Population structure of the blue jack mackerel (Trachurus picturatus) in the NE Atlantic inferred from otolith fingerprinting

• ¹ Centro Interdiscilinar de Investigação Marinha e Ambiental (CIIMAR-CIMAR), Portugal
• ² Instituto Ciências Biomédicas Abel Salazar da Universidade do Porto (ICBAS-UP), Portugal
• ³ Faculdade de Ciências da Saúde da Universidade Fernando Pessoa (FCS-UFP), Portugal

The blue jack mackerel Trachurus picturatus is a pelagic fish widely distributed in the NE Atlantic, also found in the Mediterranean and Black Seas. In the Azores, Madeira and Canary Islands this species is an economically important resource. Although, there are some background studies on age, growth, reproductive seasons and parasites, information about the population structure of this species has not been, so far, published. For that, fluctuations in the captures and landings are difficult to explain. In this study, the elemental signatures of whole sagittal otoliths was determined by inductively coupled plasma mass spectrometry. Adult fish were sampled in the fishery grounds of the Islands of Azores, Madeira and Canaries and in the Portuguese mainland coast at Matosinhos, Peniche and Portimão, during the spring-summer of 2013. The Sr:Ca, Li:Ca, Mg:Ca, Mn:Ca, Ba:Ca, Pb:Ca and Fe:Ca were used to discriminate the individuals from different fishing grounds. The canonical analysis of the element:Ca ratios provided a clear separation of the individuals in four main regions – Azores, Madeira, Canary Islands and Portugal mainland - although with some degree of overlapping in the samples from the Portuguese mainland coast. The Jackknifed classification accuracy was high, ranging from 65 % (Matosinhos) to 85 % (Azores), and an overall mean of 76 % was recorded. The results suggest that the population of T. picturatus in the NE Atlantic may be separated in, at least, 4 population units - Azores, Madeira, Canary Islands and Portugal Mainland - which indicates that, in terms of fisheries management, this species should be treated as different stocks. Nevertheless, more methodologies (including molecular biology analysis) are being applied to the collected individuals to complement the data obtained in a way of having an holistic approach to this issue.