Fidelity of adult cod to spawning grounds in Scottish waters

This study investigates site fidelity of Atlantic cod (Gadus morhua) to spawning grounds in Scottish coastal waters from a synthesis of historic and recent surveys of spawning distribution combined with an analysis of tag-recapture experiments conducted between 1960 and 1986. Recent surveys of spawning fish distribution in ICES area VIa (West of Scotland) suggested the persistence of the main spawning concentrations identified over 50 years ago by egg surveys. From 383 cod tagged during the spawning season and recaptured during successive spawning seasons >90% were recaptured within 80 km of coastal release sites, such as the Clyde, Moray Firth and the Minch. Cod released at these coastal spawning grounds also tended to remain in these areas during the summer feeding season implying that they belonged to resident spawning groups. Tag recapture experiments conducted within a much larger network of spawning grounds to the north of Scotland indicated that cod from this area moved more extensively. The study further highlights the diversity of migratory patterns found in Atlantic cod and has relevance to the management and conservation of the depleted VIa and North Sea stocks.