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Structure and biology of the southern component of blue whiting : (Micromesistius poutassou) population in northeast atlantic
Publication . Gonçalves, Patrícia de Jesus, 1976-; Cabral, Henrique N., 1969-; Melo, António Ávila de
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 processing for symmetry shape analysis between left and right otolith. On blue whiting the otolith images should be obtained from the concave side (distal surface). Microsatellites’ genetic based results showed a lack of differentiation between samples from north to south of the NEA, and even at the Mediterranean coast of Spain. However, was verified a clear differentiation between the samples from the Adriatic Sea and the rest of the areas. The otolith shape showed differences between Ireland, Portuguese coast and Mediterranean. Small scale differences in the otolith shape of immature individuals were identified associated with different depth distributions along the Portuguese coast, but those differences have not been reflected in the comparison between the Portuguese coast and the adjacent areas (Ireland coast and Mediterranean). The main conclusion was that blue whiting presents a unique population structure along the Portuguese coast which is different from the populations at north (Ireland coast) and at the Mediterranean.The basis, that will allow in a near future assess blue whiting considering two stock components, in a more sustainable and conservative based-approach for their effective management across the Northeast Atlantic, have started being created.
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Fundação para a Ciência e a Tecnologia
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SFRH
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SFRH/BD/88092/2012