Changes in growth of North Sea plaice since 1950 in relation to density, eutrophication, beam-trawl effort, and temperature

Annual length increments of female North Sea plaice were back-calculated from distances between rings in otoliths. Growth of the smaller size classes (<25 cm) increased from the mid-1950s and decreased in the 1980s. Length increments of intermediate size classes varied more or less randomly, and those of the larger size classes (>35 cm) increased from 1970. Growth changes of the smaller size classes were significantly correlated with indices of plaice density, eutrophication, and seabed disturbance by beam trawling. Moreover, they could be related to spatial and temporal patterns in variations in eutrophication and beam trawling. No correlation was observed with temperature. The analysis led to a consistent interpretation suggesting that eutrophication and beam trawling have both affected the growth rate of plaice. The contributions of these factors differed in space. Effects of eutrophication dominated in the shallow coastal waters, whereas beam trawling dominated in the waters further offshore.