The krilltrawl was used with different weights on the lower wings. Two hauls with 80 kg weights on the wings gave trawl openings of 10 and 13.5 m. When the weights were increased to 190 kg, the vertical opening varied between 12 and 18.5 m. Higher speed gave smaller vertical opening.
To compare the efficiency of the Krill-trawl and the Harstad trawl, 10 parallel trawl hauls were carried out. The opening 2 of the trawls are 250 m2 and 400 m2 for the Krill and Harstad trawl respectively. The catches were corrected according to their openings and the results of the trials are given in Table 4.
If we look at catches per nautical mile, the Krill trawl caught in average 143 kg and the Harstad trawl 82 kg This difference was analysed using a Wilcoxon paired-sample test, and found to be significant.
The Harstad trawl was towed with higher speed as it was difficult to keep the speed constant during the trials. Average catch per hour trawled for the Krill trawl and the Harstad trawl was 293 and 203 kg respectively. This difference was also analysed and found to be significant.
Possibly a larger part of the smallest fish are filtered through the meshes in the Harstad trawl than in the Krill trawl. Then fish caught in the Harstad trawl should be expected to be larger than those caught in the Krill trawl. Fig. 9 shows the length distribution for the fish caught in the Krill trawl and Harstad trawl in the 10 parallel trawl hauls. The Figure does not give any reason to believe that there is any significant difference in size.
In the same way we have split these length distributions in fish, caught at day and at night with the two trawls, but none of the distributions indicate a difference in size of fish from the two trawls.
For further details about the trawl tests see Appendix I.
