长江口南支水域刀鲚仔稚鱼资源量的年度变化

Annual variation of the resources of Coilia nasus larvae and juveniles in the southern branch of the Yangtze River estuary

摘要:

为了进一步探明长江口南支刀鲚（Coilia nasus）仔稚鱼的分布和丰度变化，2018年6-10月在该水域设置8个站点，采用大型仔稚鱼网（口径1.3 m，网目0.5 mm）在每月的大潮期间按月进行表层水平拖网调查，并与2014和2015年在相同水域和相同时期的研究结果作比较。共拖网58网次，采集刀鲚仔稚鱼4 611尾，平均密度0.123尾/m³，体长范围3.10~61.74 mm。发育阶段从前弯曲期到稚鱼期，其中：以前弯曲期仔鱼（3.10~18.12 mm）最多，占总数的86.18%；其次是弯曲期仔鱼（4.90~24.05 mm），占8.50%；后弯曲期仔鱼（9.75~30.36 mm）和稚鱼（24.22~61.70 mm），分别占4.60%和0.72%。白天涨潮期采集刀鲚仔稚鱼4 211尾，平均体长11.18 mm，平均密度0.169尾/m³；退潮期采集339尾刀鲚仔稚鱼，平均体长10.52 mm，平均密度（0.029尾/m³）低于涨潮期密度。St.8的夜间涨退潮期调查显示，涨潮期密度（0.005尾/m³）大于退潮期密度（0.002尾/m³）。刀鲚仔稚鱼的发育阶段组成，2014年以卵黄囊期仔鱼为主，2015和2018年均以前弯曲期仔鱼为主。各年刀鲚仔稚鱼出现的持续时间和高峰期基本相似，主要集中在6-8月，9-10月出现量极少。仔稚鱼密度分布表明，3年间各站位点密度差异不显著。

Abstract:

To clarify the distribution and abundance of Coilia nasus larvae and juveniles,8 stations were set along the southern branch of Yangtze River Estuary from June to October 2018 and compared with the same period result of 2014 and 2015. A total of 4 611 individuals of Coilia nasus larvae and juveniles were collected in the 58 trawls at the spring tides in the surface layer by a larval net (1.3 m mouth-diameter, mesh aperture 0.5 mm). The average density was 0.123 ind./m³. The body length ranged from 3.10-61.74 mm,with developmental stages from preflexion larvae stage to juvenile stage. The most dominant developmental stages was preflexion larvae whose body length ranged from 3.10-18.12 mm, accounting for 86.18% of the total number, followed by flexion larvae whose body length ranged from 4.90-24.05 mm for 8.50%, postflexion larvae whose body length ranged from 9.75-30.36 mm for 4.60% and juveniles whose body length ranged from 24.22-61.70 mm for 0.72%. A total of 4 211 individuals of Coilia nasus were collected at flood tide during the day, the average body length was 11.18 mm,the average density was 0.169 ind./m³. 339 individuals of Coilia nasus were collected at ebb tide during the day, the average body length was 10.52 mm and the average density was 0.029 ind./m³. At St.8, the average density was 0.005 ind./m³ at flood tide and 0.002 ind./m³ at ebb tide at night. Development stage showed a similar tendency and preflexion larvae were dominant in 2015 and 2018, however, yolk-sac larvae were dominant in 2014. Coilia nasus larvae and juveniles were mostly collected from June to August each year, and rarely collected from September to October. The density was not significantly different among stations.