Cormorant: recovery
The cormorant has profited greatly from its protected status.
Trend until the 1960s
The cormorant feeds on fish, such as ruffe, perch, roach, smelt and eel. The fishing industry sees it as a formidable competitor, even though many of the fish caught by the cormorant are of little commercial importance.
The cormorant used to be vigorously controlled. In 1955, for example, the government decreed that the number of breeding pairs should be limited to 1200, distributed among three colonies. In the 1960s water pollution began to take its toll: the number of pairs fell to 800 and the number of colonies fell to two (Naardermeer and Wanneperveen).
Trend post 1960
In 1965 the cormorant was given full protection. Numbers then rose. In 1978 a colony established in the Oostvaardersplassen. This has since become the largest in the Netherlands, with 4975 pairs nesting there in 2001. There are other large colonies in the Lepelaarplassen (near Almere), in the Naardermeer, in Oostvoorne, in Wanneperveen and on some Wadden islands.
After 1993 the national population fell as a result of a sharp decrease in the Oostvaardersplassen triggered by a decline in numbers of suitable prey fish in the IJsselmeer area. The cormorants also found it more difficult to catch fish because the clearer waters in the area gave the fish more advance warning of attack. Cormorant numbers in the IJsselmeer area have now stabilised at a lower level. Since 1993-1994, numbers have again been rising nationally, partly because the number of colonies has increased.
Technical note
The data are from the Ecological Monitoring Network's network for monitoring breeding birds.
References
- Bijlsma, R.G., F. Hustings en C.J. Camphuysen (2001). Algemene en schaarse vogels van Nederland (Avifauna van Nederland). GMB Uitgeverij/KNNV Uitgeverij, Haarlem. Utrecht.
- Dijk, A.J. van, M.J.T. van der Weide, R. Kleefstra, D. Zoetebier en C. Plate (2001). Kolonievogels en zeldzame broedvogels in Nederland in 1999. SOVON-monitoringrapport 2001/08. SOVON Vogelonderzoek Nederland. Beek-Ubbergen.
- Noordhuis, R. (red.) (2000). Biologische monitoring zoete rijkswateren. Watersysteemrapportage IJsselmeer en Markermeer. RIZA rapport 2000.050. Lelystad.
- Rijn, S. van en M. van Eerden (2001). Aalscholvers in het IJsselmeergebied: concurrent of graadmeter ? RIZA rapport 2001.058. Lelystad.
