Mortality and growth of 0-group flatfish in the brackish dollard (Ems Estuary, Wadden Sea)

The population dynamics of three 0-group species, plaice (Pleuronectes platessa L.), flounder (Platichthys flesus L.) and sole (Solea solea L.) in the Dollard (Ems Estuary, Wadden Sea) were investigated in 1992. The instantaneous rate of decrease in catch density of plaice was 0.011·d⁻¹, which corresponded with other calculated mortality rates of plaice in the western Wadden Sea. Catch densities of 0-group flounder decreased at a rate of 0.018·d⁻¹. The rate of decrease in catch density of 0-group sole was estimated at 0.011·d⁻¹, but was less accurate and probably reflected migration. The rate of increase in mean length of 0-group sole was in agreement with experimental growth studies under excess of food. The observed rate of increase in mean length of plaice and flounder appeared to decline from the beginning of June onwards in comparison with simulated growth in length. A number of factors that may be responsible for the observed differences are discussed.