Otolith phenotypic variability of the blue jack mackerel, Trachurus picturatus, from the Canary Islands (NE Atlantic): Implications in its population dynamic

Abstract

Studies have described the presence of different population units of blue jack mackerel, Trachurus picturatus, in the NE Atlantic region. However, the hypothesis of several populations has been subtly questioned due to the high similarity in the otolith shape among some regions. It suggests the possibility of migrations processes connecting them, especially between Madeira, the Canary Islands and the African coast, being the Canary Islands the region with higher potential of mixing due to the oceanographic conditions. In order to explore this hypothesis, we quantified the phenotypic variability in the otolith contour of the blue jack mackerel from Canary Islands using wavelets as mathematical descriptor. Our findings revealed the presence of three otolith phenotypes (M1, M2 and M3) in similar proportions. They were not linked to sex, age and size, but showed temporal variations associated with spawning, recruitment and feeding seasons. The best model to explain the population structure of T. picturatus in the Canary waters was based on local migration triangles and the ‘contingent theory’, where migrants and residents compose the population. In addition, we estimated different somatic growth parameters linked to these phenotypes. These results suggest a complex population structure in the region with possibility of connectivity with the closest populations inhabiting the Madeira archipelago and the African coast. However, future studies are necessary including the whole Atlantic distribution of the species, with special attention to the seasonal variations in the frequency of these phenotypes to clarify the intraspecific polymorphism and the migratory processes.