Ghost fishing by monofilament and multifilament gillnets in Izmir Bay, Turkey

To investigate and compare ghost fishing by monofilament and multifilament gillnets, six monofilament and six multifilament experimental gillnets (each 33 m long) were deployed at two locations, set at various depths between 9 and 14 m in Izmir Bay (eastern Aegean Sea). The gillnets were monitored every other day by divers. Each captured fish or crustacean was tagged to enumerate the total catch. The experimental gillnets at one location (three monofilaments and three multifilaments) were lost after the 42nd day. At the other location, ghost fishing continued for 106 days by the monofilament gillnets and for 112 days by the multifilament gillnets. A total of 29 species (22 fish, 5 crustacean, 1 cephalopod, and 1 gastropod) were captured by the ghost gillnets at the two locations. In addition, 17 specimens of the endangered species Pinna nobilis were killed during the study. Weekly fish catch rates of both gillnet types declined exponentially. Repeated-measures analyses of variance revealed that the total catch rates of fish in the monofilament gillnets were significantly higher (P < 0.05) than those in the multifilament gillnets. After six months of deployment, the effective fishing areas of the monofilament and the multifilament gillnets decreased by 55 and 63%, respectively. One year after deployment, all the multifilament gillnets had completely collapsed; one monofilament gillnet had disintegrated and totally lost its fishing ability whereas the other two monofilament gillnets were excessively colonized by biota and the nets were about to collapse.