Migration and habitat use of formerly captive and wild raggedtooth sharks (Carcharias taurus) on the southeast coast of South Africa

Abstract

Releasing aquarium-held sharks when no longer needed by the holding institution may help mitigate the impacts that aquaria have on declining wild populations. To investigate the viability of releasing display specimens, four raggedtooth sharks (Carcharias taurus) that had been held at Two Oceans Aquarium, Cape Town were released back to the wild between 2004 and 2008. To test the hypothesis that they survived and that their movement patterns were similar to wild conspecifics, wild-caught sharks were also tagged and released at the same time and locality. Aquarium- and wild-caught sharks were equipped with pop-up archival (PAT) tags, VEMCO ultrasonic tags, and numbered spaghetti dart tags. With the exception of one individual, all the aquarium-released sharks survived. Both aquarium-released and wild-captured sharks displayed eastward movements and travelled hundreds of kilometres after release. Data from the PAT tags indicated that individuals from both groups swam mainly in shallow waters, but dived as deep as 80 m to mid-shelf waters. A wide temperature tolerance was exhibited as they travelled though temperatures ranging from 10 to 22^oC. Movement tracks of the sharks revealed ‘station keeping’ and an autumn migration between April and May. Rates of movement between individuals were variable. The depth range recorded in this study supports published information on habitat and prey choice. This study illustrates that this species can survive aquarium release after years of captivity and that they appear to behave similarly to wild-caught conspecifics.

Keywords:

• Raggedtooth sharks
• pop-up archival tags
• shark behaviour
• aquarium release

Published in collaboration with the University of Bergen and the Institute of Marine Research, Norway, and the Marine Biological Laboratory, University of Copenhagen, Denmark

Published in collaboration with the University of Bergen and the Institute of Marine Research, Norway, and the Marine Biological Laboratory, University of Copenhagen, Denmark

Acknowledgements

This project would not have been possible without the financial support of Two Oceans Aquarium, Save Our Seas Foundation, Bayworld and the National Research Foundation. Assistance by TOA staff with capture, transport and release of the sharks is gratefully acknowledged. This research project was part of the Maxine, Science, Education and Awareness Programme (M-Sea), which included a website with broad-based shark related information developed by AfriOceans Conservation Alliance. Michelle Du Toit generated the GIS-based maps. This research complied with all laws in the Republic of South Africa. Constructive comments from two anonymous reviewers and the editors improved an earlier draft of the manuscript.

Notes

Published in collaboration with the University of Bergen and the Institute of Marine Research, Norway, and the Marine Biological Laboratory, University of Copenhagen, Denmark