Habitat use of the Japanese eel (Anguilla japonica) and marbled eel (Anguilla marmorata) in the large subtropical Pearl River

Anguilla spp. are catadromous fish and with a high economic value in Asia. The Pearl River is the largest river in southern China and is an important area for wild populations of Anguilla spp. However, until now, there has been little research on the eel's population structure and habitat use in the Pearl River. This study analyzed the population structure and habitat use characteristics of the Japanese eel (Anguilla japonica ) and the marbled eel (Anguilla marmorata ) in the Pearl River based on data collected from 2015 to 2018. A total of 181 Japanese eels and 56 marbled eels were collected, over half of which were middle-sized eels between 255 and 600 mm in length. Although they are sister species, Japanese eels mainly inhabit complex river habitats characterized by high river fractals and coefficients of fluvial facies, while marbled eels mainly inhabit wider and deeper river sections. The impact of physical environmental factors (such as river fractals, coefficients of fluvial facies and river width) on the distribution of these two species is greater than the impact of small-scale water quality environmental factors (such as DO concentration, temperature and clarity). The results of this study showed that wild Anguilla spp. resources in the Pearl River were extremely low and there was an urgent need for conservation and management of eel resources in south China.