Comparative analysis of two sampling gillnets of rocky reef area in Gouqi Islands,Shengsi,Zhejiang

Abstract

The survey experiment of two different type of gillnets was carried out at rocky reef area to find the suitable survey nets for rocky habitat during July and August in 2009.Indices such as Sorensen similarity,Margalef's species richness index,Shannon-Wiener diversity,Peilou's species evenness index were calculated,and the constitution and difference of catch were analyzed.Results showed that(1)Catch and species of European gillnet were lower than multi-mesh trammelnet.20 species was caught by European monolayer gillnet,and total weight was 8 572.6 g while 29speceies and 20 793 g catch by multi-mesh trammelnet.(2)Dominant species of European gillnets were:Sebastiscus marmoratus,Hexagrammos agrammus,Collichthys lucidus and multi-mesh trammelnets' dominant species were:Sebastiscus marmoratus,Hexagrammos agrammus,Collichthys lucidus,Scomber japonicas.The selectivity of European gillnets was much higher than multi-mesh trammelnets.(3)European gillnet and multi-mesh trammelnets had no significant difference in community structure index,but index of Sorensen similarity was only 0.41,which showed that the species of two gillnets is different.(4)It is suggested that the selectivity of two gillnets was different,the average length of catch was 106.1 mm for European gillnet and 119.1 mm for trammelnets.(5)Different species are distributed in different mesh gillnets,the dominant species such as Sebasticus marmoratus,Hexagrammos agrammus distributed mainly in five mesh gillnets.Our research indicates that the indices of fish community have no significant difference,however,multi-mesh trammelnet has a high catch efficiency,and is more durable than European monolayer gillnets for survey in rock reef area.