南极磷虾声学物质特性的季节变化及其对资源评估的影响

Sound-speed and density contrasts (h and g respectively), two important material properties of Antarctic krill (Euphausia superba), are key for its target strength (TS) modelling and biomass estimates. A few percentage change in the h and g would result as much as 100-fold uncertainty in Antarctic krill biomass estimates. Also, it has been indicated that the acoustic material properties of some Euphausia species would change with their growth, especially the seasoal variation of lipid content. Therefore, a comprehensive study is needed to investigate the seasoal variation of the acoustic properties of Antarctic krill. The proposed project will investigate the seasonal variation of the acoustic material properties of Antarctic krill based on in situ measurement onboard krill fishing vessel through whole fishing season. Meanwhile, the seasonal variation of biological characteristics and lipid content of krill will also be measured to evalute their effects on the material properties. Subsequently, the theorectical TS model of Antarctic krill could be improved by introducing the the seasonal factor of the acoustic material properties. The research will provide evidents for improving the accuracy of acoustical estimation of krill biomass, which will certainly benefit for comprehensive understanding of the marine ecosystem of the south ocean and the sustainable exploitation of Antarctic krill.

声学物质特性(与海水的声速比和密度比)是南极磷虾目标强度模型构建和资源量评估的关键参数。声学物质特性的微小变化会导致南极磷虾资源声学调查评估结果产生成倍的误差。已有研究表明，磷虾类浮游动物的声学物质特性会随其季节生长，尤其是含脂量的变化而变化。因此，有必要对南极磷虾声学物质特性的季节变化规律进行深入研究。为此，本研究将通过搭载南极磷虾渔船开展海上现场实验，对南极磷虾声学物质特性进行整渔季的跟踪测定研究，以探究南极磷虾声学物质特性的季节变化规律；同时，对同步采集的磷虾样品进行基础生物学观测和含脂量测定，分析南极磷虾季节生长及含脂量变化对其声学物质特性的影响。在此基础上，构建和优化南极磷虾目标强度模型，评估声学物质特性季节变化对其资源评估的影响。上述研究，将有助于提高南极磷虾资源声学调查评估的准确性，从而为南极海洋生态系统的深入研究和南极磷虾资源的可持续开发利用提供科学依据。

南极磷虾倾角分布、肥胖度（体周长）、声学物质特性（与海水的声速比和密度比）等参数对南极磷虾目标强度模型构建和资源量评估有重要影响。而已有研究表明，磷虾类浮游动物的肥胖度、声学物质特性会随其季节生长，尤其是含脂量的变化而变化。本研究通过数值仿真定量研究发现，参数的微小变化会导致南极磷虾资源声学调查评估结果产生成倍的误差；通过搭载南极磷虾渔船和雪龙号南极科考船采集了丰富的磷虾生物学样品，研发并组装了磷虾声速、密度测量装置，为探究南极磷虾声学物质特性的季节变化规律提供了必要支撑；对同步采集的磷虾样品进行基础生物学观测和含脂量测定，初步分析了南极磷虾体长的季节变化及不同体长组含脂量的变化。此外，项目组在CCAMLR工作组中组织建立并验证了基于集群的磷虾声学识别新方法，参与完成了2019年斯科舍海南极磷虾大尺度国际联合调查与资源评估，研究南设德兰群岛附近南极磷虾资源密度的年际变化，发现过去20年磷虾资源量并未明显下降；构建基于有限元-边界元方法（FEM-BEM）的南极磷虾声学散射新模型。上述研究，将有助于提高南极磷虾目标强度估计及资源声学调查评估结果的准确性，从而为南极海洋生态系统的深入研究和南极磷虾资源的可持续开发利用提供科学依据。