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

Abstract

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.

Keywords: Barotrauma; catch-and-release; mortality; reflex; stress.

Figure 1

Totalled impairment scores for (A) summer reflex, (B) summer barotrauma and (C) fall barotrauma predictors in lake trout (S. namaycush) sampled following angling. Reflex metrics include (1) tail grab, (2) body flex, (3) head complex, (4) vestibular–ocular response, and (5) orientation. Barotrauma metrics include (1) oral organ eversion, (2) exophthalmia, (3) bloating, (4) anal organ eversion, and (5) haemorrhaging.

Figure 2

Concentrations of (A) plasma cortisol, (B) plasma lactate, (C) plasma glucose and (D) extracellular pH in lake trout (S. namaycush) sampled at 0 (n = 32) or 0.5 h (n = 26) following summer angling. Thick black horizontal lines denote median values, boxes contain all data within the 25th and 75th quartiles, whiskers show the range of data and outliers are depicted as black dots. Asterisks above horizontal brackets denote effect size (^***Cohen’s d ≥ 0.8, ^**Cohen’s d ≥ 0.5, ^*Cohen’s d ≥ 0.2).

Figure 3

Mean (A) ODBA and (B) depth use over time post-capture by lake trout (S. namaycush) exhibiting normal (n = 9) and impaired behaviour (n = 42) possibly due to barotrauma injuries following summer angling. Also, mean (C) ODBA and (D) depth use over time post-capture by male (n = 15) and female (n = 15) lake trout following angling during the spawning period. Standard error is depicted as grey bands.

Figure 4

Concentrations of (A) plasma cortisol, (B) plasma lactate, (C) plasma glucose and (D) extracellular pH in lake trout (S. namaycush) sampled at 0 h (n males = 5, n females = 5) or 0.5 h (n males = 5, n females = 5) following fall angling. Thick black horizontal lines denote median values, boxes contain all data within the 25th and 75th quartiles, whiskers show the range of data and outliers are depicted as black dots. Asterisks above horizontal brackets denote effect size (^***Cohen’s d ≥ 0.8, ^**Cohen’s d ≥ 0.5, ^*Cohen’s d ≥ 0.2).