The Decline and Impending Collapse of the Atlantic Salmon (<i>Salmo salar</i>) Population in the North Atlantic Ocean: A Review of Possible Causes

Dadswell, Michael J.; Spares, Aaron D.; Reader, Jeffrey M.; McLean, Montana F.; McDermott, Tom; Samways, Kurt M.; Lilly, Jessie

doi:10.1080/23308249.2021.1937044

Cited by 45 publications

(40 citation statements)

References 277 publications

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“…Populations of Atlantic salmon have long been declining as a consequence of habitat destruction and overfishing ( Dadswell et al, 2021 ; Pardo et al, 2021 ; Parrish et al, 1998 ), with more recent threats coming from sea cage aquaculture that spreads parasitic copepodids onto wild seaward migrating fish ( Johnsen et al, 2020 ; Krkošek et al, 2007 ). These parasites exert a substantial increased energetic burden on infected fish ( Hvas and Bui, 2022 ), coinciding with observed reductions in body conditions of salmon returning from sea ( Susdorf et al, 2018 ).…”

Section: Introductionmentioning

confidence: 99%

Swimming energetics of Atlantic salmon in relation to extended fasting at different temperatures

Hvas

2022

Conservation Physiology

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Predicted future warming of aquatic environments could make fish vulnerable to naturally occurring fasting periods during migration between feeding and spawning sites, as these endeavours become energetically more expensive. In this study, Atlantic salmon (Salmo salar) acclimated to midrange (9°C) or elevated suboptimal (18°C) temperatures were subjected to critical (Ucrit) and sustained (4 hours at 80% Ucrit) swimming trials before and after 4 weeks of fasting. Fasting caused weight losses of 7.3% and 8.3% at 9°C and 18°C, respectively. The Ucrit was unaffected by fasting, but higher at 18°C. Fatigue was associated with higher plasma cortisol, osmolality, Na+ and Cl− at 18°C, and ionic disturbances were higher in fasted fish. All fish completed the sustained swim trials while maintaining constant oxygen uptake rates (ṀO2), indicating strictly aerobic swimming efforts. At low swimming speeds ṀO2 was downregulated in fasted fish by 23.8% and 15.6% at 9°C and 18°C, respectively, likely as an adaptation to preserve resources. However, at higher speeds ṀO2 became similar to fed fish showing that maximum metabolic rates were maintained. The changes in ṀO2 lowered costs of transport and optimal swimming speeds in fasted fish at both temperatures, but these energetic alterations were smaller at 18°C while routine ṀO2 was 57% higher than at 9°C. As such, this study shows that Atlantic salmon maintain both glycolytic and aerobic swimming capacities after extended fasting, even at elevated suboptimal temperatures, and adaptive metabolic downregulation provides increased swimming efficiency in fasted fish. Although, improved swimming energetics were smaller when fasting at the higher temperature while metabolism becomes elevated. This could affect migration success in warming climates, especially when considering interactions with other costly activities such as coping with parasites obtained when passing aquaculture sites during seaward travel or gonad development while being voluntarily anorexic during upriver travel to spawning grounds.

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Section: Introductionmentioning

confidence: 99%

Swimming energetics of Atlantic salmon in relation to extended fasting at different temperatures

Hvas

2022

Conservation Physiology

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“…Further, some males never leave their home river and instead mature at a small size at the parr life stage, and so, mature individuals returning from the sea can be several thousand times larger than their mature river-bound counterparts. In recent decades, wild Atlantic salmon stocks have been in decline, with factors suggested to have contributed to this decline including climate change, aquaculture, illegal fishing, hydropower dams and harvesting of prey species (Chaput, 2012;Czorlich et al, 2022;Dadswell et al, 2021;Harvey et al, 2022;ICES, 2019;Vollset et al, 2022). Some of these factors have also been associated with life-history changes in the wild stocks, with some populations experiencing a decrease in the number or proportion of early-maturing individuals (Vollset et al, 2022), while others are reporting a decrease in large, late-maturing, individuals (Czorlich et al, 2018(Czorlich et al, , 2022Olmos et al, 2019).…”

Section: Introductionmentioning

confidence: 99%

Strong effects of temperature, population and age-at-maturity genotype on maturation probability for Atlantic salmon in a common garden setting

Åsheim

Debes

House

et al. 2022

Preprint

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Age at maturity is a key life history trait and involves a trade-off between survival risk and reproductive investment, has close connections to fitness, and is an important factor for population structures. Temperature can have a dramatic influence on life history in ectotherms, but this influence may differ between populations. While an increasing number of studies have examined population-dependent reactions with temperature, few have investigated this in the context of maturation timing. Atlantic salmon is a highly relevant study species for improving understanding of this topic as it displays considerable variation in life-history strategies, including maturation timing. Additionally, a large amount of this variation in maturation timing has been associated with a genomic region including the strong candidate gene vgll3, but the effect of this gene in the context of different environments and populations has not been studied. Using a large-scale common-garden experiment, we find strong effects of temperature, population, and vgll3 genotype on maturation in 2-year-old male Atlantic salmon. Observed maturation probability was 4.8 times higher in individuals reared at a mean temperature of 8.6°C compared to 6.9°C. This temperature effect was population-specific and was higher in the southern population compared to the northern population, potentially due to a higher intrinsic growth in the southern population as well as growth-temperature interaction. The early-maturation vgll3*E associated with a significantly higher maturation probability, but there was no vgll3-interaction with temperature or population. Both body condition and body mass associated strongly with maturation; the body-condition association was stronger in fish carrying the vgll3*E allele, and the body mass association was only present in the warm treatment. Our findings demonstrate that the relative effect of vgll3 on maturation timing is similar for two populations and two thermal environments and gives new perspectives on the relative effect of vgll3 compared to such influences. Additionally, we show that populations can vary in their response to temperature change in terms of maturation timing, and that high intrinsic growth could potentially be associated with higher thermal sensitivity for life history variation.

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“…Over the past three to four decades, adult Atlantic salmon abundance has declined markedly (Chaput et al ., 2019; Dadswell, 2000; Kocik & Brown, 2002; Mills et al ., 2013; Potter & Crozier, 2000). Long‐term tagging studies have shown a generally consistent and marked decline in the proportion of salmon returning from migration to sea (Chaput, 2012; Chaput et al ., 2019; Dadswell et al ., 2021). For example, adult return rates in the River Corrib, Ireland, declined from 10% to 20%.y −1 before 1990 to 4%‐8%.y −1 after 1990 (Potter & Crozier, 2000); the River Esk, Scotland, showed an adult return rate of 1.0%‐6.9%.y −1 for 1 SW and 0.5%‐3.0%.y −1 for 2 SW fish before 1985 which declined to 0.2%‐1.0%y −1 for both age classes after 1988 (Friedland et al ., 2000).…”

Section: Changing Migration Costsmentioning

confidence: 99%

An opinion piece: the evolutionary and ecological consequences of changing selection pressures on marine migration in Atlantic salmon

Adams

Chavarie

Rodger

et al. 2022

Journal of Fish Biology

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There are strong signals that the selection forces favouring the expression of longdistance sea migration by Atlantic salmon (Salmo salar) are changing. Unlike many other behavioural traits, the costs of migration are incurred before any fitness benefits become apparent to the migrant. The expression of this behaviour has thus been shaped by selection forces over multiple generations and cannot respond to short interval (within a single generation) environmental change as many other behavioural traits can. Here we provide a framework to examine the evolutionary and ecological consequences of a sustained increase in migration cost. We argue that Atlantic salmon may have entered an evolutionary trap, where long-distance sea migration has become maladaptive because of shifting environmental conditions. We predict that if higher migration costs (affecting survivorship and ultimately fitness) persist, then shifting selection pressures will result in continuing declines in population size. We suggest, however, that in some populations there is demonstrable capacity for evolutionary rescue responses within the species which is to be found in the variation in the expression of migration. Under a scenario of low to moderate change in the selection forces that previously promoted migration, we argue that disruptive, sexbased selection would result in partial migration, where females retain sea migration but with anadromy loss predominantly in males. With more acute selection forces, anadromy may be strongly selected against, under these conditions both sexes may become freshwater resident. We suggest that as the migration costs appear to be higher in catchments with standing waters, then this outcome is more likely in such systems. We also speculate that as a result of the genetic structuring in this species, not all populations may have the capacity to respond adequately to change. The consequences of this for the species and its management are discussed.

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The Decline and Impending Collapse of the Atlantic Salmon (Salmo salar) Population in the North Atlantic Ocean: A Review of Possible Causes

Cited by 45 publications

References 277 publications

Swimming energetics of Atlantic salmon in relation to extended fasting at different temperatures

Swimming energetics of Atlantic salmon in relation to extended fasting at different temperatures

Strong effects of temperature, population and age-at-maturity genotype on maturation probability for Atlantic salmon in a common garden setting

An opinion piece: the evolutionary and ecological consequences of changing selection pressures on marine migration in Atlantic salmon

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