Cortisol predicts migration timing and success in both Atlantic salmon and sea trout kelts

Abstract

Kelts – individuals of anadromous fish species which have successfully spawned and may return to sea to repeat the cycle – are perhaps the least studied life stage of iteroparous fish species. To date, our understanding of what makes them successful in their return migration to sea is limited. We investigated the relationship between three physiological parameters (baseline cortisol, baseline glucose and low molecular weight antioxidants) and the timing and success of Atlantic salmon (Salmo salar) and sea trout (Salmo trutta) kelt migration. To do so, we combined blood samples obtained within 3 minutes of capture and acoustic telemetry to track 66 salmon and 72 sea trout as they migrated out of rivers, into fjords and out at sea. We show that baseline cortisol may be a good predictor of migration success. Individuals with high baseline cortisol levels exited the river earlier but were less likely to successfully reach the sea. Similar relationships were not observed with glucose or antioxidants. We provide the first evidence to support the role of physiological status in migration success in Atlantic salmon and sea trout kelts. Our findings contribute to our understanding of the relationship between physiology and fitness in wild animals. Further, we suggest that migration timing is a trade-off between stress and readiness to migrate.

Nutritional correlates of the overwintering and seaward migratory decisions and long-term survival of post-spawning Atlantic salmon

“…Although the majority of kelts with low body condition initiated downstream migration in the autumn, in contrast with previous studies (i.e. Halttunen et al, 2013; Birnie-Gauvin et al, 2019), no kelts from our study entered the sea before spring and instead decided to overwinter in the lower section of the Middle River or near its mouth. Complementary to our findings on the condition-dependent downstream migration timing of kelts, nutritional status was also linked to overwinter riverine survival, so that the survival probability of 2SW kelts decreased with decreasing post-spawning triglyceride concentration (i.e.…”

“…Similar condition-dependent migration timing of Atlantic salmon kelts, with depleted individuals initiating downstream movement soon after spawning, was previously described by Halttunen et al (2013). In addition to a lower body condition factor in autumn migrating Atlantic salmon kelts (Halttunen et al, 2013), Birnie-Gauvin et al (2019) reported that early migrants tended to have higher baseline plasma cortisol levels compared to spring migrating kelts. This might suggest that kelts perceive low nutritional state and low resource availability as a stressful stimuli, which might trigger the upregulation of cortisol levels for feeding and preparation for salt water.…”

“…Whilst the timing of downriver migration to the marine environment, and to some extent the overwinter survival of Atlantic salmon kelts, have both been linked to nutritional condition and stress state (Belding, 1934; Halttunen et al, 2013; Bordeleau et al, 2018a; Birnie-Gauvin et al, 2019), the few previous telemetry studies documenting natural variation in post-spawning condition and its influence on the migratory behaviour and survival of post-spawned Atlantic salmon were limited in time and space (i.e. to ocean entry; Halttunen et al, 2013; Birnie-Gauvin et al, 2019). As such, it remains unclear how post-spawning condition and the initial decision about when to initiate downstream migration then affect the marine migratory behaviour and longer-term survival of Atlantic salmon kelts that either recondition at sea for from a few months (i.e.…”

Anadromy, potamodromy and residency in brown trout Salmo trutta: the role of genes and the environment

“…Birnie‐Gauvin et al . () also found baseline cortisol to be associated with the migration timing and success of anadromous S. trutta kelts. Birnie‐Gauvin et al .…”

One Hundred Pressing Questions on the Future of Global Fish Migration Science, Conservation, and Policy

“…state and that internal state can in turn influence migration. For example, recent evidence suggests that stress levels and nutritional status can both impact migration distance and success in salmonids (Bordeleau et al, 2018;Birnie-Gauvin et al, 2019a). Few such studies exist, but these can shed light on the mechanistic links between internal state and migratory behavior.…”