Density-dependent and independent changes in somatic growth of female North Sea plaice Pleuronectes platessa between 1930 and 1985 as revealed by back-calculation of otoliths

Abstract

During 1940-49 growth rate was reduced, which coincided with a 3-fold increase in the plaice stock due to the closure of the fishery during the second world war. The growth reduction was largest in large fish (>45cm) compared to medium sized fish (30-40cm), but could not be detected in the size classes <20cm. In large plaice the growth reduction occurred later in time compared to the medium sizes fish. At some time in the 1950s and 1960s a growth acceleration started in the size classes up to 30cm, levelling off in the 1970s. This growth acceleration was largest in the smallest size classes. Within the period of growth acceleration, the 1963 year class, which was about three times the average year class strength, showed a slight but significant reduction in growth. The reduction in growth was restricted to size clases <30cm and was largest in smaller fish. Growth rate in plaice is reduced at high density both in the juvenile phase (pre-war period and year class 1963) and in the adult phase (period 1940-49). The increase in growth of juvenile plaice starting in the 1950s appears to be related to an increase in the availability of food in the coastal waters of the S North Sea. -from Authors