Essential habitats are context-dependent for the cosmopolitan scalloped hammerhead shark (Sphyrna lewini)

Essential habitats often shift throughout ontogeny as different life stages have distinct life history requirements. The scalloped hammerhead shark (Sphyrna lewini) is a cosmopolitan species known to undergo ontogenetic habitat shifts. However, the characteristics of habitats considered important for the species varies among and within geographic regions. While research into habitat use in scalloped hammerhead sharks has been extensively documented in the Eastern Tropical Pacific, information from other parts of their global range remains limited. To address this gap, we conducted a literature review to: (1) examine global similarities and differences in habitat use across ontogeny; (2) identify contextual drivers of variation in habitat use; and (3) identify plausible essential habitats in data-poor areas. Across regions, scalloped hammerheads appeared to follow two main life history strategies, where they used either predominantly coastal (Model 1) or offshore (Model 2) habitats. Both strategies were observed in all well-studied areas (e.g., the East Pacific) and were associated with environmental contexts, notably the proximity to oceanographic features related to either inshore or offshore habitats. Connectivity between both model scenarios was evident, especially between oceanic females and coastal nursery areas. By synthesising variation in habitat use across ontogeny, this review provides a framework and future directions for identifying essential habitats for threatened elasmobranchs in data-poor regions. Furthermore, this work highlights that environmental context can have a profound influence on the life cycle of a species and should be considered when defining essential habitats.