插网网目尺寸及采样时间对潮沟游泳动物采样的影响

在长江河口九段沙盐沼湿地的一条潮沟中，我们比较了两种不同网目尺寸（4mm和8mm）的插网（fyke net）及日夜潮对游泳动物群落采样效率的影响。共捕获鱼类16种5476尾、虾2种4982只。采用方差分析、柯尔莫诺夫-斯米尔诺夫非参数检验法和无度量多维标定分析对两种网目插网的捕获效率，样品的体长分布，群落结构及日夜潮间的差异进行了分析。结果表明，网目尺寸对样品中游泳动物的物种数和鱼类的多度没有影响，但是小网目的插网对虾类有较高的捕获率。两种网目尺寸的插网均在夜潮中捕获较多的鱼类个体，但虾类在日潮捕获较多。在日潮中，网目尺寸对捕获物中五种优势游泳动物的体长分布无显著影响。在夜间，小网目的插网对斑尾复缎虎和脊尾白虾的较大个体具有较高的捕获率，但对较大个体鲅的捕获率不如大网目的插网。样品中游泳动物的群落组成在日夜潮间存在明显差异，大网目捕获物的样本间差异比小网目小。

Effects of fyke net mesh size and sampling period on the catch of nekton in an intertidal creek

The present study was carried out in an intertidal creek in Jiuduansha saltmarsh of the Yangtze River Estuary,China. Fyke nets of two mesh sizes,4mm and 8mm,were applied to determine the effects of mesh size and day-night period on the catch of nekton. Through the sampling of five consecutive 24 h periods,a total of 5476 fish of 16 species and 4982 shrimp of two species were collected. Analyses indicated that mesh size had no significant effect on the species number and abundance of fish caught,but smaller mesh had higher catch rates of crustaceans. More individuals of fish were caught at night than in the daytime for both 4mm and 8mm mesh nets,but more crustacean individuals were caught by day. In the daytime,different mesh sizes had no significant effect on the length distribution of five most abundant nekton species caught by the nets. In night sampling,nets with smaller mesh captured a greater proportion of large individuals of some predominant species(e.g. Synechogobius ommaturus and Exopalaemon carinicauda),but reverse result occurred in other species such as Liza haematocheila. Community structures of nekton in night and day samples were different. Nets with smaller mesh sizes show relatively low sampling precision values.