Effect of mesh size in monofilament and multifilament gillnets on catch efficiency in the Black Sea whiting (Merlangius merlangus) fishery

Gillnets are widely used fishing gear for targeting various fish species. Gillnet fisheries use different gear configurations such as different mesh sizes and number of netting twines (mono- or multifilament) depending on the species targeted. Gillnet fishery targeting whiting (Merlangius merlangus) is one of the economically important year-round fisheries in the Black Sea. However, large bycatch of whiting below minimum landing size (MLS) has led to a stock decrease, questioning sustainability of this fishery. This study evaluated how netting twine construction and mesh size can affect the capture probability of whiting. The results showed that changes in gillnet mesh size significantly affect the capture probability with increased mesh size reducing the average capture probability of undersized whiting from around 60%–5%. The results showed no significant differences in the average catch efficiency between monofilament and multifilament gillnets of the same mesh sizes; however, monofilament gillnets showed an increased catch efficiency for some length classes of whiting > MLS. Based on these results, use of 32 or 34 mm mesh size monofilament gillnets is advisable for sustainable whiting fisheries management in the Black Sea. •Different mesh sizes and netting twines are used in gillnet fisheries.•This study evaluated gillnet twine construction and mesh size effect on catches.•Changes in gillnet mesh size significantly affect the capture probability of whiting.•Increased mesh size reduced the average capture probability of undersized whiting.•Monofilament nets had an increased catch efficiency for some whiting length classes.