After the spawn and on the hook: Sea trout Salmo trutta biophysical responses to different components of catch and release in a coastal fishery

Abstract

This study investigated the biophysical responses of sea run brown trout Salmo trutta to catch-and-release in the coastal fishery around Gotland, Sweden. It used information recorded on individual angled S. trutta (n = 162), including fight time, handling time, total air exposure time, injury, bleeding, fish length, body condition, spawning status, water temperature, hook location and difficulty of hook removal. Reflex action mortality predictors (equilibrium, operculum beats, tail grab response, body flex response and vestibular-ocular response), tests of blood glucose and lactate, and observation of hooking injury were used to measure the relative impact of the angling event on the fish's physical state and stress experienced. The results of this study suggest low rates of post-release mortality and generally limited stress responses to angling events, and relatively high post-release survival supported by the recapture of many tagged S. trutta. However, a number of scenarios were identified in which stress responses are likely to be compounded and where anglers should take additional action to reduce sublethal physiological disturbances and the risk of delayed mortality. Particular care should be taken to limit cumulative total air exposure to <10 s, and to reduce handling time and risk of additional injury in angling events with extended fight times, when water temperatures >10 C, or where S. trutta show evidence of being physically compromised by injury or having recently spawned. The results also indicate the importance of using appropriately sized single hooks rather than larger treble hooks to reduce hooking injury and handling time during unhooking.

hysiological and Behavioural Responses of Lake Trout to Catch-And-Release Angling

“…There is limited knowledge on how angling impacts fish that have completed or are actively spawning. Sea-run brown trout (Salmo trutta) angled after a recent spawn displayed no reflex impairment immediately after capture in 48% of fish (Blyth and Bower 2022). In another study, reflex impairment increased predictably with air exposure during angling treatments on Pacific salmon caught after their arrival to spawning locations (Raby et al 2013).…”

“…Female fish also display elevated levels of lactate and glucose (Jeffries et al 2012). Increased lactate levels are generally associated with fight time Twardek et al 2018a;Blyth and Bower 2022), which is to be expected due to lactate being a by-product anaerobic exercise (Milligan and Wood 1986). Surprisingly lactate was not significantly higher in females in the present study.…”