Blog post

2nd survey day – New calibration and the ferry route

Published on
October 19, 2011

We started surveying at 8 in the morning and as the weather is better than yesterday, from the beginning saw more small schools.

As the weather is becomes worse the fish schools tend to be more spread and vice versa with better weather conditions schools are rather grouped together.

1st fishing track

We did our first fishing track of the day already at 8.30 (26 kg) and caught mainly sprat (90%), a few herring(10%) and small lumpsucker (Cyclopterus lumpus, NL = Snotolf).

Lumpsuckers are commercially mainly used to produce the so called fake caviar (very popular in the Scandinavian countries).

For the rest up to now the weather is rather fine with a few clouds, though outside the sheltered areas waves should still be over 3 m.

2nd fishing track

The second haul was executed at 10.40. We caught a total of 50 kg again composed of 10% herring and 90% sprat.


Initially it was planned to do target strength measurements of jelly fishes (measuring the echo strength of jelly fishes) today but as we did some mistakes in the settings during the calibration, we decided to change our plan, do the normal zig-zag transects and follow the ferry route today. This allows us to be back earlier in the harbour and do another calibration.

In the end the calibration was successful, but of course as in almost any calibration of a 200 kHz transducer mysterious, things do happen. As it happens during the calibration you look for single targets namely the calibrated sphere. We could very well see a nice target on our normal echogram all the time but very little to no single targets were detected. In general what you do in such a case is play around with the single target detection settings until you get a nice signal. Hence Dirk and me tried for quite some time until we decided this can not be it. We were convinced it most be a hardware problem but then just before taking the equipment out of the water… We remembered: We are working on WIndows! The solution of the riddle is probably a hidden bug in the unknown spheres of software codes. Changing the transmission speed and power to then change it back did the trick and we could all call it a day after the calibration stuff was put back to where it belongs... Now since the last calibration it is much easier to put back together the towed body after the calibration due to a very good invention of Koos, unfortunately I am not allowed to give any more details, as I am not sure if this will become a patent ;).