Wednesday, March 25, 2015

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

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