Learned hook avoidance of lemon sharks (Negaprion brevirostris) based on electroreception and shock treatment

Abstract

Long-line surveys, conducted over the past 24 years from Bimini, Bahamas reveal a decline of 83% in the number of lemon sharks caught annually compared with catches for the same period 20 years ago. We suggest that resident lemon sharks might have learned to avoid long-line equipment based on their ability to detect electric fields. We tested whether juvenile lemon sharks were able to learn to avoid baited metal hooks. Six sharks were individually presented with two visually similar, baited hooks: a metal circle hook and a plastic replica. If the sharks attempted to feed from the control hook (plastic), they were undisturbed and allowed to take the bait. If the sharks attempted to feed from the metal hook, they were mechanically disturbed by the observer to create a negative stimulus. To test for active learning, the correct response (taking the bait off the plastic hook) was correlated with the number of experimental sessions. Despite an average of 146 trials, statistical evidence for learning in any of the sharks could not be conclusively demonstrated. Thus it was not possible under the present experimental conditions to confirm whether lemon sharks could actively avoid long-line hooks using electroreception.

Keywords:

• Conditioning
• electroreception
• hook avoidance
• learning behaviour
• lemon sharks

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

We would like to thank all the staff and volunteers at the BBFS for their help throughout this investigation. We are also very grateful to Dr Stephen Kajiura for letting us use his sharklab at the Florida Atlantic University and his assistance with the electrical field measurements. Special thanks go to Prof. Dr Ulrich Saint-Paul (ZMT, Bremen, Germany) for his advice and support throughout the duration of this study. This project was partially supported by a DAAD scholarship.

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