Habitat Characteristics of the Indonesian Shortfin Eel (Anguilla bicolor McClelland, 1844) in a River System on Java’s Southern Coast, Indonesia

The Indonesian shortfin eel, Anguilla bicolor, is an economically valuable fishery resource in Southeast Asia, yet it faces significant threats from overfishing, habitat degradation, migration barriers, and pollution. However, limited knowledge regarding its distribution and habitat preferences creates uncertainty in managing and conserving the species effectively. This study aimed to explore the habitat preferences of A. bicolor, particularly during its yellow eel stage, by examining its distribution across different environmental conditions. Over the course of 2020, a total of 89 specimens were collected from 18 sites along the Cikaso River System, located on the southern coast of Java, including both the mainstream and coastal swamp areas. Environmental parameters were also recorded at each site, and multivariate Principal Component Analysis (PCA) was applied to assess their relationship with eel occurrence. Although eels were detected year-round, with sizes ranging from 20.1 to 42.2cm, their numbers were notably higher in the coastal swamp areas compared to the mainstream river. The findings suggest that A. bicolor demonstrates a broad tolerance to a variety of environmental conditions but exhibits a clear preference for brackish waters over freshwater habitats. Specific characteristics of coastal swamp areas, such as salinity, depth, turbidity, and substrate type, were found to be crucial in determining eel distribution. These results highlight the coastal swamp areas as critical habitats during the yellow eel stage. This study highlights the importance of integrative management approaches to protect these vital habitats, ensuring the sustainable future of A. bicolor and other anguillid eel species within the Cikaso River System.