VELDKAMP R (1986) Decline and recovery of the Cormorant Phalacrocorax carbo in NW. Overijssel. LIMOSA 59 (4): 163-168.

Great Cormorant Phalacrocorax carbo Since 1820, the Cormorant breeds in NW. Overijssel in or near the Bakkerskooi, from 1918 onwards. The last one is the eldest colony in the Netherlands (fig. 1). Several times the colony changed from nesting place (fig. 2). In 1900-40, the numbers declined because of shooting, cutting of nesting trees, and exploitation of the chicks. The main reason for the reduction measures were fishery and duck decoy interests. In 1934, the Bakkerskooi became a nature reserve, after which the numbers increased. In 1941-58, the numbers were controlled because of fishery interests and the conservation of the nesting trees. In 1941-44, quite a lot of adult and juvenile birds were killed. This caused a movement of part of the birds to Otterskooi and Naardermeer. The latter holds also a large colony nowadays. From 1932 onwards, the circumstances at the feeding grounds have changed as result of the building of the Afsluitdijk, which caused a desalination of the IJsselmeer. In 1942, the Noordoostpolder was reclaimed, in 1957 Oostelijk Flevoland (fig. 3). Notwithstanding the feeding area became smaller, and direct measures were taken against the birds in 1940-50, the numbers in NW. Overijssel fluctuated around 2000 pairs. Up to 1959, the numbers in the Bakkerskooi were controlled. However, after then the numbers still declined up to 1972. From this year onwards, the numbers raised, but more slowly than in the rest of the Netherlands. It is suggested that the numerical decline in 1952-71 has mainly been the result of high residues of mercury and PCB's in the estuary of the river IJsse!. This probably was also the reason why the recovery in numbers was more slowly than in the rest of the Netherlands. At

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