温台渔场3种经济鱼类体长频次分布与采样量间关系的比较

Comparison of the relation between the length frequency distribution and sample size for several commercial fish species in the Wentai fishing ground

摘要:

为了量化和比较温台渔场3种经济鱼类体长频次分布与实际收集的观测样本之间的关系，本研究基于收集的样本体长信息能够反映研究区域鱼种真实的体长组成信息这一假设，根据春、夏两季在温台渔场采集的3种经济鱼类 (小黄鱼、银姑鱼和龙头鱼)的体长数据，利用计算机模拟方法设计了不同的样本量方案。利用均方差异值(mean square difference, MSD)来量化不同体长组数据之间的频次分布差异，t检验来检测3个研究对象的平均体长是否存在季节性差异。结果显示，①3个研究对象的平均体长存在显著的季节性差异，春季小黄鱼的平均体长 [(135.20±19.62) mm]大于夏季小黄鱼 [(123.90±19.47) mm]，春季银姑鱼的平均体长 [(105.00±46.84) mm]大于夏季银姑鱼 [(86.14±21.60) mm]，夏季龙头鱼的平均体长 [(199.60±17.40) mm]要大于春季 [(180.00±17.92) mm]。此外，3个研究对象的主要体长范围也具有季节性差异。鱼种间的生物学差异及其体长组成季节性差异会影响体长频次分布精度与不同样本量之间的关系；②模拟研究中体长组个数的设置会影响体长频次精度的估计。当样本量较小时，MSD值随体长组个数的增加而增加，研究结果认为在有效样本量为50的假设前提下，体长组设置为10组对于体长频次精度的估计更加有利。③体长频次分布的精度变化可作为设置有效样本量的依据。在基于单个站点50个样本量能够反映温台渔场3种经济鱼类真实体长结构的假设下，根据研究结果，建议将春季小黄鱼的采样量设置为30~40个，春季银姑鱼的采样量设置为42~48个，春季龙头鱼的采样量设置为34~40个。

Abstract:

One of the basic requirements for conducting fishery stock assessment and management research is to obtain effective fishery and biological information for target species. Length frequency distribution (LFD) can provide insight into fishery population dynamics and is easier to collect compared with other data type such as age structure and abundance index. However, it is hard to determine the effective sample size required to describe the length structure for specific fish stock. The quantitative relationship between the precision of LFD and the sample size of fish length data could be regarded as an indicator to optimize the sample size of fishery survey design. In order to quantify and compare the relationship between the precision of LFD and sample size of fish length data for three commercial fish species (Larimichthys polyactis, Pennahia argentata and Harpadon nehereus) on the Wentai fishing ground, a simulation study was conducted to calculate the mean square difference (MSD) of LFD based on actual sample size and various simulated sample sizes based on observed length data collected during spring and summer on the Wentai fishing ground. The simulation study assumed that the observed length data are able to reflect the true length structure for three species. In addition, t-test was used to examine the significant difference of mean length for three species in spring and summer. The results showed that, ① Factors such as biology difference and seasonal variation would affect the relationship between the precision of LFD and sample size. All three species showed significant difference of mean length in spring and summer. The dominate length ranges for three species were different between two seasons. ② The accuracy for estimating the precision of LFD would be impacted by the setting numbers of size bin. The MSD values increased with the number of size bin when sample size was small and this relationship did not have seasonal variation. We recommend setting 10 size bins when the effective sample size was set at 50. ③ The precision of LFD could be considered as an effective indicator to optimize sample size. Given the assumption that 50 fish samples per each station can reflect the true length structure for three species in this study, we recommend setting the sample size at the range of 30-40 individuals for L. polyactis, 42-48 individuals for P. argentata and 34-40 individuals for H. nehereus in spring.