The effect of different sweep lengths on length composition of bottom sampling trawl catches

摘要

Abundance estimates of North-east Arctic cod and haddock aregiven annually on the basis of combined bottom trawl and acousticsurveys. Both survey methods use data from bottom trawl catchesin the calculations. The surveys are conducted in the BarentsSea and the Svalbard area with the same bottom trawl, but withdifferent sweep wire length. The bottom trawl indices arecalculated for both areas assuming an effective path width of 25m.In this paper results from parallel trawling experiments with thestandard sampling trawl equipped with different sweep lengths areanalyzed. These show that the total catch increases withincreasing sweep length. Small fish are relatively underestimatedby the trawl with the longer sweeps, but no speciesselection was observed. It is concluded that combining surveyresults without compensating for the effect of using differentsweep length will bias the estimates. The variability in the presented results demonstrates the complexity of combining datafrom trawl surveys conducted with different sweep lengths on thebottom trawl.