MORTALITY AND GROWTH OF O-GROUP FLATFISH IN THE BRACKISH DOLLARD (EMSESTUARY, WADDEN-SEA)

The population dynamics of three 0-group flatfish species, plaice (Ple uronectes platessa L.), flounder (Platichthys flesus L.) and sole (Sol ea solea L.) in the Dollard (Ems Estuary, Wadden Sea) were investigate d in 1992. The instantaneous rate of decrease in catch density of plai ce was 0.011 . d(-1), which corresponded with other calculated mortali ty rates of plaice in the western Wadden Sea. Catch densities of 0-gro up 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 increa se in mean length of 0-group sole was in agreement with experimental g rowth studies under excess of food. The observed rate of increase in m ean length of plaice and flounder appeared to decline from the beginni ng of June onwards in comparison with simulated growth in length. A nu mber of factors that may be responsible for the observed differences a re discussed.