Study of the blue whiting movements around the Bay of Biscay using acoustic methods

During March-April 1994 and 1996 two cruises were carried out around Bay of Biscay in order to study movements of blue whiting using acoustic methods. These cruises consisted in a double coverage of an area from 47 degrees 30 'N, 7 degrees 15'W to 43 degrees 30'N, 6 degrees 30'W along the French and Spanish continental shelf-break (200-1000 m isobaths). Changes in spatial s tructure, abundance estimation, age structure and maturity stages have been analysed in each survey and coverage. Blue whiting is known as an important migratory species in the North Atlant ic. By February/March, adult fish are concentrated around Porcupine Bank wh ere they spawn. After this, it is believed that the fish migrate northward. From this study, rapid changes in both number of fish and population struc ture of blue whiting are clear. In 1994 the age structure was Found and the : differences in maturity stages together with an increasing in fish abunda nce from the first to the second leg, could indicate a southward movement a fter the spawning season from the main spawning ground. Results in 1996 wer e different from those of 1994. Juvenile fish were predominant and there wa s an important decrease from the first to the second trip. Nevertheless, it seems most likely that any southward postspawning migration from Porcupine Bank is undertaken by only a few young mature fish, but this migration is sparse compared to that undertaken northward. Due to the absence of adult fish, the abundance of younger fish as well as the lack of significant known spawning grounds, the studied area should be regarded as a nursery area as a result of a juvenile migration or a southwa rd larvae drift. This process could be suggested rather than a postspawning migration. (C) 2001 Elsevier Science B.V. All rights reserved.