The dynamic simulation of the pelagic longline deployment

Abstract

It is important to understand the deployment of pelagic longline gear for reducing non-target species interactions, and increasing fishing efficiency. In the present study hook depth data, simultaneous settlement data, and three-dimensional (3D) ocean current data were collected aboard the fishing vessel “Huananyu 716” while operating near the Cook Islands (10°50'S–15°05'S, 156°14'W–168°01'W) from September 2012 to November 2012. Taking into account the hydrodynamic force of longline fishing gear floats, dynamic equations of pelagic longline gear deployment were built using the lumped mass method and solved by the Euler–Trapezoidal method. The space shape and tension distribution of the longline gear were analyzed, a model was derived, and then verified. Results indicate that: (1) there were no significant differences (P>0.05) between the hook depth measured by Temperature Depth Recorders (TDRs) during settlement and the simulated hook depth, except for the first hook (P<0.001); (2) during the settlement, the tension of the nodes of the main line increased greatly; and (3) the fluctuations of gear space shape, tensile, and hydrodynamic forces of the main line nodes were closely associated with current velocities of the water column where the gear was located. The stronger the current, the larger the fluctuation in spatial location of the fishing gear. These results suggest that the dynamic model of longline fishing gear developed in the present study could be used: (1) to calculate the tension of nodes and floats in a variety of ocean current conditions; (2) to present the dynamic process of the deployment and settlement of each node and the 3D shape of the longline in a variety of ocean currents