Shark populations have been suffering a tremendous decrease in recent years, with many species currently threatened, mainly due to overfishing and climate change. Most fishing accounts for sharks occur when they are accidentally captured as bycatch. To mend this issue, shark repellent research has been developing over the last 70 years, however, it is mostly hampered by physical or technical constraints that result in no clear solutions. Sharks are behaviorally complex organisms, which only entangles the path to find a single and simple repellent device even more. In this dissertation, the effectiveness of different repellents was tested on a well-studied model shark (Scyliorhinus canicula) based on the most recent advances in the field. Under this context, I exposed sharks to a wide variety of repellents: i) chemicals (necromones), and ii) electrosensory, permanent magnets (neodymium (Nd), ferrite (α-Fe)), repellent X, and a procedural control, that is a component of repellent X, both in control conditions and in a climate change scenario (ocean warming; 19ºC). The present results indicate that the presence of the repellent X significantly decreased the number of shark bites, both under warming conditions and when combined with necromones. Our findings represent a promising step towards finding an effective and technologically simple shark repellent device. The repellent X possess low acquisition costs, no detectable dissolution rates, easy maintenance and appliance, and a positive repelling effect. Furthermore, to improve the repelling effect, a combination of two types of repellents, such as necromones and repellent X, could be used. Future studies should focus on field work experiments, to test the efficency of this repellent on wild shark species. As their populations continue to decline at a rapid rate, the need to develop economic, harmless, and successful shark repellents is more urgent than ever.

Tese de mestrado, Ecologia Marinha, 2023, Universidade de Lisboa, Faculdade de Ciências