Study on the blue shark highlights the importance of protecting and preserving underwater cannons

Study reveals blue shark behavior patterns and the impact of boat noise on the species. Crucial to maintaining the stability and health of marine ecosystems, the blue shark is one of the most commonly caught shark species worldwide. Classified as 'Near Threatened' by the International Union for Conservation of Nature in 2019, in Portugal it is often the victim of the surface longline fleet, which targets large fish such as tuna and swordfish. ​

A team of researchers from MARE deployed remote camera systems with bait off the coast of the Arrábida Natural Park to observe and characterize the behavioural patterns of blue sharks (Prionace glauca), and the effect of boat noise in terms of behavioural changes. A study carried out as part of the PhD thesis of researcher Noélia Ríos, as part of the INFORBIOMARES project, has just been published in the journal Marine Ecology Progress Series.

These highly sensitive species are very difficult to observe and study, especially when it comes to their behavior in the wild. The cameras used by the researchers were able to record the behavior of 79 sharks, revealing different patterns between juveniles and adults depending on the season and distance from the coast.

The research revealed that juvenile sharks were sighted more frequently in shallower waters and during spring, which coincides with the species' breeding season, thus reinforcing the enormous importance of the area off the Arrábida Natural Park, in the Lisbon canyon area, as a potential nursery area for the blue shark. These observations lead the researchers to defend the need to look at underwater canyons as areas to be protected and preserved.

The study also revealed that, in the presence of boat noise, blue sharks altered some behavioral patterns, suggesting that there may be a hidden effect of noise on the efficiency of foraging and catching food, paving the way for further dedicated studies to confirm this hypothesis.  

Sharks play a crucial role in maintaining the stability and health of marine ecosystems. Excessive commercial fishing of these species, whether directed or bycatch, puts enormous pressure on shark populations globally, causing ecological imbalances with repercussions throughout the ecosystem. 

The blue shark is one of the most commonly caught shark species worldwide, and in 2019 it was classified as 'Near Threatened' by the IUCN Red List. In Portugal, it is the species of shark most caught by the surface longline fleet, a fishery using lines and hooks, targeting large fish such as tuna and swordfish, but which often catches sharks, attracted by the bait.

Text obtained from Press Release