The impact of twine materials on the catch efficiency of abandoned, lost or otherwise discarded fishing gear (ALDFG) on crustaceans: an experimental study from Turkish inland set net fishery

Abstract

Context Abandoned, lost or otherwise discarded fishing gear (ALDFG) represent a persistent pollution source in freshwater ecosystems, continuously capturing crustaceans long after being converted into ghost nets. Aim This study aims to experimentally determine the effects of the twine material (monofilament or multifilament) of ghost set nets (gillnets and trammel nets) on the catch efficiency on crustaceans. Method The study, conducted in Eğirdir Lake (south-western Türkiye) during 2014–15, using gillnets of varying mesh size (80–90–100-mm stretched mesh size) and trammel nets (110–120–130-mm inner panel stretched mesh size), all rigged with monofilament or multifilament twine materials. Set net panels, each measuring 25 m in headrope length, were randomly joined by their headropes and deployed simultaneously on the same day. Over the course of the 1-year study, the nets were retrieved from the lake on Days 1, 7, 15, 30, 60, 90, 120, 150, 180, 210, 240, 270, 300, 330 and 360. In total, 13,500 m of experimental set nets were used in the study (25-m panel × 6 different mesh sizes × 2 twine materials × 3 stations × 15 harvest periods). The length and weight measurements of the crustaceans caught in the experimental ghost nets were recorded. Key results The study determined that there was no statistically significant difference in catch yield between monofilament and multifilament ghost nets; however, monofilament nets were found to be more effective than were multifilament nets on individuals below the minimum conservation reference size (MCRS), although this difference was not statistically significant. Conclusions Consequently, although their effectiveness varied according to size class, both twine materials caused significant harm to crustaceans when converted into ghost nets, indicating that net material type alone is insufficient to mitigate ALDFG impacts. Implications These findings underscore the urgent need to develop biodegradable net materials and self-disabling fishing gear designs, while implementing comprehensive ghost net recovery programs and strengthening regulatory enforcement in vulnerable freshwater ecosystems to protect crustacean populations and ensure sustainable fisheries management.