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

Abstract

Background:Tope sharks (Galeorhinus galeus) aggregate in large numbers during spring and summer in closedgulfs 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 aimwas to evaluate the short-term diving behaviour and habitat preferences of tope sharks using electronic tagging.Findings:Five female tope sharks, four adult and one sub-adult, were tagged with pop-up satellite archival tags inthe Natural Reserve of Bahía San Blas, northern Patagonia, during spring 2011 and 2012. High-resolution archiveddata 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 wereno diel changes in preference. Individuals spent most of the time within 10 m of the surface during the day (80%) andat night (83%), and were primarily in water between 17°C and 19°C (day, 75%; night, 70%). Moreover, tope sharksexhibited vertical oscillatory movement (‘yo-yo diving’). Maximum vertical speeds and dive depths were recordedat night. Ascents from depth had a greater speed than descents, overall.Conclusions:Female tope sharks were found in shallow coastal areas during November at Bahía San Blas, near thesurface at relatively restricted depths and temperatures. Longer tracking periods will be important for describingthe species’migratory movements across the south-west Atlantic.