Variations in North Sea sole distribution: variation in North Sea sole distribution with respect to the 56°N parallel perceived through scientific survey and commercial fisheries

The Dutch commercial fisheries report that sole (Solea solea) catches in the north of the North Sea have been increasing over the past years. While the large majority of North Sea sole catches are taken by beam trawl with 80mm mesh size, fishing with this gear is currently not allowed north of 56°N. In order to be able to get permission for a dedicated sole fishery (80 mm) in that area, scientific proof is needed for the increase in sole in the area north of 56°N. This study analyses data collected during the Beam Trawl Survey and STECF landing and effort data to investigate whether the spatial distribution of North Sea sole has changed over the last two decades. The study focusses in particular on the part of the North Sea to the north of the 56°N parallel where the main sole targeting fishery (beam trawl with 80mm mesh size) is currently not allowed to fish. Results based on the survey data show that the abundance and the extent of the distribution of sole in the area north of 56°N has increased (nearly doubled) since 2010. The proportion of the stock distributed north of 56°N also increased, but remains overall low (less than 7.5%). Over the same period, the centre of gravity of the stock has remained at a similar location. The only fleet operating at a scale large enough to provide information on sole at the scale of the North Sea was the Danish gillnet fishery. The proportion of landings of this fleet taken north of 56oN (in front of northern Denmark) has increased markedly since 2012, even when potential changes in the spatial distribution of the effort are taken into account. These results suggest an expansion of the stock at the margin of the distribution, while the core of the distribution of the stock has remained in the southern and central part of the North Sea (south of 54°N).