Population structure and trophic ecology of a critically endangered hammerhead shark (Sphyrna) lewini in a subtropical coastal area of the western South Atlantic

• Grant number: 25/24071-1
• Support Opportunities: Scholarships in Brazil - Scientific Initiation
• Start date: February 01, 2026
• End date: December 31, 2026
• Field of knowledge: Biological Sciences - Zoology - Applied Zoology
• Principal Investigator: Otto Bismarck Fazzano Gadig
• Grantee: Diana Beatriz Rosa dos Santos Souza
• Host Institution: Instituto de Biociências (IB-CLP). Universidade Estadual Paulista (UNESP). Campus Experimental do Litoral Paulista. São Vicente , SP, Brazil

Abstract

Sharks and rays are vertebrates with a long evolutionary history. There about 1,250 known extant species, characterized by a cartilaginous skeleton, claspers as copulatory organs, and skin covered with dermal denticles. Their biological traits (long life cycle, slow growth, longevity, late sexual maturity, and low relative fecundity) make them vulnerable to unnatural mortality caused by human activities, like fisheries. They are meso- and top predators in marine ecosystems, remarkably Carcharhinidae and Sphyrnidae sharks. The hammerhead shark, Sphyrna zygaena, is a large oceanic-coastal pelagic species (reaching almost 4 meters in length) with a worldwide distribution in surface waters. Juveniles occur along the coastal areas mainly during winter and spring in southeastern Brazil.The aim pf the present study is to quantitatively describe the diet of juvenile individuals of this species along the coast of São Paulo. For diet analysis, the following data will be used: numerical percentage (%N), gravimetric percentage (%M), frequency of occurrence (%FO), and the index of relative importance (%IRI). To estimate the lipid reserves used in metabolic activities, the Hepatosomatic Index (HSI) will be analyzed. Food overlap analysis will be performed using the Morisita Index in association with the Horn Index, and niche breadth analysis will employ the Shannon-Wiener and Levins indices.This study aims to the species' diet in the coastal area of the State of São Paulo, providing data on essential ecological parameters for ecosystem studies and the development of conservation plans. (AU)