Using functional diversity to assess fish community susceptibility to multi-species coastal gillnetting in the East and South Brazilian Shelves

The Brazilian coast hosts various fisheries, including the poorly understood practice of gillnetting, known for being species-unselective, that is, it reaches far more species than its intended targets. We examined fish community susceptibility between gillnet catch in the East Brazilian Shelf (Large Marine Ecosystem [LME] 16) and the South Brazilian Shelf (LME 15) through functional diversity. In both regions, fusiform demersal bony fishes were the most susceptible to gillnets (e.g. drums, grunts). However, the species representing these functional entities varied and were proportionally different due to regional community composition and species availability. Gillnets in LME 15 generally reached larger, higher trophic level fishes and larger sharks, while LME 16 gillnets reached more compressed/short, lower trophic level bony fishes. Functional indices suggest this fishery is taxonomically and functionally unselective. Functional evenness was lower in LME 15 compared to LME 16 (in which more functional entities were reached), contrary to the known pattern of lower evenness in tropical environments, suggesting that tropical fish communities are more susceptible to gillnets. Mesh size is key in modulating species and functional selectivity, highlighting its importance as a target of management. More species and functional entities were reached in deeper areas and during spring and autumn in LME 15 (especially sharks and catfishes). These seasonal and spatial conditions demand more attention, as they could potentially have roles in plans to minimize bycatch. We demonstrate the potential of functional diversity in assessing small-scale fisheries, and highlight the need for comprehensive fisheries monitoring to enhance sustainability and minimize bycatch in this fishery.