Analysis of size-composition of endangered Tor putitora in the critical breeding and nursery grounds of the Nayar (Western Himalaya)

Abstract

Size composition gives an overall estimate of the prevalent length of individuals in the fish stock and, hence, the stock's health. The present study analyzed the size-composition and population structure of Golden Mahseer, Tor putitora in the river Nayar that form their breeding and nursery grounds. The Nayar is located in the critical stretch of Devpryaag and Rishikesh (Garhwal Himalaya), free of any dam/barrage in the river Ganga. The Nayar basin is undergoing rapid land use changes due to increased mining and fellow land formations. This analysis was based on length frequency analysis data obtained from three sampling stations, S1, S2, and S3, in the Nayar River. The highest length frequency (53.3%) of Mahseer was recorded from the size class ranging between 10-20 cm, like earlier records, while only one individual measuring 121.9cm was procured. The length frequency decreases with increasing size beyond 30cm. In contrast to the past, the present study revealed a comparatively distorted population structure in the Nayar, where the pre-reproductive size groups showed dominance over the reproductive population. The reduced spawning biomass could jeopardize the recruitment of the next generation.