A study on settlement performance of falling-net based on GAM

In order to comprehensively understand the settlement performance of falling-net, as well as to provide references for the development of falling-net model test and improvement of fishing gear and method, we conducted sea trials in the central-southern South China Sea in March 2016, and studied the settlement performance of falling-net based on polynomial regression and Generalized Additive Model (GAM). The results show that: 1) Free settlement was a more critical factor affecting the total settlement depth. 2) 90.0–119.9 s was an appropriate free settlement time based on the settlement performance of the falling-net. 3) The free settlement speed first increased in a short time and then decreased, the maximum value occurring at 10^th s. The damping settlement speed remained relatively stable in the first 50 s with little change, but then decreased rapidly. 4) Free settlement time (T_f), wind speed (S_w), and direction angle between wind and current ( \alpha ) had significant influences on free settlement depth. T_f, S_w, drift speed of fishing boat (S_b) and \alpha had significant influences on damping settlement depth. The study suggests that: 1) The influences of S_w and \alpha on free settlement depth and damping settlement depth are complex and non-linear, and may affect the settlement of falling-net through waves and changing the relative position between fishing boat and falling-net. 2) S_b has a significant influence on damping settlement depth. This may be caused by the fact that S_b affects the degree of closure of net-mouth and hauling of purse line.