Diving behaviour of the critically endangered tope shark Galeorhinus galeus in the Natural Reserve of Bahia San Blas, northern Patagonia

Juan Cuevas,Mirta García,Edgardo Di Giacomo

doi:10.1186/2050-3385-2-11

Abstract

BackgroundTope sharks (Galeorhinus galeus) aggregate in large numbers during spring and summer in closed gulfs and bays in northern Patagonia; these locations are considered the main nursery areas for the species. However, little is known about the spatial ecology or diel behaviour of this critically endangered species. The aim was to evaluate the short-term diving behaviour and habitat preferences of tope sharks using electronic tagging.FindingsFive female tope sharks, four adult and one sub-adult, were tagged with pop-up satellite archival tags in the Natural Reserve of Bahía San Blas, northern Patagonia, during spring 2011 and 2012. High-resolution archived data were collected for 40 days, including 29 days for two recovered tags. Sharks travelled up to 51.2 km after release. Archived data indicated that female tope sharks preferred to remain within 24.5 m of the surface and that there were no diel changes in preference. Individuals spent most of the time within 10 m of the surface during the day (80%) and at night (83%), and were primarily in water between 17°C and 19°C (day, 75%; night, 70%). Moreover, tope sharks exhibited vertical oscillatory movement (‘yo-yo diving’). Maximum vertical speeds and dive depths were recorded at night. Ascents from depth had a greater speed than descents, overall.ConclusionsFemale tope sharks were found in shallow coastal areas during November at Bahía San Blas, near the surface at relatively restricted depths and temperatures. Longer tracking periods will be important for describing the species’ migratory movements across the south-west Atlantic.

Highlights

The use of shark satellite tagging has increased over the past decade, facilitating the description of migratory patterns, habitat use and diving behaviour for a variety of species [1,2]
Female tope sharks were found in shallow coastal areas during November at Bahía San Blas, near the surface at relatively restricted depths and temperatures
The tope shark, Galeorhinus galeus, is a transient coastal species [3] distributed between Brazil and Argentina in the south-west Atlantic Ocean [4]

Summary

Introduction

The use of shark satellite tagging has increased over the past decade, facilitating the description of migratory patterns, habitat use and diving behaviour for a variety of species [1,2]. The tope shark, Galeorhinus galeus, is a transient coastal species [3] distributed between Brazil and Argentina in the south-west Atlantic Ocean [4]. In the south-west Atlantic Ocean, tope sharks are classified as critically endangered [8], largely as a result of overfishing. This study provides the first observations of short-term diving behaviour and habitat preferences of G. galeus in northern Patagonia and the south-west Atlantic Ocean. Tope sharks (Galeorhinus galeus) aggregate in large numbers during spring and summer in closed gulfs and bays in northern Patagonia; these locations are considered the main nursery areas for the species. The aim was to evaluate the short-term diving behaviour and habitat preferences of tope sharks using electronic tagging

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Discussion

Conclusion