应用一般线性模型估算鲐、鲹大型灯光围网渔业的捕捞效率

Fishing efficiency for mackerel and scad in the large light purse seine fishery estimated by generalized linear model

大型灯光围网是我国近海捕捞鲐、鲹的主要作业方式之一,探讨和估算捕捞效率对其渔业资源评估和管理有着重要的意义。根据1998-2003年东黄海我国鲐、鲹大型机轮灯光围网生产统计数据,利用一般线性模型对其捕捞效率进行了估算,讨论了线性模型误差结构的选择及数据变换对结果的影响。根据鲐、鲹单位捕捞努力量的渔获量(CPUE)数据呈正偏,以及CPUE均值与方差在对数尺度下的线性关系,选择了负二项分布、伽马分布与对数正态分布作为误差分布。研究表明,由于CPUE零值的存在,其对误差分布结构有很大影响。当采用最大似然估计时,对数正态分布与伽马分布的CPUE需加一常数(δ),δ取值对结果有较大影响,随δ增大将使估计的捕捞效率对比度得到压缩。为了避免δ取值的影响,同时采用了Delta-GLM方法。通过不同模型的比较,选择了Delta-负二项或Delta-伽马方法。根据Delta-负二项或Delta-伽马方法估算结果,各渔业公司间的捕捞效率存在很大的差异,且具有明显的区域性。32°N以北海区,捕捞效率高低依次为苏渔、辽渔、青渔、舟渔、宁渔、沪渔;台湾东北部海区,捕捞效率高低依次为苏渔、辽渔、舟渔、沪渔、宁渔、青渔。

Reliable estimation of effective fishing effort, which is proportional to fishing mortality, can provide information critical to the assessment and management of fisheries resources. To estimate effective fishing effort, we need to understand fishing efficiency and factors that may influence it. In this study fishing efficiency was estimated for mackerel and scad purse seine fisheries using generalized linear model. This was done for different companies involved in the fisheries. Different choices of error structures were considered in the estimation and their impacts on the estimation were discussed. The negative binomial distribution, gamma distribution, and log-normal distribution were chosen as error distributions according to log-linear regression of variance versus log-mean of CPUE （catch per unit effort）. Zero CPUE values had great impacts on the assumed error structure and adding a constant （δ） to CPUE was needed for gamma distribution and log-normal distribution in maximum likelihood estimation. As 8 increased, the contrast of estimated fishing efficiency was reduced greatly. Delta approaches were also chosen as an alternative way to deal with zero CPUE value in this study. Comparing the results of different models, we considered Delta- negative binomial and Delta-gamma as most appropriate error distributions for this study. The results showed that the fishing efficiency differed greatly among fisheries companies and among different areas.