潮汐对长江口南支刀鲚仔稚鱼垂直分布及昼夜变化的影响

为了探讨潮汐对长江口南支刀鲚仔稚鱼的垂直分布及昼夜变化的影响,2017年5—9月在长江口南支的南北纵向断面设立2个站位点,采用大型仔稚鱼网(口径1.3 m,网目0.5 mm)在每月大潮期间依据潮汐(涨潮采样4次和退潮采样4次)逆流进行昼夜、表中层水平拖网,共拖网160次,采集刀鲚仔稚鱼369尾,发育阶段由前弯曲期仔鱼到稚鱼。表层刀鲚仔稚鱼平均密度(0.851尾/100 m~3)大于中层(0.145尾/100 m~3)。涨潮时前弯曲期仔鱼和弯曲期仔鱼密度,表层大于中层,白天大于夜间;退潮时表层大于中层,白天大于夜间。后弯曲期仔鱼的平均密度白天小于夜间,涨潮小于退潮;稚鱼白天涨潮的平均密度表层为0,中层为0.14尾/100 m~3,白天退潮表层为0.14尾/100 m~3,中层为0。研究结果表明:在涨潮和退潮时,前弯曲期和弯曲期仔鱼表层分布大于中层,后弯曲期仔鱼和稚鱼趋于中层分布;后弯曲期仔鱼和稚鱼白天涨潮时趋于中层,白天退潮时又趋于表层,夜间分布大于白天。

Vertical distribution and changes during day and night of Coilia nasus larvae and juveniles depending on flood and ebb tide in southern branch of Yangtze River estuary

The vertical distribution and changes during day and night of Coilia nasus larvae and juveniles depending on flood tide and ebb tide in the southern branch of Yangtze River estuary. According to the tidal changes, monthly 4 flood trawls and 4 ebb trawls were set at two stations (surface layer and middle layer) from May to September in 2017 using a larval net (1.3 m mouth-diameter, 0.5 mm mesh-aperture) againsting to the current at every station. A total of 369 individuals of Coilia nasus were collected,with developmental stages from pre-flexion larva to juvenile. The average density in the surface layer was 0.851 ind./100 m³ which was higher than 0.145 ind./100 m³ in the middle layer.The average density at pre flexion larva and flexion larva is higher in the surface than in the middle layer, at flood tide than at ebb tide,in the daytime than in the night time. While the average density at post flexion larva in the daytime is lower than that in the night time, at flood tide than at ebb tide. At flood in the daytime, the average density of juveniles is 0 in the surface and 0.14 ind./100 m³ in the middle layer. At ebb tide in the daytime, the average density of juvenile is 0.14 ind./100 m³ in the surface and 0 in the middle layer. The results show some tendency that pre flexion larva and flexion larva trend to the surface and post-flexion larva and juvenile trend to the middle layer. At flood tide in the daytime,post-flexion larva and juvenile trend to the middle layer. At ebb tide in the daytime, post-flexion larva and juvenile trend to the surface. The average density of post-flexion larvae and flexion larvae is higher in the daytime than in the night time.