Impact of catch-and-release practices on behavior and mortality of Atlantic salmon ( Salmo salar L.) kelts

Abstract

Kelts of Atlantic salmon (spent Salmo salar L .) are often caught and released (C&R) by anglers before and during their seaward migration in the river, but the extent of captures and the biological and management implications have not been previously evaluated. In this study, we investigate the impact of C&R on behavior and mortality of kelts by using telemetry. In total 73 Atlantic salmon kelts were tagged with acoustic tags after angling in spring 2008 in the sub-arctic River Alta, Norway. They were tracked manually in the river and recorded during their initial marine migration on arrays of acoustic receivers deployed across the Alta Fjord up to 30 km from the river mouth. To increase the sample size – in order to reliably quantify capture rates of kelts during the recreational angling season – telemetry was combined with mark-recapture. Recapture rates, behavior and survival of the angled and tagged kelts were compared to a control group of salmon ( n = 17) tagged acoustically 7–10 months earlier, and therefore considered unaffected by recent angling and tagging. The recapture rate of the control group kelts (18%) did not differ from the recapture rate of the kelts tagged in spring (14%), and only a small proportion of the tagged kelts (2%) was recaptured more than once the same season. In total, 4% of the kelts died after C&R in the river and 92% migrated out the fjord on average 1 month after catch, tagging and release. The C&R fish descended the river slower than the uncaught control group, but no difference in the start of their marine migration, migration progression or survival was observed between the compared groups. We conclude that (1) C&R affected the post release behavior of kelts only by delaying the river descent, and (2) the delayed post release mortality rate of C&R kelts was not elevated despite the reduced energy levels and physiological condition of kelts. Hence, releasing angled kelts can be a viable management strategy to enhance the return rate of repeat spawners.