西南印度洋深海散射层昼夜垂直迁移特征研究

Study on the diel vertical migration characteristics of the deep scattering layer in the southwestern Indian Ocean

本研究根据2011−2020年西南印度洋56个声学断面数据观察到的深海散射层201次昼夜垂直迁移现象,分析了其昼夜垂直迁移特征及时空差异。研究结果表明,该海域散射层具有分层现象,第一散射层位于200 m以浅水层,其海洋面积散射系数(NASC)峰值的平均水深为(58.66±24.63)m,夏季和冬季之间存在显著性差异(p<0.001);第二散射层位于400~700 m水层,其NASC峰值的平均水深为(589.02±66.33)m,夏季和冬季之间无显著性差异(p=0.51)。散射层向上迁移的开始时间平均为16:20,结束迁移的平均时间为18:31,迁移的平均速率为(5.28±1.53)cm/s;向下迁移的开始时间平均为4:38,结束迁移的平均时间为6:52,迁移的平均速率为(5.56±2.13)cm/s。随着纬度的增加,散射层向下迁移的开始时间变晚,迁移速率变慢;随着经度的增加,散射层迁移速率变慢,且不同经度海域之间存在显著性差异(p<0.001)。分析认为,研究海域理化环境的季节性变化以及散射层中生物的不同生活史阶段是造成散射层垂直结构和昼夜垂直迁移特征时空差异的主要原因,其对解释金枪鱼的昼夜垂直迁移行为和指示金枪鱼渔场分布等具有重要意义。

Based on the data from 56 acoustic survey sections in the southwestern Indian Ocean from 2011 to 2020,a total of 201 diel vertical migration were observed.The characteristics of diel vertical migration of the deep scattering layer and its spatiotemporal differences were analyzed.The research results show that the deep scattering layer in the southwestern India Ocean exhibits a stratification phenomenon,with the first scattering layer located in the shallow water layer below 200 m.The average depth of its nautical area scattering coefficient(NASC)peak is(58.66±24.63)m,and there is a significant difference between summer and winter(p<0.001);the second scattering layer is located in the water layer between 400 m and 700 m,with an average depth of(589.02±66.33)m for its NASC peak.There is no significant difference between summer and winter(p=0.51).The average time for the scattering layer to migrate upwards is 16:20,the average time for the end of migration is 18:31,and the average migration rate is(5.28±1.53)cm/s;the average time for the scattering layer to start migrating downwards is 4:38,and the average time for the end of migration is 6:52.The average migration rate is(5.56±2.13)cm/s.As latitude increases,the start time of downward migration become later and the migration rate slows down;as the longitude increases,the migration rate of the scattering layer also slows down,and there is a significant difference between different longitude sea areas(p<0.001).Analysis suggests that studying the seasonal changes in the physical and chemical environment of the sea area,as well as the different life cycle stages of organisms in the scattering layer,are the main reasons for the spatiotemporal differences in the vertical structure and diurnal vertical migration characteristics of the scattering layer.They are of great significance in explaining the diurnal vertical migration behavior of tuna and indicating the distribution of tuna fishing grounds.