Publication Abstract

The dispersal patterns and behaviour of North Sea Cod (Gadus morhua) studied using electronic data storage tags

K. Turner, D. Righton and J.D. Metcalfe

Cod (Gadus morhua) is a commercially important demersal species, which makes seasonal migrations between spawning, nursery and feeding grounds. The North Sea stock was once abundant but it is now subject to drastic quota cuts in order to prevent stock collapse. In the future, additional conservation measures will be required to safeguard stock recovery and an increased knowledge of migration patterns and behaviour is needed. We used electronic data storage tags (DSTs) which record depth, temperature and light, to study the behaviour of adult cod in the North Sea. Fifty-one cod were tagged and released off Lowestoft in late March 1999, twenty-two of which were returned by March 2000, yielding over 1500 days of data. Two main patterns of behaviour were discernible from the tag data. Between March and June, as individuals migrated north from spawning grounds, they were highly active and spent much of their time swimming in mid-water. In contrast, from July to September, individuals were predominantly inactive and typically remained on the seabed for most or all of the time. Geographical reconstruction of the tag record during this period places the individuals throughout the central North Sea on putative summer feeding grounds. During October and November, individuals still at liberty switched back to a behavioural pattern of high activity, probably accounting for the migration south to spawning grounds. Our results provide unique insights into the dispersal patterns and behaviour of post-spawning cod tagged on a migratory route and demonstrate that individual-based studies of fish behaviour can provide information relevant to fisheries management.

Reference:

K. Turner, D. Righton and J.D. Metcalfe (2002) The dispersal patterns and behaviour of North Sea Cod (Gadus morhua) studied using electronic data storage tags. Hydrobiologica, 483(1-3): 201-208