Coupled use of data storage tags and otolith microchemistry to assess population dispersal and intra-specific diversity in migratory behaviour in North Sea plaice (Pleuronectes platessa L.)

In high dispersal fish species, large scale genetic homogeneity of populations is considered axiomatic. However, in these species, sampling artefacts due to the active migrations of adults might lead to seemingly unstructured populations while, in fact, inbreeding occurs. This seems to be the case in North Sea plaice (Pleuronectes platessa L.), for which previous studies have identified geographically discrete feeding aggregations (sub-stocks) during the summer, from which the adults migrate to spawn during the winter. In this context, otoliths of mature female plaice tagged with electronic data storage tags (DST) were examined for their potential to reconstruct population structure and fish lifetime migratory history. DST allow continuous records to be made of ambient conditions experienced by free swimming fish in their natural environment over periods of up to 18months, from which their annual geographical movements can be reconstructed. Most fish also record ambient conditions throughout their lifetimes by the accretion of calcium carbonate on their ear-stones (or “otoliths”), the chemical composition of which reflects the environmental history of individual fish. Here we use the otoliths from tagged plaice adults to illustrate how DST data can be linked with otolith microchemistry to allow the retrospective positioning of the fish in space throughout their lifetimes. These data could not easily be obtained using conventional techniques, and link for the first time pre and post recruitment fish behaviour. This unveils precious information about population structure in this commercially important species, which is essential for the sustainable management of its North Sea stocks.