The horizontal migration of hammerhead sharks along the southern Brazilian coast, based on their exploitation pattern and considerations about the impact of anchored gillnets activities on these species

Jorge Eduardo Kotas,Antônio Alberto Da Silveira Menezes,Elizabethe Lobão Veras Micheletti,Miguel Petrere Jr,Celso Fernandes Lin,Ajax Bustamante,Roberta Aguiar Dos Santos

doi:10.37002/revistacepsul.vol3.32245-68

Jorge Eduardo Kotas, Antônio Alberto Da Silveira Menezes + Show 5 more

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https://doi.org/10.37002/revistacepsul.vol3.32245-68

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Abstract

Between 1995-2009 hammerhead sharks were sampled from the landings ofthe industrial fleets based in the harbours of Itajaí and Navegantes, SC State,and Ubatuba, SP State, Brazil. In this case, fishing boats which operated with gillnetslonglines and trawls along the southern Brazilian Economic Exclusive Zone and internationaladjacent waters were targeted. A total of 2483 and 353 S. lewini and S. zygaena carcasses respectively were sexed, measured and converted to total lengths (LT). Additionallyinformation about, year, season, latitude/longitude and local depth (m) from the catches,by fishing category, were obtained. During the considered period, intense fishing mortalityover pups was caused by gillnets and trawls operating on shallow waters (≤20m) and overjuveniles along the continental shelf (>20m and ≤200m). Additionally, adults were exploitedby driftnets and longlines along the shelf border and slope (>200m). Therefore,both hammerhead species are exploited at all life-stages and throughout their migratory circuit.This includes during their inshore-offshore migration while they are growing from pupsto juveniles and as the offshore-inshore migration of pregnant females to pupping areas inshallower waters. This apparently unsustainable exploitation pattern, over different sizeclasses (newborns-juveniles-adults), and the economic pressure caused by the internationalfin market, is one of the reasons for population declining of these two species in southernBrazil. Non fishing zones for the hammerheads, protecting their migratory circuit, which isdriven by their growth pattern and reproduction, are necessary. Additionally, fishing effortreduction and a control over the international fin market are recommended.

Highlights

The scalloped hammerhead shark, Sphyrna lewini (Griffith & Smith, 1834), which occurs in tropical and warm-temperate waters, is considered a coastal and semi-oceanic species, being distributed over the continental shelf and oceanic adjacent waters, from the intertidal zone to deep water hypoxic zone at 980 m (Stevens, 1984; Chen et al, 1988; Stevens & Lyle, 1989; Jorgensen et al, 2009)
The adults were found over the shelf border and slope, while pregnant females migrate to shallower coastal areas to give birth
Between 1995 and 2009, the hammerhead shark carcasses landed by gillnetters, longliners, shrimp trawlers and pair trawlers based in Ubatuba (São Paulo State), Itajaí and Navegantes (Santa Catarina State) harbours, which operated along the southern Brazilian Economic Exclusive Zone and international adjacent waters, were sampled (Fig. 1)

Summary

Introduction

The scalloped hammerhead shark, Sphyrna lewini (Griffith & Smith, 1834), which occurs in tropical and warm-temperate waters, is considered a coastal and semi-oceanic species, being distributed over the continental shelf and oceanic adjacent waters, from the intertidal zone to deep water hypoxic zone at 980 m (Stevens, 1984; Chen et al, 1988; Stevens & Lyle, 1989; Jorgensen et al, 2009). It is differentiated from its congener S. zygaena, by having a median indentation in the anterior margin of its head (Cephalophoil), whitish pattern and a transversal section over the precaudal pit is ellipsoidal (Castro, 1993). Juvenile’s females have higher growth rates and mature at bigger sizes than males (Clarke, 1971; Schwartz, 1983; Klimley, 1987)

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