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Density, growth and annual food consumption of plaice (Pleuronectes platessa L.) and flounder (Platichthys flesus (L.)) in Lake Grevelingen, The Netherlands

1984; Elsevier BV; Volume: 18; Issue: 3-4 Linguagem: Inglês

10.1016/0077-7579(84)90014-0

1873-1406

G. Doornbos, F. Twisk,

Fish Biology and Ecology Studies

Within the scope of a carbon budget study in the 108 km2 saline Lake Grevelingen, investigations on the plaice and flounder populations were made during October 1979 to December 1981. Both populations were dominated by the 1979 year class that presumably entered the lake as larvae in the year the Brouwerssluice, which opens to the North Sea, was operative the whole year round. Due to high summer temperatures in the lake, juvenile plaice (year class 1981) attained a mean length of 13.0 cm and a fresh weight of 27.4 g at the end of their first growing season. At the end of their third year, year class 1979 males measured on average 27.7 cm and females 29.7 cm, which is about 3.5 cm more than plaice of the same age in the North Sea. Flounder reached a mean length of 26.3 cm in 3 years. Total stock of plaice, excluding year class 1981, was estimated at an average of 1.3 million over 1980 and at 0.6 million fish over 1981. For flounder these figures were 0.7 million and 0.2 million and 0.2 million fish, respectively. In September 1981 the number of O-group plaice was assessed at about 0.2 million individuals. About 56% of the plaice food consisted of polychaetes, mainly consisting of in 1980 Arenicola marina (41%) and in 1981 A. marina (15%), Nereidae (15%) and Nephtys hombergii (11%). Larger plaice consumed significantly more Arenicola and less Tharyx marioni than smaller ones. Polychaetes and crustaceans were eaten the whole year rounf while the consumption of molluscs was restricted to the summer period and the of fisg to autumn and winter. In 1980 the flounder population preyed predominantly upon crustaceans (41%) and polychaetes (37%), with Arenicola marina (36%) and Crangon crangon (25%) as the most important species. In 1981 relatively more polychaetes (53%) and less crustaceans (14%) were eaten. Total consumption of plaice population, excluding year class 1981, in 1980 and 1981 was estimated at 1.68 g and 1.41 g ADW·m−2·a−1. Annual consumption of O-group 1981 plaice was assessed at about 0.06 g ADW. The corresponding consumption of the flounder population was 1.14 g and 0.44 ADW, respectively.