Effects of the static fishing gears, gillnets and longlines, on benthic habitats

Abstract This study examines the ecological impacts of static gears (gillnets and longlines) on benthic habitats. To achieve this, two surveys were conducted on circalittoral rocky habitats structured by the yellow scleractinian coral D. cornigera and the sponge Phakellia spp. The habitat quality, in terms of density, four diversity indices, and biological traits responses, was analyzed in relation to a fishing effort gradient obtained from VMS data. Additionally, Principal Component Analysis (PCA) and Redundancy Analysis (RDA) were applied to assess the relationships between environmental and biological variables, providing insights into the key drivers of community changes under different fishing pressures. Gillnets caused significant damage to structuring species, reducing their densities and altering community traits. The rigid, branched structure of D. cornigera makes it highly susceptible to gillnets, which drift or drag through habitats, causing physical damage. In contrast, longlines showed minimal effects except at high effort levels, where Phakellia robusta experienced density declines. The study highlights the need for gear-specific spatial management, emphasizing restrictions on gillnets in highly sensitive habitats. Tools such as the BESITO index, developed for trawling impacts, could be adapted to assess gillnet effects but require broader pressure gradients and reference zones for calibration. For longlines, further studies are needed in more vulnerable habitats with larger species (e.g. Asconema setubalense) to develop a specific index for managing these fisheries. Future research should refine ecological indicators linked to pressure gradients, enabling habitat quality mapping to guide policies.