OVER: Picture of krill from one of the stereo cameras
Right: Georg Skaret with the platform on which the stereo camera and echo sounder is mounted.
Stock size estimations are based on acoustic measurements. This means that sound waves are sent from echo sounders and sonars which bounce of various objects in the water. The returned echoes are then measured.
- The problem is that a krill’s echo varies quite a bit according to how the krill is orientated in the water when hit by the sound waves, Georg explains.
When horizontal the krill returns a much larger echo than when vertical.
- This means that the stock estimates will vary greatly according to the assumed orientation of the krill, Georg says.
Platform with stereo camera.
This makes it important to learn more about the natural behaviour of krill. Georg does this by lowering a platform into the ocean equipped with an echo sounder looking downwards and a stereo camera taking pictures horizontally. Pictures from the stereo camera can be combined into three dimensional images which will tell both the size of krill photographed and its orientation. Georg assumes that krill caught by the stereo camera behaves similar to those detected by the echo sounder.
- By combining this information we can find the echo of the krill when located in its natural environment. Our aim is to obtain better stock size measurements, Georg says.
The stereo camera is also used on another type of submerged platform which is moored to the bottom. The majority of Georg’s data collection will take place around South Georgia because this is an area known for its krill abundance but he also expects to deploy the stereo camera at later stages of this cruise.
Analysis and comparison of the images from echo sounders and stereo camera will start when he returns to Bergen. According to schedule he will be able to present results within this year.
A krill photographed in the ship's laboratory.