A ROV called Trident

For our expedition, one of the great tools that we plan to use is the Trident Remotely Operated Vehicule (ROV) from OpenROV. This is basically the underwater version of a drone. It "flies" through the water and thanks to its integrated camera, let you see and explore the ocean just like if you were diving. Unlike many ROVs, it is small, very portable and can be controlled from shore or from any type of boats (motor boats, kayaks, etc.). This amazing little instrument will be key for many aspects of our expedition.

Searching for good deployment sites. Once we have selected the general location of our study sites, we need to find the perfect spot to deploy our hydrophone and camera array. It needs to be relatively flat for the structure to be stable and close to fish aggregations, so we can capture their sounds. The Trident will be used before the deployment to identify good locations for the array.

Retrieving the hydrophone array. Deploying the hydrophone array on the ocean floor is easy. We just lower it down from the boat with a line. Once the array is on the bottom, we let go one end of the line and pull on the other end to get it back. To retrieve the array, this is more tricky. We need to find a way to attach the line back to the array. We can't leave a surface float on the array like crab or lobster traps because it would make too much noise that would contaminate our acoustic recordings. So, instead we will use the Trident to hook the line back to the array. Just like the video below. Then, we can pull the array back at the surface from the boat using that line. This retrieval technique is efficient, requires only 2 persons and will allow us to deploy in many places around the BC coast.

Cataloging fish sounds. Many fishes like to hide and hang out in rocks and boulders. Unfortunately, due to its size and shape, our hydrophone and camera array can only be deployed in areas where the bottom is relatively flat. So, we will design a small array of 2 or 3 hydrophones that we will attach to the Trident. These hydrophones combined with the camera from the Trident will allow us to catalog fish sounds in much more complex habitats than with the fixed array. This idea is actually not new. Rodney and Francis have already tried to add hydrophones to ROVs almost 10 years ago (see their paper here). But what they found at the time is that regular ROVs are very noisy and make the recording of fish sounds very challenging. With its much smaller and streamlined design, we are very confident that the Trident won't have that problem.

I am so excited to start playing with this really neat ROV!