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Using nonlethal tissue biopsies, we investigated somatic energy, lipid composition, and condition in post-spawned Atlantic salmon (Salmo salar) (kelts, n = 69) returning to sea in the spring and explored contrasts as a function of previous migration and spawning history, length and sex. Using mark–recapture analysis, we also explored linkages between spawning history and probability of future repeat spawning. Lipid density was significantly higher in previously spawned individuals compared to first-time spawned fish and in females compared to males. Fatty acid composition differed significantly among spawning histories. Return rates to consecutive spawning the following year were consistent with spawning history-dependent differences in lipid density, as first-time spawned kelts had lower return rates compared to consecutive repeat spawned kelts. We suggest that spawning history related contrasts in nutritional state in post-spawned Atlantic salmon may be a carry-over effect of differences in the feeding habitat as affected by spawning-history-dependent migration strategies. Alternatively, it may represent an adaptive response to increased survival and recovery potential with age. [ABSTRACT FROM AUTHOR]

Atlantic salmon are facing population declines and loss of productivity within populations due to anthropogenic impact factors and reduced survival at sea. Biobanking is an increasingly used tool to conserve the genetic integrity and diversity of populations threatened by extirpation. The aim of the current article is to discuss the opportunities and challenges that increased use of cryopreservation brings to biobanking activities, using the Norwegian Gene Bank (NGB) for Atlantic salmon as a model system. The NGB was established in 1985 and involves a traditional living gene bank, as well as "frozen gene bank" where paternal germplasm is stored as cryopreserved sperm. Cryopreservation is a method where cells or tissues are frozen in liquid nitrogen to temperatures where all biological processes are paused, thus allowing the cells to remain viable after later warming/thawing to temperatures above 0°C. Cryopreservation is therefore used in long‐term preservation of genetic diversity and characteristics of wild populations. Until recently, implementation of large scale use of cryopreserved sperm in the live gene bank has been limited by a lack of protocols/capacity to preserve larger portions of sperms. More recent developments in cryopreservation methodologies, now enables preservation of samples sufficient for mass fertilization. Mass fertilization by cryopreserved sperm opens new opportunities to gene bank operations, including increased capacity to restore lost populations, mitigation of genetic changes in broodstock fish, as well as increased capacity at live gene bank facilities through the replacement of older males with frozen sperm. Knowledge demands regarding potential genetic damage to cryopreserved milt and potential epigenetic effects caused by the cryopreservation procedure should, however, be addressed. [ABSTRACT FROM AUTHOR]

Migratory behaviour may vary according to the life history and demographic attributes of fish and lead to the spatial segregation of distinct population segments during the non-breeding season. In adult Atlantic salmon, spawning history differences are associated with intra-population variation in marine movements, but the degree of connectivity in spatial resource use among and within maiden and repeat spawning salmon is not well understood. We analysed muscle fatty acids (FAs), δ13C and δ15N of Atlantic salmon returning to spawn, and found significant differences among spawning histories. Maiden and alternate repeat spawning Atlantic salmon were differentiated from consecutive repeat spawners by fatty acid biomarkers associated with distinct biogeographic regions of the Labrador Sea, consistent with differential migration and divergent feeding locations. The presence and pattern of feeding contrasts among spawning history groups were further supported by dorsal muscle δ15N, which covaried with FA compositional values and distinguished consecutive repeat spawners from the two other groups. Because the degree of connectivity among population segments affects the ecological factors faced by such groups, an improved understanding of differential migration is necessary to better predict potential population responses to environmental change. [ABSTRACT FROM AUTHOR]

Owing to the iteroparous nature of Atlantic salmon (Salmo salar), a seaward migrating cohort may consist of juveniles and adults that differ in size, maturity, experience, and in the motivation and consequences of migratory movements. Few studies have investigated the role of ontogeny in shaping intrapopulation variability in movement patterns among Atlantic salmon monitored under the same environmental conditions. This study contrasted the movements of smolts and kelts in two Canadian (Newfoundland) populations from marine entry through coastal embayments and quantified the influence of local water temperatures on movement patterns. Significant differences in migration routes, migration speed, and diel movements between smolts and kelts were present. Kelts generally displayed faster, more directed, and less nocturnal movements compared with smolts. Temperature influenced seaward movement positively, as well as the degree of diurnal movement. Prolonged nearshore residency by smolts and kelts in the two embayments was accompanied by a considerable improvement in ocean thermal conditions, hypothesized to promote open ocean entry during conditions favorable to migration performance. [ABSTRACT FROM AUTHOR]

Iteroparity occurs when organisms reproduce more than once, and is seen as a bet-hedging reproductive strategy. Despite a wealth of research on iteroparous Atlantic salmon, steelhead, brown trout, and Arctic charr, the determinants of reproductive investment, the intra- and interspecific differences in the degree of iteroparity, the drivers of repeat spawning, and the contribution of repeat spawners to populations and sustainability remain unclear. In particular, the knowledge base is stronger for Atlantic salmon and brown trout, but relatively weak for Arctic charr and steelhead. While juveniles, maiden spawners and repeat spawners are facing similar challenges, many threats specific to the kelt stage are emerging (e.g., downstream migration passed barriers after spawning). Recent work has quantified the benefits of iteroparity for population resilience, and the potential for iteroparity to increase when anthropogenic stressors are mitigated. This is the first literature review paper synthetizing the growing knowledge base that exists on various aspects of the ecology and biology of repeat spawners in freshwater and at sea, the threats they face, the proximate and ultimate mechanisms underlying iteroparity in salmonids, the importance of iteroparity for population-level processes, as well as highlighting pressing areas of research. Collectively, this work offers a valuable resource to fisheries scientists and managers by shedding light on an important life-history stage that warrants more attention to mitigate these threats and restore healthy wild salmonid populations. [ABSTRACT FROM AUTHOR]

We investigated the response of Atlantic salmon (Salmo salar) to capture and handling stressors by analyzing fine-scale locomotor activity using accelerometer data loggers and broader-scale movements by tracking migration with radiotelemetry. Half the sample population was exposed to experimental exercise and air exposure and released with a control group to simulate fisheries handling. All but two of the surviving fish (both in the treatment group) returned to the counting fence to resume the 2016 spawning migration (survival = 86%–91%). There were no differences in postrelease locomotor activity, measured by an index of total body action (jerk), between control and treatment salmon (p = 0.81). Comparison of mean time to return to the counting fence against a null model revealed that treatment salmon were significantly delayed in returning to the counting fence (p < 0.01), whereas control fish were not (p = 0.24). Both the abiotic environment and human interactions influenced locomotor activity of the migratory fish and synchrony of the migration with untreated conspecifics. [ABSTRACT FROM AUTHOR]