Chagos 3.0 - Day 10: Last-Minute Mantas

After 10 busy days we are reluctantly leaving Chagos, heading to Blenheim Reef and Speaker’s Bank in the north-west on our way out of the archipelago. It’s an early start for our last day. At 4:30am I’m filling tanks, and we already have one of our final round of receiver deployments out of the way before the sun rises. Chagos treats us to one last spectacular sunrise: an orange ball floats above Ile de Passe at Salomon Atoll as we drift at the lagoon entrance while our dive team deploy the temperature and dissolved oxygen loggers used to monitor water conditions around our acoustic receiver network.

As we prepare to leave Salomon we have one last surprise. Manta rays are feeding at the surface around the boat, and eagle-eyed captain guides the tender into position allowing us to get one last satellite tag attached. Every piece of data counts, and this tag will be a valuable addition to the information this expedition can provide.

This has been a fantastic trip, and yet again the teamwork between our group of six scientists (and diving doctor) and the ship’s crew has been the key to its success. The Chagos acoustic array now comprises 63 acoustic receivers, and we have tagged over 160 animals since the project’s start in 2013. Our two VR4 Globals have been successfully repaired and we have two of last year’s sharks already ‘talking’ to us as they swim by.



As we leave Speaker’s Bank, we say goodbye to Chagos for another year.

Chagos 3.0 - Day 9: Chagos Goes Global

Deploying the latest technology in the field can be fraught with difficulties, and our Vemco VR4 Global receivers are certainly high tech. Not only do they detect and record shark movements, but they are equipped with an Iridium satellite antenna, mounted on a surface buoy, that sends information about detections straight back to us in real time, allowing us to monitor our sharks from anywhere in the world.

A Vemco VR4 Global buoy floats at the surface, uplinking
to Iridium satellites through the dome at the top.

Ensuring that each step in the chain, from detection to sending the signal to the surface unit to transmitting the signal to the satellite, is working perfectly requires patience and a lot of testing – after all it will be twelve months before we have a chance to service this equipment again.

Dr Taylor Chapple is our team’s expert on working with the ‘Globals’, and he has had a busy couple of days. Despite having no apparent issues with replacing batteries, cleaning, and reinstalling both our units earlier in the expedition, we had been getting no data sent through, despite everything apparently working perfectly. Taylor, supported remotely by the Vemco team, worked to eliminate all the possible causes by testing each link in the chain. He concluded that it might be the hydrophone – the listening tip of the system – or its connection that was causing the problems.

With spare hydrophones carefully swaddled in bubble-wrap we set out to our the first of our Global receivers again, this time with a battery of additional testing equipment. Two divers detached the hydrophone from the mooring cable and passed it up to Taylor, who carefully changed the hydrophone and checked the connections, before placing it back in the water with some test transmitters. Connecting wirelessly to the surface part of the system, he is able to see what the system sees, and he was quickly able to confirm that it was now detecting the tags. Hot on the heels of this a radio call from Robbie Schallert, back on board the ship, confirmed that the system was also sending the data back to Vemco. We were back on line! Carefully reattaching the hydrophone back to its anchor, the system was ready to go for another year of work in Chagos.

Dealing with problems like this in the field requires patience and resourcefulness, and the support of a good team at home as well!

Chagos 3.0 - Day 7: Chasing Giants

Today finds us at the Egmont Islands, off the south west corner of the Great Chagos Bank. We've come here looking for manta rays, which we know from previous visits to be a common sight around the reefs and within the lagoon. The purpose of our visit here is to acoustically tag some of the manta population and deploy some of our acoustic receivers to track their movements over the coming year. The aim is to understand how resident the mantas of Egmont are, and the influence of the tides and other natural cycles on their daily movements around this small atoll.

Firstly, however, you need to find a manta, and this year we have a new tool at our disposal – a Phantom camera drone. Able to relay live images from a bird eye view to the pilot on the deck of the boat, we can locate groups of mantas and direct the tagging team to the area.

The Phantom camera drone is on the lookout!

Tagging mantas is a somewhat different exercise to the work with sharks – rather than fishing for them (it is too hard to get plankton on a hook) we have to search for mantas feeding near the surface and then apply the tags directly, either from the boat or by free-diving alongside them. A calm approach is needed, both to avoid spooking the animals and sending them to deeper water.

The day proved to be rich in mantas, with 12 tags going out and then a reef dive in the afternoon encountering at least eight more feeding at depth along the entrance to the lagoon. The shark work continued in between manta sorties, and we acoustically tagged a further 11 animals, including our largest reef shark of the trip so far – an impressive male silvertip measuring almost two metres. With three days left here we are making good progress.

Taylor attempts to tag a manta

Aside from the science workload, our most senior scientist and the trip’s doctor have been moonlighting in the galley, producing excellent desserts to complement the already abundant meals aboard. Hopefully all the hard work on deck will keep waistlines in check!

   -Dave Tickler

Chagos 3.0 - Day 6: Corals Spawn and Constellations

Doing fieldwork in remote areas has its challenges but also its many rewards, and one of these is being in the right place at the right time for some of nature’s most amazing shows.

Coral spawn floats to the surface

We’re anchored on the northern bank of the Great Chagos Bank, catching and tagging sharks as part of an ongoing collaboration between Stanford University, the University of Western Australia and the Bertarelli Foundation. The tagging going on into the night as sharks are active after dark when planktonic food rises to the surface and a multitude of fishes feed. While tending the line we have had a real treat today as endless drifts of coral spawn, released to coincide with the total darkness of a new moon, swirl past the boat. Corals synchronise their spawning to overcome the armies of predators for which these events are a feeding bonanza, so the water is filled with millions of floating eggs that mirror the Milky Way in the sky above as they pass the underwater lights. It’s a rare treat to be in just the right place to see this happen, particularly in the midst of flat calm seas and clear skies, and for most of us it is the first time we have witnessed this spectacle. We scoop a sample of the planktonic soup into a container for inspection under a magnifying lense, which reveals a mass of spherical eggs, together with myriad small crustaceans and other free floating ocean dwellers.

Peering at the plankton

Every day in the field has these moments, whether it is rescuing a Wilson’s Storm Petrel that has become stranded on deck, or seeing one of the sky filling sunsets that have been a regular feature of this trip, and it helps remind us of the unique opportunity we have in being able to study places like Chagos.

Aaron rescues a Wilson's storm petrel

Chagos 3,0 - Day 5

Day 5 finds us exploring the northern edge of the great Chagos Bank, terra (or rather aqua) incognita for us. With the important servicing work all but completed, we are focussing our efforts on getting almost 100 electronic tags out on sharks and manta rays, the focal species for this study.

We carry three types of tag on this trip. Our workhorses are the acoustic transmitter tags that communicate with our receiver network. We have acoustically tagged 92 sharks so far in this programme and will be adding another 75 animals to our group on this trip.

Whilst the acoustic tags can tell us about the fine scale movements of shark around our monitored reefs, satellite archival tags collect information on position, depth and temperature wherever the shark goes, and then detatch from the shark, float to the surface, and transmit the data back to the lab via a satellite. This allows us to see, amongst other things, the large scale movements and the diving behaviour of sharks which is vital to understanding how they use a large area like the Chagos Reserve.

Lastly, Dr Taylor Chapple has brought his camera tags with him again this year, and with three deployments already we are building up our shark’s eye view of Chagos.

But before we can deploy any of this technology, we must first catch a shark. This involves early starts and late finishes to take advantage of the fact that predators are often more active at dawn and dusk, and so our chances of an encounter are improved. We use barbless circle hooks that minimise the chance of the shark swallowing the hook, and make for simple removal of the hook after tagging. Baited with fish, the hooks are streamed off the back of the boat and tended by one of the team at all times so that as soon as a shark takes the bait we can bring it on board and tag. It’s all about ensuring the welfare of the animal, so before we lift a shark out of the water we make certain that everything is ready to making the tagging as quick a process as possible, and that the padded tagging mat and the saltwater hose to pump water over the shark’s gills are ready.

A hose is inserted in the shark's mouth to keep oxygen-rich
water flowing over its gills, while the scientists attach an
acoustic tag

Handling even a small shark has to be approached with care as they very strong for their size –both the head and tail are controlled while they are lifted, and once on the mat at least two of the team control the shark while the others operate. The Stanford team have years of tagging experience between them, and their guidance makes sure we stay safe on the swim step.

A small shark is returned to the sea

Acoustic tagging involves a quick incision in the abdominal wall through which the tag is inserted, then a suture to close it. While this is happening another scientist takes blood and biopsy samples for genetic and other tests. Lastly, a marker tag is placed just below the shark’s dorsal fin, identifying the shark as having been tagged internally so that we will know if we capture it again next year. Both the satellite and camera tags are attached externally, one with a titanium dart just below the dorsal fin and the other to the fin itself. Both are used in combination with the acoustic tags, so that multiple types of data can be collected from the movements of a single animal. This increases the amount we can learn from our sample of sharks and rays.

So far this trip we have tagged 20 sharks – with 5 days left in Chagos the pressure is high to keep up the work rate!

      -Dave Tickler

Chagos 3.0 - Day 4

Day four, and we’re racing through our servicing work with 44 of 48 sites visited already, thanks to the support of a great crew on Vava and some of the calmest weather we’ve seen in Chagos. With flat seas and hardly a breath of wind, finding our monitoring equipment is proving easy, and the boat and diving work is a true pleasure!

Most of our monitoring array here is made up of submerged VR2W type acoustic receivers, which require diving on, but with new units ready to go in the water it take a two person team only minutes to remove the cable ties and hose clamp fastening the receiver to the mooring line, and fix the replacement in its place. We would probably all rather the dives took longer as there is always something to distract us down there, whether it is schools of fusileers circling you on a reef wall, or a carpet of garden eels stretching away across the sandy bottom of one of the channels.

Vava’s bosun, James, puts the finish touches
on a newly installed VR2W receiver

The other two types of receivers used in the Chagos array require very different approaches. The latest addition to the array in 2014, the four VR4-UWM (standing for UnderWater Modem) can be ‘talked’ to directly from the boat using a portable acoustic modem that instructs the unit on the seabed to transmit its data up to the surface. By holding station over or near the receiver, we can retrieve our data without even getting our feet wet!

Dr. Taylor Chapple enjoying some time
out of the sun while he downloads
 one of the Chagos underwater modem receivers

The last type of equipment used out here are our two VR4-Globals. These, as the name suggests, give us access to our data from anywhere in the world through an Iridium uplink build into a surface unit, connected to a hydrophone hanging below. The whole thing is fitted into a buoy that can be anchored in strategic positions to give us live data on shark detections. These are by far the most complicated to service, requiring a team tackling the surface components to coordinate closely with divers working on the hydrophone and cable. Add a ripping current and it makes for a challenging job, but it’s worth the effort to get real time feedback from our tagged sharks when we are back at our desks.

Taylor gets to work on the transmitter…

…while the dive team are busy below

With the vital servicing work nearly complete we are focussing the majority of our effort on catching and tagging sharks. More on that tomorrow.
   -Dave Tickler

Chagos 3.0

The team from Stanford University and The University of Western Australia are back for a return trip to the British Indian Ocean Territory (BIOT) to service (rebattery, download data, replace moorings and add new receivers) the acoustic array, as well as tag sharks with various electronic tags, including CATS camera tags, Wildlife Computer MiniPATs and SPOT tags, Lotek pop-ups, and Vemco acoustic tags.

   -Robbie Schallert

Dr. Aaron Carlisle tapes up a
Vemco acoustic receiver

Dr. Jon Dale gets the shark line ready