张网渔具选择性研究中网次间差异的探讨

传统渔具选择性研究大多忽略了非可控因素(如水深、风流等)造成的网次间差异.本试验使用套网法作为选择性试验方法,对5种不同规格网囊的张网网具进行了25网次的试验(各网具分别5网次),对黄鲫(Setipinna taty)渔获进行叉长测量并进行选择性分析.结果显示,考虑网次间差异模型的选择性参数a、b与传统的联合网次方法所估算的选择性参数没有显著性差异(p>0.05),但是参数估计的标准差却存在着显著性差异(p分别为0.008、0.016).因此认为联合网次方法估算选择性参数会低估参数估算的标准差,从而导致低估参数估计的不确定性,造成虚假的显著性统计结果,最终导致不能准确地推断出不同网具之间的选择性差异.

The Discussion of the Between-haul Variation on the Research of Selectivity of Stow Net

Most of the researches of selectivity of fishing gear ignored the between-haul Variation which is caused by uncontrolled factors such as the depth of water, direction and velocity of wind and current. Five different kinds codes of stow net were tested in the experiment and 25 hauls were implemented successfully (each code with 5 huals respectively) , using the cover net method as the experimental method. The fork length of the Anchiovy (Sepipinna taty) was measured and the research of selectivity was carried out based on these data. The result shows that selectivity parameters a, b estimated from combined haul method are not significantly different from those estimated from the model in which the between-haul variation is taken into account (p much larger than 0. 05 ). However, there is significant difference between the standard errors of the estimated parameters (p values are0. 008 and0. 016 respectively). As a result, it is considered that the combined-haul method will underestimate the standard error of the estimated parameters and cause the uncertainty in the estimation of the selectivity parameters, which will probably lead to the invalid statistical significance and incorrect inferences about the differences between nets.