Estimation of gillnets selectivity for greater lizardfish, Saurida tumbil (Bloch, 1795) in coastal waters of the Oman Sea

The selectivity of greater lizardfish (Saurida tumbil), which is one of the most abundant economic species caught by gillnets in the northeast of the Oman Sea, Iranian waters, was studied. Sampling was conducted from February to March 2021. Four types of gillnets with mesh sizes of 4.8, 6.3, 10.0, and 15.3 cm were used and 857 fish specimens were collected. The catch patterns, including (snagged, gilled, wedged, and entangled) for S. tumbil were observed in gillnets. For 4.8 and 6.3 cm mesh sizes, more than 70% of the catch was mainly obtained by gilled, followed by wedged, and no found of entanglement. For 10.0 and 15.3 cm mesh sizes, the catch of 10.0 mesh size included 16% of fish caught from wedging, though most of the fish was caught by entanglement. In particular, all catches at 15.3 cm were due to entanglement. Estimation of gillnets selectivity for S. tumbil was performed using the SELECT method. The SELECT method was used to fit three various gillnet selectivity models (log-normal, skew-normal, and bi-normal). Gillnets selectivity was best estimated by a bi-modal Selection curve. The mean lengths ±SE were estimated as 31.48±0.71, 40.3±0.97, 40.1±0.75 and 43.9±1.05 cm for 4.8, 6.3, 10.0 and 15.3 cm mesh sizes, respectively. Mean lengths increased with increasing the mesh size. Most of the fish caught in the 4.8 and 6.3 cm mesh sizes were below the first maturity length (Lm50). Considering the relative efficiency set as 0.5, that was L50 (50% retention length), the optimal mesh size was determined to be 10.0 cm. Therefore, to protect S. tumbil stock and the sustainability of the fishing resource, the gillnet mesh size should be at 10.0 cm to manage S. tumbil in this area.