Episodic Mass Invasions of Juvenile Gadoids into the Wadden Sea and their Consequences for the Population Dynamics of Brown Shrimp (Crangon crangon) |
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| Authors: | Rüdiger Berghahn |
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| Institution: | Institut für Hydrobiologie und Fischereiwissenschaft der Universitat Hamburg, Elbelabor, Groβe Elbstraβe 268. D-22767 Hamburg, Germany |
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| Abstract: | Abstract. The brown shrimp Crangon crungon is considered to be a key species in the coastal waters of the North Sea and in particular in the Wadden Sea, since it occurs in masses and acts as both a highly efficient predator and important prey. The Wadden Sea is the nursery ground for brown shrimp. In 1990, a mass invasion of O-group whiting ( Merlangius merlangus ) reduced Crangon numbers to almost zero. Similar events, which had previously been reported in the 19th century, were observed in 1959 (whiting), 1970 (cod, Gadus morhua ), and 1983 (cod and whiting).
The 1990 invasion and the decline of the shrimp stock are documented on the basis of surveys that are compared with the years preceding and following. Consequences for the food web in the Wadden Sea and the reasons for the complete recovery of the shrimp stock in each case within one year after its collapse are discussed with regard to the Crangon crungon behaviour and reproductive potential. Sampling error and the impact of fisheries are also considered. |
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| Keywords: | Predation reproductive potential shrimp fisheries |
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