Impact of derelict fishing gear on the seafloor integrity and benthic communities in the macrotidal flats from northern Gyeonggi Bay, west coast of Korea

Abstract

Derelict fishing gear (DFG) is increasingly common in the Korean tidal flats due to intensive fishing activity and the lack of monitoring system to remove the DFG from the tidal flats. Despite the widespread occurrence of DFG in the tidal flats, little is known about DFG in terms of quantity, types, distribution, and the impact on the benthic ecosystem. Unmanned aviation vehicle (UAV)-assisted photogrammetry and high-precision leveling were conducted to characterize DFG in the macrotidal flat, south of Gangwha Island, west coast of Korea. High concentration of DFG occurs preferentially in the channel where nets with stakes were installed for catching fishes. Topographic relief around DFG is more rugged and pronounced in the lower intertidal zone than in the middle intertidal zone, suggesting more dynamic sedimentary processes related to DFG in the lower intertidal zone. The density of benthic species is nearly identical in the middle intertidal zone regardless of the presence of DFG. In contrast, the density of macrofauna in the lower intertidal zone nearly doubles at the area free of DFG compared to the area affected by DFG. The biomass and primary production of the microphytobenthos (MPB) are smaller in the lower intertidal zone than the middle intertidal zone but show no discernible trend related to the presence of DFG. Strong tidal currents in the lower intertidal zone induce larger vortices over DFG and promote rapid deposition and erosion around DFG, resulting in a more hostile condition for the benthic ecosystem. The present study showcased that UAV-assisted mapping provides an effective tool to characterize the distribution and physical disturbance caused by DFG in the macrotidal flats, which will be a breakthrough for the sustainable management of rapidly deteriorating tidal flats with poor accessibility.