Third survey day
Here in the sheltered area the weather seems nice again but outside wave heights of 2.8 m are to be expected.
The first haul of the day was done at 8.30. We fished on very small schools. I wanted to see what those are and to check if the weak signals in between are really jellyfishes. As it came out we had a very small catch (5kg) with 6 lumpsuckers, 95% sprat and 5% herring.
Only one hour after the first haul we saw some a little bit bigger schools appear without any jelly fishes around, so we wanted to see what those are. In the end there was not much difference to the catch before, a total of 8 kg, 95% sprat, 5% herring and again a few small lumpsuckers.
No too many schools to be seen for a while but loads of limes (2 different water fronts colliding and provoking an acoustic disturbance). This time we are fishing near the bottom on some weak acoustical scatterers to see what it is. Surprisingly no larvae were seen but the 20 kg catch was again composed of 95% sprat and 5% herring. SO it is suggested that what we see on the echogram is too small for our net and hence is not caught (for example plankton).
We planned to make target strength(TS) measurements on jelly fishes today but up to now we couldn’t find a good spot to do so. To be able to make TS measurements we have to find a reasonable amount of jellyfishes over which we can drift and record the echo of individuals. To be able to see if the jelly fishes are hiding near the surface I decided to do a surface trawl, this appeared interesting to me even more as there were a couple of schools appearing in the upper part of the water columnThe catch confirmed that there are very well jellyfishes in the surface water.