From scientific obscurity to conservation priority: Research on angler catch rates is the catalyst for saving the hump-backed mahseer Tor remadevii from extinction

The mahseer (Tor spp.) fishes of South and Southeast Asia are iconic megafaunal species that are highly valued by recreational anglers. Knowledge on their populations is limited owing to the challenges associated with sampling these large-bodied fishes (>50 kg) in remote monsoonal rivers. Despite its global iconic status among recreational anglers, the hump-backed mahseer of the Cauvery River (South India) lacked a valid scientific name and was on a trajectory towards extinction until its rapidly declining population status was established by analyses of angler catch records. Angling records from 1998 to 2012 showed that mahseer catch rates had increased in this period. The resulting publication in Aquatic Conservation (AQC) highlighted the positive role of catch-and-release angling in providing information on data-poor species. However, further analyses showed that these catches comprised not one but two distinct phenotypes. Before 1993, all mahseer captured were hump-backed; since then, a blue-fin phenotype appeared in catches and subsequently dominated them. These results triggered further studies indicating that the hump-backed mahseer was the endemic Tor remadevii and that the blue-fin was the invasive Tor khudree, introduced in 1976 and then stocked periodically from hatcheries. The initial AQC publication successfully demonstrated the high value of organized angling as a monitoring tool for data-poor fishes and its application to assessing the temporal population patterns of large-bodied fishes in monsoonal rivers. It was also the catalyst for initiating subsequent studies on T. remadevii that, together, enabled its recent assessment as 'Critically Endangered' on the International Union for Conservation of Nature (IUCN) Red List. In the absence of the AQC paper, and the subsequent studies that it triggered, it is highly probable that the species would have remained on a trajectory towards rapid extinction. Instead, the first major steps to safeguarding its future have been taken.