Today’s song: Gigant, Noordkaap

JCR_200_30_find the blobIf you want to do on-board experiments on a specific specifies there is one proofed method to get them: Target fishing. Oh the jollies an excitement of target fishing.

Firstly the method takes advantage of the acoustics on-board the ship. To put is in the most simple of terms a sound (acoustic signal) that is sent straight down the water-column will hit object in the water-column and part of this signal will return to the ship. This idea is similar to that of radar that the ship uses to detect iceberg and other objects around us. But instead of making a sweeping movement round the ship the acoustic signal remains directed downward and follows the movement of the ship.

With these acoustic signals three different wavelengths are used. This allows discriminating between various types of objects.  Anyhow that the scientific part of it. At the beginning of a target fishing period the RMT 8 has been put on the deck at the beginning of the target fishing both nets cocked (like a gun) and ready to go.

JCR_200_31_figure sailing for shipsWhen a mark indicating a swarm of krill, is spotted (see the red blob in the picture) the bridge is phoned and a marker is put at the time when the swarm is detected. This allows the ship to find this spot again on the cruise track of the ship. Then the fun starts. A “battleship” turn is initiated. This is basically a turn for emergency situations, such as an iceberg in front of the ship or a man overboard.  The direction of this turn is specific for each ship, or rather the rotational direction of the propellers. When turning to one side the prop will actually help in making the turn, turning to the other side only the rudder will give the force needed for turning. After these manoeuvrings the ship will return in its own tracks.

JCR_200_31bThis is the time for action: we need to get on our weather gear, our safety boots, work helmet and safety harness. Some at such times feel like firemen swept up b the alarm, other like fighter pilots getting ready JCR_200_32_depoyingRMT8for a scramble, the more down to earth ones among us…. Just like fishermen… Then the net is put over board and lowered to the depth were the swarm has been seen before. When it then comes back on the screen the net is guided through the swarm opening right in front of it and closing just behind it.  Then the net is brought back in with a catch that hopefully allows people to do some work.

JCR_200_35_new boys in townIn the Southern part the catches of krill Euphasia superba were quite large however by the end of this transect other species have started to take over E. triacanta, E. valentini and Thysanoessa sp..