MEPS 753:137-154 (2025)  -  DOI: https://doi.org/10.3354/meps14765

ABSTRACT: Baited pelagic underwater videos are increasingly being used to assess ecological indices but they can also be effective in recording the behaviour of pelagic species attracted to the bait. In this study, the behaviour of 79 blue sharks Prionace glauca was recorded using drifting pelagic baited remote underwater video system (BRUVS) rigs, deployed outside the Professor Luiz Saldanha Marine Park, Portugal. Juveniles were more frequently sighted over epipelagic (depth between 60 and 200 m) and mesopelagic zones (200-1000 m), while adult sightings were more common further offshore, particularly over canyons (1200-2000 m). Importantly, juvenile sightings were more frequent in spring (breeding season), suggesting that the study area is likely an important nursery habitat. Blue sharks primarily exhibited inspection activities around the BRUVS. Generalised linear models indicated that visibility, distance to the shore, bathymetry and temperature influenced their behavioural patterns. Moreover, juveniles interacted with the BRUVS for a longer time (mean duration: 0.4 min) than adults (0.2 min). A preliminary analysis of blue sharks’ reaction to boat presence suggests that boat noise decreased both the duration of interaction with the BRUVS and the range of observed behaviours. This study provides valuable insights into the behaviour of this species in its natural environment, which is relevant for management and conservation efforts.

KEY WORDS: Baited remote underwater video systems · BRUVS · Blue shark · Foraging behaviour · Noise pollution