Resumen del producto

¹ Instituto Politécnico Nacional, Centro Interdisciplinario de Ciencias Marinas

Background
The morphology and hunting behavior of thresher sharks make them easily distinguishable. These species are distributed across the Tropical Pacific Ocean feeding on squid and small fish. However, ontogenetic changes in their feeding strategies and habitat use are still unknown in this region. Methods
We examined the d13C and d15N signatures in vertebral collagen from populations of Alopias pelagicus and Alopias superciliosus inhabiting the Galapagos Marine Reserve, focusing on three maturity stages: neonate, juvenile and adult. The vertebrae samples were taken from the seizure of illegal fishing activities carried out by a foreign fleet within the Galapagos archipelago. A total of thirty-three vertebrae from A. pelagicus and twenty-one from A. superciliosus were analyzed.
Results
Both species displayed significant differences in their d15N values (p < 0.001), but not in d13C (p = 0.230), suggesting a similar habitat use, but different prey consumption. Throughout their ontogeny, A. pelagicus displayed isotopic differences (p < 0.001), where neonates showed lower d13C values and higher d15N values compared to juveniles, probably because they still reflect the isotopic signatures of their mothers even after the first year of life. This study highlights trophic differences between both species, accompanied by an ontogenetic variation in A. pelagicus, aspects that allow us to understand the role of these species within the dynamics of the Eastern Tropical Pacific ecosystem.

Palabras clave: feeding strategies; isotopic niche; ontogenetic changes; Tropical Eastern Pacific; Thresher sharks

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