Rapidly increasing numbers of great cormorants, forming colonies near lakes and rivers, have been causing serious damage to local fish stocks such as "ayu" (sweetfish) and koi, according to researchers.
The domestic population of the great cormorant once tumbled to about 3,000 during the 1970s due to environmental pollution, but has since grown back to about 70,000 due to preservation efforts and stricter controls on pesticides.
The bird is about 80 cm long and weighs about 2 kg, but can be as big as 130 cm with its wings spread.