Improving the size selectivity of crayfish fyke-net codend, applying the hexagonal mesh and sorting grid

Context Owing to the use of fyke-nets with poor size selectivity in crayfish fishery, 40.7% of the landed undersized catch is discarded as bycatch.Aims This study investigated the effects of using hexagonal mesh (Hex34) instead of diamond nets (Com34) in the traditional crayfish fyke-net and the application of a sorting-grid (SG20, SG25, SG30) and stiff-rigged net (SRN34, SRN42, SRN50) on size selectivity.Methods A covered codend technique was used for determining the size selectivity of codends.Key results The average length at 50% retention probability (L50, in total length) for the trial groups of Com34, Hex34, SG20, SG25, SG30, SRN34, SRN42 and SRN50 was estimated as 9.1, 9.5, 10.1, 11.0, 12.3, 10.0, 10.3 and 11.1 cm respectively. Additionally, the discard rates were computed in the same order as 37.0, 27.3, 14.9, 5.8, 1.9, 19.1, 9.4 and 7.7%.Conclusions In conclusion, commercial crayfish (Com34) fyke-nets have a significantly high discard rate. In the modifications tested, the discard rate has been reduced to as low as 1.9%. When taking into account both L50 and fishing efficiency indicators, SRN42 was determined as the most successful trial group.Implications The application of the study results will make a significant contribution to the sustainability of natural crayfish stocks of Turkiye.

Crayfish are important freshwater invertebrates both ecologically and economically. In Turkey, there is no aquaculture of this species, and it is solely produced through fishing. Owing to poor size selectivity of the fyke-nets used in harvesting this species, the rate of undersized catch is quite high (40.7%). This study aimed to enhance the size selectivity of fyke-nets through various manipulations.