Applying multi-mesh gillnet to monitor fish communities in neotropical rivers

Abstract Neotropical fish diversity has been declining, driven by increasing human pressures. This accelerating loss underscores the urgent need for standardized methods capable of reliably monitoring these communities. Here, we evaluated the effectiveness of nordic multi-mesh gillnets for sampling fish communities in the Uruguay River. Species were captured from small to large mesh sizes (5–55 mm, knot to knot). Model performance varied among species, with clear evidence of size-selectivity. Size bias was observed primarily for the smallest length classes of Siluriformes species trapped in larger meshes. Nordic multi-mesh gillnets were efficient at catching small-bodied species, while their efficiency decreased for large-bodied species. These findings indicate that nordic multi-mesh gillnets are useful for monitoring Neotropical fish communities but require size-bias correction, particularly for Siluriformes. Although our study supports the use of these nordic multi-mesh gillnets, it demonstrates that they should be complemented with larger mesh sizes if large-bodied fish need to be sampled in Neotropical rivers.