Gillnets

Gillnets are nets that are hung vertically in the water column to entangle fish by their gills as they attempt to swim through. They function as barriers that species must pass through, rather than actively chasing prey. Gillnets come in various forms, including set gillnets, which are anchored in place, and drift gillnets, which are allowed to drift with currents. They are used in coastal, riverine, and offshore waters.

Construction and setup: A gillnet consists of a sheet of netting with a float line along the top and a lead line along the bottom, creating a vertical curtain. Mesh size and net material influence the species and size of fish retained; smaller mesh catches smaller fish while larger mesh allows larger fish to pass by or be gilled. Nets are deployed in a location, either fixed to the bottom or buoyed and anchored at ends, and retrieved by hauling the line.

Usage: Gillnets are employed for many species such as salmon, cod, and carp, and in both commercial and recreational fisheries. They can be set for specific depths and durations, from a few hours to several days, depending on regulations and conditions.

Impacts and regulation: Bycatch of non-target species, including seabirds, turtles, and mammals, is a major concern. Ghost fishing can occur when lost or abandoned nets continue to catch wildlife. To mitigate impacts, many jurisdictions impose gear restrictions, seasonal closures, bycatch reduction devices, escape panels, or complete prohibitions in sensitive habitats.

Variations and trends: Advances include different mesh sizes, monofilament versus multifilament nets, and BRDs (bycatch reduction devices) to improve selectivity. Regulating bodies and enforcement regimes vary by country and region, reflecting differences in ecological concerns and fisheries management.