Context-dependent impact of an ectoparasite on early marine growth in Atlantic salmon

Vollset, Knut Wiik; Barlaup, Bjørn Torgeir; Friedland, Kevin D.

doi:10.1016/j.aquaculture.2019.04.038

Cited by 10 publications

(8 citation statements)

References 27 publications

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“…Therefore, negative effects of lice on the growth of the fish are easily masked. Reduced growth rates in Atlantic salmon, due to lice infections, are shown previously, both from field and laboratory studies (Skilbrei & Wennevik, 2006; Skilbrei et al, 2013; Susdorf et al, 2018; Tveiten, Bjørn, Johnsen, Finstad, & McKinley, 2010), but depend on marine survival (Vollset, Barlaup, & Friedland, 2019).…”

Section: Discussionsupporting

confidence: 52%

Timing is everything: Survival of Atlantic salmon Salmo salar postsmolts during events of high salmon lice densities

Bøhn

Gjelland

Serra‐Llinares

et al. 2020

Journal of Applied Ecology

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Atlantic salmon in aquaculture act as reservoir hosts and vectors of parasites like salmon lice and this parasite is shown to harm wild salmonid populations. In this study, n = 29,817 tagged Atlantic salmon were studied in four release trials. Half of the released fish were given prophylactic treatment against lice, the other half represented sham control fish. We used a nested design comparing years with low and high lice density and seasonal dynamics in infestation pressure. The released Atlantic salmon thus experienced highly variable lice infestation pressures, which we linked to survival and growth in returning fish. The fish were released in a protected ‘National Salmon Fjord’ and n = 559 Atlantic salmon were recaptured after spending 1–4 years at sea. In most experimental groups 1%–2.5% of the fish were recaptured at return. However, survival of unprotected fish was extremely low for the trial released at the highest density of lice: only 0.03% of these Atlantic salmon returned to the river, compared to 1.86% in the protected group. Synthesis and applications. We document that high lice density can cause more than 50 times higher mortality risk in Atlantic salmon on their sea migration, even in a fjord with protected status. Fine‐tuned and hard‐to‐predict year‐to‐year differences in timing, both for the wild smolt migration and the population build‐up of lice released from aquaculture, means life or death to wild salmon. Management actions such as spatial segregation of farmed fish and lice (e.g. closed farm pens), and/or moving farms away from vulnerable habitats for wild salmonids (fjords and coastal areas), may be needed to ensure sustainable coexistence of wild and farmed Atlantic salmon.

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Section: Discussionsupporting

confidence: 52%

Timing is everything: Survival of Atlantic salmon Salmo salar postsmolts during events of high salmon lice densities

Bøhn

Gjelland

Serra‐Llinares

et al. 2020

Journal of Applied Ecology

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“…Effects of Atlantic salmon farming include genetic introgression of farmed genes due to spawning of escaped farmed salmon and spillover effects of salmon lice ( Lepeophtheirus salmonis ) and other parasites and pathogens that disperse through the water column ( 37 – 39 ). In farm-intensive areas, mortality of wild Atlantic salmon due to salmon lice may be considerable, and for survivors, the marine growth may be affected ( 40 ). Introgression of escaped farmed salmon also affects marine survival ( 41 , 42 ) and the size and life history of Atlantic salmon ( 43 ).…”

Section: Discussionmentioning

confidence: 99%

“…However, note that impacts of variable marine conditions are not disentangled from impacts of salmon lice. For example, the effects of salmon lice on marine growth of Atlantic salmon are much stronger during years of low marine survival compared to years with higher marine survival ( 40 ). In the face of apparent marked changes in the marine environment of Atlantic salmon, it seems even more important to reduce negative human impacts on Atlantic salmon populations in years with poor ocean conditions ( 19 ).…”

Section: Discussionmentioning

confidence: 99%

Ecological regime shift in the Northeast Atlantic Ocean revealed from the unprecedented reduction in marine growth of Atlantic salmon

Vollset

Urdal²,

Utne

et al. 2022

Sci. Adv.

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Ecological regime shifts are abrupt changes in the structure and function of ecosystems that persist over time, but evidence of contemporary regime shifts are rare. Historical scale data from 52,384 individual wild Atlantic salmon caught in 180 rivers from 1989 to 2017 reveal that growth of Atlantic salmon across the Northeast Atlantic Ocean abruptly decreased following the year 2004. At the same time, the proportion of early maturing Atlantic salmon decreased. These changes occurred after a marked decrease in the extent of Arctic water in the Norwegian Sea, a subsequent warming of spring water temperature before Atlantic salmon entering the sea, and an approximately 50% reduction of zooplankton across large geographic areas of the Northeast Atlantic Ocean. A sudden decrease in growth was also observed among Atlantic mackerel in the Norwegian Sea. Our results point toward an ecosystem-scale regime shift in the Northeast Atlantic Ocean.

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“…In the trap dataset, we also observed a significant and negative effect of sea lice intensity on marine growth. The potential negative effects from salmon lice on marine growth and survival of anadromous salmonid species have been debated for several decades, particularly in relation to areas with high density of salmon farming (Grimnes & Jakobsen, 1996 ; Krkosek et al, 2007 ; Shephard & Gargan, 2021 ; Skilbrei & Wennevik, 2006 ; Vollset et al, 2018 ). Although our data did not allow for a full study on the impact from salmon lice on the survival of salmon, we have expanded existing knowledge on drivers, including salmon lice, of marine growth in a naturally recruited salmon population.…”

Section: Discussionmentioning

confidence: 99%

Time series covering up to four decades reveals major changes and drivers of marine growth and proportion of repeat spawners in an Atlantic salmon population

Harvey

Skaala

Borgstrøm

et al. 2022

Ecology and Evolution

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Wild Atlantic salmon populations have declined in many regions and are affected by diverse natural and anthropogenic factors. To facilitate management guidelines, precise knowledge of mechanisms driving population changes in demographics and life history traits is needed. Our analyses were conducted on (a) age and growth data from scales of salmon caught by angling in the river Etneelva, Norway, covering smolt year classes from 1980 to 2018, (b) extensive sampling of the whole spawning run in the fish trap from 2013 onwards, and (c) time series of sea surface temperature, zooplankton biomass, and salmon lice infestation intensity. Marine growth during the first year at sea displayed a distinct stepwise decline across the four decades. Simultaneously, the population shifted from predominantly 1SW to 2SW salmon, and the proportion of repeat spawners increased from 3 to 7%. The latter observation is most evident in females and likely due to decreased marine exploitation. Female repeat spawners tended to be less catchable than males by anglers. Depending on the time period analyzed, marine growth rate during the first year at sea was both positively and negatively associated with sea surface temperature. Zooplankton biomass was positively associated with growth, while salmon lice infestation intensity was negatively associated with growth. Collectively, these results are likely to be linked with both changes in oceanic conditions and harvest regimes. Our conflicting results regarding the influence of sea surface temperature on marine growth are likely to be caused by long‐term increases in temperature, which may have triggered (or coincided with) ecosystem shifts creating generally poorer growth conditions over time, but within shorter datasets warmer years gave generally higher growth. We encourage management authorities to expand the use of permanently monitored reference rivers with complete trapping facilities, like the river Etneelva, generating valuable long‐term data for future analyses.

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Context-dependent impact of an ectoparasite on early marine growth in Atlantic salmon

Cited by 10 publications

References 27 publications

Timing is everything: Survival of Atlantic salmon Salmo salar postsmolts during events of high salmon lice densities

Timing is everything: Survival of Atlantic salmon Salmo salar postsmolts during events of high salmon lice densities

Ecological regime shift in the Northeast Atlantic Ocean revealed from the unprecedented reduction in marine growth of Atlantic salmon

Time series covering up to four decades reveals major changes and drivers of marine growth and proportion of repeat spawners in an Atlantic salmon population

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