Effects of mesh size on catch efficiency and catch composition of multifilament trammel nets in Beymelek Lagoon (Antalya, Türkiye)

Mesh size strongly influences catch efficiency and catch composition in trammel-net fisheries. This study evaluated the effects of four different inner panel mesh sizes (18, 22, 26, and 30 mm) on catch efficiency, catch composition, and discard proportions of multifilament trammel nets in Beymelek Lagoon (Antalya, Türkiye). Samples were obtained at four stations monthly from January to December 2019, using the haul-seine (voli) method. Catch per unit effort (CPUE) was analysed using a linear mixed-effects model with mesh size, sampling month, and sampling station as fixed effects and fishing operation as a random effect. Mesh size affected log-transformed CPUE (P <0.001), an effect that represents the combined influence of mesh size and panel position (confounded by the fixed panel order) rather than mesh size alone. Sampling month and station also contributed to variation in catches. Estimated marginal means indicated that the 18-mm mesh had a CPUE significantly lower than the 22, 26, and 30 mm meshes, but the three larger sizes were not significantly different from one another. The weight-based discard proportion was highest at the 18 mm mesh (14.4%) and significantly higher than at the 22, 26 and 30 mm meshes, which did not differ from one another; by number, discard proportions did not differ significantly among meshes once over-dispersion was accounted for. Increasing the inner-panel mesh size from 18 to 22 mm was associated with higher catch efficiency. Both catch efficiency and discard composition should therefore be considered when selecting an appropriate mesh size to support the sustainable management of Mediterranean lagoon fisheries.