Verstrikkingen van zeevogels in plastics: een probleem van toenemende omvang?

Many birds and marine mammals become entangled in fishing gear, ropes and plastics. The incidence of entanglements was thought to increase in the Netherlands in recent years and it was therefore studied in more detail, using results of beached bird surveys from 1979-89 (100,264 birds found dead). Some 200 entanglements were reported in these years, including entanglements in fish nets (38), nylon fish thread (120), ropes (24) and other, usually plastic, litter (18). The number of entanglements reported per km surveyed increased significantly (rs 0.76, p< 0.01, n= 11, figure 1), mainly because of an increase in entanglements in nylon thread (rs 0.71, p< 0.05, n= 11). Most of the nylonthread must have been thrown away by sports anglers on the shore, and birds become entangled with feet, wings and/or body. Another portion of the birds swallows hooked bait and gets entangled in any nylonthread remaining on the hook. Gannets (5.4%, n= 624), Cormorants (2.6%, n= 153), and Great Black-backed Gulls (1.3%, n= 1692) were relatively numerous as entangled birds, whereas 0.2% of all birds found dead were entangled (n= 100,264, table 1). It is concluded that the number of entanglements observed was small, but one should realize that it is an unnecessary threat to seabirds, mainly caused by litter which is deliberately thrown away. There is no evidence of large scale drowning of auks in fishing nets off the Dutch coast, although more and more gill-nets are used here by Danish fisherman. It is unknown how many divers, grebes, cormorants and wildfowl drown in nets in the Wadden Sea and the Delta area.