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

Resumen

Between 1995-2009 hammerhead sharks were sampled from the landings of
the 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 gillnets
longlines and trawls along the southern Brazilian Economic Exclusive Zone and international
adjacent 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). Additionally
information about, year, season, latitude/longitude and local depth (m) from the catches,
by fishing category, were obtained. During the considered period, intense fishing mortality
over pups was caused by gillnets and trawls operating on shallow waters (≤20m) and over
juveniles along the continental shelf (>20m and ≤200m). Additionally, adults were exploited
by 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 pups
to juveniles and as the offshore-inshore migration of pregnant females to pupping areas in
shallower waters. This apparently unsustainable exploitation pattern, over different size
classes (newborns-juveniles-adults), and the economic pressure caused by the international
fin market, is one of the reasons for population declining of these two species in southern
Brazil. Non fishing zones for the hammerheads, protecting their migratory circuit, which is
driven by their growth pattern and reproduction, are necessary. Additionally, fishing effort
reduction and a control over the international fin market are recommended.