Diet analysis of Atlantic salmon (Salmo salar) post-smolts after the ecological regime shift in the Northeast Atlantic

Hellenbrecht, Lea; Utne, Kjell Rong; Karlsen, Ørjan; Glover, Kevin A.; Wennevik, Vidar

doi:10.1016/j.fishres.2023.106672

Cited by 4 publications

(4 citation statements)

References 23 publications

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“…Hence, variation in the abundance of fish larvae available as prey may be a more important influence on the diet of Atlantic salmon postsmolts than their own body size. The supposition is partly supported by a recent study of early post-smolt diet by Hellenbrecht et al (2023) who noted post-smolts focus their feeding on fish larvae when encountering a high abundance of the prey group. Alternatively, results here may simply reflect a selective effect, with those postsmolts that successfully switch to piscivory early regardless of size tending to survive better than those that do not.…”

Section: F I G U R E 4 Directional Shift Vectors For River Namsen Ret...mentioning

confidence: 86%

“…Reliance on scales from successfully returning fish, as in this study, may bias results by effectively removing any apparent influence of body length on trophic function. There is a large spatial and temporal variation in postsmolt diet in the fjords immediately after sea entry, and a piscivorous diet is known to enhance growth and ultimately survival (Hellenbrecht et al., 2023 ). Postsmolts during the early marine migration seem to focus their feeding on fish larvae when encountering a high abundance of this prey group and have a diverse diet consisting of several different prey groups when fish larvae are absent (Hellenbrecht et al., 2023 ).…”

Section: Discussionmentioning

confidence: 99%

“…There is a large spatial and temporal variation in postsmolt diet in the fjords immediately after sea entry, and a piscivorous diet is known to enhance growth and ultimately survival (Hellenbrecht et al., 2023 ). Postsmolts during the early marine migration seem to focus their feeding on fish larvae when encountering a high abundance of this prey group and have a diverse diet consisting of several different prey groups when fish larvae are absent (Hellenbrecht et al., 2023 ). For postsmolts in the Norwegian Sea later in the summer and early autumn, reduction of highly energetic fish larvae and amphipoda in the diet is related to reduced stomach fullness and poorer condition (Utne et al., 2021 ).…”

Section: Discussionmentioning

confidence: 99%

“…Atlantic salmon are opportunistic feeders that use a wide variety of prey (Renkawitz et al., 2015 ; Rikardsen & Dempson, 2011 ; Utne et al., 2021 ), with prey use varying depending on the spatial and temporal nature of feeding and individual body size (Haugland et al., 2006 ; Hellenbrecht et al., 2023 ). Although as a group, Atlantic salmon will eat a wide variety of prey, detailed studies of stomach contents at the postsmolt and adult stages often report only a few different prey items in the stomachs of each individual (Andreassen et al., 2001 ; Jacobsen & Hansen, 2000 ), suggesting a degree of selectivity exists among individuals.…”

Section: Introductionmentioning

confidence: 99%

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Temporal shifts in the marine feeding of individual Atlantic salmon inferred from scale isotope ratios

Power,

Thorstad,

Forseth

et al. 2023

Ecology and Evolution

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Given the limited information on prey use during the marine residency period for Atlantic salmon, scales were collected from salmon at return to the River Namsen (Norway) for spawning after 1 year at sea, and scale material from the first and second summer marine feeding periods was analysed using stable isotope methods to understand dynamics of their trophic ecology. As the salmon increased in size from the first to second summer, they reduced their feeding niche and specialised more (narrowed the δ13C range) and increased their dependency on higher tropic level (δ15N) prey, likely fish. Changes in δ13C indicated a consistent pattern of movement towards the north and west between summer feeding periods. Hence, salmon during their first year at sea may have a migration route roughly resembling that of previous spawners, as inferred from earlier tagging studies. Feeding conditions and nutrient composition during the last summer at sea, i.e. in the months before returning to the river for spawning, impacted final body size and within‐season timing of return. Fish undergoing the largest trophic niche shift (δ13C and δ15N combined) between summer feeding periods, returned earliest. The earliest returning fish had the fastest specific growth rates at sea. Hence, salmon encountering abundant high‐quality fish food during the marine migration, particularly during the last months, may reach a size and energetic state whereby it is better to return early to a safer environment in freshwater than risk being eaten by a big predator at sea. Both trophic status (δ15N), resource use (δ13C) and growth rates were significantly correlated between feeding periods. Nutrient composition during the first summer at sea did not impact the fish body length after the following winter, but growth conditions during the first summer evidenced carry‐over effects from the first to the second summer of feeding.

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Section: F I G U R E 4 Directional Shift Vectors For River Namsen Ret...mentioning

confidence: 86%

Section: Discussionmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

Temporal shifts in the marine feeding of individual Atlantic salmon inferred from scale isotope ratios

Power,

Thorstad,

Forseth

et al. 2023

Ecology and Evolution

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Regional and temporal variation in escape history of Norwegian farmed Atlantic salmon

Strand,

Glover,

Meier

et al. 2023

ICES Journal of Marine Science

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Each year thousands of farmed Atlantic salmon escape from seawater net pens, and introgression has been documented in a range of wild populations. Due to greater experience in the wild, escapees that have been on the run for a longer period, and successfully transitioned to a wild diet (classified: “early escapees”), could potentially have a higher spawning success and contribute more to introgression than those that have been on the run for a shorter period and/or have not transitioned to a wild diet (classified: “recent escapees”). This is the first study to examine how the escape history of farmed Atlantic salmon captured in multiple rivers and coastal fisheries, varies in time and space. During 2011–2021, adult farmed escaped salmon were captured in four rivers and at six coastal sites in Norway. The level of linoleic acid, a terrestrial fatty acid high in commercial salmon feeds but low in the natural diet of wild salmon, was used to classify the farmed salmon as early or recent escapees. We observed temporal declines in the relative proportions of escaped vs. wild salmon in the catches, and the relative proportion of early vs. recent escapees in the most southern river (driven by samples from 2011 to 2015). Overall, 14% of the escaped salmon caught in the period were classified as early escapees. The relative proportion of early escapees was lower in the two southernmost rivers (21.2% and 6.30%), as compared to the coastal fisheries (40.9%) and the northernmost river (77.6%). Both aquaculture–management regulations and production strategies have likely influenced these observations.

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Poor performance of regime shift detection methods in marine ecosystems

Haines,

Planque,

Buttay

2024

ICES Journal of Marine Science

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Regime shifts have been reported as ubiquitous features across the world’s oceans. Many regime shift detection methods are available, but their performance is rarely evaluated, and the supporting evidence for regime shifts may be thin because of the nature of marine ecological time series that are often short, autocorrelated, and uncertain. In the Norwegian Sea, a regime shift has been reported to have occurred in the mid-2000s, with simultaneous changes in oceanography, plankton, and fish. Here, we evaluate the evidence for this regime shift using four commonly used regime shift detection methods (Strucchange, STARS, EnvCpt, and Chronological Clustering) on 32 annual time series that describe the main components of the Norwegian Sea ecosystem, from hydrography and primary production up to fish population metrics. We quantify the performance of each method by measuring its false-positive rate, i.e. the proportion of times the method detects a regime shift that was not present in simulated control time series. Our results show that all methods have high to very high false-positive rates. This challenges the evidence for a regime shift in the Norwegian Sea and questions earlier reviews of regime shifts across the world’s oceans.

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Diet analysis of Atlantic salmon (Salmo salar) post-smolts after the ecological regime shift in the Northeast Atlantic

Cited by 4 publications

References 23 publications

Temporal shifts in the marine feeding of individual Atlantic salmon inferred from scale isotope ratios

Temporal shifts in the marine feeding of individual Atlantic salmon inferred from scale isotope ratios

Regional and temporal variation in escape history of Norwegian farmed Atlantic salmon

Poor performance of regime shift detection methods in marine ecosystems

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