The Pangaea Chagos Initiative
Centre for Marine Futures | 2015-2019
Centre for Marine Futures | 2015-2019
Cover image: The M/Y Pangaea research vessel.
Although sharks are renowned predators, our understanding of their ecological role remains unclear. This is partly because it is difficult to study sharks in their natural habitat, hidden as they are behind the “blue curtain” of the ocean. The aim of the Pangaea Initiative is to draw back this curtain and examine at a global scale how sharks alter the structure of fish assemblages by supporting marine conservation research.
The research is undertaken on the M/Y Pangaea, a vessel designed to safely deliver marine research in remote areas, with state-of-the art facilities that support sampling from reef flats to offshore locations and research diving, allow for on-board storage of samples and scientific equipment, and facilitate real-time data processing with high speed internet. Importantly, Pangaea’s team includes experienced fishing guides and crew members that have supported a range of marine research programmes globally. The Pangaea Initiative is funded by a philanthropic gift to UWA from the Teach Green Foundation (USA) and Outpost Expedition Pacific Ltd, and is based on a close collaboration between professional scientists, guides and crew.
There is an urgent need to answer questions with respect to the ecological role of sharks and the implications for healthy oceans given accelerated declines in shark numbers.
The project seeks to answer whether reduction in shark abundance:
- Alters the diet of prey – how much they eat, what they eat, and the quality of the food they eat?
- Results in knock-on effects on the body condition of prey and their gene expression?
- Leads to their prey shifting to habitats that were previously too risky
- Affects prey behaviour at small scales that scale up to the level of entire ecosystems?
- Changes the structure of fish assemblages across multiple levels of the food web
Location of sampling sites at BIOT (click on map to zoom in).
Team Pangaea setting up stereo-BRUVS rigs.
Spaghetti tagged two-spot red snapper (Lutjanus bohar) captured on a BRUVS video.
To answer these questions, the Pangaea Initiative has conducted three expeditions to the remote British Indian Ocean Territory (BIOT) to date. BIOT is one of the largest no-take marine reserves in the world, established in 2010 and covering an area more than twice the size of the UK. Yet, commercial fishing in the waters now occupied by the reserve has historically 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.
Catch-and-release fly fishing
Highly experienced fishing guides with extensive experience in capturing and releasing fishes and a strong commitment to conservation play a key role with the scientists in the collection of tissue samples from focal fish species using techniques that have minimal impact on the animals. We use catch-and-release fly fishing to non-lethally collect samples from a range of fishes, including trevallies, snappers and groupers. Fly fishing conducted by experienced fishers injures fewer fishes than most other types of fishing. The Pangaea Initiative only uses flies and barbless hooks, which greatly reduce the mortality on captured samples/fish. Fish are caught at the surface which means they are not at risk of barotrauma. Because there is no chumming nor bait used, the risk of predation on caught fish is also minimised.
The measurements and tissue samples taken from caught and released fish are being used to investigate whether the loss of sharks alters the “seascape of fear”, leading to changes in the behaviour and biology of fishes. Once the fish has been reeled in, we measure its weight and body dimensions and take a small fin clip and muscle sample. These samples allow us to understand whether the loss of sharks affects the condition, and by implication the fitness, of prey, i.e. are fish “fatter” when sharks are scarce? We also use the fin clip and tissue sample for stable isotope and genetic analyses to examine whether prey fishes alter their diet, habitat use and genetic expression in response to changes in predator abundance.
Teams of scientists and Pangaea crew also deploy stereo-Baited Remote Underwater Video Systems (stereo-BRUVS) to document that status of shark and fish populations. This technique collects information on the species diversity, abundance, size and biomass of shark and fish assemblages. Stereo-BRUVS are placed on the sea floor, where they allow us to determine how fish assemblages respond to the abundance of sharks both in terms of their abundance but also in relation to the data collected from the catch and release fishing methods. They also have confirmed the non-lethal nature of catch and release fishing (see picture).
We have expanded this stereo-camera research at key locations in Australia to include mid-water BRUVS. These systems, rather than resting on the seabed floor, drift in a “long-line” configuration of 5 rigs separated each by 200 m of line. Following drifts of 2 hrs, the rigs are retrieved and the video collected for processing. This technology is the base for the GWOT and Project Pelagic and is a critical step in documenting the status of ocean wildlife and its response to protection
On each field trip we supplement our core methods with a range of other techniques. To better understand how sharks may influence the large-scale movement of prey and competitors, we deploy acoustic “tags” in sharks and large fishes, which “ping” nearby acoustic receivers when animals approach them, allowing us to understand movement patterns and habitat use on a fine scale. We use multi-beam hydroacoustic techniques to estimate fish biomass at large scales and, when twinned with stereo-BRUVS, to identify the unique acoustic “signatures” associated with conservation-critical megafauna such as turtles and sharks. Hydroacoustic methods “scan” a much greater area than stereo-BRUVs and therefore provide a useful complement to the method. The latter method can also be used to improve understanding of subtle changes in the behaviour (i.e. activity and feeding levels) of fishes in the presence of sharks, or so-called “acute” risk effects. To improve understanding of the effect of bleaching on coral reefs and how it may synergistically interact with overfishing of top predators, we also conduct stereo-DOVS at our sampling sites. Lastly, we collect oceanographic data (e.g. salinity, temperature, depth, oxygen and fluorescence) and sediment in order to characterise habitat.
Stereo-BRUVS ready for deployment (left) and just prior to deployment (right).
Stereo-BRUVS ready for deployment (left) and just prior to deployment (right).
Professional fly fisherman scouting for new catch-and-release locations.
Deploying the “Maestro” to collect oceanographic data.
Research in the British Indian Ocean Territory (BIOT)
The Pangaea Initiative has conducted three field trips to BIOT to date, in March 2015, November 2015 and May 2016. On the latter two trips we were granted permission by the British and US governments to incorporate Diego Garcia, the US military base, into our sampling regime. This was a big step forwards as the region around Diego Garcia is highly protected relative to the rest of BIOT and therefore may increase the gradient in shark abundance across the archipelago, providing a shark-rich “control” against which we can compare the shark-fished “treatments” farther north.
In order to assess whether the diversity, abundance, size and biomass of prey fish assemblages varies in a predictable way in response to variation in shark abundance, the Pangaea Initiative has deployed almost 700 stereo-BRUVS over the sampling period,. The Pangaea Initiative has also caught-and-released over 1000 fish to date, belonging to >50 different species and 12 different families.
Additional research achievements
To explore the extent of bleaching at BIOT following the 2016 El Niño warming event, we rolled out a large-scale stereo-DOVS survey targeted at filming reef transects at 38 sites across the archipelago in May 2016. On the same trip, our oceanography team deployed Conductivity, Temperature and Depth (CTD) profilers at the seabed and at the sea surface for 24 hour periods in addition to collecting sediment cores to determine particle size, organic matter content and infauna diversity. This information will be used to understand how oceanographic patterns alter shark and fish distributions across BIOT and whether conditions vary between years and seasons.
We have collected data from over 160 km of acoustic transects using a multi-frequency scientific echosounder. Of these transects, 130 were twinned with stereo-BRUVS deployments, which will allow for the first time the identification of the acoustic “signatures” of poorly studied species such as green turtle Chelonia mydas, tawny nurse shark Nebrius ferrugineus and blacktip reef shark Carcharhinus melanopterus. In November 2015, we tagged 30 two-spot red snapper Lutjanus bohar near the existing receiver arrays at Peros Banhos and Salomon atolls with acoustic transmitters. These will provide rare insights into the movement patterns of one of the most abundant and important mesopredators on the reef, and how reef shark occurrence may affect its spatial behaviour.
Research in Australian Territorial Waters: the Cocos Keeling islands
The Pangaea Initiative moved eastwards in November 2016 for its first expedition in Australian territorial waters. The Cocos Keeling islands represent a crucial “piece in the puzzle” in the Pangaea Initiative’s approach to examining the role of sharks on coral reefs. Located approximately 2,750 km north-west of Perth and 966 km southwest of Java, the southern, inhabited atoll is comprised of 26 islands. South-easterly trade winds blow for over 85% of the year (Falkland 1994) and live coral cover at most sites ranges between 50–75% (‘good’ category; (2005)). Over 500 fish species are found on the islands (Hobbs and McDonald 2010), and the region is home to more hybrid coral reef fishes than any other marine location due to its location at the nexus between the Indian and Pacific Oceans (Hobbs et al. 2009). Surrounded by deep waters, this remote island may also be a “roadhouse” for ocean wildlife as they move around the Indian Ocean.
Following the protocol of the BIOT expeditions, the team obtained tissue samples from 101 fishes representing 6 families and deployed 203 seabed stereo-BRUVS in the lagoon of the southern atoll. Combined, these data will allow us to not only document the status of reef sharks and their control of reef fish assemblages within the Cocos Keeling islands but also to compare these patterns to those documented in BIOT. Programme expansion to the surrounding open ocean areas saw 110 mid-water BRUVS deployments. These samples are the northern most contribution to the Great West Ozzie Transect and also allow for comparisons of open ocean wildlife in the central Indian Ocean (BIOT) with this location in the eastern Indian Ocean.
Catch and release
Wading for catch-and-release fish samples.
The team continues its tradition of outreach in locations where field work is conducted.
While at Diego Garcia in May 2016, the Pangaea Initiative gave three public and well-attended lectures on the Base:
• “Why the BIOT Marine Protected Area (MPA) Matters For Indian Ocean Conservation” (Prof. Jessica Meeuwig)
• “The Ecology of Fear: How Sharks Regulate Coral Reefs” (Dr. Shanta Barley)
• “Sharks, Hooks and Videotape” (Mr David Tickler).
During the Cocos Keeling islands expedition, Dr. Shanta Barley and Dave Tickler provided presentations at the community centre on West Island that was extremely well-attended. Dr. Barley and Mr Tickler combined to discuss the crisis affecting shark populations globally, why reef sharks are important for reef health, and the methods that the science team uses to sample reef and mid-water shark and fish assemblages. The presentation concluded with a highlights reel of footage captured on the expedition to Cocos Keeling. Well-received, the presentations inspired a lively but considered discussion of the role of sharks within ecosystems.
In addition, the team provided support and supplies to the Diego Garcia Shark Tagging Program, which was set up by the Pangaea Initiative to tag recreationally caught sharks with acoustic tags. The team also engaged with the Diego Garcia Saltwater Fly Fishing Club, bringing a club member on a stereo-BRUVS deployment trip and developing catch calendars for the members. While in Diego Garcia, we also provided support to the Base Environmental Services team to facilitate sub-sampling of confiscated illegal shark and fish catch. Six UK Marine escorts participated in catch-and-release sampling, and we also liaised with the British Representative Commander Edward Lees to facilitate future research in this remote and fascinating location.
In July 2017, the team engaged with the West Australian community at the Mangrove Hotel in Broome, offering insights from their four-month research journey across Australia’s Top End.
A copy of the public presentation is available below.