A three level pelagic trawl for near surface sampling of juvenile fish

Abstract

In the northeast Atlantic Ocean catch rates of juvenile fish from pelagic trawls are used to calculate indices of relative abundance which are applied as a first indication of year class strength. A major constraint for a reliable time series of these indices may arise from a varying vertical fish distribution, particularly near the surface due to sampling gear behaviour. In this paper a new three level trawl, which samples three separate depths simultaneously, is described in detail and catches are compared with catches from a standard juvenile survey trawl. The new trawl was highly more efficient in catching small juveniles in the near surface layers than the standard trawl. We concluded that changes in densities in this layer could significantly affect the reliability of the catch data from the standard trawl.