Performance of VMS and nightly satellite in monitoring light fishing vessels in the open South China Sea

With the development of satellite technology, vessel monitoring has entered a new era. In this study, through a comparison with better-recorded fishing logs, we analyzed the performance of vessel monitoring system (VMS) and nightly satellite data in monitoring fishing activities of a large-sized falling net vessel mainly targeting the purpleback flying squid (Sthenoteuthis oualaniensis) in the open South China Sea. Logbook data indicate that the studied vessel operated fishing for 57 days in the 3-month fishing season, performing a total number of 474 fishing hauls with ∼233.7 tons of catches. Our analysis indicated that with VMS data only, fishing state can hardly be distinguished from the drifting one, while even under the influence of clouds, the nightly satellite can identify most (98 %) of the fishing operations that were emitting bright lights. In addition, catch rates recorded by fishing logs significantly correlated with the numbers of lighted lamps when the nightly satellite passed over, which implies that the radiance may even be used as a proxy for catch. Although the radiance emitting from lighted lamps onboard a fishing vessel and detected by a nightly satellite is influenced by a number of factors, such as cloud conditions and satellite viewing zenith angle, jointly use of VMS and nightly satellite data can be an effective approach in monitoring and managing this type of light fishing vessels.