Expedition update: Mantis Reef

Did quite a different dive today with Steve Lindfield….(University of WA) who is using a stereo-video camera setup to survey fish on mesophotic deep reefs. The setup consists of two underwater video cameras mounted ~1m apart - when analyzed the videos allow the size and identity of all fish on the video to be accurately determined. This is a great advance from a few years ago: fish scientists working on shallow reefs used to have to slowly swim along identifying and estimating fish sizes as they went- something which took hours and would be impossible at 40m depth. However the cameras are pretty hard going - we both have to swim fast to cover the 100m required and my job was to "keep up" and sample some of our target corals as I went. The usual gang of silver tip sharks came by - looking like a bunch of naughty but pretty harmless teenagers, but then out of the murk came a very large shark- I made a little aaaghh! in my regulator but it was gone in no time; we both passed going opposite directions along the reef, each giving the other a "double take" and continuing on our business. I think it was a Silky Shark - sadly rare these days so even a quick pass in the murk was pretty special. Steve missed it- busy with his videos - and as our dive officer Jaap said when we got back to our boat "you're a very lucky man today - nearly all the big sharks are gone". I also got some nice samples of unusual corals so a pretty good afternoon dive.