Fyke net size selectivity as a sustainability key for European eel (Anguilla anguilla): current status and potential improvements from Türkiye

In this study, the size selectivity of traditional fyke nets employed in the European eel (Anguilla anguilla) fishery—a species whose natural stock has significantly declined due to predominantly anthropogenic pressures—was estimated, and the effects of specific modifications on this size selectivity were investigated. Fishing trials were conducted monthly from October 2023 to September 2024 in Bafa Lake (Aydın, Türkiye), a significant eel fishing centre in the country. The covered codend technique was employed to estimate length selectivity. This study investigated the effects on size selectivity of both varying mesh sizes (five experimental groups) and grids with different shapes and mesh sizes (eight experimental groups). For the traditional fyke net rigged with 32-mm diamond mesh, the L50 (average length at 50% retention probability) was estimated to be below the Minimum Conservation Reference Size (MCRS), and the discard rate was estimated at 27.25%. Increases in both codend mesh size and grid openings resulted in an increase in L50 length and a decrease in discard rate; however, these changes also led to economic losses. The use of 40-mm diamond mesh in the codend increased the L50 length of the catch to 48.32 cm and reduced the discard rate to 4.96%. In this context, considering a 50 cm MCRS, it is recommended that the mesh size of fyke nets used in eel fisheries in Türkiye should be above 40 mm. The placement of rectangular mesh grids with dimensions of 33 × 40 mm (width x height) or hexagonal mesh grids with a side length of 27 mm (54 mm diagonal) at the entrance of the fyke net could prevent 40% of the silver eels in Bafa Lake from entering the net.