Pangaea Initiative: Great Barrier Reef & Torres Strait DR SHANTA BARLEY & PROFESSOR JESSICA MEEUWIG

Transcription

1 2017 Pangaea Initiative: Great Barrier Reef & Torres Strait APRIL-JUNE 2017 DR SHANTA BARLEY & PROFESSOR JESSICA MEEUWIG

2 ACKNOWLEDGEMENTS This expedition was supported by the donation of ship time on the M/Y Pangaea, and funded through a gift from Teach Green to the University of Western Australia (UWA) to support marine conservation and research under the Pangaea Initiative. The research was made possible thanks to permits from the Great Barrier Reef Marine Park Authority (G17/ ) and approval from the Animal Ethics Committee at UWA (RA/3/100/1484). We are grateful to Todd Calitri, Richard Schumann, Paul Boyers, Dave Yoder, Grant Bowen and Captain Ferdi Heymann for assisting in the catch and release fish sampling with the entire Pangaea crew invaluable in their support of the science team. We also acknowledge the members of the UWA science team, Jemma Turner, Hanna Christ, Louis Maserei, Adam Jolly and Nikki de Campe. Cover photos: Sampled and tagged shark being released; blue bastards swarming a seabed baited remote underwater video system.

3 EXECUTIVE SUMMARY From April 2 nd to June 24 th 2017, scientists from the Marine Futures Lab at the University of Western Australia conducted a three month expedition on board the M/Y Pangaea to the Great Barrier Reef Marine Park (GBRMP) and the Torres Strait in order to study the role of sharks on coral reefs. Many shark populations have declined by over 90% (Baum et al. 2003) yet the effects of these losses on coral reefs remain poorly understood (Roff et al. 2016). The Pangaea Initiative uses large-scale gradients in shark abundance created by fishing and marine parks to improve understanding of ecological function: do sharks play a unique role on coral reefs or are they ecologically redundant? To date, the Pangaea Initiative has conducted research at a number of sites in the Indo-Pacific, including the British Indian Ocean Territory (2015/2016) and the Cocos (Keeling) Islands (2016). In July, the Pangaea Initiative will sample the inshore Kimberley region and Ashmore Commonwealth Marine Reserve in northwestern Australia (July 2017). The research programme is underpinned by two techniques: (1) catch-and-release (CnR) fly fishing and (2) video-based sampling using stereo Baited Remote Underwater Video Systems (BRUVS), placed on the seabed near coral reefs. The BRUVS document the diversity, abundance, size, biomass and behaviour of reef and pelagic fishes, generating data that can be used to document the structure of shark populations and explore how the removal shark abundance alters the population structure of fish communities, as per Barley et al. (2017b) and Tickler et al. (2017). On the most recent expedition to the GBRMP, the programme for the first time included stereo-bruvs suspended in mid-water that drift over the seabed, regardless of depth. Length, weight, fin and muscle samples obtained via catch and release fishing are also used to understand the effect of sharks on the morphology, diet and habitat use of prey and competitors, following Barley et al. (2017c). Collaborators at the University of Oxford will also analyse genetic samples to understand how removal of sharks affects gene expression in bony fishes, linked to, for instance flight responses and vigilance. On the most recent expedition to the Great Barrier Reef and the Torres Strait, the team obtained: Fin clip and muscle samples from 400 fishes representing 7 families, 15 genera and 23 species. These samples were collected at 26 sites in total across the GBRMP, including 12 sites within protected, unfished zones and 14 sites within unprotected, fished zones. Giant trevally, reef sharks, snapper and other species sampled on previous expeditions were targeted. i

4 Length and weight measurements from the same 400 fishes to understand condition. For the first time, we also took measurements of gape size in over 300 fishes that compete with sharks for resources, which will generate a paper exploring the mechanism by which declines in sharks alter the size structure of fish communities through competitive release. Samples of coral Acropora spp., crabs, mantis shrimp, sea cucumbers and macroalgae, which will be used to identify diet shifts in prey due to sharks via stable isotope analysis. 707 seabed stereo-bruvs samples, which recorded tiger sharks, scalloped hammerhead sharks and other rare marine wildlife. 309 video samples were obtained at 12 protected zones, 298 samples in 12 unprotected zones and 100 in the Torres Strait. The first biological and video samples ever obtained for the blue bastard. These samples will provide the first insights into the diet and social structure of these mysterious fishes, only recognised in mid-water stereo-bruvs video samples, with 25 obtained in two protected zones, 34 in 4 unprotected zones, and 20 at two sites in the Torres Strait. Ultimately, the data collected by the Pangaea Initiative will provide a foundation for policies that protect populations of reef fishes both in the Indo-Pacific and globally of direct relevance to the coral reefs across Australia s tropics. Moreover, existing collaborations between the Pangaea Initiative and the managers of marine protected areas mean that the knowledge generated from this trip will directly contribute to improved conservation outcomes. Outcomes from the first mid-water BRUVS survey of the Great Barrier Reef Marine Park and the Torres Strait will contribute to national (the Great West Ozzie Transect and the Cocos (Keeling) Islands) and international (Pristine Seas) initiatives to understand the response of pelagic fish assemblages to management. ii

5 THE GREAT BARRIER REEF The Great Barrier Reef is the world s largest coral reef ecosystem (Figure 1), covering an area of 345,000 km 2 and comprising over 3,000 reefs that extend along a 1,500 km stretch of coastline (Willis et al. 2004). The Great Barrier Reef Marine Park Authority (GBRMPA) has divided the reef into zones based on protection level (Table 1). Green or Marine National Park zones restrict all extractive activities but support tourism, boating and diving and comprise 33% of the GBRMP. Blue or Habitat Protection zones allow most forms of fishing except for trawling and comprise 28% of the GBRMP. The remainder of the GBRMP is comprised of General Use zones (light blue), Conservation Park zones (yellow), Buffer zones (olive green), Scientific Research zones (orange) and Preservation zones (pink). Figure 1: Image of a shallow water site on the Great Barrier Reef Marine Park 1

6 Table 1: Activities that are legal within GBRMP zones in which we conducted research. Permit indicates that formal permission is required. Activity Protected zone Unprotected zone Aquaculture No Permit Bait netting No Yes Boating, diving Yes Yes Crabbing No Yes Harvesting for aquaria No Permit Harvesting sea cucumbers No Permit Limited impact research Yes Yes Limited spearfishing No Yes Line fishing No Yes Netting (other than bait) No Yes Research Permit Permit Shipping Permit Permit Traditional marine resource use Permit Permit Trawling No No Trolling No Yes THE TORRES STRAIT The Torres Strait is located between the tip of Cape York and Papua New Guinea. It incorporates the northernmost section of the Great Barrier Reef but is not within the Great Barrier Reef Marine Park. Islands in the strait have been inhabited for over 9,000 years. Exploitation of marine resources probably began ~7,000 years ago, when humans began capturing stranded fish from shallow pools and channels on the reef flats at low tide (Weisler and McNiven 2016). Approximately 3,000 years ago, islanders transitioned to using large, seaworthy outriggers to catch turtles and dugongs. Today, approximately 20 of the roughly 200 islands have residents, many of whom continue to rely on the ocean for protein (Weisler and McNiven 2016). Commercial line fishing in the Torres Strait began after World War II. Today, the fishery has two components: a reef fishery and a trolling-based Spanish mackerel fishery. The former primarily targets coral trout, but also includes snappers, emperors and groupers. Most commercial fishing occurs in the north-east area of the Torres Strait, and a large, previously fished area to the west is currently closed. A prawn fishery was established in the Torres Strait in

7 EXPEDITION AIMS The aim of the Pangaea Initiative s expedition to the Great Barrier Reef Marine Park and the Torres Strait was to use large-scale gradients in shark abundance, generated by variation in fishing, to better understand how sharks affect coral reef and pelagic ecosystems. We compared protected (green) zones in the GBRMP, where fishing is prohibited and sharks are abundant, to unprotected (blue) zones and the Torres Strait, where fishing continues and sharks are thought to be relatively rare (Ayling and Choat 2008). We made several predictions about protected zones in comparison to unprotected zones: (1) Sharks would be more abundant, larger in size and have greater biomass, both on coral reefs and in pelagic systems; (2) Species of bony fishes consumed by sharks would be less abundant and have lower biomass; (3) Due to gape limitation in sharks, consumable prey species (i.e. fishes that are less than 30-40% of the length of sharks) would be less abundant and have lower biomass; (4) The diversity of custodian fishes, those that clean and maintain the reef, would be higher due to the role sharks play as the guardians of biodiversity on reefs; (5) Prey fishes would consume lower quality diets and would be lower in weight for a given length due to the effects of sharks on prey foraging behaviour; (6) Prey fishes would display differences in gene expression with the inference that these reflect anti-predator adaptations. To test these predictions, we conducted an expedition to the Great Barrier Reef Marine Park and the Torres Strait between April 2 nd and June 24 th. The team members are listed in Table 2. Seabed BRUVS and mid-water BRUVS will be used to test hypotheses (1-3). Seabed BRUVS alone will be used to test hypothesis (4). Stable isotope analysis of muscle samples and length and weight data will be used to test hypothesis (5), while genetic analysis of muscle samples and fin clips will be used to test hypothesis (6). Data from the seabed BRUVS will also help to interpret these patterns in (4) to (6) based on observed shark abundance in the protected and unprotected zones. Data from the Pangaea Initiative s expedition to the GBRMP and Torres Strait will ultimately be integrated with findings from previous and future expeditions to examine whether the role of sharks on coral reefs can be generalized at large-scales. Such research is essential to the protection of coral reefs in the Indo-Pacific, where growing human populations place increasingly unsustainable pressures on 3

8 marine resources and evidence-based policies are urgently needed to halt and reverse declines in the abundance of sharks and bony fishes and improve reef health. Table 2: Science team members that participated in the Pangaea Initiative expedition to the GBRMP and Torres Strait. Member Dr Shanta Barley Jemma Turner Hanna Jabour Christ Louis Maserei Adam Jolly Nikki de Campe Role Expedition leader, CnR sampling, BRUVS CnR sampling, BRUVS BRUVS CnR sampling, BRUVS BRUVS BRUVS RESEARCH ACHIEVEMENTS CATCH AND RELEASE FLY FISHING In total, 400 fishes were sampled spanning 23 species and 7 families including trevally (Carangidae), sharks (Carcharhinidae and Ginglymostomatidae), sweetlips (Haemulidae), snappers (Lutjanidae), emperors (Lethrinidae), tunas and mackerels (Scombridae) and groupers (Serranidae). Species considered to be major predators on reef flats were caught via wading such as giant trevally Caranx ignobilis (57), golden trevally Gnathanodon speciosus (10), blacktip reef shark Carcharhinus melanopterus (9) and permit Trachinotus blochii (9). Other species were caught from skiffs, including spanish flag snapper Lutjanus carponotatus (48), leopard coral grouper Plectropomus leopardus (60), twin-spot red snapper Lutjanus bohar (60), and coral hind Cephalopholis miniata (41). Approximately 20 Australian blacktip reef shark Carcharhinus tilstoni were also sampled. The most sampled families were Carangidae (116), Carcharhinidae (33), Lutjanidae (132) and Serranidae (106). The team sampled fishes at 12 sites in protected zones and 14 sites in unprotected zones (Table 3). No fishes were sampled within the Torres Strait. See Table 4 for a full list of all fishes sampled with reference to the numbers by species sampled on previous expeditions. Ultimately data from multiple locations and expeditions across the Indo-Pacific will be integrated to examine large-scale trends in key species in response to variations in the abundance of sharks. Species that are directly affected by shark predation or competition were selected to compare in terms of morphology, condition, diet and genetics between protected and unprotected (blue zones and the Torres Strait sites) zones. These species, which include giant trevally, golden trevally and 4

9 twin-spot red snapper, were also chosen because they represent important functional groups within the coral reef food web. Preliminary analyses that support our comparisons of shark-rich and -poor environments indicate that maximum length for some species is higher in protected zones than in unprotected zones for a number of species including giant trevally, island trevally and Australian blacktip reef sharks. This likely reflects the fact that fishes within protected zones are more protected from fishing than in unprotected zones. Regression of weight against length will be used to explore whether fishes are in better condition where sharks are rarer relative to sites where sharks are more abundant, consistent with the results from Barley et al. (2017c) in northwestern Australia. Preliminary analyses suggest that zoning in the GBRMP may also influence the condition of sharks as a function of size, with Australian blacktip reef sharks, for example, in better condition in protected zones at small sizes but in better condition in unprotected zones at larger sizes. Muscle samples will be submitted for stable isotope analysis, revealing the feeding habits of a range of important reef and flats species such as blue bastard, and allowing us to explore whether removal of sharks leads to shifts in the diet of prey, as found by Barley et al. (2017a). Samples of coral Acropora spp., sea cucumber Holothuria atra, macroalgae, jellyfish, squid, starfish and mantis shrimp will be used as baseline indicators. Muscle samples and fin clips will also undergo genetic analysis at Oxford University by PhD student Ms. Abigail Bailey, to determine whether fish display variation in gene expression in the presence of sharks. Table 3: Regions visited in the GBRMP by zone and the number of fish sampled. Region Protected Unprotected South GBRMP Middle GBRMP North GBRMP Total

10 Table 4: Species and number of fish sampled in the GBRMP and previous expeditions including Cocos (Keeling) Islands and the British Indian Ocean Territory (BIOT) expeditions I-III. Common name Species GBRMP C-K BIOT I-III Total twin spot red snapper Lutjanus bohar paddletail Lutjanus gibbus bluefin trevally Caranx melampygus roundjaw bonefish Albula glossodonta common coralgrouper Plectropomus areolatus giant trevally Caranx ignobilis leopard coralgrouper Plectropomus leopardus island trevally Carangoides orthogrammus blacksaddle grouper Plectropomus laevis spanish flag snapper Lutjanus carponotatus coral hind Cephalopholis miniata blacktip reef shark Carcharhinus melanopterus delicate round herring Spratelloides delicatulus redmouth grouper Aethaloperca rogaa yellow-edged lyretail Variola louti honeycomb grouper Epinephelus merra camouflage grouper Epinephelus polyphekadion small toothed jobfish Aphareus furca black and white snapper Macolor niger spangled emperor Lethrinus nebulosus Australian blacktip Carcharhinus tilstoni green jobfish Aprion virescens grey reef shark Carcharhinus amblyrhynchos scad Decapterus sp brassy trevally Caranx papuensis golden trevally Gnathanodon speciosus yellowfin tuna Thunnus albacares kawakawa Euthynnus affinis small-spotted dart Trachinotus baillonii snubnose pompano Trachinotus blochii dogtooth tuna Gymnosarda unicolor orange-striped emperor Lethrinus obsoletus peacock grouper Cephalopholis argus white-edged lyretail Variola albimarginata one-spot snapper Lutjanus monostigma shark mackerel Grammatorcynus bicarinatus turrum Carangoides fulvoguttatus wahoo Acanthocybium solandri bigeye trevally Caranx sexfasciatus roving coralgrouper Plectropomus pessuliferus talang queenfish Scomberoides commersonnianus

11 Common name Species GBRMP C-K BIOT I-III Total blacktail snapper Lutjanus fulvus foursaddle grouper Epinephelus spilotoceps longface emperor Lethrinus olivaceus orange-spotted emperor Lethrinus erythracanthus rainbow runner Elagatis bipinnulata spotted coralgrouper Plectropomus maculatus triple tail wrasse Cheleinus trilobatus yellow-saddle goat fish Parupeneus cyclostomus blacktip grouper Epinephelus fasciatus blue bastard Plectorhinchus caeruleonothus brown-marbled grouper Epinephelus fuscoguttatus crocodile needlefish Tylosurus crocodilus sicklefin lemon shark Negaprion acutidens spot cheek emperor Lethrinus rubrioperculatus tawny nurse shark Nebrius ferrugineus whitetip reef shark Triaenodon obesus yellowmargin trigger Pseudobalistes flavimarginatus black jack Caranx lugubris blue and gold fusilier Caesio caerulaurea blue striped snapper Lutjanus kasmira blue trevally Caranx ferdau cheeklined wrasse Oxycheilinus digramma crimson jobfish Pristipomoides filamentosus dark hind Cephalopholis urodeta dart sp Trachiotus sp leopard grouper Mycteroperca rosacea malabar grouper Epinephelus malabaricus milkfish Chanos chanos needlescale queenfish Scomberoides tol orange lined triggerfish Balistapus undulatus Picasso triggerfish Rhinecanthus aculeatus pink ear emperor Lethrinus lentjan silver biddy Gerres oyena skipjack tuna Katsuwonus pelamis small tooth emperor Lethrinus microdon snubnose grouper Epinephelus macrospilos strongspine silver-biddy Gerres longirostris titan triggerfish Balistoides viridescens tomato hind Cephalopholis sonnerati whitespotted grouper Epinephelus coeruleopunctatus yellowlip emperor Lethrinus xanthochilus Total

12 GAPE SIZE Marine predators are gape-limited and should therefore play a key role in determining the size structure of reef communities. Several papers have recently suggested that sharks are ecologically similar to large fishes such as trevally and that loss of sharks should not therefore trigger trophic cascades (Frisch et al. 2016; Roff et al. 2016). However, no data have been collected on how shark gape size compares to that of potential competitors. To investigate, gape measurements were Figure 2: Measuring the gape height of a grey reef shark obtained from species fulfilling a diverse set of ecological niches (Figure 2; Table 5). Table 5: Number of measurements for gape width (n-gw) and height (n-gh) available. Fewer gape height measurements were collected due to the difficulties of measuring height in some species. Common name Species n-gw n-gh* twin spot red snapper Lutjanus bohar leopard coralgrouper Plectropomus leopardus coral hind Cephalopholis miniata spanish flag snapper Lutjanus carponotatus giant trevally Caranx ignobilis Australian blacktip reef shark Carcharhinus tilstoni paddletail Lutjanus gibbus island trevally Carangoides orthogrammus brassy trevally Caranx papuensis 9 9 turrum Carangoides fulvoguttatus 7 7 shark mackerel Grammatorcynus bicarinatus 7 7 snubnose pompano Trachinotus blochii 7 7 green jobfish Aprion virescens 5 5 bluefin trevally Caranx melampygus 5 5 blacksaddle grouper Plectropomus laevis 5 5 golden trevally Gnathanodon speciosus 4 4 grey reef shark Carcharhinus amblyrhynchos 3 3 blacktip reef shark Carcharhinus melanopterus 3 3 talang queenfish Scomberoides commersonnianus 3 3 yellowfin tuna Thunnus albacares 2 2 whitetip reef shark Triaenodon obesus 2 2 blue bastard Plectorhinchus caeruleonothus 1 1 Total

13 Maximum prey size (MPS) was calculated by assuming that either the gape width or gape height (whichever was largest) of a predator was equivalent to the body depth of the largest prey that could be consumed. Maximum fork length of prey was then back-calculated from its body depth using known relationships between body depth and fork length. Maximum predator fork length (MPFL) was sourced for each species from Fishbase (Froese and Pauly 2016). Preliminary analysis of the gape data suggests that the gapes of sharks are small relative to body size, constraining them to consume relatively small prey compared to competitor species such as giant trevally and groupers, which have much larger gape sizes. For example, our preliminary results indicate that a ~90 cm shark can eat a maximum prey size of 30 cm, yet the same prey can be consumed by a 75 cm giant trevally or a ~50 cm coral hind (Figure 3). Thus, even though most large bony fishes never reach the same size as reef sharks, they may still be able to consume prey of a comparable size, enhancing their roles as competitors. Figure 3: Maximum prey size (MPS; %) against maximum predator fork length (MPFL) for a range of species, with sharks indicated by green diamonds and bony fish by grey circles; the regression equation is MPS = MPFL with MPFL explaining 73% of the variance in MPS. 9

14 SEABED STEREO-BRUVS In total, 707 BRUVS were deployed on the seabed (Figure 4) at 29 sites over 38 days of sampling. Of these, 309 were deployed in protected zones, 298 in unprotected zones, and 100 in the Torres Strait (Figure 5; Table 6). The average depth of the samples was 9.9 m in protected zones, 8.8 m in unprotected zones and 11.1 m in the Torres Strait. Table 6: Number of seabed BRUVS samples collected from protected and unprotected zones in the GBRMP and in the Torres Strait. Region Protected Unprotected South GBRMP Middle GBRMP North GBRMP Torres Strait Total Preliminary analysis of the seabed stereo- BRUVS videos demonstrated the presence of several shark species including grey reef sharks, tawny nurse sharks Nebrius ferrugineus, blacktip reef sharks C. melanopterus, scalloped hammerhead sharks Sphyrna lewini and tiger sharks Galeocerdo cuvier. Large sharks snapped the bait arms on five BRUVS rigs, an unprecedented rate. At Morris island, a large male tiger shark dragged the rig some distance. Grey reef sharks were significantly more abundant at northern sites in the GBRMP. Great barracuda Sphyraena barracuda, giant trevally, potato cod Epinephelus tukula, moray eels Muraenidae spp, the rare harlequin tuskfish Choerodon fasciatus and several groups of blue bastard Plectorhinchus caeruleonothus were also observed on the videos (Figure 5). Screen grabs taken from seabed BRUVS will also be used to assess bleaching in coral reefs. Each image of coral reef habitat will be scored for bleaching (0% none; 1-25% minor; 25-50% significant; 50-75% severe; % catastrophic). The resulting data will allow us to assess the extent to which bleaching has affected reefs in the GBRMP in relation to other studies such as the aerial surveys carried out by the Centre for Excellence for Coral Reefs at James Cook University, and assess recovery rates on subsequent expeditions to the area. Specifically, when analysed in conjunction with the results of the seabed BRUVS and the catch and release fish sampling, this data will improve understanding of how shark populations influence resilience of coral reefs to climate change. Figure 4: UWA scientist deploying seabed BRUV. 10

15 Figure 5: Still images captured on seabed BRUVS of a harlequin tusk fish (top) and grey reef shark and protected humphead wrasse Cheilinus undulatus, bottom. 11

16 MID-WATER BRUVS The blue-water or pelagic zone next to the GBRMP is thought to be a hotspot for species diversity (Worm et al. 2003) and is an important habitat for the larvae of many coral reef fish species (Williams and Hatcher 1983). There are also strong linkages between nominal reef species such as grey reef sharks and tunas that use both reef and pelagic habitats. Moreover, the pelagic zone will undergo drastic changes in circulation patterns in response to climate change, influencing the survival rates of the sharks, trevally, tuna, mackerel, marlin and other iconic species (Munday et al. 2007). Yet the zone remains poorly studied (Worm et al. 2003). Table 7: Number of sites sampled in protected and unprotected zones using mid-water BRUVS. Region Protected Unprotected Middle GBRMP 0 19 North GBRMP Torres Strait 0 20 Total To create a baseline understanding of the population structure of pelagic shark and fish communities in the GBRMP and Torres Strait, we deployed 79 mid-water BRUVS drops across 8 days of sampling. These drops represent the first time that mid-water BRUVS have been used to document pelagic fish assemblages in the GBRMP. We deployed 25 mid-water BRUVS in protected zones, 34 in unprotected zones, and 20 in the Torres Strait (Table 7). Preliminary analysis of the footage demonstrated the presence of blacktip sharks Carcharhinus limbatus, tiger sharks, great barracuda, Australian blacktip reef sharks, grey reef sharks, and scalloped hammerhead sharks (Figure 6). 12

17 Figure 6: Still images captured on mid-water BRUVS of a giant trevally and grey reef sharks (top) and a scalloped hammerhead, bottom. 13

18 PEER-REVIEWED PUBLICATIONS Data collected in the Great Barrier Reef Marine Park using seabed and midwater stereo-bruvs and catch-and-release fish sampling will support the publication of a number of peer-reviewed publications. These articles will improve understanding of the role that sharks play both on coral reefs and in blue water zones, in addition to providing insights into how marine protected areas influence the abundance, size, biomass, condition, diet, trophic ecology and gene expression of bony fishes and sharks. Such data will allow scientists and marine park managers to better anticipate possible trophic cascades following removal of sharks from marine systems. The data will be analysed in the context of other data collected previously by the Pangaea Initiative across the Indo-Pacific Ocean at the British Indian Ocean Territory and the Cocos (Keeling) Islands in order to test the generality of our findings at larger scales. The addition of mid-water BRUVS to the core research programme on the Great Barrier Reef will also complement existing data from the west coast of Australia (the Great West Ozzie Transect or GWOT) and other sites within the Indo- Pacific, allowing for large-scale insights into pelagic fish and shark assemblages. Indicative publications include, with method in parentheses: Diversity, abundance, size and biomass of reef shark and fish assemblages in protected versus unprotected zone on the Great Barrier Reef [seabed BRUVS] Diversity, abundance, size and biomass of pelagic shark and fish assemblages in protected versus unprotected zones on the Great Barrier Reef [mid-water BRUVS] Diet and condition of fishes in relation to reef shark abundance on the Great Barrier Reef [CnR sampling - morphometry] Changes in gene expression in reef fishes in relation to reef shark abundance on the Great Barrier Reef [CnR sampling - genetics]. Competitors or predators: how removal of sharks may influence the competitive balance of mesopredatory guilds on coral reefs through changes in gape size [CnR sampling - morphometry]. Diversity, abundance, size and biomass of pelagic shark and fish assemblages in protected versus unprotected zones on the east, north and west coasts of Australia [mid-water BRUVS] An assessment of the scale of coral bleaching on the Great Barrier Reef based on stereo- BRUVS: implications for monitoring recovery. 14

19 CONCLUSION The GBRMP is a World Heritage Site, yet it faces threats from climate change, pollution, illegal poaching and many other human factors (Robbins et al. 2006; De ath et al. 2009; Commonwealth 2015). The Pangaea Initiative uses the GBR to investigate at large, ecologically relevant scales whether healthy shark populations are essential to healthy coral reef function. We take a holistic approach to answering this research question, (1) exploring the effect of sharks on the population structure and biology of fish populations, (2) sampling multiple habitats, including reefs and open ocean and (3) investigating how bleaching (i.e. loss of habitat) and overfishing interact to alter the resilience of reefs and fish populations. Ultimately, the Pangaea Initiative s expeditions to multiple sites across the globe will generate the long-term monitoring datasets and research findings that are necessary for marine park managers to anticipate how future perturbations will affect coral reefs, in addition to providing a basis for policies that improve the resilience of reefs to future perturbations. REFERENCES Ayling AM, Choat JH (2008) Abundance patterns of reef sharks and predatory fishes on differently zoned reefs in the offshore Townsville region: Final report to the Great Barrier Reef Marine Park Authority. Research Publication No. 91. Barley SC, Meekan MG, Meeuwig JJ (2017b) Species diversity, abundance, biomass, size and trophic structure of fish assemblages on coral reefs in relation to shark abundance. Mar Ecol Prog Ser 565: Barley SC, Meekan MG, Meeuwig JJ (2017a) Diet and condition of mesopredators on coral reefs with and without sharks. PLoS One Baum JK, Myers RA, Kehler DG, Worm B, Harley SJ, Doherty PA (2003) Collapse and Conservation of Shark Populations in the Northwest Atlantic. Am Assocation Adv Sci 299: Commonwealth (2015) Reef 2050 Long-Term Sustainability Plan. De ath G, Lough JM, Fabricius KE (2009) Declining coral calcification on the Great Barrier Reef. Science (80- ) 323: Frisch AJ, Ireland M, Rizzari JR, Lonnstedt OM, Magnenat KA, Mirbach CE, Hobs JA (2016) Reassessing the trophic role of reef sharks as apex predators on coral reefs. Coral Reefs Froese R, Pauly D (2016) Fishbase. Munday PL, Jones GP, Sheaves M, Williams AJ, Goby G (2007) Vulnerability of fishes of the Great Barrier Reef to climate change. Clim Chang Gt Barrier Reef A Vulnerability Assess Robbins WD, Hisano M, Connolly SR, Choat JH (2006) Ongoing collapse of coral-reef shark populations. Curr Biol 16:

20 Roff G, Doropoulos C, Rogers A, Bozec YM, Krueck NC, Aurellado E, Priest M, Birrell C, Mumby PJ (2016) The Ecological Role of Sharks on Coral Reefs. Trends Ecol Evol 31: Tickler D, Letessier T, Koldewey H, Meeuwig JJ (2017) Drivers of abundance and spatial distribution of reef-associated sharks in an isolated atoll reef system. PLoS One 12:e Weisler MI, McNiven IJ (2016) Four thousand years of western Torres Strait fishing in the Pacificwide context. J Archaeol Sci Reports 7: Williams DM, Hatcher AI (1983) Structure of Fish Communities on Outer Slopes of Inshore, Mid-Shelf and Outer Shelf Reefs of the Great Barrier Reef. Mar Ecol Prog Ser 10: Willis BL, Page CA, Dinsdale EA (2004) Coral disease on the Great Barrier Reef. Coral Heal Dis Worm B, Lotze HK, Myers RA (2003) Predator diversity hotspots in the blue ocean. Proc Natl Acad Sci U S A 100: