Scuba diving the high seas
One of the first things Philippe Bouchet, principal investigator of the Walters Shoal expedition said during a preparation meeting back in January was: “priority will go to diving”.
Indeed, to identify mollusc, crustacean or algae specimens in the lab and carry on DNA analysis and research, samples first need to be collected from the sea floor. This is done by scientific divers either picking by hand, rubbing substrate and rocky fragments with a brush or by using a device to literally ‘hoover’ a square meter at a time of the benthic floor.
As the Walters Shoal seamount has a unique shallow element, culminating in some parts at only 18 meters’ depth, Philippe Bouchet’s Natural History Museum team could plan these activities to a maximum depth of 50 meters. We reach different locations around the seamount, all around it using a dinghy, able to take up to 4 divers at a time as frequently as the conditions allow, and using bathymetric data collected by the pelagic team of scientists.
I remembered this and thought, how exciting, we are going to descend on a submerged mountain in the middle of the South West Indian Ocean, and probably be among the very few to discover the underwater nature of this extremely isolated location with its unique features. As an underwater videographer, the idea of filming this unique site felt very appealing.
But the extremely serious aspects of diving a high seas seamount are clear. As a previous post mentioned, the R/V Marion Dufresne has a recompression chamber on board, a hyperbaric doctor and well prepared safety procedures. The marine environment here has many risks, among which the biggest being currents, which can be horizontal or vertical and virtually unpredictable.
During my first three dives, systematically, the water column was to be avoided. You needed to be either on the bottom or at the surface quickly entering or exiting the water. When a buoy and mooring is deployed, decompression stops are easier and holding on tight can be the lifeline for the diver. Each diver carries a GPS that can be activated on the surface should he get out of sight, signalling to ships 30 nautical miles around of his presence. We mainly breathe air, and use enriched air (Nitrox 40%), providing additional decompression stop mix to help desaturate upon ascent. To board the dinghy, it is first lowered by a crane into the water and we descend 10 meters down the steep pilot’s ladder.
Once all those aspects are well understood by everyone, everything then becomes very exciting! I use a Sony RX100 IV camera with a Nauticam housing, wide angle lens and 2 Fantasea video lights, to film and capture the unique marine environment, mostly composed of corallines, algae and subtropical fish species. The water temperature is around 20˚C.
There are a few unidentified species of sharks in the distance, as well as lionfish, groupers and eels.
Seamounts are underwater mountains, biodiversity hotspots and beacons of life for marine mammals, migratory fish and seabirds in the vast open ocean. As we are in international waters, diving the high seas in such a location feels even more special. We are diving, learning about the planet’s common heritage, worth protecting. These images can add to the words.
