A fish-eye view of the importance of sharks in tropical marine ecosystems

Transcription

1 A fish-eye view of the importance of sharks in tropical marine ecosystems PCI Expedition II Report 31 December 2015 Pangaea Chagos Ini tiative Expedition II November 1 D ecember **2015 Jessica Meeuwig 1, Matteo Bernasconi 2, Charlot te Birkmanis 1, Michelle Taylor 3, Christopher Thompson 1, David Tickler 1 1 Centre for Marine Futures, School for Animal Bi ology and Oceans Institute, University of Western Australia. 2 Official Department, University of St. Andrews a nd Norway. 3 Department of Zoology, Oxford University

2 Acknowledgments 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 in the Indian Ocean under the Pangaea Chagos Initiative (PCI). The research was made possible thanks to permits and support from the United Kingdom s Foreign and Commonwealth Office (FCO). We are grateful for the thorough logistical assistance provided by the British Indian Ocean Territory Administration (BIOTA), the British Representative, Commander Edward Lees and the Executive Officer, Major Andy Bridson. We thank the professional fishers who assisted in the non-destructive sampling: Todd Calitri, Andrew Parsons and Richard Schumann. The Pangaea crew, and in particular Captain Ferdi Heymann, were invaluable in their support to the science team. How to cite this report: Meeuwig JJ, Birkmanis CA, Bernasconi M, Hehre, J, Taylor M, Thompson C, and Tickler D Expedition Report for the Pangaea Chagos Initiative, November-December Report to Teach Green and the United Kingdom Foreign and Commonwealth Office. i

3 Executive summary In April 2010, the United Kingdom declared the British Indian Ocean Territory (BIOT) as a fully protected no-take marine reserve (640,000 km 2 ) and closed the international tuna longline and purse seine fisheries operating in the area. In the absence of fishing pressure the reserve has great potential to promote the health of the entire BIOT ecosystem and protect globally threatened mobile vertebrates such as reef-associated sharks. Such protection is paramount due to the important role that predators play in regulating species dynamics in tropical environments. For instance, sharks have been shown to influence both the abundance and behaviour of their prey (often medium-sized predators, referred to as mesopredators), leading to trophic cascades that may ultimately transform entire food webs. How such cascades propagate through ecosystems is still poorly understood, largely because there are few locations worldwide where shark abundance varies but fish assemblages remain relatively intact. The no-take BIOT Marine Reserve is well suited to investigating whether illegal fishing removes sufficient predators to create a spatial gradient of increasing shark abundance from the remote northern atolls exposed to illegal fishing, to the southern waters surrounding the highly secure United States of America s military base at Diego Garcia. Questions around how sharks regulate fish assemblages and the degree to which declines in shark abundance are signalled in the fish community form the basis of the five-year science plan provided to the United Kingdom s Foreign Commonwealth Office in January 2015 (Meeuwig and Meekan 2014). These questions were also central to the Chagos Science Consortium Research Plan and were identified as a key priority within the BIOT Interim Conservation Management Framework. Between November 1 st and 13 th December 2015, we conducted the second research expedition (PCI Exped II) of this programme on board the M/Y Pangaea. Activities were designed to build on the first research expedition (PCI Exped I), retaining the focus on the role that reef sharks play in regulating reef ecosystems and how they may impact the abundance, diet and condition of reef fishes. Following PCI Exped I, we requested permission from the UK Government to expand the research programme to include Diego Garcia. This request by the science team was made due to an apparent increase in illegal, unreported and unregulated (IUU) fishing in the BIOT Marine Reserve. Diego Garcia provides a control site relative to the atolls and islands of the reserve, as there is no IUU fishing for sharks at Diego Garcia and, although there is a limited amount of recreational fishing, sharks are not typically retained. PCI Exped II documented the status of reef shark and fish assemblages by twinning stereo-baited remote underwater video systems (stereo-bruvs) with active acoustic transects, and tissue/fin sample collection to determine diet and for molecular analysis of mesopredator genomics. We exclusively used non-destructive techniques, with sampling either based on video camera technology or catch-and-release methods. Favourable weather conditions and excellent facilities aboard the Pangaea allowed sampling to exceed targets. We deployed stereo-bruvs at 270 stations in waters adjacent to five atolls and islands, with the aim of replicating and expanding on both the March 2012 surveys (Tickler 2014) and PCI Exped I in March Comparison of the 2012 and two 2015 surveys will allow us to detect interannual and seasonal changes in shark and mesopredator numbers, while the inclusion of Diego Garcia will allow a spatial comparison of the reef shark and fish assemblages at this point in time. We completed 132 active acoustic transects twinned with stereo-bruvs deployments to expand the spatial scale of our understanding of reef shark and fish assemblages. Finally, we collected fin clips and tissue samples from 492 individuals of ii

4 46 species representing 12 families that will allow us to understand whether predation pressure is driving changes to fish diets as well as morphological and genetic divergence. Key achievements 1. Repeated the 2012 and 2015 shark and fish surveys using stereo-bruvs, and extended the survey to include Diego Garcia to incorporate both the use of active acoustics and to increase spatial coverage. 2. Obtained the first acoustic signatures of green turtles, and tawny nurse and black tip reef sharks. 3. Extended the collection of tissue samples for genetic and isotopic analysis to both detect fish responses in diet to Diego Garcia, and to use next generation genomics to detect variation in gene expression in relation to the abundance of sharks. iii

5 1. Introduction The British Indian Ocean Territory (BIOT), which encompasses the Chagos Archipelago, was designated a fully protected no-take marine reserve in April 2010, with the exception of the area proximate to the southernmost atoll of Diego Garcia. The territory s exclusive economic zone (EEZ) covers approximately 640,000 km 2, of which approximately 10% is comprised of coral atolls and banks (Sheppard 2012). The establishment of the BIOT Marine Reserve led to the closure of international longline and purse seine fisheries that predominantly targeted yellowfin (Thunnus albacares), skipjack (Katsuwonus pelamis), and bigeye tuna (Thunnus obesus), with reef-associated sharks also caught incidentally (Koldewey et al. 2010). Even as populations of sharks dwindle globally, essential questions about their role in oceanic ecosystems remain unanswered. There is evidence that sharks, like other apex predators, influence trophodynamics both directly through prey consumption and indirectly by altering prey behaviour and distribution (Britten et al. 2014). In the presence of predators, prey may conform to an ecology of fear whereby foraging less, avoiding risky habitats and switching to poorer quality food become prevailing strategies to reduce short-term risk but at the expense of long-term fitness gains (Lima and Dill 1990; Werner and Peacor 2003; Clinchy et al. 2013). In contrast, when predators are removed, prey mortality declines and secondary consumers consequently thrive. This phenomenon is known as mesopredator release (Estes et al. 2011; Ruppert et al. 2013), and may have substantial effects on ecosystem structure (Myers et al. 2007; Ritchie and Johnson 2009) as species shifts spiral down the food web, affecting lower trophic levels. While the impacts of changes in mesopredator abundance are documented, risk effects are more subtle, harder to observe, and have only been recognised as important and pervasive in recent times (Schmitz et al. 2004; Heithaus et al. 2008; Wirsing et al. 2008). The BIOT Marine Reserve offers a tremendous opportunity to address these issues and generate much-needed quantitative data on the effectiveness of marine reserves as well as the consequences of illegal, unregulated and unreported (IUU) fishing. Historically, commercial fishing in the waters now occupied by the BIOT marine reserve has created an ecological gradient of shark abundance that continues to be reinforced to this day by illegal fishing practices. This constitutes a large-scale natural experiment that can be mined for information relating to the impact of shark predation on mesopredator diversity, abundance, size, biomass, diet and genetic divergence. There is increasing consensus that such large-scale approaches (Friedlander and Parrish 1998; Madin et al. 2010; Ruppert et al. 2013) are the only robust way to test ecological hypotheses as localised manipulative studies have produced conflicting results (Carpenter 1990; Knowlton 1992; Schindler 1998). In order to explore the regulation of fish assemblages by sharks in the reserve, a team of scientists from The University of Western Australia (UWA), Oxford University and the University of St. Andrews travelled to BIOT in the last quarter of This expedition specifically expanded the sampling programme to include Diego Garcia as well as continuing sampling at the northern atolls within the marine reserve (Fig. 1). This decision represented growing concerns about increasing IUU within the marine reserve. Preliminary observations from stereo-bruvs on PCI Exped I in March 2015 suggested that the number of sharks present in the northern atolls had substantially decreased since our March 2012 stereo-bruvs surveys in the same areas. Additionally, sharp and stepped declines in the number of acoustically tagged sharks transmitting to receivers in the region are also 1

6 of concern as they are suggestive of illegal fishing (Tickler, unpublished data). Finally, reports on illegal fishing activity suggest the presence of larger boats that include gillnets targeting reef ecosystems. While Diego Garcia is outside the marine reserve, the presence of the United States military base on the atoll severely constrains IUU fishing. While there is a limited recreational fishery, the lagoon is also restricted access with no fishing. As such, the lagoon at Diego Garcia represents a powerful control location to assess the ecological role of sharks, allowing comparisons to the lagoons sampled in the northern atoll. Data collected on this expedition will specifically test the following hypotheses: in the presence of sharks, we expect lower abundance and biomass of mesopredators and higher abundance and biomass of their own prey. Ruppert et al. (2013) reported similar trends on the northwestern shelf of Australia (eastern Indian Ocean). This study contrasted a highly protected but small marine reserve with an area that remains open to traditional shark fishing, and showed sharp Figure 1: Sampling locations in BIOT Marine Reserve for PCI Exped I (pink) and PCI Exped II (red). differences in shark abundance between the two locations. Our analysis of the BIOT marine reserve will provide an important opportunity to determine the generality of Ruppert et al. (2013) s results in an independent and much larger location as well as exploring the resilience of large marine reserves, as generated in the Great Barrier Reef Marine Park (McCook et al. 2010). This research will also directly benefit the managers of BIOT by shedding light on the ecological impacts of IUU fishing beyond reduced shark numbers. Such information underpins decision-making under growing demands for fish protein around the Indian Ocean Rim and will support optimal allocation of often-restricted financial resources available for spatial enforcement. Promising new technology will aid in the identification of IUU fishing 1 and the monitoring of its ecological impacts in the context of populations recovering from historical fishing. Improved recognition of the vital importance of healthy shark populations for ecosystem health will also help mobilise the resources required for enforcement. The team deployed stereo-bruvs twinned with active acoustic surveys and non-destructively took fin and tissue samples for genetic and isotopic analysis. The expedition included five scientists from three organisations (Table 1). This expedition was supported through a philanthropic gift from The Teach Green Foundation to UWA with ship time on the M/Y Pangaea provided by OCS. The BIOT administration and the UK FCO provided permits and logistical support. Here we report on the results of the second expedition on the M/Y Pangaea to BIOT. Individual report sections contain 1 2

7 background and preliminary results from the field. Sample processing will take approximately one year with the results to be reported on completion of that processing. 2. Objectives, strategies and participants The following expedition objectives were identified: 1) Quantify the relative density and biomass of sharks and reef-associated fishes using stereo- BRUVS and active acoustics. 2) Identify the diets and condition of reef fishes using stable isotope and morphometric analysis as indicators of the status of shark populations. 3) Determine connectivity among mesopredators using molecular genetic analysis to understand resilience to shark removal. 4) Determine response of mesopredators using molecular genetic analysis to understand gene expression and thus resilience to shark removal. 5) Develop metrics that indicate the status of reef shark populations and signal the scale of illegal fishing. The overarching goal of our research is to improve our understanding of the role that sharks play in maintaining healthy coral reef ecosystems. This objective directly supports Action 1b of the BIOT Interim Conservation Management Framework: monitor status of reef sharks and fish assemblages to evaluate the impact of no-take and IUU controls, in a range of representative habitats, and contributes to refining enforcement activities by identifying locations exhibiting signs of shark removal (Compston 2014). It also links strongly to the objectives of the Geneva Workshop, such as objective 2: monitor key species, habitats and environmental parameter and objective 4: establish the resilience of the BIOT Marine Reserve s biodiversity and ecosystems (Gollock and Koldewey 2014). Based upon the previous experience of the expedition leader, it was decided that the overarching sampling strategy would be to follow a daily schedule with systematic replication of the key sampling activities (stereo-bruvs and acoustics, and catch-and-release sampling). A typical day of science on the M/Y Pangaea consisted of 20 stereo-bruvs deployments and completion of three acoustic transects carried out on the small catamaran, I m OK by two scientists, and catch-andrelease sampling by two scientists and two citizen scientists on the skiffs. The responsible scientists are listed in Table 1. Table 1: Participants, their organisation and research activities. Participants Professor Jessica Meeuwig, UWA Charlotte Birkmanis, PhD Candidate, UWA Dr. Matteo Bernasconi, St. Andrews Dr. Michelle Taylor, Oxford University Chris Thompson, UWA David Tickler, UWA Todd Calitri, Pangaea Andrew Parsons, Pangaea Richard Schumann, Pangaea Primary Research Activities Expedition Leader Catch-and-Release sampling Active Acoustics Catch-and-Release sampling Stereo-BRUVS Catch-and-Release sampling Catch-and-Release sampling Catch-and-Release sampling Catch-and-Release sampling 3

8 Sampling was undertaken across four locations in the northern atolls and islands of the BIOT Marine Reserve: Diego Garcia, Egmont Island, Peros Banhos and Salomon Atolls (Figure 1). 3. Characterising Shark and Fish Assemblages with Stereo-BRUVS Stereo-BRUVS are designed to provide quantitative measures of the diversity, relative abundance and size of marine wildlife, and are the preferred method for sharks and mesopredators (Watson et al. 2010; Bernard et al. 2014). Each rig consists of a tripod frame to which two GoPro small action cameras are fixed 70 cm apart on an inward convergent angle of 8 degrees (Figure 2), allowing for accurate measurements of body size. The camera mounts are integrated with a bait bag and deployed from a vessel to sit remotely on the seabed for a minimum of one hour prior to being recovered. The imagery collected by stereo-bruvs allows us to identify individuals to species level, estimate their relative numbers, and individual body length. Data can be aggregated to determine assemblage attributes such as species richness, total abundance/size distribution, and total biomass (by converting fish length to fish weight). These metrics can also be calculated across different trophic levels, as appropriate. Stereo-BRUVS are a global standard for documenting the status of sharks and fish assemblages. Our sampling efforts in BIOT build upon previous sampling in March 2012 and on PCI Exped I in Figure 2: Diagram of seabed BRUV including bait arm and bag. March Objectives 1) To describe the shark and fish assemblages in the lagoons of major atolls in BIOT in order to determine whether fish assemblage structure varies in terms of the number, size, and behaviour of mesopredators and their prey in relation to the abundance of sharks. 2) To determine the degree of seasonal variability in the shark and fish assemblages between March and November 2015 and how this varies in relation to shark abundance. 3.1 Preliminary results A total of 270 stereo-bruvs deployments were completed during PCI Exped II (Table 2). In addition to resampling the 2012 locations (Figure 3), we completed additional sampling at 105 locations stratified by depth (12-20 m and m) including a range of hard and soft bottom habitats. The balanced sampling design and high effort at each location enables characterisation of the fish assemblage in relation to shark abundance and the determination of changes through time. 4

9 Table 2: Number of samples for stereo- BRUVS, by location in March 2012 ( 12) and for PCI Exped I (I) and PCI Exped II (II). Does not include locations sampled in 2012 that were not continued under the PCI. Location 12 I II Diego Garcia Eagle Island Egmont Island Peros Banhos Salomon Three Brothers Total: Figure 3: Distribution of stereo-bruvs stations in 2012 (green), and for PCI Expeds I (turquoise) and II (blue). Preliminary review of stereo-bruvs video footage revealed a similar suite of species as in March 2012 and 2015, including relatively high numbers of blacktip reef shark (Carcharhinus melanopterus), mesopredators such as the two-spot red snapper (Lutjanus bohar), humpback red snapper (Lutjanus gibbus), bluefin trevally (Caranx melampygus), giant trevally (Caranx ignobilis), and midnight snapper (Macolor niger), and potential prey species such as schooling fusiliers (Caesonidae spp.) and the sailfin surgeonfish (Zebrasoma desjardinii). Stereo-BRUVS also captured dense schools of baitfish that were frequently observed within the lagoons and a whale shark (Rhincodon typus), a first to our knowledge using this method. 4. Characterising Shark and Fish Assemblages with Active Acoustics Active acoustics have the potential to assist in coral reef conservation by expanding the picture of the spatial distribution and abundance of fishes beyond what is possible using relatively small-scale diver-based or BRUVS-based methods, which, by definition sample limited areas. There are several challenges to the application of active acoustic systems to coral reefs, including: (1) the large number of fish species associated with these ecosystems; (2) the unknown acoustic characteristics of most reef fish; and (3) interference from the seabed with which many of these animals are strongly associated. Recognising these challenges, we here trialled a twinned program of simultaneous deployment of stereo-bruvs and active acoustics, with the former providing a visual species identification, abundance, and size to be correlated with the acoustic signals. We installed a multi-frequency scientific echosounder on the 5.8 m catamaran, I m OK that is used for deployment of stereo-bruvs. The echosounder was calibrated following standard hydroacoustic calibration procedures (Demer et al 2015; Foote et al. 1987) for three frequencies (38, 120 and 200 khz) while at anchor in Diego Garcia, our first sampling location. The transducers were mounted on the side of the boat from a secured pole the height of which could be adjusted depending on the water depth. During the acoustic recordings, we used two settings: 80 cm for shallow waters less than 3 m, and 1.30 m for depths exceeding 3 m. The calibration took place inside a wind and wave protected area when the mother ship MY/Pangaea was at anchor and I m OK was secured to its side. We calibrated all frequencies using a 38.1 mm tungsten carbide sphere 5

10 (WC38.1). We also completed CTD (conductivity, temperature and depth) casts during the entire survey using a RBR XR620 Multichannel logger to correct sound velocity and adjust the error of our acoustic measurements. Figure 4: Installation of active acoustics on I'm OK showing from left to right, transducer and scaffolding, forward securement of electronics. Objective 1) To correlate signals from active acoustics to the diversity, abundance, and size of reef sharks and fishes observed on stereo-bruvs. 2) To characterise acoustic signals of dominant reef fish to assist in interpretation of acoustic data. 3) To determine the spatial scale to which stereo-bruvs can be extrapolated based on signals from active acoustics. 4.1 Preliminary results We completed three transects associated with each set of five stereo-bruvs deployments (Fig. 5) for 44 sets of stereo- BRUVS deployments, for a total of 132 transects spanning km. For each set of five stereo-bruvs, we ran one transect as close to the deployed rigs as possible, with two transects each on either side, approximately 100 m distance. There was an additional 489 km of acoustic data collected opportunistically as I m OK transited between M/Y Pangaea and sampling locations. Notwithstanding the narrow beam of our acoustic system as a result of the relatively shallow depths in the lagoons (typically < 30 m), we were able to collect high-resolution data of individual fish and fish schools (Fig. 6). The acoustic data will now undergo post-processing using the software Echoview 3.0 (Myriax). Both echocounting and echo-integration techniques (Simmonds and MacLennan 2005) will be used and adapted to the information derived from the stereo- BRUVs to the acoustics, as has previously been done during fisheries surveys (see Nøttestad et al. 2015). The visual data from the stereo-bruvs Figure 5: Schematic of acoustic transect lines (red) relative to a set of BRUVS deployments (blue circles) for SW Salomon Atoll (inset). 6

11 will also allow us to discriminate acoustic signals and associate them with different observed species. The combination of stereo-bruvs and active acoustics also allowed us to confidently capture the acoustic signature of several large marine vertebrates. We were able to capture the signatures of a green turtle (Chelonia mydas), a tawny nurse shark (Nebrius ferrugineus) and a blacktip reef shark (Carcharhinus melanopterus) (Figure 7). To our knowledge, the acoustic signatures of these species have never been measured or described in the literature. The acoustic signal received from the green turtle (Figure 7A) gave a consistent backscattered echo energy of -14 db//1m. This high value is related to the turtle s lung structures, as described by Bernasconi et al. (2013) for cetaceans, with its lungs making the animal acoustically visible. The preliminary acoustic signal for the blacktip reef shark was -32 db//1m. This relatively low value, despite the individual s size ( cm), reflects the lack of a swim bladder in sharks. Swim bladders, Figure 6: Samples of fish schools echograms detected along coral reef bommies using three different sonar carrying frequencies (38, 120 and 200 khz.) found in most fishes, are gas-filled organs that reflect sound in distinctive manners depending on their size and position in the fish, representing approximately 98% of a fish body s reflectivity (Love 1971). The absence of a swim bladder in the shark makes it acoustically similar to, for instance, a small fish (<50 cm) with a large swim bladder. To this end, building a library of verified acoustic signatures from sharks will further our ability to detect them acoustically in reef ecosystems. Figure 7: Acoustic signatures of A) a green turtle and B) a blacktip reef shark. Conductivity, temperature, and depth (CTD) casts are essentially a vertical probe that provides an environmental profile of the water column in terms of connectivity and temperature at depth, with conductivity (corrected for temperature), providing information on salinity. Combined CTD 7

12 measurements provide information on water column profiles, and assist with the calibration of the acoustic data. We used a RBR XR620 Multichannel Logger with an Oxygen sensor at 55 stations associated with the stereo-bruvs sampling as a means of generating representative profiles for each lagoon. We typically found very little stratification to depths of 30 m, with slight increases in temperature and salinity below 20 m and a decline in oxygen with depth below 15 m (Fig. 8). Figure 8: Typical vertical profiles of temperature, salinity, sound speed and dissolved oxygen. 5. Mesopredator condition, diet and genetic diversity on reef flats as revealed by catch-andrelease sampling Reef flats often support active feeding grounds for sharks and mesopredators, and thus studying reef flats provides insights into interactions and the potential for changed behaviour with varying shark abundance. Supported by professional marine fly fishers, we targeted mesopredators foraging on these flats to acquire measurements indicative of fish condition and morphometry. Additionally, tissue samples were collected to allow diet assessment and genetic analyses. A combination of skiffs and wading was used to maximise the chance of speedy capture and to allow the most effective targeting of priority species. Condition is determined by taking length and weight measurements to determine if their ratio is lower with shark presence (Barley et al. subm.). Morphometric measurements are determined from high resolution still images that allow, for instance, the calculation of eye diameter and tail height relative to body length and to assess whether systematic differences occur in relation to shark abundance (Hammershlag et al. subm.) Evidence of diet variation can be inferred from stable isotopes, a non-intrusive alternative to lethal sampling of guts (Cocheret de la Morinière 2003; Layman et al. 2007, Vallet et al. 2014). The ratio of heavy to light isotopes of nitrogen and carbon indicate where the animal is feeding in the food web and on what primary producer (algae, seagrass, mangrove) the food web is based, respectively. The isotopes are analysed from a tissue punch of dorsal muscle, just behind the dorsal fin. Predator removal may induce genetic changes in prey species with traits selective for size, behaviour, morphology and maturity possibly affected (Jørgensen et al., 2007), but unlike predation assumes that the genetic variability exists to allow selection and expression of these traits. Such traits may include the ability to moderate foraging behaviours resulting in improved condition, morphological changes (e.g. larger tails) and reproductive output. Genetic variability in the sampled individuals and their connectivity to other conspecifics across BIOT can be assessed by sampling tissue and fin clips (Bay et al. 2004; Sharma et al., 2014; Thi et al., 2015). Additionally, we are looking at variation in gene expression based on the analysis of RNA extracted from tissue samples (Meyer et al., 2011). 8

13 Objectives 1) Identify whether condition, diet, gene expression and morphometry vary systematically with the abundance of sharks and in a manner consistent with trophic cascades and mesopredator release. 2) Determine connectivity among sharks and mesopredators using genetic kinship analysis to understand resilience to shark removal. 5.1 Preliminary results A total of 492 individual fish from 46 species were sampled from 12 families across four atolls during the expedition (Table 5; Fig. 9). The most highly sampled of these were, in order of decreasing numbers: two-spot red snapper, humpback red snapper, bonefish (Albula spp.), delicate round herring (Spratelloides delicatulus), bluefin trevally (Caranx melampygus), and squaretail coral grouper (Plectropomus areolatus). Figure 9: Location of sites sampled for isotopes and genetics for PCI Exped I (turquoise) and II (blue). Figure 10: Photograph of two-spot red snapper on measuring board with tag. 6. Progress towards metrics for the ecological detection of IUU fishing PCI Exped II has built on the success of PCI Exped I by expanding the spatial scale of sampling to include the well-protected lagoon of Diego Garcia. The expedition was successful in establishing an understanding of the ecological implications of IUU fishing. The stereo-bruvs surveys undertaken as part of this expedition have been a critical step forward in extending previous surveys to begin monitoring change through time and space. Specifically, we are now able to contrast what we know to be unfished communities at Diego Garcia with the illegally fished communities in the northern atolls as well as make contrasts between March 2012 and 2015, building on the documentation of IUU by Clark et al. (2015). For instance, we can determine whether the abundance and biomass of 9

14 mesopredators increase with declining abundance of sharks and specifically at what rate. Similarly, we will be able to develop metrics based on condition, diet, morphometrics and genetics data that indicate how rapidly these characteristics change with declining shark abundances. Due to the recent increase in poacher arrests in BIOT, these indicators will allow us to examine the implications of IUU fishing in a refuge in the middle of the Indian Ocean. The study will help quantify the magnitude of illegal fishing, identify the key areas where IUU fishing occurs and guide future funding and management options for mitigation strategies and enforcement. Table 5: The number (n) and size (mean and standard deviation (stdev) of fork length (cm)) of fish sampled for morphometrics, condition, diet, and genetics by species, with family and common names indicated. Family Scientific Name Common Name n mean stdev Albulidae Albula sp. Bonefish Balistidae Pseudobalistes flavimarginatus yellow margin trigger fish Belonidae Tylosurus crocodilus hound needlefish Carangidae Carangoides orthogrammus island trevally Caranx ignobilis giant trevally Caranx lugubris black jack Caranx sexfasciatus bigeye trevally Caranx melampygus bluefin trevally Gnathanodon speciosus golden trevally Trachinotus baillonii small spotted dart Carcharhinidae Carcharhinus amblyrhynchos grey reef shark Carcharhinus melanopterus blacktip reef shark Negaprion acutidens lemon shark Clupeidae Spratelloides delicatulus sprat (baitfish) Dactylopteridae Dactyloptena orientalis horned flying gurnard Gerreidae Gerres longirostris strongspine silver-biddy Lethrinidae Lethrinus erythracanthus orange-spotted emperor Lethrinus lentjan pink ear emperor Lethrinus obsoletus orange-striped emperor Lethrinus nebulosus spangled emperor Lutjanidae Aphareus furca smalltooth jobfish Lutjanus bohar two-spot red snapper Lutjanus fulvus black tail snapper Lutjanus gibbus humpback red snapper Lutjanus monostigma one-spot snapper Macolor niger black and white snapper Pristipomoides filamentosus rosy jobfish Scombridae Acanthocybium solandri Wahoo Euthynnus affinis Kawakawa Katsuwonus pelamis skipjack tuna Scomberoides tol needlescale queenfish Thunnus albacares yellowfin tuna Serranidae Aethaloperca rogaa redmouth grouper Cephalopholis argus peacock hind

15 Family Scientific Name Common Name n mean stdev Cephalopholis sonnerati tomato hind Epinephelus coeruleopunctatus whitespotted grouper Epinephelus fasciatus blacktip grouper Epinephelus polyphekadion snout-spots grouper Epinephelus spilotoceps foursaddle grouper Epinephelus sp. Grouper Epinephelus hexagonatus starspotted grouper Plectropomus areolatus squaretail coral grouper Plectropomus laevis blacksaddled coralgrouper Plectropomus pessuliferus roving coralgrouper Variola albimarginata white-edged lyretail Variola louti lunar-tailed grouper Total Safety There were no health or safety issues of note, including no cases of sunburn or dehydration. The M/Y Pangaea s tenders are ideal for the research being undertaken with respect to safety. 8. References Barley S, Meekan M, Meeuwig JJ. Subm. Conditioned to fear: evidence for risk effects on diet, body morphometrics and condition in mesopredators. Ecology Letters. Bay LK, Choat JH, Van Herwerden L, Robertson DR High genetic diversities and complex genetic structure in an Indo-Pacific tropical reef fish (Chlorurus sordidus): Evidence of an unstable evolutionary past? Marine Biology 144: Bernard ATF, Götz A, Parker D, Heyns ER, Halse SJ, Riddin NA, et al New possibilities for research on reef fish across the continental shelf of South Africa. South African Journal of Science dx.doi.org/ /sajs.2014/a0079. Bernasconi M, Patel R, Nøttestad L and Brierley AS (2013). Fin whale (Balaenoptera physalus) target strength measurements. Mar Mam Sci 29(3): Britten GL, Dowd M, Minto C Predator decline leads to decreased stability in a coastal fish community. Ecology Letters 17(12): Carpenter RC Mass mortality of Diadema antillarum I. Long-term effects on sea urchin populationdynamics and coral reef algal communities. Marine Biology 104: Clark, Moir, J, Duffy, H, Pearce, J, Mees, CC Update on the catch and bycatch composition of illegal fishing in the British Indian Ocean Territory (BIOT) and a summary of abandoned and lost fishing, MRAG Ltd, London. Clinchy M, Sheriff MJ, Zanette LY Predator-induced stress and the ecology of fear. Functional Ecology 27(1): Cocheret de la Morinière E, Pollux B, Nagelkerken I, Hemminga M, Huiskes A, van der Velde G Ontogenetic dietary changes of coral reef fishes in the mangrove-seagrass-reef continuum: stable isotopes and gut-content analysis. Marine Ecology Progress Series 246:

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