Development of tidally related behaviour of a newly settled 0-group plaice (Pleuronectes platessa) population in the western Wadden Sea

Abstract

Tidal migration in a 0-group plaice Pleuronectes platessa population on a tidal flat in the western Wadden Sea was studied. Immigrating plaice larvae from the North Sea tended to settle on the tidal flats at some distance from the ed ge of the tidal channel in 2 to 8 cm of water. Tidal migrations developed towards the gullies and channel during ebb tide. The low water refuge gradually shifted from small gullies near the settlement area to the deeper tidal channel. In contrast to the view that tidal migration develops as a means to exploit feeding grounds present in the tidal area, the unfavourable temperature and oxygen conditions on the Balgzand from Jun onwards, in particular during low water, suggest that tidal migration has to be considered as a forced escape behaviour of plaice from the feeding grounds. During nighttime, when O sub(2) deficiency is higher, plaice as a rule left the flats earlier after high water. The last group of newly settled larvae may suffer under these conditions, which might even result in mortality. Since abundant larval years are associated with a relatively strong settlement in Apr, such a mortality factor might have a density-dependent component between years.