Stage-dependent trace metal bioaccumulation in Scomber colias across the ontogenetic transition

Habitat transitions linked to ontogeny can markedly alter contaminant exposure in marine fishes, yet their effects on trace-metal bioaccumulation remain poorly quantified. This study examines how the shift from pelagic to benthic habitats shapes muscle concentrations of aluminium (Al), cadmium (Cd), copper (Cu), iron (Fe), lead (Pb) and zinc (Zn) in the Atlantic chub mackerel Scomber colias, a key commercial species in the NE Atlantic. A total of 201 individuals from artisanal fisheries in the Canary Islands were classified as young (<28 cm total length, TL) or mature (≥28 cm TL) adults. Segmented regressions, non-parametric tests, multivariate analyses, functional metal ratios and a Potential Ecological Risk Index were applied. Metal concentrations increased sharply with size, with mature adults showing approximately 6-, 2-, 2.5- and 2-fold higher levels of Cd, Pb, Fe and Zn, respectively, than young adults. Breakpoints in the length–metal relationships occurred between 22.4 and 35.6 cm TL, defining a tipping size near 28 cm that coincides with the onset of benthic feeding. Environmental monitoring and seafood safety risk assessment as well as fisheries management are directly impacted by these findings. • Ontogenetic shift at 28 cm alters muscle trace metal burdens in S. colias • Mature adults show higher Cd, Pb, Fe and Al than young adults • Segmented models show non-linear bioaccumulation with size (R2 > 0.94) • Metal ratios (Cu/Zn, Cd/Pb) indicate stage-specific exposure.