Actions WP 1 2016-2017

Otoliths shape

1296 soles have been collected during scientific surveys (SMAC recruitment, CGFS, IBTS) and by fishermen with the support of the POs according to the sampling scheme below. 522 soles have also been provided by our british colleagues from CEFAS and 300 by our belgian colleagues from ILVO. the collection of otoliths is now over and analysis will be carried out in 2018. Zones d'échantillonnage.jpg

Otoliths microchemistry

1- build a library of chemical signatures of the different nurseries and spawning areas in the EEC; 

Larvae sampling (spring 2017) and juvenile sampling (summer 2016 and 2017) have been carried out according to the map below. Analysis have already been performed on 25 juveniles to characterise their larval stage and juvenile stage chemical signatures. In 2018, we are planning to analyse 34 more juveniles from 2016 and 50 from 2017 as well as the larvae collected in  2017. This will enable to finalize the chemical signature reference maps to which 107 adults from 2017 and 100 (depending on catches) in 2018 will aim to be assigned.

The 5 coloured areas are nurseries, the 3 white areas are spawning areas. The map displays the numbers of juveniles sampled in each nurseries with the name of the survey between parenthesis.

b) Compare otoliths from adults and juveniles to those libraries to identify their spawning areas and nurseries of origin.

Adults have been collected (see map below). By analysing their larval stage and juvenile stage chemical signature in the otolith and comparing them to our libraries, we aim at allocating them to their spawning areas and murseries of origin, and therefore to retrace their spatial movements through life stages. Either a Bayesian reallocation model or clustering methods (LDA, Random Forest, Artificial Neural Network) will be used.

c) Validation by comparing reallocation results with tagging/recapture results.

Tagging actions on juveniles (age 2 mainly) have been carried out in 2017 with specific red tags. Those soles, if recaptured offshore as adults, will allow us to empirically validate the reallocation model (by comparing their actual nurseries of origin with the one identifed from the reallocation model).