|Studies on the fish fauna of an estuary in the S.W. Netherlands, before and after its change into the stagnant, saline Lake Grevelingen|
Vaas, K.F. (1979). Studies on the fish fauna of an estuary in the S.W. Netherlands, before and after its change into the stagnant, saline Lake Grevelingen. Hydrobiol. Bull. 13(2-3): 177-188
In: Hydrobiological Bulletin. Netherlands Hydrobiological Society: Amsterdam. ISSN 0165-1404, more
Ecological succession; Pisces [WoRMS]; ANE, Netherlands, Grevelingen L. [Marine Regions]; Marine
The Grevelingen was fished with a beam-trawl during the years 1960-1963; it was in open connection with the North Sea as well as with the river Rhine, during the years 1966-1969. The connection with the river was blocked by a dyke, during 1971-1976, and when the connection with the sea was also blocked by a dyke and the stagnant, saline Lake Grevelingen was created. The (mainly) demersal fishes captured were classified into (1) frequent species spawning within the area; (2) frequent species spawning outside the area, and (3) incidental visitors from the coastal sea. After closure the incidental visitors either became much less frequent or dropped out entirely. Some of the larger spawners decreased in numbers. Their place was occupied by smaller fishes, such as sand smelts and the stickleback. As piscivorous fishes almost completely dropped out, the above small species were able to increase and so were the two gobies present before the closure. The turbot and the brill increased in numbers and there are indications that both spawn in the lake. These two species are the only large piscivorous fishes left at the moment and the nearly empty niche, created by the absence of other, incidental visiting, marine piscivores, is now filled by numbers of markedly increased grebes and cormorants. It is concluded that in the stagnant, saline lake, species diversity decreased and food chains became shorter, as compared with the more mature situation in the open estuary.