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Abstract
The coastal gillnet fishery is crucial for the livelihoods of fishers in Phan Thiet City, Binh Thuan Province. However, this activity faces the risk of overexploiting juvenile small pelagic fish due to the prevalent use of small mesh sizes, while quantitative data on the local impact of such practices remains lacking. Therefore, this study aimed to assess the exploitation level of immature fish and determine the selectivity parameters (optimal length, Lopt; selection factor, SF) for four common mesh sizes of monofilament gillnets (24, 26, 30, and 34 mm) for four key target species: Goldstripe sardinella (Sardinella jussieu), Dotted gizzard shad (Konosirus punctatus), Japanese scad (Decapterus maruadsi), and Indian mackerel (Rastrelliger kanagurta). Data were collected from 160 fishing hauls from April to May 2022, analyzing the fork length (FL) of 6,995 individuals. Holt’s (1963) method was employed to estimate gear selectivity. The results revealed a high proportion of immature fish being caught, particularly by the 24 mm (>98%) and 26 mm (>92%) mesh sizes, as their optimal retention lengths (Lopt) were considerably lower than the length at first maturity (Lm) for the target species. Even with the 30 mm and 34 mm meshes, the Lopt remained lower than the Lm for most species (with S. jussieu being a partial exception), and selection factors (SF) ranged from 3.5–3.7. This implies that the widespread use of small-mesh gillnets in Phan Thiet results in poor selectivity towards juveniles, exerting significant fishing pressure on stock recruitment potential. Consequently, this study provides a crucial scientific basis for revising fishing gear regulations to ensure the sustainability of the local coastal gillnet fishery.
Key words: Juvenile fish, Size selectivity, Gillnet, Phan Thiet, Fisheries management