Sex and season influence behaviour and physiology of lake trout following angling

Catch-and-release angling exposes fish to challenges that may result in sub-lethal effects or mortality. Lake trout (Salvelinus namaycush) undergo high rates of release because of size-based harvest regulations or voluntary angler behaviour. Here, we examine short-term impairment in lake trout angled during the summer (n = 74) and fall spawning period (n = 33) to inform best practices for angling. Immediately following capture or 0.5 h post-capture, fish underwent reflex and barotrauma assessments, and a small blood sample was collected. Fish were also fitted with an externally mounted biologger equipped with depth, temperature and tri-axial acceleration sensors, that was tethered to allow retrieval of the logger after 14 min. In the summer, reflex impairment and barotrauma at 0 and 0.5 h were significantly correlated. Loss of orientation and bloating were the most observed indicators. Larger fish and those captured at increased depth had higher barotrauma scores, while prolonged fight times decreased the barotrauma score regardless of sampling time. Plasma cortisol, lactate and glucose increased 0.5 h after capture, and extracellular and intracellular pH decreased, all signs that angling was inducing a metabolic response. However, no relationships were found between blood indices and mortality (18.9%). The time required to reach maximum depth after release was longer for fish with increased air exposure but shorter for those with longer fight times. During the fall, fish displayed no mortality or reflex impairment. Anal prolapse was the most observed indicator of barotrauma but only observed in females. Blood indices were most altered 0.5 h after capture, with increased cortisol values for fish that were female, particularly large or captured at deeper depth. Locomotor activity was highest for males and increased with depth. Together, our findings suggest that the effects of catch-and-release angling may be dependent on several factors, including sex, season and angling depth.

Walleye Responses to Barotrauma Relief Treatments for Catch-and-Release Angling: Short-Term Changes to Condition and Behavior

Barotrauma causes stress and impairment in fish and can cause mortality after catch and release. Relief of barotrauma symptoms is necessary to reduce mortality, but we currently know little about sublethal effects associated with relief methods. Here, we assess the condition and behavior of tournament-caught Walleye Sander vitreus with barotrauma by using three popular relief methods: 1) swim bladder venting, 2) deep-water release (descending), and 3) livewell reorientation with fin weights. In a short-term ex situ experiment, 50% of untreated fish with barotrauma did not recover sufficiently to be released after 20 h. Fin weighting immediately improved condition by enabling fish to regain correct orientation; however, only 53% of fin-weighted fish recovered sufficiently to be released. All vented fish were negatively buoyant, but 73% were releasable after the holding period. In a concurrent in situ study, acoustic telemetry showed that Walleye without barotrauma (controls) made variable postrelease movements (total distance: 5.1–27.6 km), descended fish behaved similarly to controls (4.7–28.6 km), and vented fish made the shortest movements (2.6–16.7 km). However, there were no statistically significant differences in distance metrics among groups. Control and descended fish used larger areas and volumes of the lake than vented fish. Descended fish also used significantly deeper depths than vented fish, and control fish were intermediate in the depth used. Telemetry did not indicate mortality of any fish in the in situ study. Our data suggest that without treatment, mortality of Walleye with barotrauma could be as high as 50%. Fin weighting is not an effective catch-and-release aid for Walleye with moderate-to-severe barotrauma, and swim bladder venting may alter short-term, postrelease movements and habitat use. The consequences of these short-term changes to Walleye behavior from a fisheries management perspective are unclear. Eliminating catch-and-release angling in deep water is the best means of managing barotrauma in Walleye. If deep-water angling cannot be avoided, we recommend noninvasive descending over venting.