Study on the diel vertical migration characteristics of the deep scattering layer in the southwestern Indian Ocean
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 scatter-ing 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 scatter-ing 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 scat-tering layer to migrate upwards is 16:20,the average time for the end of migration is 18:31,and the average migra-tion 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 in-creases,the start time of downward migration become later and the migration rate slows down;as the longitude in-creases,the migration rate of the scattering layer also slows down,and there is a significant difference between dif-ferent 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 char-acteristics of the scattering layer.They are of great significance in explaining the diurnal vertical migration behavi-or of tuna and indicating the distribution of tuna fishing grounds.
deep scattering layerdiel vertical migrationspatiotemporal differencessouthwestern Indian Ocean
万方数据
维普
