Nighttime fishing vessel observation in Bohai Sea based on VIIRS fishing vessel detection product (VBD)

Abstract

Remote sensing of night light can be used to detect lights at night and identify the location of fishing boats at sea. Visible Infrared Imaging Radiometer (VIIRS) onboard NASA's SNPP (Suomi National Polar Partnership) satellite has remarkably improved the detection capabilities compared to previous satellites, therefore enabling the production of VBD (VIIRS Boat Detection) with better quality. In this study, we investigated the relationship between fishing activities and environmental factors using generalized additive models (GAMs). We utilized three spatial indexes: cluster index, heterogeneity index, and geographical center, to study the spatiotemporal distribution of fishing boats at night and their seasonal variation in the Bohai Sea based on the 12-months data in 2020. We observed that fishing activities fluctuated over time, with troughs in February and from May to August, which were respectively influenced by the lunar new year and summer fishing moratorium. At the end of the lunar new year and the moratorium, the fishing activities rebounded significantly. Returning boats from Shandong province caused a secondary peak in December. Spatially, detected fishing activities mostly took place in near-shore fishing grounds, such as Bohai Bay and Liaodong Bay, but were rare in central Bohai Sea. The convex hull of monthly geographical centers resembles a triangle. The shifting monthly geographical centers within the triangle was caused by the clustering of fishing boats in three fishing grounds: Liaodong Bay, Bohai Bay and Laizhou Bay, at different time. The results of this study can be used as a reference for the monitoring of fishery activities and fishery economic research in the Bohai Sea. The research methodology provides a low-cost way to track and monitor fishing vessels, therefore providing necessary information for decision making.