David Curnick in Chagos - The Final Push

David Curnick

Blenheim reef is a submerged atoll in the north east of the archipelago and has only ever been explored by a handful of people.  The water was crystal clear and teeming with sharks including two large nurse sharks that circled us for five minutes as if to inspect our work. As with most days, the afternoon was spent undertaking a spot of shark fishing. To our surprise, our bait was overrun with juvenile grey reef sharks, some of which were smaller than the bait they were trying to pinch. One greedy individual hooked himself meaning the whole line needed to be hauled in to release him. On closer inspection we could see the umbilical scar on his underside meaning that this individual would have been less than 1 year old. Although interesting, these little guys were too small for tagging so we decided to move elsewhere in the hope of finding some larger specimens.

Grey reef shark; Chagos; Tagging; Juveniles
Grey reef sharks follow the bait in Chagos during tagging study

After relocating to Salomon atoll we still had 18 satellite tags and a camera tag to deploy. We were particularly keen to deploy the camera tag after the disappointment of not managing to retrieve the previous one. The problem was that both camera and satellite tags require larger sharks and so far on the trip we hadn’t had much luck in finding any. Our luck would soon change. Whilst we were watching the shark lines, one of the tenders called over the radio that they had caught a large shark. They slowly inched their way back to the main boat before transferring the line to one of the team on the back deck. It was a large silvertip, perfect for attaching Taylor’s camera tag. The shark was too big to bring on the boat so all data was collected whilst the shark was in the water. The final thing to do was to attach the camera to the dorsal fin.  The tag would clamp onto the fin for a few hours before detaching and floating to the surface. However, during the release the shark thrashed and shook off the tag. Disaster! Luckily, after a few more hours, we caught another large shark. This time the tag went on without any trouble and was bobbing on the surface three hours later. That night was spent watching the video of the shark as it cruised over the reef with every other fish keeping a suitably wide berth. Very cool!

The next day we were joined in Peros Banhos by the other research expedition. They had brought our long overdue equipment with them which we had finally managed to get shipped out of Singapore. Robbie was particularly excited given that he had spent so much time on the phone trying to get the equipment to the boat. The result of them being two weeks overdue was that we now only had four days to all the new receivers.  

The delivery also meant that we were finally able to make use of the giant buoys that we had spent hours painting on the first day. Underneath each buoy was a VR4 receiver. These are essentially the same as the VR2s, in that they would detect and record any tagged sharks that swam by. However, they also had built-in satellite connectivity meaning that they would be able to send data back to Stanford in real time.

During the last few days we frantically whizzed around Salomon and Peros Banhos deploying the last remaining receivers. The dives were highlighted by large schools of blue trevally, turtles and Napoleon wrasse, but the awful weather made for challenging diving conditions. Sadly we also came across more illegal FADs (fish aggregation devices); this time they were caught on the reef. This was not the end we wanted to the trip.

The weather and intense dive schedule meant that we weren’t really able to devote much time to tagging in the final days of the expedition. On our last day, after all the dives had been completed, we set a few trawl lines in the hope of attracting some of the ocean’s top predators and were lucky enough to catch a 7ft sailfish. Although not our original target, the opportunity to tag such a wonderful animal was one not to pass up.  It was released with a new miniPAT attached. Where will it go? Well we will find out in 5-6 months’ time.  

Sailfish; Tagging; Chagos
Sailfish being tagged to study its movements in Chagos

It was a great way to end the expedition. We had achieved our primary objective to service and download the existing receivers and had tagged some amazing fish along the way.

I have now transferred to the other research vessel to spend the next couple of weeks researching the reefs of the archipelago. There will be a regular blog uploaded at www.chagos-trust.org and I will continue to post tweets through @david_curnick using #Chagos14

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