Size selectivity of trammel nets applied in small-scale fisheries of Lake Nasser, Egypt

In spite of the significance of trammel nets for small-scale fisheries (SSFs) in Egypt in what concerns landings, economic value, vessels and fishermen numbers, few studies on their size selectivity have been conducted. This study investigates the trammel nets’ size selectivity as a key métier of SSFs in three areas of Lake Nasser. A full survey of the commercially used trammel nets and experimental fishing trials using different models of trammel nets were carried out. The results of the survey indicated that the catch had a limited species variation, which included mango tilapia (Sarotherodon galilaeus), Nile tilapia (Oreochromis niloticus), and redbelly tilapia (Coptodon zillii). Regarding experimental fishing, four different mesh sizes (83, 95,108, and 120 mm) were applied and the nets selectivity curves indicated that the size-frequency distributions of all species showed shifting of the mean length to the right with increased mesh size in all nets. The best model was determined from the outcomes of model comparisons and it was the log-normal model for O. niloticus and bimodal for both S. galilaeus and C. zillii. This information can be useful in applying the technical measures for fisheries that depend on the trammel nets.