Vertebral elemental composition reveals ontogenetic changes in habitat use in a Northeast Atlantic mesopredator shark

Sharks are increasingly threatened with extinction due to overexploitation. Research priorities to mitigate these trends include identifying ontogenetic variations in spatial and temporal habitat use, as well as critical habitat areas to protect key life stages and processes. Here we demonstrate the regional applicability of laser ablation inductively coupled plasma mass spectrometry with natural tags (barium, magnesium, manganese, strontium) for investigating broad-scale habitat use patterns amongst at risk elasmobranchs in the Northeast Atlantic. We assess vertebral elemental composition in smallspotted catsharks Scyliorhinus canicula as a model species in the Bristol Channel and English Channel, UK, and identify ontogenetic variations throughout the sampling area, with shared habitat use by young-of-year and sub-adults distinct from adult life stages. We find sex segregation only amongst adults, which appears to be driven by male dispersal. Finally, we suggest that distinct adult populations appear to use multiple birthing grounds which therefore are potentially critical habitats for population recruitment, but with differential importance according to usage. Together these findings present an opportunity to integrate precautionary management into current conservation planning in the UK; S. canicula is centrally important to marine food webs, therefore strengthening population robustness against emerging fisheries and environmental perturbations should be a key objective. • We propose standardised protocols to enable regionally comparable LA-ICPMS studies. • Scyliorhinus canicula sexual segregation varies with ontogenetic development. • Possible evidence of use of multiple birthing grounds by discrete adult stocks.