Spatiotemporal analysis of illegal Coilia nasus fishing linked to suitable habitats modeled with MaxEnt in China

Abstract

Coilia nasus is an endangered freshwater fish in China. Due to overfishing and ecological environment deterioration, its resources are rapidly declining and even facing the risk of extinction. Therefore, conservation measures must be taken immediately to ensure the sustainable resources of C. nasus. The purpose of this study is to predict the suitable habitats of C. nasus in the Yangtze River and to make a spatiotemporal and geographical analysis of the illegal fishing cases of C. nasus in the Yangtze River as part of the conservation efforts. In this study, the MaxEnt model was used to predict the suitable habitats of C. nasus, and the distribution characteristics of illegal fishing cases involving C. nasus were revealed through a spatiotemporal geographic analysis. Based on the collected data of 19 climatic variables, three topographic variables and one flow accumulation variable, we constructed the MaxEnt model, optimized the parameter settings of the MaxEnt software, and called the R package Kuenm to screen and determine the optimal parameters from the MaxEnt model with 1240 different parameter combinations, and predicted the suitable habitats of the C. nasus in the Yangtze River Basin. The results showed that the main breeding areas of C. nasus were mainly concentrated in Chongqing in the upper reaches of the Yangtze River and Jiangsu Province and Shanghai in the middle and lower reaches of the Yangtze River, which had suitable hydrological and topographic conditions for C. nasus survival. In addition, river flow accumulation and temperature are the main variables affecting the distribution of C. nasus in the Yangtze River. At the same time, we analyzed the spatial and temporal distribution of illegal fishing cases of C. nasus and found that there were relatively serious illegal fishing activities in Chongqing and Shanghai, especially in highly suitable habitats areas, where illegal fishing cases broke out frequently, and suggested that high-suitability areas should be prioritised as conservation areas of C. nasus.