Fisheries-induced evolution in growth, maturation and reproductive investment of the sexually dimorphic North Sea plaice (Pleuronectes platessa L.)

Changes in the onset of sexual maturation, reproductive investment and growth of North Sea plaice are studied between three periods: 1900s, 1980s and 2000s. Probabilistic maturation reaction norms of both males and females, describing the probability of becoming mature conditional on age and size, shifted towards smaller sizes and younger ages, indicating a fisheries-induced evolutionary change. A higher rate of change was observed during the past 20 years, which may be related to higher temperature conditions. Reproductive investment was estimated from the decrease in lipid, protein, dry weight content and condition factor of the whole body between pre- and post-spawning adults. Reproductive investment expressed as the energy loss over the spawning period increased with body size from 19% at 20 cm to 30% at 40 cm in males and from 35% at 30 cm to 48% at 50 cm in females. No change in reproductive investment could be detected between the 1980s and the 2000s. Von Bertalanffy (VB) growth parameters showed a decrease in L∞ the asymptotic size and an increase in K, the velocity to reach L∞, in both males and females. The changes in VB growth are consistent with an increase in energy acquisition and reproductive investment. The observed changes in maturation, reproductive investment and growth are consistent with fisheries-induced evolution, but the changes in reproductive investment and growth need further investigation to disentangle the role of phenotypic plasticity.