Numerical simulation-based hydrodynamic interaction of bottom-set gillnet with current and ecological implications

Abstract

Bottom-set gillnets, consisting of flexible netting, are extensively utilized in coastal waters worldwide for capturing aquatic organisms. However, their efficiency and selectivity can be significantly affected by changes in shape and mesh opening due to external forces during practical operations. In this study, a comprehensive investigation of knotless nylon bottom-set gillnets under uniform current conditions was conducted using numerical simulations based on the mass-spring model. The simulations allowed us to calculate the netting configuration, mesh opening, and tension distribution of gillnets under different current velocities. The results suggest that with the increase in current velocity, the tension within the gillnet system shows a progressive increment, with higher tension observed at the diagonal corners. The vertical projection area, or effective operation area, of the netting diminishes with increasing current velocity, which is accompanied by a less uniform distribution of mesh openings. The simulation outcomes are in strong agreement with experimental measurements obtained from a set of model testing carried out in a circulating flume tank. Through simulations of structural optimization, we observed that low-profile gillnets with narrower dimensions exhibit a vertically stretched configuration resembling a wall, with meshes uniformly opened in a diamond-shaped pattern. These findings hold significant implications for the improvement of bottom-set gillnet design and the mitigation of ecological risks posed to marine fauna.