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

The blue jack mackerel, Trachurus picturatus, is an economically important fishery resource of the NE Atlantic, commonly captured around the Macaronesian islands of Azores, Madeira and Canaries, but also along coastal Portugal mainland. Despite this, information regarding the T. picturatus population structure is, at present, non-existent. One hundred and twenty individuals of T. picturatus were collected in 2013 from six important fishery regions of the NE Atlantic: Azores, Madeira, Canaries and Portugal mainland − Matosinhos, Peniche and Portimão. Elemental and isotopic signatures of whole sagittal otoliths were determined by inductively coupled plasma mass spectrometry and isotope ratio mass spectrometry, respectively. Elemental (Sr/Ca, Ba/Ca, Mg/Ca, Pb/Ca, Li/Ca, Fe/Ca and Mn/Ca) and isotopic ratios (δ18O and δ13C) were analysed with univariate and multivariate statistics to determine whether these chemical signatures provide insight into regional population structure. Whole otolith signatures gave distinct regional signatures, mainly driven by spatial differences in Sr/Ca, Ba/Ca, Li/Ca and δ13C, namely between the Portugal mainland and the oceanic islands. Furthermore, the results suggest for the first time that Portugal mainland, Azores, Madeira, and Canaries should be regarded as different population units. The high re-classification success rate (an overall of 81%) for these regions obtained from the quadratic discriminant function analysis supports these findings, and suggests the management of this fishery in the NE Atlantic as different stocks.