长江靖江段沿岸凤鲚丰度的时间格局及生物学研究

Temporal distribution and biological characteristics of Coilia mystus in Jingjiang section of the Yangtze River

为探究长江南通段以上凤鲚(Coilia mystus)的资源动态,通过在靖江段沿岸连续10年(2008—2017年)的定置张网实地监测,初步分析了该江段凤鲚丰度的时间格局;采用逐年拟合群体体长-体质量关系,绘制体长和体质量频率曲线图,分析了凤鲚生物学参数的时间变化。结果显示,在10年343次采样中,采集到凤鲚样本130次,出现率为37.9%。凤鲚在靖江段渔获物中的数量与重量占比分别仅为0.72%、0.44%,且丰度和出现率在年间均呈递减趋势。在繁殖季节共采集到721尾,占全部个体数的87.5%;在非繁殖季节采集到103尾,占全部个体数的12.5%,表明在非繁殖季节仍有少部分凤鲚个体滞留在淡水。互相关分析显示,靖江沿岸凤鲚丰度与当年长江口凤鲚繁殖期的捕捞量呈显著的正相关关系(r=0.819,P<0.05),表明长江口繁殖群体中有部分个体可继续上溯到靖江以上的上游江段。生物学研究显示,凤鲚群体平均体长和体质量分别为(105.6±1.8)mm和(5.07±0.28)g,体长-体质量关系式为:W=2.958×10-6L3.020(R2=0.9647)。与同期长江口的风鲚群体相比,靖江段群体的体长和生长参数b均很接近,但体质量和丰满度略小。

In order to explore the resource dynamics of Coilia mystus above the Nantong section of the Yangtze River,a combination set-net set up along the Jingjiang section of the Yangtze River for 10 consecutive years(2008—2017)was used to monitor the resource data of tapertail anchovy Coilia mystus.Based on long-term monitoring data,the temporal pattern of C.mystus abundance in the Jingjiang section of the Yangtze River was preliminarily analyzed.Results showed that in 343 samplings over 10 years,C.mystus was collected 130 times,with an occurrence rate of 37.9%.The abundance and biomass percentage of C.mystus were only 0.72%and 0.44%,respectively,and the abundance and occurrence rate of C.mystus showed a decreasing trend.Among them,721 individuals were collected in the reproductive migration season,accounting for 87.5%of the total number;while 103 individuals were collected in the non-reproductive season,accounting for 12.5%of the total.The cross-correlation analysis showed that a significant positive correlation was found between the abundance of C.mystus in Jingjiang section and annual catch of C.mystus in the Yangtze Estuary(r=0.819,P<0.05)during the same period.C.mystus in Jingjiang section was mainly derived from the reproductive population of the Yangtze Estuary,and a few individuals may continue to migrate upward to the upper reaches of the Jingjiang section.In addition,biological studies showed that the average body length and body weight were(105.6±1.8)mm and(5.07±0.28)g,respectively,and LWR was W=2.958×10-6L3.020,and the coefficient of determination(R2)was 0.9647.The results also showed that the allometric coefficient(b)almost approached 3,which indicated isometric growth in C.mystus stock form 2008 to 2010.However,b values were significantly smaller than 3(P<0.05),indicating negative-allometric growth in C.mystus stock from 2011 to 2017.According to the frequency density curve of body length and body weight,the inter-annual changes were analyzed to show that the mean body length and body weight of the Colia mystus decreased in the decade from 2008 to 2017.Similarly,the condition factor of C.mystus also decreased.In recent years the continually heavy fishery pressure has increased the growth speed in the body length of C.mystus,which may be the main reason for the decrease of condition factor and the negative allometric growth of the stock.