the GBRMP and elsewhere (Speed et al. 2010; Knip et al. 2012d). However, even small and relatively site- 24 25 209 attached species can include individual members that roam more widely (Stevens et al. 2000), thereby 26 27 210 increasing gene flow between populations (Speed et al. 2010; Knip et al. 2012d). Conversely, even wide-ranging 28 29 211 species return regularly to an area where the probability of encountering prey is high (Heithaus et al. 2006). 30 31 212 Whilst a range of environmental and other factors may drive patterns of movement and side fidelity (Heupel et 32 33 213 al. 2003; Heupel and Simpfendorfer 2008), prey availability is likely to be one of the key drivers of shark 34 35 214 movement and distribution (Knip et al. 2010). Prey abundance may be more important than prey type, given that 36 37 215 dietary specialisation is uncommon in sharks (Wetherbee and Cortes 2004). Dietary preferences may exist as a 38 39 216 measure to avoid competition; in northern Australian waters, despite a general dominance of fish in shark 40 41 217 stomach contents, cephalopods formed an important component of the diets of S. lewini, the sandbar shark 42 43 218 Carcharhinus plumbeus and the fossil shark Hemipristis elongata. Similarly, S. mokarran, L. macrorhinus, C. 44 45 219 amboinensis, R. taylori, the whitecheek shark Carcharhinus dussumieri and the winghead shark Eusphyra 46 47 220 blochii had a high (>20%) proportion of crustaceans in their diets (Stevens and Lyle 1989; Stevens and 48 49 221 McLoughlin 1991). In Moreton Bay (Australia), the diet of Australian weasel shark Hemigaleus australiensis 50 51 222 consisted of 96% of benthic octopus (Taylor and Bennett 2008). Prey abundance may not be a driver for 52 53 223 movement patterns in all species, however; no correlation between prey abundance and movement was found 54 55 224 for the ornate wobbegong Orectolobus ornatus in New South Wales (Carraro and Gladstone 2006) and juvenile 56 57 225 C. leucas in Florida (Heithaus et al. 2009). 58 59 9 60 61 62 63 64 65 226 Many sharks use inshore areas as nursery grounds or for feeding, mating or pupping (Knip et al. 2010; Tillett et 1 2 227 al. 2011), and some species are likely to use all habitats (inshore, inter-reef, pelagic and reef) at some stage 3 4 228 during their life cycle, thereby creating large-scale trophic connections (Chin 2005). For instance, C. 5 6 229 amboinensis, C. limbatus and C. plumbeus use inshore areas as juveniles, moving to offshore inter-reef habitats 7 8 230 as adults, whilst C. sorrah and R. acutus are inshore specialists during their entire life cycle (Castro 1996; Knip 9 10 231 et al. 2010; Knip et al. 2012a; Knip et al. 2012c). Typically, large, slow-growing species derive greater benefit 11 12 232 from predator avoidance when young and therefore tend to use shallow nursery areas to a greater degree than 13 14 233 smaller, fast-growing species (Yates et al. 2012). Localised species composition is correlated with substratum 15 16 234 type; generally, predators appear drawn to areas of greater habitat complexity where prey diversity is greater 17 18 235 (Stowar et al. 2008). Species composition may change seasonally (Simpfendorfer and Milward 1993), or in 19 20 236 response to changes in the physical characteristics of the habitat (Matich and Heithaus 2012). In the GBRMP, 21 22 237 only Cleveland Bay near Townsville (Australia) has been identified as a shark nursery area used by multiple 23 24 238 species (Simpfendorfer and Milward 1993), but similar embayments along the coast may serve the same 25 26 239 purpose. 27 28 29 240 Ontogenetic shifts in habitat use are poorly understood, and can vary regionally; S. lewini tends to remain in 30 31 241 inshore areas of the GBRMP (Harry et al. 2011a), but not in South Africa (De Bruyn et al. 2005) or Brazil 32 33 242 (Hazin et al. 2001). Similarly, maturing C. melanopterus travelled from coastal nursery grounds to offshore 34 35 243 reefs over distances of up to 81 km in the GBRMP (Chin et al. 2013), but were found to be much more 36 37 244 sedentary at Aldabra (Stevens 1984) and Palmyra Atolls (Papastamatiou et al. 2009). As with reef sharks, some 38 39 245 latitudinal patterns are known to exist; H. hyugaensis and C. plumbeus are not found in the northern quarter of 40 41 246 the GBRMP, H. elongata is only recorded from the northernmost section and E. blochii from the northern third; 42 43 247 the bignose shark Carcharhinus altimus may only occur in the southern reaches of the GBRMP, whilst C. 44 45 248 tilstoni may be absent from the southern GBRMP (Last and Stevens 2009). A broad-scale study of the GBRMP 46 47 249 with Baited Remote Underwater Video (BRUV) found that C. tilstoni and C. limbatus were most common in 48 49 250 shallow, mid-shelf, inter-reef habitats of the far northern section of the GBRMP; C. albimarginatus was 50 51 251 prevalent in deep offshore habitats; N. ferrugineus was typically found in shallow outer-shelf areas, and G. 52 53 252 cuvier was broadly distributed across all the above mentioned habitats but considered indicative of offshore 54 55 253 assemblages (Cappo et al. 2007). Inshore specialists are the group most vulnerable to coastal human impacts 56 57 254 (Speed et al. 2010; Yates et al. 2012). Reef sharks that routinely use inshore non-reef habitats may also be 58 59 10 60 61 62 63 64 65 255 periodically at risk from interactions with humans; fishery data show that at least C. melanopterus, N. acutidens, 1 2 256 S. fasciatum, and the brownbanded bamboo shark Chiloscyllium punctatum are sometimes caught in non-reef 3 4 257 habitats, and that the catch of C. melanopterus is dominated by juvenile individuals (Chin et al. 2012). 5 6 7 258 Pelagic and bathyal habitats 8 9 259 Pelagic and bathyal or deep water (> 200 m) habitats of the GBRMP are relatively oligotrophic and lack 10 11 260 permanent upwelling features, although seasonal aggregations of organisms form in pelagic outer-shelf and 12 13 261 offshore areas (Flynn and Paxton 2012). For instance, black marlin Makaira indica aggregate seasonally to 14 15 262 spawn on the outer GBRMP near the city of Cairns (Speare 2003; Domeier and Speare 2012). Ten species of 16 17 263 pelagic sharks were identified for the GBRMP (Table 1). The most common pelagic sharks include blue shark 18 19 264 Prionace glauca, shortfin mako Isurus oxyrinchus, silky shark Carcharhinus falciformis and oceanic whitetip 20 21 265 shark Carcharhinus longimanus (Fig. 2). Some pelagic species, such as I. oxyrinchus and P. glauca undertake 22 23 266 deep foraging dives (to 650 and 1,000 m, respectively), and the cookie-cutter shark Isistius brasiliensis and 24 25 267 smalleye pygmy shark Squaliolus aliae are known for their vertical migrations of over 1,000m (Last and 26 27 268 Stevens 2009), thereby creating trophic links between surface waters and deeper ocean layers (Abascal et al. 28 29 269 2011; Bromhead et al. 2012). Depth partitioning among pelagic sharks seems rare, with most ranging between 30 31 270 the surface and > 500 m, with the exception of S. aliae, which ranges between 150 and 2,000 m. Many species 32 33 271 that are pelagic and migratory as adults use coastal waters as juveniles (Herndon et al. 2010), and philopatry has 34 35 36 272 recently been inferred for C. longimanus in the Bahamas (Howey-Jordan et al. 2013). 37 38 273 Twenty-eight species of bathyal sharks were identified in the GBRMP (Table 1), but distribution and abundance 39 40 274 information is scarce for these species. An analysis of shark distribution with depth has shown that sharks are a 41 42 275 conspicuous component of deep-sea communities down to around 2,000 m, but that few sharks can be found 43 44 45 276 below 3,000 m, ostensibly due to their high energy requirements (Priede et al. 2006). The deepest parts of the 46 47 277 GBRMP measure approximately 3,000m, indicating that sharks are likely to be present through the entire depth 48 49 278 range of the GBRMP (Priede et al. 2006). There are likely to be both depth and latitudinal gradients in the 50 51 279 distribution of the GBRMP’s deepwater sharks. For instance, the bluntnose sixgill shark Hexanchus griseus can 52 53 280 be found close to the surface (Fig. 2), while the shallowest recorded depths for the false catshark Pseudotriakis 54 55 281 microdon, the Endeavour dogfish Centrophorus moluccensis and the black shark Dalatias licha are 100 m, 300 56 57 282 m and 450 m, respectively. Latitudinally, the sharpnose sevengill shark Heptranchias perlo, the piked spurdog 58 59 11 60 61 62 63 64 65 283 Squalus megalops, the Philippine spurdog Squalus montalbani, C. moluccensis, the blackbelly lanternshark 1 2 284 Etmopterus lucifer, the Pinocchio catshark Apristurus australis, the bigfin catshark Apristurus platyrhynchus, 3 4 285 the saddled swellshark Cephaloscyllium variegatum and the bigeye sixgill shark Hexanchus nakamurai are not 5 6 286 known from the northernmost quarter of the GBRMP, and D. licha is known only from the southern end of the 7 8 287 GBRMP (Last and Stevens 2009). Some species were recorded in limited collections, such P. microdon, the 9 10 288 prickly shark Echinorhinus cookei, the Taiwan gulper shark Centrophorus niaukang, the short-tail lanternshark 11 12 289 Etmopterus brachyurus, the pink lanternshark Etmopterus dianthus, the lined lanternshark Etmopterus 13 14 290 dislineatus, the smoothbelly catshark Apristurus longicephalus, the darksnout houndshark Hemitriakis abdita, 15 16 291 the longnose houndshark Iago garricki, and the bartail spurdog Squalus notocaudatus (Last and Stevens 2009), 17 18 292 which can lead to the assumption of rarity and limited range for these species that may simply be under- 19 20 293 sampled. 21 22 23 294 Deep-water sharks are widely known to be highly vulnerable to exploitation, especially to deepwater trawl 24 25 295 fisheries, as the conditions inherent in their environment reduce growth rates and reproductive output (Kyne and 26 27 296 Simpfendorfer 2010). No data exist on patterns of habitat use of bathyal sharks in the GBRMP, although 28 29 297 research conducted elsewhere suggests that ontogenetic movements occur in H. griseus (Andrews et al. 30 31 298 2011).These lesser-known sharks contribute considerably to the overall biodiversity of a region, and aid the 32 33 299 understanding of broad patterns of biogeography (Kyne et al. 2011; Last and White 2011). However, 34 35 300 distribution studies of deepwater sharks are generally hampered by low and inconsistent catch rates (Dunn et al. 36 37 301 2010). 38 39 40 302 Conservation status 41 42 43 303 Of the 82 species of sharks considered in this review, 46 (56.1%) are listed under State, Federal and (or) 44 45 304 international legislation as requiring some form of protection (Table 1). The International Union for the 46 47 305 Conservation of Nature (IUCN) categorizes 17 (36.9%) of the 46 listed species as globally ‘threatened’ 48 49 306 (Vulnerable or Endangered), while the remaining 25 (54.3%) are considered ‘near threatened’. Global 50 51 307 population sizes of 24 (57.1%) of the threatened and near threatened species are decreasing; population sizes of 52 53 308 the remaining 26 species are currently ‘unknown’. Of the remaining 36 species listed in other categories, 16 are 54 55 309 data deficient and 18 are listed as ‘least concern’. Of the data deficient species, the population trend of one 56 57 310 species is listed as declining. Of the 36 data deficient and least concern species combined, the population trends 58 59 12 60 61 62 63 64 65 311 of 28 species are unknown. Only five species are considered to be of least concern with stable populations (C. 1 2 312 tilstoni, creek whaler Carcharhinus fitzroyensis, epaulette shark Hemiscyllium ocellatum, northern wobbegong 3 4 313 Orectolobus wardi and grey gummy shark Mustelus ravidus), but the inclusion of C. tilstoni is questionable (see 5 6 314 Tobin et al. 2010), especially given the difficulty of distinguishing it from C. limbatus, C. amblyrhynchoides 7 8 315 and even C. sorrah (Stevens and Wiley 1986). The most highly threatened species that have been recorded in 9 10 316 the GBRMP include the speartooth shark Glyphis glyphis and C. taurus. Glyphis glyphis is extremely rare on the 11 12 317 Queensland east coast, and only Princess Charlotte Bay (a large embayment in the far north of the GBRMP 13 14 318 coast) has been identified as an important habitat for remnant populations of this species (DEEDI 2011b). 15 16 319 Among the vulnerable species, those that have attracted the most attention globally have been the white shark 17 18 320 Carcharodon carcharias and the whale shark Rhincodon typus. 19 20 21 321 Even for large species of high conservation significance, basic ecological parameters such as abundance, 22 23 322 population structure and genetic diversity are only just beginning to be quantified (Bansemer and Bennett 2011; 24 25 323 Blower et al. 2012). The eastern Australian population of C. taurus is listed as critically endangered, which has 26 27 324 prompted studies of life history, migration dynamics and genetic structure (Bansemer and Bennett 2011). How 28 29 325 far north they occur in the GBRMP is unclear; intensive studies have been limited to the northern New South 30 31 326 Wales coast, well south of the GBRMP (e.g. Otway et al. 2004; Bansemer and Bennett 2009; Otway and Ellis 32 33 327 2011). They are known to migrate north seasonally from their known subtropical range, but whether this occurs 34 35 328 in winter or summer is still under discussion (Bansemer and Bennett 2011). Their trophic role and influence on 36 37 329 prey communities has yet to be studied in any detail. Knowledge of C. carcharias and R. typus in the GBRMP is 38 39 330 even more limited. C. carcharias appears in QSCP records as far north as Cairns, but extremely rarely. Tagging 40 41 331 studies also suggest movements towards the GBRMP from southern Australia (Bruce et al. 2006). Evidence of 42 43 332 R. typus in the GBRMP is limited to anecdotal observations. 44 45 46 333 Endemism varies among the suite of shark species found in the GBRMP and is likely to influence their 47 48 334 vulnerability. Some species have global (e.g. I. brasiliensis, Isurus spp.) or circumtropical (e.g. the crocodile 49 50 335 shark Pseudocarcharias kamorahai, R. typus) distributions, which may make them more resilient to over- 51 52 336 exploitation. On the other hand, Australian and / or GBRMP waters may offer a level of protection not afforded 53 54 337 by other nations (Rowat and Brooks 2012). Other species have more restricted distributions, occurring only in 55 56 338 the Pacific (e.g. E.cookei) or the Indo-Pacific (e.g. nervous shark Carcharhinus cautus, C. niaukang, C. 57 58 59 13 60 61 62 63 64 65 339 punctatum, E. brachyurus, tasselled wobbegong Eucrossorhinus dasypogon, S. aliae, S. montalbani); 46% of 1 2 340 Australia’s tropical chondrichthyans are considered regional endemics (Last and White 2011). At least 16 of the 3 4 341 GBRMP’s shark species are endemic to Australian waters (A. australis, pale spotted catshark Asymbolus 5 6 342 pallidus, eastern banded catshark Atelomycterus marnkalha, Colclough’s shark Brachaelurus colcloughi, C. 7 8 343 fitzroyensis, C. tilstoni, C. variegatum, narrowbar swellshark Cephaloscyllium zebrum, E. dislineatus, northern 9 10 344 sawtail shark Figaro striatus, H. australiensis, eastern spotted gummy shark Mustelus walkeri, R. taylori, 11 12 345 eastern highfin spurdog Squalus albifrons, eastern longnose spurdog Squalus grahami, S. notocaudatus). Some 13 14 346 of these species may extend into the waters of Papua New Guinea or other adjacent Exclusive Economic Zones, 15 16 347 but their restricted distribution is nevertheless likely to increase their vulnerability. 17 18 19 348 Exploitation and fisheries management 20 21 22 349 The East Coast Inshore Fin Fish Fishery 23 24 350 The ECIFF, which is the main fishery for sharks in the GBRMP, catches over 20 species of sharks (DEEDI 25 26 351 2011c). The rapid increase in shark catches by the ECIFF in the last decade prompted a review of management 27 28 352 strategies in 2008 / 2009 (DEEDI 2011c). The ECIFF is currently moving towards species-specific management 29 30 353 goals and collecting data to support stock assessments of the most commonly caught and most vulnerable shark 31 32 354 species (Tobin et al. 2010). Other measures implemented to improve the sustainability of the shark catch are the 33 34 355 limited allocation of shark licenses, a total allowable catch of 600t, a maximum size limit of 150cm TL, 35 36 356 restricted take or protection of high-risk species, and improved reporting mechanisms (DEEDI 2011d). 37 38 357 However, these management instruments tend to be based on precautionary principles rather than derived 39 40 358 demographic parameters. Therefore, the conservation status and sustainability of sharks in the ECIFF remains 41 42 359 uncertain and cause for concern. 43 44 45 360 Additionally, there is not yet a proposed solution for assessing the risks of cumulative impacts to species caught 46 47 361 by more than one fishery (Halliday et al. 2001; Chin et al. 2012). Other issues still to be addressed are 48 49 362 identification errors in catch and bycatch reporting (Tillett et al. 2012), and the hybridisation of C. limbatus and 50 51 363 C. tilstoni (Morgan et al. 2012), and perhaps also the closely related C. amblyrhynchoides (Ovenden et al. 2010) 52 53 54 364 and C. sorrah (Stevens and Wiley 1986). Hybridisation could be problematic for fisheries sustainability if 55 56 365 hybrids have reduced fitness and are common, in which case population productivity is lower than predicted and 57 58 366 harvesting at current levels could result in overfishing (Morgan et al. 2012). A recent genetic study revealed 57 59 14 60 61 62 63 64 65 367 hybrid black tip sharks of 126 individuals sampled along 2,000 km of coastline (Morgan et al. 2012). 1 2 368 Carcharhinus tilstoni is only found in northern and eastern Australian waters, whilst C. limbatus has a global 3 4 369 distribution in tropical and warm temperate waters (Last and Stevens 2009; Boomer et al. 2010). Due to its 5 6 370 potential effects on fishery yields, hybridisation also needs to be investigated in other closely related species 7 8 371 with overlapping distributions, including C. melanopterus and C. cautus, C. plumbeus and C. altimus, and C. 9 10 372 amblyrhynchos and C. albimarginatus (Morgan et al. 2012). 11 12 13 373 Commercial shark catches and fishing effort are concentrated in inshore areas close to major towns, especially 14 15 374 off Maryborough, Bundaberg, Gladstone, Rockhampton, Bowen, Townsville and Cairns (Fig. 5, DEEDI 2011a). 16 17 375 It is not possible to accurately ascertain species composition of captured sharks because most catch records are 18 19 376 pooled at various levels (i.e. they are not species-specific) (DEEDI 2011d). Nonetheless, it appears that the most 20 21 377 commonly caught species in commercial net and line fisheries operating on the GBR shelf are C. tilstoni, C. 22 23 378 limbatus and C. amblyrhynchoides (aggregate weight ~171 tonnes, about 30% of the catch), followed by 24 25 379 Sphyrna spp. (aggregate weight ~47 tonnes, 11% of the catch) and C. brevipinna (~38 tonnes, ~10%) (DEEDI 26 27 380 2011a; d). Carcharhinus sorrah is also frequently harvested (~5-9% of the catch), and is considered one of the 28 29 381 most productive sharks caught by the fishery (Tobin et al. 2010). In some species, such as C. leucas, high 30 31 382 proportions of juveniles are caught by the fishery (Ley et al. 2002). Although the ECIFF generally avoids reef 32 33 383 habitats, small numbers (~2% of the catch) of reef sharks are caught in this fishery, including C. melanopterus, 34 35 384 N. acutidens, S. fasciatum, C. amblyrhynchos, C. punctatum, and T. obesus (Chin et al. 2012). A range of other 36 37 385 shark species are captured, but not necessarily retained, by the ECIFF, including wobbegongs, catsharks, B. 38 39 386 colcloughi, sawfish, N. ferrugineus and S. fasciatum (DEEDI 2011a). 40 41 42 387 The Queensland Shark Control Program 43 44 45 388 The QSCP, consisting of baited drumlines and gill nets at popular swimming beaches, was initiated in the 1960s 46 47 389 (Sumpton et al. 2011). Initially, the catch of large sharks (>2m TL) was >2,000 individuals per year, but this 48 49 390 declined by 85% during the ensuing 45 years. In response, the proportional composition of small carcharhinid 50 51 391 sharks initially increased, but these smaller sharks subsequently declined as well (Ferretti et al. 2010). In 1992, 52 53 392 there was a change in gear type off GBRMP beaches (north of the Capricorn Coast) from nets, which 54 55 393 preferentially caught smaller sharks, to drumlines, which favoured larger species (Sumpton et al. 2011). 56 57 394 However, the timing of this change does not match the data time series we present and as such does not explain 58 59 15 60 61 62 63 64 65 395 the continuing decline in large sharks and the increase and subsequent decline in smaller species. Between 1997 1 2 396 and 2011, G. cuvier was the most abundant species caught by the QSCP, followed by C. leucas (Fig. 4). Other 3 4 397 frequently caught sharks were ‘blacktip’ sharks (assumed to be a combination of C. tilstoni and C. limbatus), C. 5 6 398 altimus, other whaler sharks (family Carcharhinidae) and S. lewini. A few oceanic species (e.g. C. falciformis 7 8 399 and I. oxyrinchus) were also caught, suggesting that these species occasionally venture into inshore waters. 9 10 400 Total shark catch (including predatory and other sharks) has declined steadily over the last 14 years (Fig. 6), in 11 12 401 accordance with findings from previous decades (Ferretti et al. 2010), although the catch of some species (e.g. 13 14 402 C. leucas) has remained stable in recent years. Catch rates of all other recorded species have declined. Some, 15 16 403 such as S. mokarran, C. obscurus and C. amboinensis were always caught in very low numbers, and all but 17 18 404 disappeared from the records in 2003-2004. Others, such as the blacktip sharks (C. limbatus and C. tilstoni), C. 19 20 405 brevipinna and S. lewini, declined rapidly in 2008-2009, also for unknown reasons. There may be a high degree 21 22 406 of overlap between the species caught by the QSCP and the ECIFF, but the interacting effects of these two 23 24 407 sources of shark mortality in the GBRMP’s coastal habitats are unknown. 25 26 27 408 The Coral Reef Fin Fish Fishery 28 29 409 The CRFF, which is wholly a line fishery, has a high level of reef shark bycatch, particularly of C. 30 31 410 amblyrhynchos, T. obesus and C. melanopterus (Hisano et al. 2011). As a result, there are far fewer sharks on 32 33 411 reefs open to fishing compared with closed reefs (Heupel et al. 2009). Experimental fishing surveys found no 34 35 36 412 change in shark catch-per-unit-effort (CPUE) during the period 1989 to 2006, but underwater visual census 37 38 413 found that population sizes of C. amblyrhynchos and T. obesus were declining by 17 and 7% per year, 39 40 414 respectively (Robbins et al. 2006; Hisano et al. 2011). Higher estimates of CPUE and density (as estimated by 41 42 415 underwater visual survey) in no-take zones indicated that these areas are effective at protecting a portion of the 43 44 416 reef shark population from exploitation (Robbins et al. 2006; Ayling and Choat 2008; Heupel et al. 2009). Reef 45 46 417 sharks are known to be vulnerable to overfishing, with declines reported from various reefs in the Pacific 47 48 418 (Sandin et al. 2008; Chin et al. 2011), the Caribbean (Ward-Paige et al. 2010) and Indian Oceans (Graham et al. 49 50 419 2010). Line fishing can also lead to cryptic mortality and sub-lethal effects such as injury, infection, stress, and 51 52 420 impaired feeding (Lynch et al. 2010). This has been well-documented for C. taurus (Bansemer and Bennett 53 54 421 2010; Robbins and Peddemors 2010), but probably occurs in a number of reef sharks throughout the GBR. Post- 55 56 422 release mortality is considered to have a major impact upon shark populations in areas targeted by recreational 57 58 59 16 60 61 62 63 64 65 423 line fishing (Lynch et al. 2010). Information from longline fisheries suggests a variety of stress responses and 1 2 424 susceptibilities among species (e.g. Marshall et al. 2013). 3 4 5 425 The Eastern Tuna and Billfish Fishery 6 7 426 Further offshore, the Eastern Tuna and Billfish Fishery (ETBF) harvests sharks as byproduct - especially I. 8 9 427 oxyrinchus, Sphyrna spp., P. glauca and C. longimanus (Evans 2007). While this fishery does not operate inside 10 11 428 the GBRMP, it may affect the abundance of pelagic shark species within the GBRMP because of their extensive 12 13 429 movement capabilities. The occasional record of some pelagic species in the QSCP catch confirms that these 14 15 430 species use habitats within the GBRMP, although the frequency of movements towards coastal areas is 16 17 431 unknown. 18 19 20 432 The East Coast Trawl Fishery 21 22 23 433 Although the CRFF shark catch and some of the ETBF shark catch can be classified as bycatch, most 24 25 434 information on the amount and survival rates of discarded sharks comes from trawl fisheries (Kyne 2008; Welch 26 27 435 et al. 2008), probably because this gear type generates the greatest amount of by-catch (Goni 1998). In fact, it is 28 29 436 estimated that half the global shark catch is bycatch (Stevens et al. 2000a). The East Coast Trawl Fishery 30 31 437 (ECTF) catches and discards a total of 37 chondrichthyan species (one holocephalan, 19 batoids and 17 sharks) 32 33 438 from 18 families (Kyne 2008). In the tiger / Endeavour prawn sector, which operates in the GBRMP, shark 34 -1 35 439 bycatch rates were considered low (0.02–0.12 individuals ha trawled overall, although rates varied widely 36 37 440 between surveys), while they were considered medium in the scallop sector operating in the central GBRMP 38 39 441 (0.31 individuals ha-1 trawled). The shark species caught by both sectors that operate within the GBRMP include 40 41 442 E. dasypogon, C. punctatum, H. australiensis, C. brevipinna, C. dussumieri, L. macrorhinus, R. acutus and R. 42 43 443 taylori (Courtney et al. 2007). Bycatch reduction devices and turtle excluder devices are compulsory on all 44 45 444 ECTF vessels, but their effectiveness at reducing shark mortality is considered low; the in-net mortality of large 46 47 445 sharks is typically 82-98% (Huber 2003; Kyne 2008). 48 49 50 446 In comparison, it is estimated that Australia’s Northern Prawn Fishery, which has many similarities with the 51 52 447 ECTF, catches 56 elasmobranch species from 16 families, although just four species account for 65% of the by- 53 54 448 catch: C. tilstoni, C. dussumieri, giant guitarfish Rhynchobatus djiddensis and black-spotted whipray Himantura 55 56 449 toshi (Stobutzki et al. 2002). A combination of fishery research surveys and observer data revealed that during 57 58 59 17 60 61 62 63 64 65 450 normal fishing operations, 56% of the bycatch died in the trawl net (Stobutzki et al. 2002). This study also found 1 2 451 that a large proportion of species were caught at small (pre-reproductive) sizes, and that sustainability of 3 4 452 captured species was lowest for sawfishes (Pristidae) and highest for C. tilstoni and C. macloti. 5 6 7 453 Shark finning 8 9 454 Despite strict laws requiring the retention of trunks with shark fins, the practice of finning (removing fins from a 10 11 455 live shark and dumping the carcass at sea) occurs illegally in Australia and has been identified as a key non- 12 13 456 compliance issue in the ECIFF (DEEDI 2011d). The demand for shark fin is driven primarily by an expanding 14 15 457 Chinese middle class, and fins can fetch up to $60 USD per kilogram (Herndon et al. 2010). In Hong Kong, the 16 17 458 main market for shark fins, commonly traded fins originate from P. glauca (17.3%), C. falciformis (3.5%), C. 18 19 459 plumbeus (2.4%), C. leucas (2.2%) and G. cuvier (0.19%) (Clarke et al. 2006). It is not known what proportion 20 21 460 of the shark fin trade is comprised of Australian or GBRMP sharks, but the GBRMP has been identified as a 22 23 461 very important region for sharks considered valuable to the shark fin trade (Lucifora et al. 2011). Increasingly, 24 25 462 the same shark species that have been sought-after for their fins are also targeted for their meat (Baum and 26 27 463 Blanchard 2010; Herndon et al. 2010). 28 29 30 464 Cumulative catch – affected species 31 32 33 465 Twelve of the GBRMP’s shark species are caught in at least three different fisheries (counting the QSCP as a 34 35 466 fishery), a further 22 species are caught in at least two fisheries and 13 species are caught by at least one fishery 36 37 467 (Table 1). Among the species caught by two or more fisheries are the highly vulnerable C. obscurus, S. lewini, 38 39 468 T. obesus and C. tilstoni (see below). Differences in catch-reporting metrics (e.g. weight in the CRFF and 40 41 469 ECIFF, numbers in the ETBF, QSCP and ECTF) make comparisons of the severity of the interacting fishery 42 43 470 pressure on each species impossible to calculate. Standardised reporting is vital for informing management of 44 45 471 the overall levels of exploitation suffered by each species. 46 47 48 472 Vulnerability, catch rates and trophic roles 49 50 51 473 The vulnerability to exploitation index has been widely recognized as a suitable indicator of the vulnerability of 52 53 474 fish populations to fishing (Reynolds et al. 2005). The index incorporates data pertaining to age at first maturity, 54 55 475 the parameter K, natural mortality rate, maximum age, maximum length, geographic range, fecundity and spatial 56 57 476 behavior strength (based on the propensity to aggregate, Table 2). For sharks, previous assessments of 58 59 18 60 61 62 63 64 65 477 vulnerability and risk from the ECIFF were performed by Gribble et al. (2005), Salini et al. (2007), Tobin et al. 1 2 478 (2010) and Harry et al. (2011b), but estimates of input parameters varied slightly between assessments (Table 3 4 479 2). Gribble et al. (2005)’s risk assessment found that nine of 20 species (45%) occurred in the high risk 5 6 480 quadrant: C. falciformis, C. brevipinna, T. obesus, creek whaler Carcharhinus fitzroyensis, G. cuvier, S. lewini, 7 8 481 C. amboinensis, C. dussumieri and S. mokarran. Salini et al. (2007)’s risk assessment generated similar results, 9 10 482 although an additional 10 species (C. leucas, C. limbatus, C. tilstoni, Glyphis sp. A, N. acutidens, C. 11 12 483 amblyrhynchoides, C. cautus, C. melanopterus, R. typus and E. blochii) were categorized in the high risk 13 14 484 quadrant. 15 16 17 485 18 19 20 486 Tobin et al. (2010) assessed vulnerability on the basis of productivity (the biological ability of a species to 21 22 487 sustain fishing or recover from overfishing) and susceptibility (the level at which a species is likely to be 23 24 488 affected by fishing). At the two ends of their susceptibility scale were the green sawfish Pristis zijsron (most 25 26 489 susceptible – although only two individuals were caught and this measure was set precautionarily) and C. cautus 27 28 490 (least susceptible). A wide range of susceptibility levels, to some extent determined by fishing gear selectivity, 29 30 491 were found among the five species that dominated catches. Very high risk was attributed to only two species: P. 31 32 492 zijsron and C. tilstoni. High risk species were C. melanopterus and C. amboinensis, largely driven by their low 33 34 493 productivity, and medium risk species were C. limbatus, C. fitroyensis, S. mokarran and C. sorrah. Harry et al. 35 36 494 (2011b) analysed the life stages at which different species were most susceptible, based on observer data from 37 38 495 the ECIFF, highlighting that 95% of the catch is composed of the families Carcharhinidae, Hemigaleidae and 39 40 496 Sphyrnidae. They found that all size classes of C. tilstoni and C. sorrah were caught in equivalent proportions, 41 42 497 whilst larger sharks like C. amboinensis and C. brevipinna were predominantly caught as juveniles. 43 44 45 498 46 47 48 499 In addition to gear selectivity, natural mortality also confounds assessments of vulnerability for sharks, since 49 50 500 this parameter is not known for most species. In fact, most estimates of natural mortality are based on very 51 52 501 young juveniles, which have inherently higher mortality rates due to their reduced probability of escaping 53 54 502 predation and lower level of experience in accessing prey (Knip et al. 2012b). Survival of older adult individuals 55 56 503 is important to population recovery because their greater experience gives them a lower intrinsic mortality rate, 57 58 59 19 60 61 62 63 64 65 504 and they are therefore more likely to contribute offspring to future generations (Knip et al. 2012b). Fishing 1 2 505 mortality can account for a high proportion of the overall mortality rate; in Cleveland Bay, fishing accounted for 3 4 506 70% of mortalities suffered by C. amboinensis and C. sorrah, with five times more of the former caught than the 5 6 507 latter (Knip et al. 2012b). Estimates of absolute and proportional mortality rates due to different factors need to 7 8 508 be obtained for all species, especially those at risk from multiple sources of anthropogenic mortality. 9 10 11 509 12 13 14 510 Here we take a substantially different approach and use the intrinsic vulnerability index developed by Cheung et 15 16 511 al. (2005) and available for each species on Fishbase (Froese and Pauly 2012), plotted against the proportional 17 18 512 abundance of each species in the catch records of fisheries specific to three different GBRMP habitats: inshore 19 20 513 and coastal habitats (ECIFF and QSCP catch), coral reefs (CRFF bycatch) and offshore pelagic habitats (ETBF 21 22 514 catch and bycatch). This vulnerability index combines the intrinsic vulnerability of each species based on life 23 24 515 history parameters, their most recently recorded exploitation levels, and a proxy for their position in food webs 25 26 516 (and therefore an indicator of the strength of their ecological role). Bubble sizes for each species are reflective of 27 28 517 their mean Marine Trophic Index (also available in Froese and Pauly 2012). 29 30 31 518 32 33 34 519 C. leucas had the highest catch-vulnerability score in the QSCP (Fig. 7a). Other sharks with high proportional 35 36 520 catch rates, but intermediate vulnerability, were C. melanopterus and G. cuvier. Carcharhinus obscurus, C. 37 38 521 carcharias and C. plumbeus, which rated as the most vulnerable species, occurred in a lower proportion in the 39 40 522 catch records. Smaller inshore and shelf species generally ranked lower on the vulnerability and catch 41 42 523 proportion scale, but some ranked relatively high on the trophic scale despite their small size. The highest 43 44 524 trophic scores tended towards the low end of the catch axis but occurred along the entire vulnerability axis (Fig. 45 46 525 7a). 47 48 49 526 50 51 52 527 Unlike the QSCP, the highest combined score in the ECIFF was attributed to S. lewini (Fig. 7b). Carcharhinus 53 54 528 tilstoni had the highest catch score and relatively high vulnerability, and the highest vulnerability scores were 55 56 529 obtained by C. leucas and C. obscurus, which are caught in moderate proportions. Smaller species generally 57 58 59 20 60 61 62 63 64 65 530 ranked lower along both axes, but R. taylori had a relatively high trophic level. Trophic levels were evenly 1 2 531 distributed across the axes, but none of the lowest trophic categories appear in the highest catch proportions or 3 4 532 the highest vulnerability (Fig. 7b). These results (including assignment of ‘very high risk’ to S. lewini) are 5 6 533 compatible with Gribble et al. (2005), Salini et al. (2007) and Tobin et al. (2010).. 7 8 9 534 10 11 12 535 Among the sharks caught in the CRFF, T. obesus and C. albimarginatus ranked as the most vulnerable (Fig. 7c). 13 14 536 These two species are caught in intermediate proportions. Carcharhinus amblyrhynchos and C. melanopterus, 15 16 537 both caught in the highest proportions, are lower on the vulnerability scale than the other two species. No catch 17 18 538 data were available for the other species of reef sharks. Carcharhinus amblyrhynchos, whilst not the largest 19 20 539 species, appears highest on the trophic level scale (Fig. 7c). 21 22 23 540 24 25 26 541 As a group, pelagic sharks scored higher on the vulnerability scale than the inshore and reef sharks; most species 27 28 542 caught in the ETBF are large and have high trophic levels (Fig. 7d). Interestingly, there was a relatively high 29 30 543 proportion of G. cuvier in the catch, although this species is generally thought to be associated with continental 31 32 544 shelves and coastal habitats. Prionace glauca and I. oxyrhinchus had the lowest vulnerability score, but the 33 34 545 highest proportional catch rate. This may be because their life history makes them more abundant, and therefore 35 36 546 more prominent in catch records, or because the more vulnerable sharks have already suffered population 37 38 547 declines. Catchability may also play a role; a study in the western Pacific found that the species composition of 39 40 548 the catch varied according to the depth at which longline hooks were set (Bromhead et al. 2012). Despite 41 42 549 relatively low catch rates in most fisheries, C. obscurus scored highest on the vulnerability scale in coastal / 43 44 550 shelf and pelagic habitats. This is an important species in the temperate Western Australian shark fishery 45 46 551 (Simpfendorfer et al. 2002), but its biology and habitat use in the GBRMP are poorly known. 47 48 49 552 50 51 52 53 54 55 56 57 58 59 21 60 61 62 63 64 65 553 Discussion 1 2 3 554 What do we know about sharks in the GBRMP? 4 5 555 Knowledge about sharks in the GBRMP has been driven by the need to inform fisheries management; almost all 6 7 556 the more comprehensive data on sharks in Australian waters comes from fisheries catches. Fisheries- 8 9 557 independent shark research is restricted to a relatively small number of species and a few localised geographic 10 11 558 areas. Such research has been dominated by observational and biological studies on a few species (reef- 12 13 559 associated, and therefore relatively sedentary, or species of fisheries value); these are likely to be the most 14 15 560 abundant in the most accessible habitats, but not necessarily the most important in food webs. Large, wide- 16 17 561 ranging species are difficult to study, but studies conducted elsewhere suggest they may have key roles in 18 19 562 structuring ecosystems. There is some preliminary knowledge on latitudinal and cross-shelf patterns in shark 20 21 563 abundance and species composition (Last and Stevens 2009; DEEDI 2011a). Whilst knowledge gaps exist in all 22 23 564 habitats and for all species, least known are the biology and ecology of deepwater sharks, the abundance of 24 25 565 purely pelagic species within the GBRMP, the trophic roles of most species, especially larger ones, and the 26 27 566 stock structure and population dynamics of all exploited species. 28 29 30 567 Recent and ongoing research from the GBRMP is beginning to provide clearer insights into the vulnerability of 31 32 568 a number of species and some localised patterns of habitat use, but does not yet allow a clear view of the overall 33 34 569 predatory role of sharks in this region. Firstly, widespread shark removal had already occurred before their 35 36 570 influence as predators could be measured; it may be that the system has already stabilised in an alternate state. 37 38 571 Secondly, the plasticity of feeding behaviour and prey selected by most species of GBR sharks (Wetherbee and 39 40 572 Cortes 2004) complicates the detection of flow-on effects. Thirdly, ontogenetic changes in habitat use and 41 42 573 ecological roles complicate the understanding of functional roles; small sharks can act as both predators and 43 44 45 574 prey, especially in multispecies assemblages and in nursery grounds (Yates et al. 2012). The magnitude of the 46 47 575 spatial scale, the diversity of the habitats and the complexity of predator-prey interactions have, so far, made it 48 49 576 impossible to predict the importance of sharks and the possible consequences of their demise. Whole-of- 50 51 577 ecosystem comparisons of areas where shark populations have been protected (e.g. no-take or no-entry zones) 52 53 578 with areas where they have been subjected to human extraction have yet to be completed. The GBRMP offers 54 55 579 the possibility to undertake such comparisons in all three of the main habitats considered in this review, as the 56 57 580 existing management plan was designed to protect ~20% of each bioregion represented within the GBRMP 58 59 22 60 61 62 63 64 65 581 (Fernandes et al. 2005). Fisheries catches offer the opportunity for stomach contents analyses on captured 1 2 582 individuals to determine diet. Only rigorous community-level time series and detailed, species-specific studies 3 4 583 of diet and behaviour can give insight into sharks’ ecological roles (Speed et al. 2012). To date, the ecological 5 6 584 role of the GBRMP’s sharks must be inferred from studies conducted elsewhere. 7 8 9 585 10 11 12 586 Ecological roles and evidence for top-down control 13 14 587 The disruption of biological processes through overfishing has been well-documented in a number of areas. 15 16 588 Rapid increases in numbers of mesopredators in areas where large sharks are targets of fisheries have been used 17 18 589 as a key indicator of the top-down effects of removing large sharks (Graham et al. 2001; Ferretti et al. 2005; 19 20 590 Ward and Myers 2005; Levin et al. 2006; Polovina et al. 2009; Ferretti et al. 2010). In a study reviewing the 21 22 591 empirical evidence for trophic cascades as a result of apex predator removal, Baum and Worm (2009) 23 24 592 considered 29 papers on top-down control by higher-order predators, of which only three papers considered 25 26 593 sharks as the primary high-order predators (other papers focused on teleosts and mammals). The three papers 27 28 594 attributing top down control to large sharks included a study in the northwest Atlantic where the fishing of large 29 30 595 sharks led to mesopredator release in the form of a 10-fold increase in smaller elasmobranchs (Myers et al. 31 32 596 2007), a study in the same broad region in which mesopredator release of cownose rays resulted in the collapse 33 34 597 of a scallop fishery (Myers et al. 2007), and a study showing that overfishing of large sharks in the Gulf of 35 36 598 Mexico (Baum and Myers 2004) resulted in mesopredator release of deepwater sharks (Shepherd and Myers 37 38 599 2005). 39 40 41 600 42 43 44 601 Since Baum and Worm (2009)’s review, only a few further studies have demonstrated or implied top-down 45 46 602 effects of sharks. Studies by Heithaus et al. (2008; 2010) in Western Australia have demonstrated changes in 47 48 603 habitat use and feeding behaviours of large-bodied animals such as turtles, dolphins and dugongs in response to 49 50 604 changes in tiger shark numbers; these behavioural changes have cascading effects down to benthic communities 51 52 605 such as seagrass beds. Modelling studies demonstrated trophic cascades and reduced resilience in modelled 53 54 606 systems from which sharks had been removed, due to the concomitant decline in omnivory (Bascompte et al. 55 56 607 (2005). Stevens et al. (2000a) predicted that removing tiger sharks from coastal environments would release the 57 58 59 23 60 61 62 63 64 65 608 populations of mesopredatory seabirds, mammals and elasmobranchs, in turn causing a decline in tunas. In other 1 2 609 models, such as for coral reefs and pelagic systems, the removal of sharks had little effect (Stevens et al. 2000a). 3 4 610 The only direct indication of shifts in food webs within the GBRMP comes from Ferretti et al. (2010)’s analysis 5 6 611 of QSCP catches over five decades. They estimated an 85% decline in catches over this period, and a brief 7 8 612 period of ‘predator release’ response of small sharks between 1986 and 2001. As large species such as C. leucas 9 10 613 and G. cuvier declined, smaller carcharhinids increased from approximately 20 individuals per year to around 11 12 614 120, before declining again to the original catch rate by the early 2000s (Ferretti et al. 2010). However, evidence 13 14 615 of top-down effects of removing sharks in the GBRMP remain problematic, especially because fisheries remove 15 16 616 not just the apex predators, but also smaller mesopredators, effectively confounding the role of large sharks. 17 18 19 617 Shark protection and management 20 21 618 The standard protocol in fisheries has been reactive management, where catch quotas, size restrictions and other 22 23 619 actions designed to protect a stock from overexploitation are enacted only after the stock is discovered to be 24 25 620 overexploited or at risk of overexploitation (Pauly 2009). More recently, the view that fisheries management 26 27 621 must consider more than the stock of the target species, and must consider complicated interactions between 28 29 622 biological, environmental, social and economic issues, has been increasingly voiced (Gerrodette et al. 2002). It 30 31 623 has been argued by some that the burden of proof should rest with the fisheries, whereby those hoping to exploit 32 33 624 a resource must demonstrate a priori that fishing does not cause any ecologically significant long-term changes 34 35 36 625 to populations and ecosystems (Dayton 1998). In the case of a multi-species fishery operating within a World 37 38 626 Heritage Area, such as the ECIFF, in which life history and ecological parameters of most target species are 39 40 627 unknown or uncertain, we argue that reversal of the burden of proof is warranted. 41 42 628 There is some evidence that both fisheries management and marine protected areas can contribute to the 43 44 45 629 preservation and / or recovery of shark populations. Ward-Paige et al. (2012) recently reviewed research in 46 47 630 which shark population increases had been detected, and found evidence of 40 increasing populations, of which 48 49 631 25% could be attributed directly to a reduction in human exploitation. The remaining 75% of increases were 50 51 632 attributed to predation release. Of the species considered in this review, the only ones reported to have benefited 52 53 633 from a decrease in fishing pressure were G. cuvier in the northwest Atlantic, S. lewini in the northwest Atlantic 54 55 634 and the Gulf of Mexico, and C. carcharias in Australia (Ward-Paige et al. 2012). Closer to the GBRMP, a 56 57 635 reduction in fishing pressure in northern Australia resulted in population recovery of C. sorrah (Field et al. 58 59 24 60 61 62 63 64 65 636 2012). Such patterns have yet to be documented in the GBRMP, as the management responses to increasing 1 2 637 catches in the 1990s and 2000s are very recent (DEEDI 2011d). 3 4 5 638 In recent years, large portions of the Exclusive Economic Zone of several nations have been turned into shark 6 7 639 sanctuaries, including Palau, the Maldives, Honduras, the Regent of Raja Ampat, Indonesia, the Bahamas and 8 9 640 the Republic of the Marshall Islands (Ward-Paige et al. 2012). No-take areas have proven to be beneficial for 10 11 641 populations of reef sharks, which are highly site-attached (Robbins et al. 2006; Ayling and Choat 2008; Heupel 12 13 642 et al. 2009; Hisano et al. 2011; Knip et al. 2012a), and for juvenile C. leucas in mangrove estuaries (Ley et al. 14 15 643 2002). However, no-take areas still suffer from compliance issues, and fewer sharks are correlated with higher 16 17 644 human use (Ayling and Choat 2008; Hisano et al. 2011). The effectiveness of no-take areas for protecting 18 19 645 sharks is dependent on each species’ home-range and activity patterns, with larger reserves affording greater 20 21 646 levels of protection for highly mobile species. Although most of the world’s no-take areas are small (<5 km2; 22 23 647 Wood et al. 2008), they still confer measurable conservation benefits to highly mobile and migratory species 24 25 648 (Baum et al. 2003; Worm et al. 2003; Claudet et al. 2010; Jensen et al. 2010; Knip et al. 2012a). This is 26 27 649 especially true for species that exhibit some degree of reproductive philopatry; the recurring use of specific 28 29 650 areas for breeding by individuals has major implications for management strategies that aim to maintain genetic 30 31 651 structure within meta-populations, especially for endangered species (Tillett et al. 2012; Howey-Jordan et al. 32 33 652 2013). 34 35 36 653 The intrinsic rebound potential of shark populations varies between species, but is based primarily on life 37 38 654 history characteristics and can therefore be calculated (Smith et al. 1998). The highest recovery potential is 39 40 655 attributed to small species such as C. sorrah, C. macloti, R. acutus and R. taylori. Galeocerdo cuvier, C. 41 42 656 limbatus, P. glauca and T. obesus also have a high rebound potential due to their relatively fast growth and early 43 44 657 maturation. Some species also have high reproductive output; G. cuvier, for instance, can produce up to 30-50 45 46 658 offspring. The lowest recovery potential is expected for medium to large, slow growing, late-maturing coastal 47 48 659 sharks such as C. leucas, C. amboinensis, C. obscurus, C. plumbeus and N. acutidens (Smith et al. 1998). 49 50 51 660 Despite a recent increase in research, relatively few studies have considered the distribution, role and status of 52 53 661 sharks on the GBR and in adjacent waters; even the most basic population parameters are yet to be determined 54 55 662 for many species. Consequently, the vulnerability of lesser known species to over-exploitation may be 56 57 663 underestimated. Quantification of relevant population parameters for each exploited shark species (either as a 58 59 25 60 61 62 63 64 65 664 target or as bycatch) is an obvious priority for future research. These data are crucial as inputs for population 1 2 665 assessments, ecosystem models, and management evaluations. For example, knowledge of shark movement 3 4 666 patterns is critically important for assessing the effectiveness and connectivity of no-take reserves. Another 5 6 667 priority is to improve the current system of catch reporting. The principal unanswered question concerning the 7 8 668 role and importance of sharks on the GBR is: “How does removal or depletion of sharks affect the function and 9 10 669 overall health of the GBR?” The zoning system of the GBRMP provides a useful platform on which to answer 11 12 670 this question because it generates strong gradients in fishing pressure and, as a result, strong gradients in shark 13 14 671 density (Ayling and Choat 2008). Studies of no-entry zones embedded within large no-take zones will be critical 15 16 672 for observing and quantifying interactions between predatory sharks and their prey, because these zones 17 18 673 encompass the least disturbed areas of the GBR. Potentially rewarding avenues of research include theoretical 19 20 674 modelling, exclusion experiments, analyses of diet and stable isotopes, and correlative analyses of predator-prey 21 22 675 relative abundance. 23 24 25 676 Conclusions 26 27 677 Progress is being made in understanding the distribution, mobility, genetics and population structure of 28 29 678 exploited sharks in the GBRMP. However, we argue that in poorly understood multi-species fisheries, the 30 31 679 burden of proof needs to be reversed. The current situation is "business as usual" until a problem can be found 32 33 680 (e.g. declining abundance). However, given the global declines of most shark species, extractive activities 34 35 36 681 should not proceed until it is proven that exploited populations and / or associated ecosystem components are 37 38 682 not harmed, or are minimally harmed relative to the social and economic benefits derived from them. Sharks are 39 40 683 worthy of stricter management because (1) mounting evidence suggests that some sharks are keystone species 41 42 684 that regulate community structure and contribute to ecosystem resilience, and (2) their intrinsic characteristics 43 44 685 (e.g. K selection) predispose them to over-exploitation. A key challenge for the future is to convince the public 45 46 686 and policy makers that the need for shark conservation is both beneficial and urgent. 47 48 49 687 50 51 52 688 Acknowledgements 53 54 689 An early version of this review was commissioned and funded by the Great Barrier Reef Marine Park Authority, 55 56 690 and benefited from guidance from R. Owens, M. Russell and S. King. Data were provided by N. Engstrom, P. 57 58 59 26 60 61 62 63 64 65 691 Salgado, G. Coleman, T. Ham and W. Sumpton from DEEDI. We are grateful for guidance on species selection 1 2 692 and the use of the MTI by D. Pauly and T. Donaldson. Finally, for fruitful discussions and information sharing, 3 4 693 we thank J. H. Choat, D. Bellwood, C. Simpfendorfer, A. Tobin, A. Chin, T. Smith, B. Kerrigan, H. Sweatman, 5 6 694 M. Emslie, T. Timmiss, K. Evans and M. Cappo. 7 8 9 695 10 11 12 696 13 14 15 697 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 27 60 61 62 63 64 65 698 References 1 2 3 699 4 700 Abascal FJ, Quintanos M, Ramos-Cartelle A, Mejuto J (2011) Movements and environmental preferences of the 5 6 701 shortfin mako, Isurus oxyrinchus, in the southeastern Pacific Ocean. 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Shark 15 16 1078 diagrams (from Last and Stevens 2009) and abbreviations (see Table 1) are shown at their maximum depth in 17 18 1079 their primary habitats. For species that also use other habitats or depths during their life cycle, their occurrence 19 20 1080 in a secondary habitat (e.g. in a nursery area) is shown with their abbreviation in brackets. Shark sizes and 21 22 1081 distances across the shelf are not to scale. Superscripts symbolise additional species found in the same habitat / 23 24 1082 depth range, and are: 1) Gg, 2) Ebl, 3) Ama, 4) Cso, Lm, Rta, Smo, 5) Cao, Cma, Cti, Hga, 6) Hoc, Htr, Owa, 25 26 1083 Stf, 7) Eda, 8) Ctu, Oma, 9) Oor, 10) Hep, Pde, Apa, Fis, Sqa, Sqg, Sqn, Hab, Muw, 11) Hen, Ggr, Sqe, Sqo, 27 28 1084 Iag, 12) Edi, Edl, 13) Alo, 14) Ec, Aau, Apl, 15) Pka. 29 30 31 1085 Fig. 3 Proportional catch of inshore shark species by the ECIFF (DEEDI 2011d). The species list starts at 0° and 32 33 1086 proceeds clockwise. C.: Carcharhinus, S.: Sphyrna, R.: Rhizoprionodon, G.: Galeocerdo 34 35 36 1087 Fig. 4 Species specific annual shark catch (mean ± 1 S.E.) for the Queensland Shark Control Program between 37 38 1088 1997 and 2010. G.: Galeocerdo, C.: Carcharhinus, S.: Sphyrna, N.: Negaprion, R.: Rhizoprionodon, E.: 39 40 1089 Eusphyra 41 42 43 1090 Fig. 5 Mean annual catch in tonnes (2003-2010) for all carcharhinid (whaler) sharks. Excludes catches from grid 44 45 1091 cells where less than five boats were operating, due to data confidentiality agreements 46 47 48 1092 Fig. 6 Annual total of sharks caught in the Queensland Shark Control Program between 1997 and 2010. The 49 50 1093 annual catch is recorded by financial year, rather than calendar year 51 52 53 1094 Fig. 7 Vulnerability scores and (log) proportional catch of key species, with bubble size according to the mean 54 55 1095 trophic index. QSCP: Queensland Shark Control Program; ECIFF: East Coast Inshore Fin Fish Fishery; CRFF: 56 57 58 59 47 60 61 62 63 64 65 1096 Coral Reef Fin Fish Fishery; ETBF: Eastern Tuna and Billfish Fishery. Bubble size was calculated at follows: 1 2 1097 ((MTIi / MTIlowest)-1) x 100, where i is the shark species in question and lowest is the species with the lowest MTI. 3 4 5 1098 6 7 8 1099 9 10 1100 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 48 60 61 62 63 64 65 Figure

R. typus O. wardi O. ornatus I. brasiliensis H. trispeculare G. glyphis A. marnkalha B. colcloughi P. microdon A. superciliosus P. kamoharai E. dasypogon P. zijsron O. maculatus I. paucus C. longimanus L. macrorhinus C. carcharias C. plumbeus C. almus C. cautus C. taurus H. elongata H. australiensis I. oxyrinchus S. fasciatum C. obscurus C. falciformis Species E. blochii P. glauca C. albimarginatus A. cuspidata N. acudens N. ferrugineus C. amblyrhynchoides C. leucas C. punctatum C. fitzroyensis C. maclo S. mokarran C. limbatus C. dussumieri C. brevipinna R. acutus G. cuvier R. taylori C. lstoni C. amboinensis H. ocellatum T. obesus C. sorrah S. lewini C. amblyrhynchos C. melanopterus 0 10 20 30 Number of studies Figure Figure

C. fitzroyensis 0.8 C. dussumieri 0.8 G. cuvier C. obscurus 0.6 R. acutus, R. taylori & C. macloti

3.6 S. lewini 3.6 3.8 C. leucas & C. amboinensis 4 C. tilstoni, C. limbatus & 34.2 C. sorrah 4.2 C. amblyrhynchoides

Unspecified shark 4.8

C. melanopterus 5.4

Other sharks 5.6 7.6 11.6 C. brevipinna 9.4 Carcharhinidae, unspecified Sphyrna spp. Figure

160

140

120

100

80

60

40 Mean NumberMean Individualsof 20

0

Species Figure

Figure

1000

G. cuvier 100 C. leucas

10 S. lewini S. mokarran C. amboinensis

Total Number of Individuals (log10) Individuals of Number Total C. carcharias C. lstoni / limbatus C. taurus I. oxyrinchus C. obscurus 1

Financial Year Figure

1 QSCP 1 ECIFF C. obscurus 0.9 0.9 o C. leucas C. obscurus oC. leucas C. carchariasoooC. plumbeus o 0.8 o S. lewini 0.8 o S. lewini o oC. falciformis o o A. cuspidata oH. elongata o C. amboinensis 0.7 0.7 o C. amboinensis o oC. taurus C. melanopterus G. cuvier C. melanopterus C. amblyrhynchoides S. mokarrano G. cuvier S. mokarran o o o C. amblyrhynchoides E. blochii oo C. brevipinna 0.6 E. blochii o o oC. brevipinna 0.6 o oo o ty Index o C. limbatus o

ili o 0.5 R. acutus 0.5 C. amblyrinchos R. acutus o o oo oC. sorrah C. dussumieri o oo o C. dussumieri C. sorrah R. taylori o Vulnerab 0.4 oR. taylori 0.4 o

0.3 0.3

0.2 0.2

0.1 0.1

0 0 0.0001 0.001 0.01 0.1 1 0.0001 0.001 0.01 0.1

1 1 CRFF ETBF

0.9 0.9 oC. obscurus T. obesus 0.8 o 0.8 C. falciformiso oA. superciliosus o C. albimarginatus o I. paucus oC. longimanus 0.7 0.7 G. cuvier P. glauca oC. melanopterus o o oI. oxyrhinchus 0.6 0.6 ty Index ili oP.mka orahai 0.5 0.5 C. amblyrhynchos o

Vulnerab 0.4 0.4 o I. brasiliensis

0.3 0.3

0.2 0.2

0.1 0.1

0 0 0.001 0.01 0.1 1 0.0001 0.001 0.01 0.1 1 table

Table 1 Shark species (82) of the GBRMP, with Mean Trophic Index (MTI) from Froese and Pauly (2012) and maximum total length (TL), from Last and Stevens (2009).

Typical habitat preferences adapted from Chin and Kyne (2007), depth ranges from Last and Stevens (2009). Conservation status includes listings under State, Federal and

international legislation. International Union for the Conservation of Nature (IUCN) categories: DD: Data Deficient; LC: Least Concern; Vu: Vulnerable; En: Endangered;

NT: Near Threatened. Population trends are also given. Environment Protection and Nature Conservation Act 1999 (EPBC) categories: CE: Critically Endangered; Vu:

Vulnerable; Mar: listed Marine; Mi: listed Migratory. Other – Queensland Nature Conservation Act 1992 (QNCA) category: T: Threatened; Bonn: listed under The

Convention on the Conservation of Migratory Species of Wild Animals. GBRMP shark species caught in one or multiple fisheries. The QSCP is treated as a fishery, as it

removes sharks from the ecosystem. Vulnerability ranking from Cheung et al. (2005), available in Froese and Pauly (2012).

Family Species Common Name MTI (SE) Max Typical habitat Conservation Fisheries Vulnera TL and depth range Status (IUCN bility (cm) (population status)/EPBC/ QNCA) Alopiidae Alopias superciliosus Bigeye thresher (As) 4.5 (0.8) 484 Pelagic (0-700m) Vu (decreasing)/-/- ETBF 0.79 Brachaeluridae Brachaelurus colcloughi Colclough’s shark 3.5 (0.37) 75 Coastal/Inshore & Vu (unknown)/-/- ECIFF 0.45 (Bc) Shelf (0-100m) Carcharhinidae Carcharhinus albimarginatus Silvertip shark (Cal) 4.2 (0.7) 275 Reef & Shelf (0- NT (unknown) /-/- CRFF 0.74 800m) Carcharhinidae Carcharhinus altimus Bignose shark (Cat) 4.5 (0.5) 300 Shelf & Bathyal DD (unknown)/-/- ECIFF/QSCP 0.74 (80-430m) Carcharhinidae Carcharhinus amblyrhynchoides Graceful shark (Cay) 4.2 (0.7) 170 Coastal/Inshore (0- NT (unknown) /-/- ECIFF/QSCP 0.6 50m) Carcharhinidae Carcharhinus amblyrhynchos Grey reef shark (Cam) 4.1 (0.6) 225 Reef (0-280m) NT (unknown) /-/- ECIFF/CRFF/QSCP 0.47 Carcharhinidae Carcharhinus amboinensis Pigeye shark (Cao) 4.3 (0.7) 280 Coastal/Inshore & DD (unknown)/-/- ECIFF/QSCP 0.72 Shelf (0-100m) Carcharhinidae Carcharhinus brevipinna Spinner shark (Cb) 4.2 (0.7) 300 Coastal/Inshore & NT (unknown) /-/- ECIFF/QSCP/ECTF 0.62 Shelf (0-75m) Carcharhinidae Carcharhinus cautus Nervous shark (Cc) 4.5 (0.8) 150 Coastal/Inshore DD (unknown)/-/- ECIFF 0.58 (shallow) Carcharhinidae Carcharhinus dussumieri Whitecheek shark 3.9 (0.6) 90 Coastal/Inshore (0- NT (unknown) /-/- ECIFF/QSCP/ECTF 0.46 (Cd) 170m) Carcharhinidae Carcharhinus falciformis Silky shark (Cf) 4.5 (0.6) 330 Pelagic (0-500m) NT (decreasing) /-/- ETBF/QSCP 0.79 Carcharhinidae Carcharhinus fitzroyensis Creek whaler (Cfi) 4.1 (0.7) 135 Coastal/Inshore (0- LC (stable)/-/- ECIFF/QSCP 0.55 40m) Carcharhinidae Carcharhinus leucas Bull shark (Cle) 4.3 (0.7) 340 Coastal/Inshore (0- NT (unknown) /-/- ECIFF/QSCP 0.88 150m) Carcharhinidae Carcharhinus limbatus Common blacktip 4.2 (0.7) 250 Coastal/Inshore & NT (unknown) /-/- ECIFF/ETBF/QSCP 0.55 shark (Cli) Shelf (epipelagic) Carcharhinidae Carcharhinus longimanus Oceanic whitetip 4.2 (0.6) 350 Pelagic (0-150m) Vu (decreasing)/-/- ETBF 0.75 shark (Clo) Carcharhinidae Carcharhinus macloti Hardnose shark 4.2 (0.7) 110 Coastal/Inshore & NT (unknown) /-/- ECIFF/QSCP 0.45 (Cma) Shelf (0-170m) Carcharhinidae Carcharhinus melanopterus Blacktip reef shark 3.9 (0.6) 140 Reef (shallow) NT (decreasing) /-/- ECIFF/CRFF/QSCP 0.64 (Cme) Carcharhinidae Carcharhinus obscurus Dusky shark (Cob) 4.5 (0.8) 365 Coastal/Inshore & Vu (decreasing)/-/- ECIFF/ETBF/QSCP 0.88 Shelf (0-400m) Carcharhinidae Carcharhinus plumbeus Sandbar shark (Cpl) 4.5 (0.8) 185 Shelf (0-280m) Vu (decreasing)/-/- ECIFF/QSCP 0.86 Carcharhinidae Carcharhinus sorrah Spot-tail shark (Cso) 4.2 (0.6) 160 Coastal/Inshore & NT (unknown) /-/- ECIFF/QSCP 0.46 Shelf (0-80m) Carcharhinidae Carcharhinus tilstoni Australian blacktip 4.2 (0.7) 200 Coastal/Inshore & LC (stable)/-/- ECIFF/ETBF/QSCP 0.625 shark (Cti) Shelf (0-150m) Carcharhinidae Galeocerdo cuvier Tiger shark (Gc) 4.5 (0.7) 600 Coastal/Inshore & NT (unknown) /-/- ECIFF/ETBF/QSCP 0.64 Shelf (0-150m) Carcharhinidae Glyphis glyphis Speartooth shark (Gg) 4.2 (0.7) 175 Coastal/Inshore En (decreasing)/CE/- 0.6 (shallow) Carcharhinidae Loxodon macrorhinus Sliteye shark (Lm) 4 (0.6) 90 Coastal/Inshore & LC (unknown)/-/- ECIFF/ECTF 0.38 Shelf (0-100m) Carcharhinidae Negaprion acutidens Lemon shark (Na) 4.1 (0.7) 300 Reef (0-100m) Vu (decreasing)/-/- ECIFF/QSCP 0.78 Carcharhinidae Prionace glauca Blue shark (Pg) 4.2 (0.7) 383 Pelagic (0-1,000m) NT (unknown) /-/- ETBF 0.67 Carcharhinidae Rhizoprionodon acutus Milk shark (Rac) 4.3 (0.7) 100 Coastal/Inshore (0- LC (unknown)/-/- ECIFF/QSCP/ECTF 0.47 200m) Carcharhinidae Rhizoprionodon taylori Australian sharpnose 4.5 (0.8) 67 Coastal/Inshore & LC (unknown)/-/- ECIFF/QSCP/ECTF 0.41 shark (Rta) Shelf (0-110m) Carcharhinidae Triaenodon obesus Whitetip reef shark 4.2 (0.7) 170 Reef (0-40m) NT (unknown) /-/- ECIFF/CRFF 0.83 (To) Centrophoridae Centrophorus moluccensis Endeavour dogfish 4.3 (0.7) 100 Bathyal (300-500m) DD (decreasing)/-/- 0.69 (Cmo) Centrophoridae Centrophorus niaukang Taiwan gulper shark 4.3 (0.7) 170 Bathyal (98- NT (decreasing) /-/- 0.87 (Cni) 1,000m) Dalatiidae Dalatias licha Black shark (Dli) 4.2 (0.7) 180 Bathyal (450-850m) NT (unknown) /-/- 0.81 Dalatiidae Isistius brasiliensis Cookiecutter shark 4.3 (0.5) 50 Pelagic (0-1,000m) LC (unknown)/-/- ETBF 0.42 (Ib) Dalatiidae Squaliolus aliae Smalleye pygmy 4.4 (0.57) 22 Pelagic (150- LC (unknown)/-/- 0.11 shark (Sal) 2,000m) Echinorhinidae Echinorhinus cookei Prickly shark (Ec) 4.4 (0.7) 400 Bathyal (70- NT (unknown) /-/- 0.83 1,100m) Etmopteridae Etmopterus brachyurus Short-tail lanternshark 4.2 (0.7) 50 Bathyal (400-610m) DD (unknown)/-/- 0.43 (Ebr) Etmopteridae Etmopterus dianthus Pink lanternshark 4.1 (0.5) 41 Bathyal (700-880m) LC (unknown)/-/- 0.34 (Edi) Etmopteridae Etmopterus dislineatus Lined lanternshark 4.2 (0.5) 45 Bathyal (590-800m) LC (unknown)/-/- 0.38 (Edl) Etmopteridae Etmopterus lucifer Blackbelly 4.2 (0.5) 47 Bathyal (400-900m) LC (unknown)/-/- 0.4 lanternshark (Elu) Ginglymostomatidae Nebrius ferrugineus Tawny nurse shark 4.1 (0.5) 320 Reef (0-70m) Vu (decreasing)/-/- CRFF 0.61 (Nef) Hemigaleidae Hemigaleus australiensis Australian weasel 4.2 (0.5) 110 Coastal/Inshore & LC (unknown)/-/- ECIFF/ECTF 0.47 shark (Hga) Shelf (0-170m) Hemigaleidae Hemipristis elongata Fossil shark (Hel) 4.3 (0.6) 230 Coastal/Inshore & Vu (decreasing)/-/- ECIFF/QSCP 0.73 Shelf (0-130m) Hemiscylliidae Chiloscyllium punctatum Grey carpetshark 4.1 (0.6) 132 Reef/Coastal (0- NT (decreasing) /-/- ECIFF/ECTF 0.53 (Chp) 85m) Hemiscylliidae Hemiscyllium ocellatum Epaulette shark (Hoc) 3.4 (0.5) 107 Reef (shallow) LC (stable)/-/- 0.46 Hemiscylliidae Hemiscyllium trispeculare Speckled carpetshark 3.5 (0.4) 79 Reef (shallow) LC (unknown)/-/- 0.34 (Htr) Hexanchidae Heptranchias perlo Sharpnose sevengill 4.2 (0.6) 139 Bathyal (100-400m) NT (unknown) /-/- 0.73 shark (Hep) Hexanchidae Hexanchus griseus Bluntnose sixgill 4.3 (0.5) 480 Bathyal (0-2,500m) NT (unknown) /-/- 0.84 shark (Heg) Hexanchidae Hexanchus nakamurai Bigeye sixgill shark 4.2 (0.7) 180 Bathyal (90-600m) DD (unknown)/-/- 0.81 (Hen) Lamnidae Carcharodon carcharias White shark (Cac) 4.5 (0.7) 600 Shelf (0-1,280m) Vu (unknown)/Vu/-; ETBF/QSCP 0.86 Bonn Lamnidae Isurus oxyrhinchus Shortfin mako (Iso) 4.5 (0.7) 394 Pelagic (0-650m) Vu (decreasing)/-/-; ECIFF/ETBF/QSCP 0.86 Bonn Lamnidae Isurus paucus Longfin mako (Isp) 4.5 (0.8) 417 Pelagic (epipelagic) Vu (decreasing)/-/-; ETBF 0.76 Bonn Odontaspididae Carcharias taurus Grey nurse shark 4.5 (0.8) 318 Reef (0-190m) Vu ETBF/QSCP 0.68 (Ctu) (decreasing)/CE2/T Orectolobidae Eucrossorhinus dasypogon Tasselled wobbegong 4 (0.6) 125 Reef (0-50m) NT (decreasing) /-/- ECTF 0.86 (Eda) Orectolobidae Orectolobus maculatus Spotted wobbegong 4.2 (0.6) 170 Reef (0-218m) NT (unknown) /-/- ECTF 0.85 (Oma) Orectolobidae Orectolobus ornatus Dwarf banded 4 (0.6) 110 Reef (0-100m) NT (unknown) /-/- 0.75 wobbegong (Oor) Orectolobidae Orectolobus wardi Northern wobbegong 4 (0.61) 63 Reef (shallow) LC (stable)/-/- 0.29 (Owa) Pristiophoridae Pristiophorus delicatus Tropical sawshark 3.9 (0.6) 84 Bathyal (245-405m) LC (unknown)/-/- 0.33 (Pde) Pseudocarchariidae Pseudocarcharias kamoharai Crocodile shark (Pka) 4.2 (0.6) 118 Pelagic (0-590m) NT (unknown) /-/- ETBF 0.54 Pseudotriakidae Pseudotriakis microdon False catshark (Pmi) 4.3 (0.7) 296 Bathyal (100- DD (unknown)/-/- 0.68 1,890m) Rhincodontidae Rhincodon typus Whale shark (Rty) 3.6 (0.5) 120 Pelagic (epipelagic) Vu (decreasing)/Vu,Mi/-; Bonn, UNCLOS 0.33 0 Scyliorhinidae Apristurus australis Pinocchio catshark 3.7 (0.5) 83 Bathyal (485- DD (unknown)/-/- 0.34 (Aau) 1,035m) Scyliorhinidae Apristurus longicephalus Smoothbelly catshark 3.7 (0.5) 59 Bathyal (680-900m) DD (unknown)/-/- 0.35 (Alo) Scyliorhinidae Apristurus platyrhynchus Bigfin catshark (Apl) 3.8 (0.5) 71 Bathyal (730- DD (unknown)/-/- 0.45 1,000m) Scyliorhinidae Asymbolus pallidus Pale spotted catshark 3.9 (0.6) 47 Bathyal (225-400m) LC (unknown)/-/- 0.29 (Apa) Scyliorhinidae Cephaloscyllium variegatum Saddled swellshark 4.1 (0.6) 74 Shelf/Bathyal (115- NT (decreasing) /-/- 0.39 (Cev) 605m) Scyliorhinidae Figaro striatus Northern sawtail 3.9 (0.6) 42 Bathyal (300-420m) DD (unknown)/-/- 0.27 shark (Fis) Scyliorhinidae Galeus gracilis Slender sawtail shark 3.9 (0.5) 34 Bathyal (290-470m) DD (unknown)/-/- 0.24 (Ggr) Scylirhinidae Atelomycterus marnkalha Eastern banded 3.9 (0.6) 48 Coastal (10-75m) DD (unknown)/-/- 0.29 catshark (Ama) Sphyrnidae Eusphyra blochii Winghead shark (Ebl) 4.05 186 Coastal/Inshore NT (unknown) /-/- ECIFF/QSCP 0.6 (0.61) (shallow) Sphyrnidae Sphyrna lewini Scalloped 4.1 (0.6) 350 Coastal/Inshore & En (unknown)/-/- ECIFF/ETBF/QSCP 0.81 hammerhead (Sle) Shelf (0-275m) Sphyrnidae Sphyrna mokarran Great hammerhead 4.3 (0.7) 600 Coastal/Inshore & En (decreasing)/-/- ECIFF/ETBF/QSCP 0.64 (Smo) Shelf (0-80m) Squalidae Squalus albifrons Eastern highfin 4.3 (0.7) 86 Bathyal (131-450m) DD (unknown)/-/- 0.61 spurdog (Sqa) Squalidae Squalus grahami Eastern longnose 4.3 (0.6) 64 Bathyal (220-450m) NT (unknown) /-/- 0.57 spurdog (Sqg) Squalidae Squalus megalops Piked spurdog (Sqe) 4.3 (0.7) 64 Shelf & Bathyal (0- DD (unknown)/-/- 0.59 580m) Squalidae Squalus montalbani Philippine spurdog 4.4 (0.7) 91 Shelf (295-670m) Vu (decreasing)/-/- 0.64 (Sqo) Squalidae Squalus notocaudatus Bartail spurdog (Sqn) 4.2 (0.6) 62 Bathyal (220-450m) DD (unknown)/-/- 0.54 Stegostomatidae Stegostoma fasciatum Zebra shark (Stf) 3.1 (0.4) 235 Reef (shallow) Vu (decreasing)/-/- ECIFF/CRFF 0.77 Triakidae Hemitriakis abdita Darksnout 4.3 (0.7) 60 Bathyal (225-400m) DD (unknown)/-/- 0.65 houndshark Triakidae Hypogaleus hyugaensis Pencil shark (Hyg) 4.2 (0.7) 150 Shelf (40-230m) NT (unknown) /-/- 0.62 Triakidae Iago garricki Longnose houndshark 4.5 (0.37) 75 Bathyal (250-475m) LC (unknown)/-/- 0.45 (Iag) Triakidae Mustelus ravidus Grey gummy shark 3.6 (0.5) 78 Shelf /Bathyal (100- LC (stable)/-/- 0.38 (Mur) 300m) Triakidae Mustelus walkeri Eastern spotted 3.7 (0.5) 112 Shelf /Bathyal (50- DD (unknown)/-/- ECTF 0.53 gummy shark (Muw) 400m)

Note: the bronze whaler shark, Carcharhinus brachyurus, is sometimes considered to occur in the GBR Region, but see Last and Stevens (2009).

1Sources of data for relative abundance scores: Queensland Shark Control Program 1996 – 2011, Queensland Fisheries catch data 2003-2010, AUF (2008), Ayling and Choat

(2008), Cappo et al. (2009), DEEDI (2011), Dudley and Gribble (1999), Evans (2007), Gribble et al. (2005), Halliday et al. (2001), Harry et al. (2011), Heupel et al. (2008),

Heupel et al. (2009), Kyne et al. (2007), Robbins (2006), Robbins et al. (2006), Salini et al. (2007), Simpfendorfer et al. (2008), Sumpton et al. (2009), Tobin (2009),

Williams (2007)

2The east coast population, which overlaps with the GBR, is Critically Endangered. The west coast population is considered Vulnerable. table

Table 2 Life history and other parameters used to calculate measures of vulnerability, productivity or recovery

potential in sharks by Cheung et al. (2005), Gribble et al. (2005), Salini et al. (2007) and Tobin et al. (2010).

Parameter Cheung et al. Gribble et al. Salini et al. Tobin et al.

2005 2005* 2007* 2010

Age at first maturity (Tm)    

Length at first maturity (Lm)   

Maximum age (Tmax)   

Maximum length (Lmax)   

Age at maturity/maximum size 

Age at length=0 (t0) 

VBGF parameter K (K)   

Length-weight relationship

constants (a,b)

Natural mortality rate (M) 

Geographic range (Range (km)) 

Fecundity (Fec (egg/pup individual -  

1 year-1))

Mean litter size  

Reproductive periodicity  

Spatial behaviour strength (SB) 

Depth range  Resulting Index Vulnerability Productivity Recovery Productivity

potential

*Ranked each parameter and calculated the index from the averaged ranks.