长江口南支水域刀鲚仔稚鱼资源量的年度变化

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月在长江口南支设置8个站点,采用大型仔稚鱼网(口径1.3m,网目0.5mm)在每月大潮期间按月进行表层水平拖网调查,研究结果与2014年、2015年同水域和同期的研究结果比较,旨在揭示长江口南支刀鲚仔稚鱼资源的年度变化。本研究共拖网58网次,采集刀鲚仔稚鱼4611尾,平均密度0.123 ind./m3,体长范围3.1～61.74mm,发育阶段从前弯曲期到稚鱼期,其中前弯曲期仔鱼(3.1～18.12mm)最多,占总数86.19%,其次是弯曲期仔鱼(4.9～24.05mm),占8.5%,后弯曲期仔鱼(9.75～30.36mm)和稚鱼(24.22～61.7mm),分别占4.6%和0.72%。白天涨潮采集刀鲚仔稚鱼4271尾,平均体长11.18mm,平均密度0.169 ind./m3,退潮时采集336尾刀鲚仔稚鱼,平均体长10.52mm,平均密度(0.029 ind./m3)低于涨潮密度；St.8夜间涨退潮调查显示,涨潮密度(0.005 ind./m3)大于退潮密度(0.002ind./m3)。三年间刀鲚仔稚鱼发育阶段组成,2014年以卵黄囊期仔鱼为主,2015年和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,主要在6-8月出现,9-10月出现量极少。三年仔稚鱼密度分布表明,各站位点以及各月平均密度差异均不显著(P＞0.05)。

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

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. A total of 4611 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 0.123ind./m3. The body length ranged from 3.1-61.74mm,with developmental stages from preflexion larvae stage to juvenile stage. The most dominant developmental stages was preflexion larvae whose body length ranged from 3.1-18.12 mm, accounting for 86.19% of the total number, followed by flexion larvae whose body length ranged from 4.9-24.05 mm for 8.5%, postflexion larvae whose body length ranged from 9.75-30.36mm for 4.6% and juveniles whose body length ranged from 24.22-61.7mm for 0.72%. A total of 4271 individuals of Coilia nasus were collected at flood tide during the day,the average body length was 11.18 mm,the average density was 0.169ind./m3.336 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 0.029ind./m3.At St.8, the average density was 0.005 ind./m3 at flood tide and 0.002ind./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. Most Coilia nasus larvae and juveniles were collected from June to August in each year, and rarely collected from September to October. The density was not significantly different(P> 0.05) among stations and months.