2017

Pangaea Initiative: Great Barrier Reef & Torres Strait

APRIL-JUNE 2017

DR SHANTA BARLEY & PROFESSOR JESSICA MEEUWIG

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 (G17/39150.1) 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.

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EXECUTIVE SUMMARY

From April 2nd to June 24th 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.

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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 2015.

79 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.

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THE GREAT BARRIER REEF

The Great Barrier Reef is the world’s largest coral reef ecosystem (Figure 1), covering an area of

345,000 km2 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

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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 1970.

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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 2nd and June 24th. 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

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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 Role

Dr Shanta Barley Expedition leader, CnR sampling, BRUVS

Jemma Turner CnR sampling, BRUVS

Hanna Jabour Christ BRUVS

Louis Maserei CnR sampling, BRUVS

Adam Jolly BRUVS

Nikki de Campe 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

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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 95 83

Middle GBRMP 62 72

North GBRMP 71 17

Total 228 172

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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 60 0 247 307

paddletail Lutjanus gibbus 18 0 111 129

bluefin trevally Caranx melampygus 5 0 77 82

roundjaw bonefish Albula glossodonta 0 0 79 79

common coralgrouper Plectropomus areolatus 0 2 66 68

giant trevally Caranx ignobilis 57 1 10 68

leopard coralgrouper Plectropomus leopardus 60 0 0 60

island trevally Carangoides orthogrammus 10 13 27 50

blacksaddle grouper Plectropomus laevis 5 0 44 49

spanish flag snapper Lutjanus carponotatus 48 0 0 48

coral hind Cephalopholis miniata 41 0 1 42

blacktip reef shark Carcharhinus melanopterus 9 20 12 41

delicate round herring Spratelloides delicatulus 0 0 41 41

redmouth grouper Aethaloperca rogaa 0 0 30 30

yellow-edged lyretail Variola louti 0 0 25 25

honeycomb grouper Epinephelus merra 0 20 4 24

camouflage grouper Epinephelus polyphekadion 0 2 20 22

small toothed jobfish Aphareus furca 0 2 20 22

black and white snapper Macolor niger 0 0 20 20

spangled emperor Lethrinus nebulosus 0 0 20 20

Australian blacktip Carcharhinus tilstoni 19 0 0 19

green jobfish Aprion virescens 6 2 9 17

grey reef shark Carcharhinus amblyrhynchos 3 11 2 16

scad Decapterus sp 0 16 0 16

brassy trevally Caranx papuensis 13 0 0 13

golden trevally Gnathanodon speciosus 10 0 2 12

yellowfin tuna Thunnus albacares 2 2 7 11

kawakawa Euthynnus affinis 0 0 10 10

small-spotted dart Trachinotus baillonii 0 0 10 10

snubnose pompano Trachinotus blochii 9 0 0 9

dogtooth tuna Gymnosarda unicolor 0 0 8 8

orange-striped emperor Lethrinus obsoletus 0 2 6 8

peacock grouper Cephalopholis argus 0 0 8 8

white-edged lyretail Variola albimarginata 0 0 8 8

one-spot snapper Lutjanus monostigma 0 0 7 7

shark mackerel Grammatorcynus bicarinatus 7 0 0 7

turrum Carangoides fulvoguttatus 7 0 0 7

wahoo Acanthocybium solandri 0 1 5 6

bigeye trevally Caranx sexfasciatus 0 3 2 5

roving coralgrouper Plectropomus pessuliferus 0 0 5 5

talang queenfish Scomberoides commersonnianus 5 0 0 5

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Common name Species GBRMP C-K BIOT I-III Total

blacktail snapper Lutjanus fulvus 0 0 4 4

foursaddle grouper Epinephelus spilotoceps 0 0 4 4

longface emperor Lethrinus olivaceus 0 0 4 4

orange-spotted emperor Lethrinus erythracanthus 0 0 4 4

rainbow runner Elagatis bipinnulata 0 1 2 3

spotted coralgrouper Plectropomus maculatus 0 2 1 3

triple tail wrasse Cheleinus trilobatus 0 0 3 3

yellow-saddle goat fish Parupeneus cyclostomus 0 0 3 3

blacktip grouper Epinephelus fasciatus 0 0 2 2

blue bastard Plectorhinchus caeruleonothus 2 0 0 2

brown-marbled grouper Epinephelus fuscoguttatus 0 0 2 2

crocodile needlefish Tylosurus crocodilus 0 0 2 2

sicklefin lemon shark Negaprion acutidens 0 0 2 2

spot cheek emperor Lethrinus rubrioperculatus 0 0 2 2

tawny nurse shark Nebrius ferrugineus 2 0 0 2

whitetip reef shark Triaenodon obesus 2 0 0 2

yellowmargin trigger Pseudobalistes flavimarginatus 0 0 2 2

black jack Caranx lugubris 0 0 1 1

blue and gold fusilier Caesio caerulaurea 0 0 1 1

blue striped snapper Lutjanus kasmira 0 0 1 1

blue trevally Caranx ferdau 0 0 1 1

cheeklined wrasse Oxycheilinus digramma 0 0 1 1

crimson jobfish Pristipomoides filamentosus 0 0 1 1

dark hind Cephalopholis urodeta 0 1 0 1

dart sp Trachiotus sp 0 0 1 1

leopard grouper Mycteroperca rosacea 0 0 1 1

malabar grouper Epinephelus malabaricus 0 0 1 1

milkfish Chanos chanos 0 0 1 1

needlescale queenfish Scomberoides tol 0 0 1 1

orange lined triggerfish Balistapus undulatus 0 0 1 1

Picasso triggerfish Rhinecanthus aculeatus 0 0 1 1

pink ear emperor Lethrinus lentjan 0 0 1 1

silver biddy Gerres oyena 0 0 1 1

skipjack tuna Katsuwonus pelamis 0 0 1 1

small tooth emperor Lethrinus microdon 0 0 1 1

snubnose grouper Epinephelus macrospilos 0 0 1 1

strongspine silver-biddy Gerres longirostris 0 0 1 1

titan triggerfish Balistoides viridescens 0 0 1 1

tomato hind Cephalopholis sonnerati 0 0 1 1

whitespotted grouper Epinephelus coeruleopunctatus 0 0 1 1

yellowlip emperor Lethrinus xanthochilus 0 0 1 1

Total 400 101 1003 1504

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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

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 59 58

leopard coralgrouper Plectropomus leopardus 50 50

coral hind Cephalopholis miniata 36 36

spanish flag snapper Lutjanus carponotatus 35 35

giant trevally Caranx ignobilis 28 26

Australian blacktip reef shark Carcharhinus tilstoni 17 15

paddletail Lutjanus gibbus 14 14

island trevally Carangoides orthogrammus 10 10

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 312 307

Figure 2: Measuring the gape height of a grey reef shark

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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 = -0.22×MPFL+ 67.6 with MPFL explaining 73% of the variance in MPS.

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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.

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; 75-100% 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.

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 149 120

Middle GBRMP 40 158

North GBRMP 120 20

Torres Strait 0 100

Total 309 398

Figure 4: UWA scientist deploying

seabed BRUV.

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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.

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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).

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).

Table 7: Number of sites sampled in protected and

unprotected zones using mid-water BRUVS.

Region Protected Unprotected

Middle GBRMP 0 19

North GBRMP 25 15

Torres Strait 0 20

Total 25 54

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Figure 6: Still images captured on mid-water BRUVS of a giant trevally and grey reef sharks (top)

and a scalloped hammerhead, bottom.

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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.

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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.

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