Ghost net removal in ancient Lake Ohrid: A pilot study

Abstract

A pilot study on the occurrence of abandoned, lost or otherwise discarded fishing gear (ALDFG) was conducted in the Macedonian part of Lake Ohrid. Focussing on abandoned gill nets, different methods for detection and removal of these so-called ghost nets were tested and effects on biota assessed. As shown with the help of echo sounding, diving and creeping (i.e. towing of armed anchors and grapnels, respectively, over the ground), ghost nets were found to be widely present in this freshwater habitat. Altogether more than 12,000 m of nets were retrieved from water column and lake bottom. Free-floating nets were effectively detected using echo sounding, whereas masses of nets accumulated at underwater obstacles were easier to detect by diving. Creeping led to removal of less numerous but actively fishing ghost nets. Ghost nets contained fish at different stages of decomposition (in addition to birds and crustaceans) indicating that abandoned gear continues fishing over extended periods. Together, the results show that ghost nets are not only a marine problem but can significantly pollute freshwater lakes, too.