Vertebral Chemistry Distinguishes Nursery Habitats of Juvenile Shortfin Mako in the Eastern North Pacific Ocean

Abstract

Shortfin Mako Isurus oxyrinchus are ecologically and economically important apex predators throughout the global oceans. The eastern North Pacific Ocean contains several coastal nurseries for this species, where juveniles can forage and grow until venturing into offshore pelagic habitats, where seasonal migration and reproduction occurs. Opportunistically sampled vertebrae from both male and female juvenile Shortfin Mako (65.5–134.4 cm total length, neonate to age 2) were sourced from two distinct nurseries in the eastern North Pacific: the Southern California Bight (n = 12), USA, and Bahía Sebastián Vizcaíno (n = 11), Mexico. Mineralized vertebral cartilage was analyzed to determine concentrations of selected elements (Li, Mg, Mn, Zn, Sr, Ba, standardized to Ca) using laser ablation inductively coupled plasma mass spectrometry, targeting growth bands at specific life stages, including postparturition at the birth band and the recent life history of the individual at the vertebral edge. The elemental variation exhibited by these individuals over ~1 month of life before capture was explored by comparing recent vertebral concentrations, with Zn:Ca, Sr:Ca, and Ba:Ca concentrations significantly different between nurseries (Southern California Bight versus Bahía Sebastián Vizcaíno). Element variability through ontogeny was detected, as Li:Ca, Mg:Ca, and Zn:Ca concentrations were significantly different between individual past and recent vertebral bands. These findings suggest that vertebral chemistry approaches may enhance understanding of nursery habitat sources of migratory sharks.