Evidence of a Potential Nursery Area for the Great Hammerhead Shark, Sphyrna mokarran, in the Largest Coral Reef System of the Southwestern Atlantic.

Identifying Essential Fish Habitats (EFHs) is fundamental for the conservation of threatened sharks, particularly those affected by overfishing and habitat degradation. The great hammerhead shark (Sphyrna mokarran), listed as Critically Endangered globally and regionally, remains poorly studied in terms of habitat use and early life ecology. Here, we present evidence suggesting that the Abrolhos Bank (the largest coral reef system in the southwestern Atlantic) may be used for early life stages of S. mokarran. Between April 2018 and May 2019, 58 individuals were recorded from artisanal gillnet fisheries operating in the region. Most specimens were identified as neonates or young-of-the-year (YOY) based on total length and presence of umbilical scars. Kernel density estimation revealed spatially structured aggregations, with neonates concentrated in shallow reef-associated areas. Temporal variation in catch per unit effort (CPUE) indicated recruitment pulses during late summer and early autumn, consistent with localized parturition. Although the study was limited to 1 year and subject to gear selectivity, the predominance of neonates and YOY, their persistence across consecutive months, and the absence of mature sharks suggest localized use by early life stages. These findings partially meet recognized nursery criteria and highlight the ecological significance of the Abrolhos Bank for S. mokarran. Protecting this coastal habitat through the expansion of marine protected area boundaries, adoption of bycatch-reduction measures, and implementation of long-term monitoring programs may contribute to the recovery of this imperiled species.