| Summary: | Blue whiting, Micromesistius poutassou (Risso, 1827), is a mesopelagic gadoid widely distributed in the North Atlantic and the Mediterranean Sea, inhabiting waters over the shelf edge and continental slope. The species plays an important role in the marine food web feeding on pelagic crustaceans and mesopelagic fish and being consumed by a wide range of predators from pelagic and benthic habitats. It is a species of commercial interest, exploited in the northern colder areas of the Mediterranean. Despite its ecological and commercial significance, information on its biology and behaviour is mostly restricted to the Atlantic waters, and the information for this species in the Mediterranean is very scarce. In the last decade, blue whiting population has displayed a decreasing trend in the NW Mediterranean, and now it remains at very low levels. In this context, this Ph.D. thesis aims to unveil the main drivers (physical, biological and anthropogenic) of the population dynamics of blue whiting in the NW Mediterranean Sea. The blue whiting population parameters have been updated and the growth of the species and its relationship among reproduction and energy reserves have been described. Blue whiting reaches the first maturity at around 18 cm TL for both sexes that is achieved the spawning season following its birth. Females and males show different growth curves, with females reaching higher sizes than males. Spatial segregation by age and size has been observed. While smaller individuals (age 0 and 1) remain in the shelf break (130-250 m depth), the large ones (age >2) are more abundant in the upper slope (250-550 m). The largest individuals (>26 cm TL, age >3) display movements along the year and approach the coast in winter for reproduction, disappearing in summer and autumn. The study of the feeding ecology highlight the relevance of the Myctophidae fish as the main prey for blue whiting. This energetic prey is mainly consumed in spring and summer, which might allow the species to recover energy ...
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