Migratory behaviour of Atlantic cod Gadus morhua: Natal homing is the prime stock-separating mechanism

Abstract

The migrations of cod (>37 cm) in the Skagerrak and Kattegat were investigated in an archival tagging programme conducted between 2003 and 2006. Cod tagged at different localities showed non-random, directional movements in agreement with the hypothesis that the cod population in this region comprises a mixture of resident and migratory stocks. Cod tagged off the eastern Skagerrak coast migrated towards the North Sea, predominantly during the spawning period January to April, and most of these fish returned to the eastern Skagerrak later in spring. The putative spawning runs were associated with changes in habitat, as the migratory cod visited shallower and colder waters. In contrast, concurrently tagged cod in the Kattegat and the Gullmar Fjord (Skagerrak) showed a higher degree of resident behaviour. However, some fish also left these 2 areas for migration towards the North Sea, predominantly during the spawning period, in accordance with the theory that recruits from the North Sea will eventually leave the Kattegat and the eastern Skagerrak coast for their natal spawning sites. Taken together, these findings imply natal homing behaviour to be the intrinsic mechanism which underlies population separation in marine fishes. © Inter-Research 2007.