Report of a joint Norwegian-Soviet acoustic survey on blue whiting, spring 1991

Abstract

During spring 1991 the second Norwegian-Soviet joint survey on the blue whiting spawning stock was carried out. The result of a ship-to-ship calibration of the acoustic instruments allowed a 1:1 relationship between the two vessels acoustic data to be used. According to this, the data were then combined and presented as common results. Blue whiting was recorded from south of the Porcupine bank to north of Shetland, but this year the densest concentrations over the Porcupine bank were distributed more to the east than previous years. While the abundance in the southern part of the surveyed area was approximately the same as estimated the last years, it was found to be significantly reduced in the north. The over all spawning stock size was then estimated to 4.4 mill. tonnes which is 1 mill. tonnes less than observed in 1990. The 1989-yearclass as expected was found to be the richest one, with a contribution of 23% of the stock. Although the temperature below 200 m depth in the southern part was in general higher than in 1990, the maturation process of the blue whiting gonads was observed to be somewhat retarded with the peak of spawning 1-2 weeks later than in 1990.