In this work package, we want to adress to questions:
(a) Which spawning areas and which nurseries contribute to the stock harvested in the Eastern English Channel ?
(b) Which patterns of movements for adult soles (1) within the EEC, (2) with the Western EC and the southern North Sea ?
Tagging campaigns will be carried out in order to estimate mixing rates between potential sub-units within the EEC stock, as well as with the Western EC and the North Sea stock.
Tagging will take place in 2016 and 2017 during existing surveys, as well as aboard fishing vessels.
2. otolith shape analysis
Otolith shape is influenced both by genetic and environment. Otolith shape analysis can therefore allow to differentiate stocks, and even sub-populations occupying distinct regions with a spatially refined sampling scheme. In this method, otolith contours are described using thematic functions: each otolith is therefore described by the parameter values of this function.
Otoliths will be collected on soles fished in pre-defined sampling areas during 2016 and 2017 with the assistance of the 3 PO partners : CME, From Nord, and OPN.
In 2017, the shape of the collected otoliths will be analysed.
3. otoliths microchemistry
The otolith chemical signature will be used to investigate the spatial structure of the sole population and the connectivity between the different life stages in the English Eastern Channel. This method lies on the transfer of trace elements from the surrounding environment into the otolith structure in a chronological and permanent way. We will:
1- build a library of chemical signatures of the different nurseries and spawning areas in the EEC;
The spawning area library will be built over a year of sampling: the 3 areas will be sampled twice during the spawning season (3 water samples and 10 adult soles), otoliths from sole larvae will also be analysed. The nurseries library will be built over 2 years of sampling: the 5 nurseries will be sampled once a year (10 juveniles of age 0 and 10 of age1 and 3 water sampling). The chemical composition (major, minor, trace elements) of water and otoliths will be analysed using ICP-MS (inductively coupled plasma mass spectrometer) et Laser-ICP-MS respectively.
2- Compare otoliths from adults and juveniles to those libraries to identify their spawning areas and nurseries of origin.