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Shark repellents: a comparison of alternative methods to mitigate bycatch
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Resumo(s)
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.
Descrição
Tese de mestrado, Ecologia Marinha, 2023, Universidade de Lisboa, Faculdade de Ciências
Palavras-chave
repelentes de tubarão captura acidental de tubarões redução de mordidas novos materiais Teses de mestrado - 2023