Human-Shark Interactions: Citizen Science Potential in Boosting Shark Research on Madeira Island

Sharks are regularly considered to be an indicator of the ocean ecosystem's health and are generally difficult to study in their natural environment. Citizen science has been increasing, being a cost-effective method for particularly important species that have low encounter rates or are logistically challenging to sample. Madeira Island has a considerable gap in terms of its coastal shark species data and studies, which this work aims to complement. To achieve this goal, online questionnaires to citizens and specific interviews of spearfishers were conducted, with questions related to species size, distribution, and behaviour. Exactly 129 reports of shark sightings were obtained, including seven different species exhibiting four different types of behaviour around the coastal areas of the different municipalities of Madeira Island. Individuals seem to aggregate around the east and west edges of the island due to localised upwelling phenomena. Also, a relation was found between size and distance to coast and depth, as smaller sharks tend to stay close to the shore, probably reflecting the role of Madeira as a nursery area, but further studies are necessary to confirm the reliability of this hypothesis.