New Study Reveals Blue Shark Behavioural Patterns and Impact of Boat Noise in the Portuguese Coast.
Researchers from MARE - Marine and Environmental Sciences Centre and FISHBIOACOUSTICS LAB deployed baited remote cameras off the coast of Arrábida Natural Park to study the behaviour of blue sharks (Prionace glauca) and assess the impact of boat noise. This study, part of Noelia Ríos' PhD research within the INFORBIOMARES project, has been published in Marine Ecology Progress Series (https://doi.org/10.3354/meps14765).
Observing blue sharks in their natural habitat is challenging, but the cameras recorded 79 individuals, revealing distinct behavioural patterns between juveniles and adults depending on the season and distance from shore. Juveniles were more frequently sighted in shallower waters during spring, coinciding with the species' breeding season, highlighting the ecological importance of the Lisbon and Setúbal Canyons as a potential nursery ground. The study also found that boat noise altered shark behaviour, suggesting a possible impact on their foraging efficiency, warranting further research.
Sharks play a crucial role in maintaining marine ecosystem stability, yet overfishing—both targeted and bycatch—puts immense pressure on their populations. The blue shark is one of the most heavily fished shark species globally and was classified as 'Near Threatened' by the IUCN Red List in 2019. In Portugal, it is the most commonly caught shark species in surface longline fisheries, which primarily target tuna and swordfish but often catch sharks attracted to the bait.
Ref: Ríos, N., Jimenez, M., Franco, G., Ramos, G., Pais, M. P., Gonçalves, E. J., Amorim, M.C.P. & Silva, G. (2025). Characterising the behaviour of bait-attracted blue sharks Prionace glauca using pelagic drift video. Marine Ecology Progress Series, 753, 137-154. https://doi.org/10.3354/meps14765