Sub-lethal responses of mahseer (Tor khudree) to catch-and-release recreational angling

Fishes exhibit a range of biological responses to the process of catch-and-release recreational angling. In the last decade, research has begun to consider how such fisheries interactions alter the behaviour (e.g., movement, feeding activity, reproduction) of fish upon release. In this study, we assessed reflex impairment and then affixed radio telemetry transmitters to 34 blue-finned mahseer (Tor khudree) angled on the Cauvery River, India, between February and May of 2015. We then tracked their movements over two time scales: continuously for 90 min post-release, and hourly over a 24 h period. When testing reflex impairment, mahseer were more likely to first lose orientation, followed by loss of tail grab response, then loss of regular operculum beats. Neither reflex impairment nor time taken for fish to swim away from the release site varied significantly with air exposure or handling time. Similarly, movement rates of mahseer were consistent amongst tagging periods. However, trends did indicate that larger fish subject to longer angling and handling times took longer to leave the release site, moved less during the initial release period, and moved less over a 24 h cycle. We recommend that anglers view impairment of multiple reflexes in blue-finned mahseer as an indication that caution in handling is warranted. We also recommend further study of size- and age-based differences in mahseer behaviour, including specific research on responses of trophy-sized mahseer to catch-and-release angling. Our work contributes to the understanding of sublethal behavioural consequences of catch-and-release while generating some of the first information to guide development of best practice guidelines for those catching and releasing blue-finned mahseer.