Counterintuitive migration patterns by Atlantic salmon <scp><i>Salmo salar</i></scp> smolts in a large lake

Honkanen, Hannele M.; Rodger, Jessica R.; Stephen, Alastair; Adams, Keith L.; Freeman, James; Adams, Colin E.

doi:10.1111/jfb.13650

Cited by 23 publications

(43 citation statements)

References 10 publications

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“…Tagged smolts showed migratory behavioral patterns that were both similar and distinct to other migratory salmonid populations experiencing high predation risks. Residence period and rate of movement of smolts while migrating indicated that a shorter time spent within the river was related to migration success, corroborating the notion that the River Endrick is a high-risk landscape for salmonid juveniles (Furey et al 2016, Honkanen et al 2018, Furey et al 2021). Despite the evidence of high predation pressure found in the river, smolts travelled during the day, especially as they moved further downstream.…”

Section: Discussionsupporting

confidence: 67%

The benefits of merging passive and active tracking approaches: new insights into riverine migration by salmonid smolts

Chavarie

Honkanen

Newton

et al. 2021

Preprint

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The process of smolting is a critical phase in the life-cycle of anadromous salmonids and it has been associated with substantial rates of mortality. Survival during freshwater and marine migration is known to have population level effects, thus an understanding of the patterns of mortality has the potential to yield important insights into population bottlenecks. Despite important advancements in tracking techniques, the specifics of mortality events in anadromous salmonids during their initial migration to sea remains somewhat elusive. Here, we develop a framework combining spatial and temporal detections of smolt riverine migration from two tracking techniques, which enable inferences to be made about mortality locations, causes, and rates. We embed this framework into a fine-scale behaviour study of migration and social structure. In this study, we demonstrate that during their initial riverine transitional phase, smolts were particularly vulnerable to predators. Specifically, avian predation appeared to be the main cause of mortality (42%), although piscine predation events were not trivial (14%). Our results suggested some direct and indirect tagging-induced mortality (e.g., through increased predation vulnerability), which highlights the importance of determining tagging mortality in a telemetry study to ensure adequate interpretation of migration success. There is evidence that predation induced selection on smolt morphology. Unsuccessful river salmon migrants with a phenotype comprising a shorter head and jaw and smaller eye had a higher probability of mortality in the later parts of riverine migration where avian and aquatic predation mortality dominated. In contrast, mortality earlier in river migration was independent of phenotype, most likely a result of tagging effects. Successfully river migrants were found to be interacting with each other, often in a pair or as a trio, indicating that a few individuals of Atlantic salmon and sea trout formed notable intra- and interspecific social associations. However, the heterogeneity of the social associations of successful migrants did not support the assumption that social network features attributed any clear specific benefits of reduced predation risk. Overall, by estimating migration loss and its variability, our study framework should help to guide management actions to mitigate the widespread population declines these species are currently facing.

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Section: Discussionsupporting

confidence: 67%

The benefits of merging passive and active tracking approaches: new insights into riverine migration by salmonid smolts

Chavarie

Honkanen

Newton

et al. 2021

Preprint

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“…Similarly, lacustrine–adfluvial S. trutta can migrate through other lakes to reach their destination lake (Huusko et al ., ). Given that both mortality and energy expenditure of salmonid smolts are considerably increased in passage through lakes compared with rivers (Honkanen et al ., ; Schwinn et al ., ), it might be expected that S. trutta smolts would not continue through a lake unless programmed to do so. In coastal Californian rivers, summer sandbars at estuary mouths result in seasonally closing estuaries that form small productive freshwater lagoons.…”

Section: Migration Destinationmentioning

confidence: 98%

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

Ferguson

Reed

Cross

et al. 2019

Journal of Fish Biology

147

176

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Brown trout Salmo trutta is endemic to Europe, western Asia and north‐western Africa; it is a prominent member of freshwater and coastal marine fish faunas. The species shows two resident (river‐resident, lake‐resident) and three main facultative migratory life histories (downstream–upstream within a river system, fluvial–adfluvial potamodromous; to and from a lake, lacustrine–adfluvial (inlet) or allacustrine (outlet) potamodromous; to and from the sea, anadromous). River‐residency v. migration is a balance between enhanced feeding and thus growth advantages of migration to a particular habitat v. the costs of potentially greater mortality and energy expenditure. Fluvial–adfluvial migration usually has less feeding improvement, but less mortality risk, than lacustrine–adfluvial or allacustrine and anadromous, but the latter vary among catchments as to which is favoured. Indirect evidence suggests that around 50% of the variability in S. trutta migration v. residency, among individuals within a population, is due to genetic variance. This dichotomous decision can best be explained by the threshold‐trait model of quantitative genetics. Thus, an individual's physiological condition (e.g., energy status) as regulated by environmental factors, genes and non‐genetic parental effects, acts as the cue. The magnitude of this cue relative to a genetically predetermined individual threshold, governs whether it will migrate or sexually mature as a river‐resident. This decision threshold occurs early in life and, if the choice is to migrate, a second threshold probably follows determining the age and timing of migration. Migration destination (mainstem river, lake, or sea) also appears to be genetically programmed. Decisions to migrate and ultimate destination result in a number of subsequent consequential changes such as parr–smolt transformation, sexual maturity and return migration. Strong associations with one or a few genes have been found for most aspects of the migratory syndrome and indirect evidence supports genetic involvement in all parts. Thus, migratory and resident life histories potentially evolve as a result of natural and anthropogenic environmental changes, which alter relative survival and reproduction. Knowledge of genetic determinants of the various components of migration in S. trutta lags substantially behind that of Oncorhynchus mykiss and other salmonines. Identification of genetic markers linked to migration components and especially to the migration–residency decision, is a prerequisite for facilitating detailed empirical studies. In order to predict effectively, through modelling, the effects of environmental changes, quantification of the relative fitness of different migratory traits and of their heritabilities, across a range of environmental conditions, is also urgently required in the face of the increasing pace of such changes.

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“…A number of diadromous fish species have experienced dramatic declines throughout their range due to disruption of habitat connectivity due to anthropogenic barriers such as weirs, dams and hydropower facilities (Dadswell and Rulifson 1994;Birnie-Gauvin et al 2018;Puijenbroek et al 2019). Many freshwater systems have anthropogenic barriers impeding fish movement, as well as lakes that diadromous fishes must navigate through to reach the marine environment (Limburg and Waldman 2009;Nunn and Cowx 2012;Honkanen et al 2018Honkanen et al , 2021. How diadromous fishes navigate through standing waters is poorly understood (Honkanen et al 2018;Lennox et al 2021;Honkanen et al 2021).…”

Section: Introductionmentioning

confidence: 99%

Combining acoustic telemetry with a mechanistic model to investigate characteristics unique to successful Atlantic salmon smolt migrants through a standing body of water

et al. 2021

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The Atlantic salmon, Salmo salar Linnaeus 1758, is a charismatic, anadromous species that has faced dramatic declines throughout its range. There is currently a lack of information on the effect of free-standing bodies of water on a key life event, sea migration, for the species. This study extends our understanding in this area by combining acoustic telemetry with a correlated random walk model to try to examine potential morphological and behavioural factors that differentiate successful from unsuccessful migrants through Scotland’s largest lake. Consistent with other studies, we found that smolts experienced a high rate of mortality in the lake (~ 43%), with approximately 14% potentially predated upon by birds and 4% by Northern pike. Migration speed in the lake was slow (the mean minimum movement speed between centres of activity was 0.13 m/s), and pathways frequently deviated away from the outlet river. There was no evidence of a morphological or behavioural trait or migratory pathway that distinguished successful from unsuccessful smolts. This suggests that migration movement direction in the main body of Loch Lomond appeared to be random. This was further supported by the output of a correlated random walk model which closely resembled the pathway and migration speed and distance patterns displayed by successful migrants. However, once successful smolts came within ~2 km of the lake exit, a high proportion remained in this region prior to entering the River Leven. We suggest that this “goldilocks zone” is where directional cues become apparent to migrating fish. Future studies should combine random walk models with environmental variables to determine if external factors are driving the apparently random movement patterns exhibited by smolts in lakes.

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Counterintuitive migration patterns by Atlantic salmon Salmo salar smolts in a large lake

Cited by 23 publications

References 10 publications

The benefits of merging passive and active tracking approaches: new insights into riverine migration by salmonid smolts

The benefits of merging passive and active tracking approaches: new insights into riverine migration by salmonid smolts

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

Combining acoustic telemetry with a mechanistic model to investigate characteristics unique to successful Atlantic salmon smolt migrants through a standing body of water

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