Analysis of meso scaled spatial distribution of dab Limanda limanda in the German Bight: does the type of fishing gear matter?

ABSTRACT:   In the North Sea, studies are carried out to assess the effect of offshore windmills on the spatial distributions of various fish species, based on data often obtained from different fishing gears. In this study, spatial analysis of three size classes of dab Limanda limanda in the German Bight was undertaken and the effect of different fishing gear type on analyzing spatial patterns are assessed, using geostatistics. In an area equal in size to a wind park (with ∼ 200 windmills), a comparative fishing experiment was carried out, where a 7 m-beam trawl and an otter trawl were employed. Structural analyses showed a presence of spatial autocorrelation in the catch data in all cases. The use of an efficient sampling gear led to an improved resolution of spatial structuring, but did not necessarily result in reduction of nugget variability. Ecological parameters derived from a spatial analysis were in good agreement in cases of high abundance and similar gear efficiency. Thus, it is shown that the type of gear matters in cases of low species abundance. Therefore, to achieve reliable results of a structural analysis and an accurate spatial assessment of fisheries data, it is recommended that the abundance of the target species (biological group) and efficiency of the sampling gear are considered.