Temporal variations in fish diversity in the main channel of the Chaliyar River, Western Ghats, Kerala, India

The present study examined the temporal patterns in ichthyofaunal diversity of the Chaliyar River over a three-year period (2017–2020), including the extreme flood year of 2018. Fish samples were collected from eight sampling stations distributed across three river stretches during pre-monsoon, monsoon, and post-monsoon seasons using multiple fishing gears. A total of 2,347 specimens belonging to 53 species, 25 families, and 11 orders were recorded. Biodiversity assessment was performed using species richness, dominance index, and Shannon–Wiener diversity index, along with dominance curves and cluster analysis. The results indicated a noticeable decline in fish diversity during 2018 (0.94), coinciding with the flood event, suggesting ecological disturbance in the river system. Cypriniformes and Perciformes dominated the ichthyofaunal assemblage across the study period. Cluster analysis highlighted distinct seasonal patterns, with monsoon observations forming a separate cluster. Conservation assessment highlighted the ecological sensitivity of the Chaliyar River and emphasised the need for community-based conservation, continuous monitoring, and scientifically informed management strategies to sustain riverine fish diversity.  Keywords: Dendrogram, Dominance index. Ecological disturbance, Fish samples, Ichthyodiversity, Monsoon, Species richness