This study investigates ontogenetic changes in trophic position and isotopic niche of the smooth-hound sharks Mustelus mustelus and Mustelus punctulatus using vertebral stable isotope analysis (δ13C and δ15N) as a long-term chemical archive. Vertebrae were collected in the Egadi Islands Marine Protected Area (central Mediterranean), allowing reconstruction of trophic trajectories from the prenatal stage to adulthood. Both species exhibited elevated δ15N values at the birthmark, consistent with a maternal isotopic signal, but showed contrasting postnatal patterns. M. mustelus displayed a marked decline in δ15N after birth followed by stabilization through juvenile and adult stages. In contrast, M. punctulatus showed a progressive enrichment in δ15N with growth, reflecting a gradual shift towards higher-trophic-level prey, with adult females reaching significantly higher values than males. δ13C values were comparatively stable across life stages in both species, suggesting limited ontogenetic shifts in basal carbon sources and a persistent reliance on coastal benthic production. Isotopic niche metrics revealed a narrow niche during juvenile stages and increasing differentiation in adults, particularly in M. punctulatus , supporting the occurrence of ontogenetic and sex-related niche partitioning. The δ13C variation was more limited than δ15N variation, but M. mustelus showed clearer ontogenetic changes than M. punctulatus , suggesting moderate shifts in carbon sources during development. These life-stage-dependent differences might likely reduce interspecific competition and facilitate coexistence of sympatric demersal sharks in Mediterranean coastal ecosystems. The use of vertebral stable isotopes proved effective in reconstructing long-term trophic histories and maternal effects, providing life-history-scale ecological information that is essential for understanding the functional roles of vulnerable elasmobranch populations and supporting conservation-oriented assessments under increasing fishing pressure.
Ontogenetic trophic shift and niche partitioning among two sympatric demersal sharks (Mustelus mustelus and Mustelus punctulatus) revealed by vertebral stable isotope analysis
Madia, Manfredi;Bellodi, Andrea;Follesa, Maria Cristina;
2026-01-01
Abstract
This study investigates ontogenetic changes in trophic position and isotopic niche of the smooth-hound sharks Mustelus mustelus and Mustelus punctulatus using vertebral stable isotope analysis (δ13C and δ15N) as a long-term chemical archive. Vertebrae were collected in the Egadi Islands Marine Protected Area (central Mediterranean), allowing reconstruction of trophic trajectories from the prenatal stage to adulthood. Both species exhibited elevated δ15N values at the birthmark, consistent with a maternal isotopic signal, but showed contrasting postnatal patterns. M. mustelus displayed a marked decline in δ15N after birth followed by stabilization through juvenile and adult stages. In contrast, M. punctulatus showed a progressive enrichment in δ15N with growth, reflecting a gradual shift towards higher-trophic-level prey, with adult females reaching significantly higher values than males. δ13C values were comparatively stable across life stages in both species, suggesting limited ontogenetic shifts in basal carbon sources and a persistent reliance on coastal benthic production. Isotopic niche metrics revealed a narrow niche during juvenile stages and increasing differentiation in adults, particularly in M. punctulatus , supporting the occurrence of ontogenetic and sex-related niche partitioning. The δ13C variation was more limited than δ15N variation, but M. mustelus showed clearer ontogenetic changes than M. punctulatus , suggesting moderate shifts in carbon sources during development. These life-stage-dependent differences might likely reduce interspecific competition and facilitate coexistence of sympatric demersal sharks in Mediterranean coastal ecosystems. The use of vertebral stable isotopes proved effective in reconstructing long-term trophic histories and maternal effects, providing life-history-scale ecological information that is essential for understanding the functional roles of vulnerable elasmobranch populations and supporting conservation-oriented assessments under increasing fishing pressure.
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