Satellite Observation of the Marine Light-Fishing and Its Dynamics in the South China Sea

Huiting Li,Chao Sun,Siyu Zhang,Yongxue Liu,Yanzhu Dong

doi:10.3390/jmse9121394

Abstract

The South China Sea (SCS) is one of the most important fishery resource bases in the world. Marine fisheries, as a crucial component of regional food security and national revenue, raise wide concern about marine ecology, social-economic and political consequences at regional, national and local scales. The large-scale dynamic detection and analysis of fishing activity in the SCS is still unclear because of the accessibility of in-site data, finite automatic identification system (AIS) usage, complex geopolitics and poor additional data coverage. Nighttime light imagery (NTL) derived from low light imaging sensors and the popularity of light fishing in the SCS offers a unique way to unveil fishing activities and its dynamics. In this study, we proposed a set of algorithms for automatic detection of nighttime fishing activity and provided the first large-scale dynamic analysis of nighttime fishing activity in the SCS using monthly Visible Infrared Imaging Radiometer Suite (VIIRS) images between 2012 and 2019. The proposed method effectively minimized the spatio-temporal fluctuations in radiance values of background and their implications to ship detection by integrating high radiance gradient detection and local adaptive thresholding. Further, nighttime fishing activity trajectories were decomposed into trend and seasonal components by using Hilbert-Huang transformation (HHT) to accurately access general trends and the seasonality of nighttime fishing activity in the SCS. The typical subregions analysis, environmental driver analysis, correlation coefficient analysis and hot spot analysis were integrated to characterize the nighttime fishing activity. It appears that the nighttime fishing activity in the SCS exhibited spatio-temporal variability and heterogeneity and was shaped by policy and natural factors such as holidays, annual Chinese fishery moratoria in the Chinese Exclusive Economic Zone (EEZ) and seasonal tropical storm activity.

Highlights

We have developed a set of algorithms for automatic detection of fishing than those of the background
We have developed a set of algorithms for automatic deactivity and further investigated large-scale fishery dynamics in the South China Sea (SCS) using monthly tection of fishing activity and further investigated large-scale fishery dynamics in the SCS
Only a small portion of fishing activity was detected in the deep sea

Summary

Introduction

The South China Sea (SCS) is one of the most important fishery resource bases in the world. It remains one of the top five most productive fishing areas in the world in terms of fisheries catch and simultaneously possesses immense marine aquaculture production quantity [1]. From the late 1980s to the early 1990s, fishery product exports from the SCS comprised an average of 11% of annual world exports, increasing to 27% by 2011. Fisheries resources in the SCS play a crucial role in marine ecology, coastal livelihoods, food security, and export trade to surrounding countries [2,3]

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