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Gill nets are a particular hazard to diving seabirds and have been implicated in the decline of seabird populations in some parts of the world.
In northern Norway, for example, the breeding populations of guillemots at two sites are estimated to have declined by 95% from the early 1960's to 1989, a figure which could be explained by gill net mortalities, based on observed catch rates.
The numbers of birds killed in nets depends on their abundance, diving habits and distribution within the fishery area.
Species which have been caught in these nets include shearwaters, red-throated divers, Leach's petrel, gannet, shag, guillemot, razorbill, and great northern diver, and ducks such as the common scoter and long-tailed duck are also known to have become entangled and die in set nets.
Inshore gill nets can have a relatively high incidental by-catch around diving seabird colonies, or where there are high densities gathered on the water surface, making it inadvisable to set nets in such areas.
Large numbers of razorbills are known to have drowned in gill nets at the mouth of the Tagus estuary in Portugal, for example, where this species congregates on occasions.
Nets set for bass have caught large numbers of diving birds (mostly razorbills and divers), and in one incident in the UK, an estimated 900 auks were caught over 8 days in nets set below seabird colonies.
Herring nets and bottom-set cod nets have also killed large numbers of diving seabirds (an estimated 25,000 in the southeast Kattegat between 1982 and 1988), most of which were found in the bottom-set cod nets.
Courtesy UK Marine SACs Project
http://www.ukmarinesac.org.uk/index.htm
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