Blog post

Change of plans

Published on
April 2, 2011

After discussion with our survey colleagues we decided to slightly change the survey design.

Because the Russian vessel was held up by bad weather on her initial passage from Murmansk to the survey area, she will not be able to complete a second run of transects, as initially agreed. That means that the southern survey area (Porcupine bank) can not be covered twice by both responsible vessels. Additionally, most blue whiting has so far been recorded in the northern part of the survey area (Hebrides/Rockall trough). Therefore, it was decided to reallocate the survey effort of Tridens to the northern area and increase coverage there. Rather than going for a second run of the already covered transects, Tridens will now continue surveying northwards, interlacing with the Norwegian G.O. Sars and Irish Celtic Explorer.

The “new” Tridens transects covering the northern area (grey):
transects.jpg

This gives a new survey design with increased effort allocation in the northern area:

all_transects.jpg

Another change of plan is due to the approach of severe weather conditions. There is a front rapidly approaching from the west, reaching the survey area by Sunday afternoon and culminating in heavy winds and rough sea conditions for the next 3 days. Here a few weather charts showing predicted wave heights and winds, and pressure situation for the next few days:

waves.jpg
Rtavn368.png
FSXX00T_72.jpg

This means that tomorrow evening, after finishing our next transect at 53º32’N, we will have to go and shelter from the bad weather. Such bad weather situations actually reduce the survey quality by causing “missing pings” in the acoustic data due to increased wave action – potentially resulting in under estimation of fish biomass. Additionally, fishing, and hence collecting biological samples is also not possible. Therefore the decision to “sit out” a few days and continue when the situation has improved!