Spatio-temporal dynamics of Atlantic cod (Gadus morhua) in the Irish and Celtic Sea: results from a collaborative tagging programme

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Spatio-temporal dynamics related to sub-structuring of Atlantic cod stocks may affect how the populations in different management areas respond to recovery measures. Using data from mark recovery and electronic tag studies, we test the assumption that there is an exchange of cod between two adjacent cod management areas, one in the Irish Sea (ICES Division VIIa) and the other in the western English Channel and Celtic Sea (ICES Divisions VIIe-k). We evaluate 1522 archived and current mark recovery data (1960’s- present day) to assess the seasonal changes in distribution of cod within ICES Divisions VIIa and VIIe-g. In addition, we report on the results of a collaborative electronic data storage tagging (DST) programme of cod in the Irish and Celtic Sea, spanning the years 1999 to 2009. During this time, 693 DSTs have been deployed on cod between 43cm and 110cm, and 54 of the tags have been returned yielding over 2700 days of data. We used a tidal geolocation model to determine the daily locations of each cod to reconstruct in detail the migrations of cod tagged with DSTs. The results are the first to describe fundamental features of cod spatial ecology in the Irish and Celtic Sea, such as the location of feeding and spawning grounds (and the migratory pathways between them), the seasonality of migration and habitat occupation and the potential impact upon sub-stock structure.