Cormorant damage prevention at a fish farm in the Netherlands

Published source details Moerbeek D.J., van Dobben W.H., Osieck E.R., Boere G.C. & de Jong C.M.B. (1987) Cormorant damage prevention at a fish farm in the Netherlands. Biological Conservation, 39, 23-38.
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This study is summarised as evidence for the following.

	Action	Category
	Use netting to exclude fish-eating birds Action Link
	Scare birds from fish farms Action Link

Use netting to exclude fish-eating birds

A series of experiments in Flevoland, the Netherlands, in 1981-3 (Moerbeel et al. 1987) found that nylon lines and ropes did not prevent cormorants from landing on fish ponds, but did change behaviour (from quick incursions by many birds to smaller numbers staying in ponds for longer). Effects on fish stocks are not reported. In 1981 nylon lines (forming 20 x 20 m squares) were placed over a 5 ha pond; in winter 1981-1982, 10 x 10 m squares were tested, and four ponds fitted with 20 x 20 m squares, with an irregular pattern over another; in 1983 over a 5 ha pond, ropes were stretched downwards from 10 m towers in the pond centre to the sides, with spacing between lines of 14-15 m). The effect of scaring birds from fish ponds is discussed in ‘Scare birds from fish farms’.
Scare birds from fish farms

A series of experiments in Flevoland, the Netherlands, in 1981-3 (Moerbeek et al. 1987) found that pistol-fired flash cartridges (detonation after a light flash, or a flash only) appeared the most effective method of deterring great cormorants Phalacrocorax carbo from ponds and scared most birds away (although some alighted on nearby ponds). Gas cannons (producing a bang at regular or irregular intervals) had little effect as birds soon habituated to the noise; an overflying helicopter scared cormorants from ponds but they soon returned (on the day following the 2-day trial large numbers were present). An ultra-light aircraft proved inconclusive.