Variation in hatch date distributions, settlement and growth of juvenile plaice (Pleuronectes platessa L.) in Icelandic waters

Hatch date distribution, larval phase and subsequent growth of juvenile plaice (Pleuronectes platessa L.) in different regions around Iceland were determined by otolith microstructure analysis. Length, age and hatch date frequency distributions were obtained from juveniles captured in a 1 m beam trawl on 31 stations at 0.5–1 m depth all around Iceland in July 2006. The main spawning has previously been assumed to take place on the south and south-west coasts with eggs and larvae then distributed by currents along the west and north coasts. Contrary to this expected dispersal pattern, both size and age of juvenile plaice decreased from south to north. The results indicate that the observed spatial variation in size of the juveniles is not explained by different growth rates but by age. The juveniles at the south coast hatched earlier than juveniles on the north and east coasts and had a shorter larval period. Growth differed between regions and was partially explained by temperature. The study provides evidence that the juvenile plaice population may in fact originate from multiple spawning sites located not only along the south and south-west coasts, but along the entire coast of Iceland. The findings are discussed in relation to currents and temperature in Icelandic waters.