Influence factors on the netting gear loss rate of gillnet in coastal waters of China

The primary source of ALDFG is from the coastal and oceanic fishery and the maximum risk to produce ALDFG is from the coastal fishing industry. Gillnetters along the coast of China accounted for about 56% of the total number of fishing boats along the coast of China in 2018, and were one of the biggest potential source to produce ALDFG in China. Lost netting of gill net can keep the high rate of ghost fishing for more than 2 years. ALDFG produced by the gill net fishery along the coast of China will cause great influence to the coastal marine ecosystems in China. In order to understand the factors and their impact degree on the netting loss rate of gillnet in waters near China, a questionnaire survey was conducted among the Chinese coastal fishermen from June to December, 2019 and the areas covered Liaoning, Shandong, Jiangsu, Zhejiang and Guangdong provinces. The data from 41 gillnetters were collected including 13 variables, i.e. gross tonnage, power, vessel length, vessel age, captain age, annual fishing days, average voyage days, voyage gear carrying weight, net average weight, annual procurement number, annual gear procurement weight, fishing depth and the lost numbers of gillnet netting. Based on the questionnaire survey data, software SPSS 23 was used to analyze the multicollinearity among 12 independent variables, and eliminate gradually 3 variables that had multicollinearity with other independent variables. The remaining 9 independent variables that had no multicollinearity among them were used to analyze the relationship with the netting loss rate of gillnet in waters near China by GAM and to determine the best GAM based on the AIC value. The results indicate that, (1) The factors (explanation deviation) that effect the netting loss rate of gillnet (R_G) in waters near China are as follows: average voyage days (86.8%), annual fishing days (4.2%), voyage carrying netting weight (2.8%), fishing depth (2.4%), gross tonnage (0.9%) and annual gear procurement number (0.1%); (2) The GAM can be used to study the relationship between the netting loss rate of gillnetters and the fishing boat parameters, annual fishing gear procurement information and fishing ground information; (3) With the increase of voyage days and annual fishing days, R_G shows an increasing trend; (4) With the increase of fishing depth and the voyage carrying netting weight exceeding 18000 kg, R_G shows an decreasing trend. The measures recommended to reduce the netting loss rate of gillnetters are as follows: (1) The voyage days should not exceed 30 days and reduce the annual fishing days; (2) According to the gross tonnage of fishing boat, the voyage carrying netting weight should be more than 18000 kg; (3) The fishing depth and fishing area should be regulated according to the height of gillnet gear. We should specify the maximum height of gillnet gear according to the current and seabed topography of the fishing ground in waters near China; (4) The gross tonnage of fishing boat should be smaller than 200 gross tons.