Today was the last diving day in the northern atolls of Chagos. Tomorrow we will spend the day using the BRUV units on some deeper seamounts just to the north of Diego Garcia.
In the morning a group landed on Danger Island. This was a very difficult landing as Danger has a very steep beach and was surrounded by crashing waves. This meant that we had to jump from the inflatables and swim through the surf onto the beach. A very strong undertow, caused by water pouring over the reef and out through the channel that we were using to swim to the shore, made the access very hard work and a couple of us were unable to swim against the strong current and so had to turn back and return to the boat which was hovering off to make sure we all landed safely.
Danger Island is a small island and, like Nelsons Island, one of the more remote and isolated islands, it has a good stand of very healthy native hardwood trees, especially Pisonia, as it was never cultivated during the plantation days. Possibly due to the difficulty of landing on it! The question of how Danger Island got its name is always asked and other than the possibility of it being to do with the difficulty in landing, no one knows. The healthy and significant bird community on Danger is thriving well.
Another group dived on a shallow offshore bank which, on the last expedition, was discovered to be covered with seagrass. There is always the hope out here that we will discover dugongs, these large seagrass eating mammals, after all one island in the group is called Sea Cow, another name for the dugong, and one is called Vache Marin, Sea Cow in French. We didn’t see any today but there is a lot of the Great Chagos Bank still to explore.
In the afternoon we moved south to Egmont Atoll where one dive team recovered more temperature data loggers that had been positioned on previous expeditions and replaced them with new loggers. More cores from a large coral head were taken to allow the calibration of the logger data with the palaeoclimatic data collected on a previous expedition. The second dive group were again collecting data from transects surrounding four more dead coral heads, which are being collected to analyse the communities which inhabit them as part of an international study.
Throughout the day the BRUVers were busy deploying units. Tom Letessier tells the story.
“We are now nearing the end of our expedition, and from a BRUVing perspective, it has been a resounding success. We have conducted over 175 camera deployments, giving unprecedented insights into the Chagos reefs and fish ecology. Our collection amounts to over 350 hours of film, which will be used for species identification, estimates of the relative numbers of fish, and size measurement, important variables in ecology.
The support we have received from the master, officers, and crew of the Marlin in conducting our activities has been extraordinary. Long hours, heavy seas, equipment failures, demanding scientists, nothing has affected the good mood or the daily running of the ship. Today for example, the chief engineer Les and his team spent the better part of the morning AND the evening fixing the engine of the ships Fast Rescue Crafts, enabling us to get 16 camera drops in during the afternoon.
Tomorrow will be our final day at sea, and will perhaps bring our greatest challenge yet! We hope to deploy BRUVs on shallow seamounts situated on our last leg to Diego Garcia. The prospect of sampling at 100 m depth is exciting, but will provide some interesting challenges, similar to landing an aircraft in a Swiss airport. These mounts are very easy to miss, and are apparently needle sized! Wish us luck.”
Tomorrow I will report on their success!