| Summary: | Tese de doutoramento, Ciências do Mar, Universidade de Lisboa, Faculdade de Ciências, 2017 Blue whiting (Micromesistius poutassou) is a mesopelagic gadoid widely distributed along the Northeast Atlantic (NEA). Recent studies pointed out the existence of two stock components on their whole area of distribution, with a separation border line at the Porcupine Bank (Ireland western coast). However, the blue whiting continues to be assessed as a single stock, due to the lack of knowledge regarding the biology and structure of their southern component. The present thesis aimed to fill some of these important gaps in the biology and structure of blue whiting at the southern part of stock distribution, the Portuguese coast. Besides, this work also intended contributes to the enlargement of the knowledge on this species assessment. Smaller blue whiting (12cm–24cm) were mostly found in shallow areas down to 200m to 300m while larger individuals (>24cm) were spread deeper down to 400m until 500m. Blue whiting condition (Fulton K) differed significantly between seasons (autumn and winter) in all the three main areas off Portugal (north, southwestern and south) and between sexes. The proportion of females changed between seasons and across depths. The blue whiting life-history parameters analysis shown differences in growth, length, age of first maturity, in the peak spawning and also differences on females spawning stock biomass, between the Portuguese coast and the main spawning ground (west of Ireland Islands and Porcupine Bank), which supports the existence of two components on the blue whiting off NEA. Furthermore, OtoRing, an open source software for otolith age reading, was developed with the principal advantages of: allow the storage and posterior revision of age classifications in an easy way; perform calibrations between readers; and help on the training of new readers. The otolith face orientation (distal versus proximal) on image analysis reveal that it must be taken into account during the otoliths images ...
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