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Friedland, K. D., MacLean, J. C., Hansen, L. P., Peyronnet, A. J., Karlsson, L., Reddin, D. G., Ó Maoiléidigh, N., and McCarthy, J. L. 2009. The recruitment of Atlantic salmon in Europe. – ICES Journal of Marine Science, 66: 289–304.
The stock complex of Atlantic salmon, Salmo salar, in Europe has experienced a multidecadal decline in recruitment,...
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Context 1
... impressions of clean scales were made in cellulose acetate strips. From the impressions, the distances from the scale focus to the beginning of sea growth and the 1SW annuli were determined ( Figure 2). Using linear back-calculation based on size at capture, the post-smolt growth increment was determined as the difference between the total 1SW increment and the fresh-water increment. ...
Context 2
... samples were impressed into acetate slides, or for the Girnock Burn, the scales were mounted between glass slides. Using image processing, the spacings between successive pairs of circuli were measured along a transect on the 3608 axis from the first pair of marine circuli to the edge of the scale, so measuring all circuli spacings in the marine growth zone ( Figure 2). The first pair of marine circuli is identified as the first wide circuli spacing after the relatively tightly spaced circuli of the fresh-water zone. ...
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W Polsce występują dwa gatunki anadromicznych ryb łososiowatych: łosoś atlantycki Salmo salar L. i troć wędrowna morska Salmo trutta m. trutta L., które są rozsiedlone w rzekach pomorskich oraz w dorzeczu Odry i Wisły. Pogarszające się warunki środowiska i nadmierna eksploatacja bez rekompensacyjnych zarybień prowadziły do zmniejszania się liczebno...
Citations
... While fisheries and global warming were assumed as main drivers of the decline of fish population, the influence of environmental factors at a more local scale may be greater than previously expected (Nicola et al., 2018;Otero et al., 2011). As such, it has been suggested that Atlantic salmon population monitoring should take into account local environmental fluctuations in rivers, as it could be a key to the maintenance of the species (Friedland et al., 2009;Jonsson & Jonsson, 2017;Nicola et al., 2018). ...
Conservation of the Atlantic salmon Salmo salar requires to monitor the spatial distribution and abundance of juveniles at a local scale in tributaries. However, tributaries are rarely accounted for in monitoring programs despite their importance for juvenile life stages. This is mainly because inventories of young salmon populations in tributaries can be technically challenging with traditional methods, as the number of tributaries in a watershed can be important and their access limited compared to the main stem. In this study, we tested the use of environmental DNA (eDNA) to quantify the abundance of juvenile Atlantic salmon in tributaries. We successfully detected eDNA of juvenile Atlantic salmon in 19 tributaries of three main rivers of the Gaspé Peninsula (Québec, Canada) using quantitative real‐time PCR analyses. By comparing the eDNA approach with electrofishing surveys conducted in parallel to water sampling, we found that eDNA concentrations positively correlated with juvenile abundance, total biomass, and body surface area. The use of the allometrically scaled mass (ASM) instead of abundance improved the correlation. Furthermore, we demonstrated that the levels of eDNA molecules detected for juvenile Atlantic salmon were also correlated with water temperature and canopy cover measured in each tributary. Finally, we tested if eDNA concentrations measured in a tributary could be used as a reliable indicator of juvenile abundance or biomass in that tributary. We found that our models slightly better predicted juvenile biomass than juvenile abundance. The use of ASM did not improve model prediction, suggesting that further refinement would be required in the future. Our method will facilitate the implementation of conservation practices appropriate to the ecology of juvenile Atlantic salmon in tributaries.
... ) are strongly and significantly correlated with spring rod catches in the Dee(Youngson et al., 2002 and Figure 4a), showing that population trends in Girnock salmon are highly likely to be more generally representative of those experienced in the upper tributaries of the Dee and other rivers where spring stocks dominate. Further, the Girnock acts as a key index monitoring site for comparison with salmon populations elsewhere in Europe and North America(Friedland et al., 2009). ...
Long-term data are crucial for understanding ecological responses to climate and land use change; they are also vital evidence for informing management. As a migratory fish, Atlantic salmon are sentinels of both global and local environmental change. This paper reviews the main insights from six decades of research in an upland Scottish stream (Girnock Burn) inhabited by a spring Atlantic salmon population dominated by multi-sea-winter fish. Research began in the 1960s providing a census of returning adults, juvenile emigrants and in-stream production of Atlantic salmon. Early research pioneered new monitoring techniques providing new insights into salmon ecology and population dynamics. These studies underlined the need for interdisciplinary approaches for understanding salmon interactions with physical, chemical and biological components of in-stream habitats at different life-stages. This highlighted variations in catchment-scale hydroclimate, hydrology, geomorphology and hydrochemistry as essential to understanding freshwater habitats in the wider landscape context. Evolution of research has resulted in a remarkable catalogue of novel findings underlining the value of long-term data that increases with time as modelling tools advance to leverage more insights from "big data". Data are available on fish numbers, sizes and ages across multiple life stages, extending over many decades and covering a wide range of stock levels. Combined with an unusually detailed characterization of the environment, these data have enabled a unique process-based understanding of the controls and bottlenecks on salmon population dynamics across the entire lifecycle and the consequences of declining marine survival and ova deposition. Such powerful datasets, methodological enhancements and the resulting process understanding have informed and supported the development of fish population assessment tools which have been applied to aid management of threatened salmon stocks at large-catchment, regional and national scales. Many pioneering monitoring and modelling approaches developed have been applied internationally. This
... Salmonid populations have declined globally due to several anthropogenic pressures, such as dam building, habitat destruction, pollution, climate change, decreased food availability at sea, and an extensive fishery (Dadswell et al., 2022;Friedland et al., 2009;Limburg & Waldman, 2009). Population declines caused by predation from, for example, birds, are less well-studied (Steinmetz et al., 2003;Strøm et al., 2019). ...
Juvenile salmonids often experience high mortality rates during migration and bird predation is a common source of mortality. Research suggests that hatchery‐reared salmonids are more prone to predation than wild salmonids, and that Atlantic salmon ( Salmo salar ) experience lower predation than Sea trout ( Salmo trutta ), yet telemetry studies have displayed equivocal results. Here, using a large data set on passive integrated transponder (PIT) tagged hatchery‐reared and wild juveniles of Atlantic salmon and Sea trout (25,769 individuals) we investigate predation probability by piscivorous birds (mainly Great Cormorants Phalarocorax carbo ) on salmonids originating from River Dalälven in Sweden. Bird colonies and roosting sites were scanned annually (2019–2021), and the temporal dynamics of bird predation on salmonids released in 2017–2021 was assessed. Hatchery‐reared trout was clearly most susceptible to cormorant predation (0.31, 90% credibility interval [CRI] = 0.14–0.53), followed by wild trout (0.19, 90% CRI = 0.08–0.37), hatchery‐reared salmon (0.13, 90% CRI = 0.07–0.23), and wild salmon (0.08, 90% CRI = 0.04–0.14), in subsequent order. This order in predation probability was consistent across all studied tag‐ and release‐years, suggesting that the opportunistic foraging of cormorants affects the overall survival of juvenile salmonids, but that the inherent predation risk between different salmonid types differs systematically.
... Future climate change could pose a further threat to the species; predictive modelling indicates a contraction of Atlantic salmon distribution by the end of the century (Lassalle and Rochard, 2009). The post-smolt period, when salmon first migrate into the marine environment, is considered a critical stage during which growth and survival has declined dramatically (Friedland et al., 2009;Soto et al., 2018). If exposure to elevated temperatures, reduced food availability or other stressors during the post-smolt period is reflected in scale cortisol levels, this biomarker could be used to examine physiological stress responses to environmental change during the marine migration. ...
... However, much uncertainty remains with regards to baseline levels of scale cortisol in salmonids and other species, what causes them to vary and how they change in response to environmentally relevant stressors. As wild salmon are exposed to a wide range of interacting stressors including sea lice (Lepeophtheirus salmonis, Krøyer) infestation (Poole et al., 2000), maturation (Baker and Vynne, 2014), and climatic patterns (Friedland et al., 2009), direct stress responses to temperature will be difficult to establish. Nonetheless, this study has demonstrated that under laboratory conditions, scale cortisol levels can vary in response to temperature and feeding conditions during the postsmolt phase of Atlantic salmon, while highlighting sex-specific differences and interactive effects. ...
... Differences in diets, in turn, are believed to have possible carry-over effects on fitness-related traits such as body condition, parental quality and survival (Harrison et al., 2011). Identification of dietary patterns and their links to survival and growth (Friedland et al., 2009;Utne et al., 2022) are likely to be of increasing importance given the large-scale changes that have occurred in the ocean food webs (Beaugrand & Reid, 2003) on which Atlantic salmon rely (Beaugrand & Reid, 2012;Dempson et al., 2010) and the importance of food webs for determining fish condition and survival (Frank et al., 2007;Todd et al., 2008;Vollset et al., 2022). ...
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 δ ¹³ C range) and increased their dependency on higher tropic level (δ ¹⁵ N) prey, likely fish. Changes in δ ¹³ C 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 (δ ¹³ C and δ ¹⁵ N 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 (δ ¹⁵ N), resource use (δ ¹³ C) 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.
... This is especially true for the anadrome Atlantic salmon, as underlined by the observed elevation effect. Yet, as previously shown (see e.g., Friedland et al., 2009;Jonsson & Jonsson, 2004), an increase in the NAO-index positively affected both species (in terms of biomass and density), for example, NAO-index can enhance the growth and development of salmonid species, promoting their overall fitness and reproductive success. ...
Healthy populations of salmonids are integral for the functioning of ecosystems and a valuable part of the socio‐cultural identity of locals. Past declines were attributed to anthropogenic stressors, raising concern about the sustainability of populations. Accordingly, many salmonids are listed on red lists and protected by national legislation. One region where salmonid populations are threatened is Northern Spain, the most southern distribution of both the Atlantic salmon (protected under the EU Habitat Directive) and the brown trout. Here, we collated ~700 biomonitoring samples of both species collected across 177 sites over a 10‐year period (2010–2019) to describe ongoing trends in these species and to relate them to site characteristics and potential drivers which may modulate these trends. We showed that both species have declined substantially, with stocked individuals constituting the majority of both populations. Natural reproduction was almost entirely absent for the brown trout (<1%), but present in the Atlantic salmon (~20%). Both species expressed distinct spatial patterns, likely related to their stocking and habitat preferences. As such, the observed trends for both species illustrate that reproduction is almost entirely lacking, underlined by a lack of adult salmonids. As a result, we not only underline alarming conditions of both species, but also question the effectiveness of currently employed stocking. Given that both species are of increasing conservation concern, river basin‐specific analyses are required to identify limiting factors on which conservation actions can be taken. In the river systems evaluated, identified targets include dam removal and pollution reduction. Just as the implementation of more effective stocking practices to reduce dependency and maximize conservation benefits for aquatic populations.
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... Most mortality between smolt and adult stages is generally considered to take place during the first year of life at sea when survival, maturation, and migration trajectories are being defined [39,[160][161][162]. The first year of salmon at sea, known as the post-smolt year, is characterized by variable rates of mortality [163]. ...
... Warmer temperatures in the North Atlantic have modified oceanic conditions, reducing the growth and survival of salmon by decreasing marine feeding opportunities [39,162,178,179]. Spring plankton blooms and therefore the peak of higher trophic resources available for salmon may be advanced in the season and may occur in different places [180][181][182], thus potentially creating a mismatch between salmon smolt migration and available resources [170,183]. ...
The migratory life history of anadromous salmonids requires successful migration between nursery, feeding and spawning habitats. Smoltification is the major transformation anadromous salmonids undergo before migration to feeding areas and prepares juvenile fish for downstream migration and entry to seawater. We reviewed the effects of climate change on smolt ecology from growth of juveniles in freshwater to early post-smolts in sea. Shift in the suitable thermal conditions by climate change is causing Atlantic salmon to expand their range northwards, while in the southern edge of their distribution populations struggle with high temperatures and occasional droughts. Climatic conditions, particularly warmer temperatures, are affecting growth during freshwater phase in the river. Better growth in the northern latitudes leads to earlier smoltification. Thermal refuges, the areas of cooler water in the river, are especially important for salmonids impacted by climate change. Restoring and maintaining connectivity and suitable diverse mosaic habitat in rivers are important for survival and growth throughout the range. The start of the smolt migration has shifted earlier as a response to increasing water temperatures, which has led to concerns of mismatch with optimal conditions for post-smolts in the sea decreasing their survival. A wide smolt window allowing all migrating phenotypes from early to late migrant’s safe access to sea is important in changing environmental conditions. This is true also for regulated rivers, where flow regulation practices cause selection pressures on migrating salmonid phenotypes. Life history in freshwater affects also marine survival, and there is a need for better collaboration across life stages and habitats among researchers and managers to boost the smolt production in rivers.
... However, variable environmental conditions in the ocean, rather than competition-induced shortages, have been hypothesized to influence marine growth more strongly (Peyronnet et al., 2007). Friedland et al. (2009) found that survival of post-smolts in the Northeast Atlantic was positively associated with plankton and possibly post-smolt food abundance and these prey abundances had declined since the 1970s. Several studies have reported on of ecosystem changes resulting in reduced prey quality including capelin in the Labrador Sea (Renkawitz et al., 2015) and Atlantic herring in the Gulf of Maine (Golet et al., 2015). ...
WGNAS met to consider the status of and threats to Atlantic salmon in the North Atlantic Salmon Conservation Organisation (NASCO) commission areas: West Greenland (WGC), North American (NAC), and Northeast Atlantic (NEAC). Many updates are provided for 2021 and 2022 as WGNAS was not able to address all terms of reference (ToRs) in 2022. Information on the catch and exploitation, including salmon caught and released, and nominal harvest, as well as tagged and marked fish releases are provided by country and jurisdiction. Emerging threats are presented, including the first report of Infectious Salmon Anaemia (ISA) in Iceland, red skin disease in Europe, and Norway is evaluating new offshore farming sites. New scientific advancements reported on include non-lethal Gyrodactylus treatment, homewater return rate estimation methods, and genetic tools to understand the reproductive success of salmon that have been caught and released. ICES did not conduct a full assessment for salmon in NEAC because the Framework of Indicators (FWI) did not indicate that the forecast estimates of abundance for the four NEAC stock complexes had been underestimated.
WGNAS was asked to provide information on three key issues in 2023, namely:
1. the causes of variability in return rates between rivers within regions of the North Atlantic, concluding that factors at river-specific, regional and oceanic scales interact to affect marine survival rates and maturation schedules, and it is unlikely that a single factor alone accounts for temporal variations and the decline of wild salmon in the North Atlantic;
2. the current state of knowledge on freshwater and marine predation by cormorants, concluding that cormorants can have substantial impacts on salmon abundance in areas where cormorant populations have increased or declines in other cormorant prey abundance have occurred, an issue of special concern where salmon populations are already threatened or endangered; and,
3. an evaluation of the risk of salmon bycatch occurring in pelagic and coastal fisheries, and effectiveness and adequacy of current bycatch monitoring programmes, concluding that ICES ability to evaluate the risk of bycatch is limited because few pelagic fisheries are screened for bycatch and screening covers small proportions of catch. To advance our capacity to evaluate such risks, a series of data deficiencies, monitoring needs and research requirements are identified.
Looking forward, a Bayesian life-cycle assessment model and data inputs were discussed in connection with the 2023 benchmark.
... Studying marine growth at the basin scale can be informative for several reasons (Friedland et al., 2000(Friedland et al., , 2006(Friedland et al., , 2009Peyronnet et al., 2007;McCarthy et al., 2008;Hogan and Friedland, 2010;Tillotson et al., 2021;Barajas et al., 2021;Todd et al., 2021;Vollset et al., 2022). First, temporal and spatial synchrony can inform the extent to which different salmon populations are affected by the same environmental factors. ...
ICES, in consultation with the North Atlantic Salmon Conservation Organisation (NASCO), convened a series of workshops to explore how to use biological and environmental data in models
to advance the conservation of wild Atlantic salmon (Salmo salar L.) at sea. This workshop set out
to consider multiple candidate hypotheses contributing to changes in the temporal patterns of
abundance, and agree the priority research questions.
No agreement on the development of a set of priority marine mortality hypotheses was reached.
This resulted from the recognition of the hierarchical nature of ecosystem controls, and important complexities introduced by evolutionary diversity. An integrated ecological-evolutionary framework was proposed for the evaluation of hypotheses, and to identify key points in
space and time. There was an agreed need for the continuation of cooperative initiatives to examine drivers of marine growth change using standardized approaches, and in the evolutionary
delineation of stock units. These were seen as productive pathways to significantly enhance understanding of the marine factors affecting species abundance.
The workshop recognized that options for developing and testing hypotheses remain constrained by the availability and quality of data, and identified ways to mobilize existing
knowledge resources on key aspects of salmon ocean ecology. These focused on the synthesis of
physical ocean data and model outputs, involving ocean basin-wide evaluations of available energy from surveys of lower trophic levels, and updating of population-specific biological information. The workshop agreed on the need for a specific call for data from pelagic commercial
fisheries, given the broad scale of this activity and potential overlap with salmon migrations.
There was also the recognition that Atlantic salmon should be included in the ICES Working
Group on Bycatch of Protected Species (WGBYC) Protected, Endangered and Threatened Species
list.
Much of the work required to mobilize useful data sources was recognized as being outside the
scope of existing ICES data calls, or the constituted core work of ICES Working Group on North
Atlantic Salmon (WGNAS). Recommendations for the third workshop are for 1. More detailed
consideration of how to access the work needed for data mobilization, and 2. The identification
of well-defined, achievable outcomes.
... Human represents the main indirect as well as direct threat to the species. Atlantic salmon are subjected to increased freshwater and seawater temperatures and shifts in food web composition (Friedland et al. 2009). As a result of air pollution and associated acid precipitation, riverine pH reduction has led to a complete loss of an Atlantic salmon population in southern Norway (Hesthagen and Hansen, 1991). ...
Summary
Skeletal deformities in farmed Atlantic salmon (Salmo salar, L.) and other farmed teleost fish raise concern about animal welfare. Severe vertebral deformities reduce animal growth rate and overall skeletal health. In aquaculture, this leads to product quality degradation. One of the most commonly discussed factors that influences skeletal health is dietary phosphorus (P). Dietary P is essential for a proper mineralisation of the skeleton. To prevent deformity development in Atlantic salmon it is currently common practice to add P in the diet in a higher amount than required. Still, P supplementation in the feed for farmed fish requires appropriate management. An excess of dietary P increases the dietary P to calcium ratio, which reduced zinc absorption, a trace element involved in immunity, growth and mineralisation. Zinc is the central atom of alkaline phosphatase which removes pyrophosphate, a potent bone mineralisation inhibitor. High dietary P increases animal P excretion. The resulting P discharge from fish farms can lead to environmental pollution. Importantly, the source of dietary P is non-renewable which further emphasises the need for its responsible use. Another factor possibly affecting skeletal health is elevated CO2 level in the water, a common and unwanted consequence of increased rearing densities and recirculating systems used in aquaculture. Like a deficiency of dietary P, high levels of CO2 have been previously suggested as a factor inducing skeletal deformities in Atlantic salmon.
The research within the frame of this PhD thesis aims to test (i) the effect of low and high levels of dietary P fed to farmed Atlantic salmon in freshwater on bone formation and mineralisation in the vertebral column, and the recovery from low and high dietary P feeding in seawater Atlantic salmon, and (ii) the synergistic effect of low or high dietary P and carbon dioxide (CO2) injected into the environment on Atlantic salmon post-smolts.
The aims outlined above are addressed in three chapters, following an introductory chapter that outlines the fundamentals of skeleton development, vertebral deformities, P metabolism, life cycle, and distribution of Atlantic salmon, and its relation to aquaculture.
Chapter II analyses the results of a mono-factorial study (spanning 11 weeks) on the impact of feeding low or high levels of dietary P on the structure of the vertebral bodies in the freshwater parr stage of Atlantic salmon. This study revealed the presence of a background level of mild vertebral deformities in all groups, irrespective of dietary P. Low dietary P did not increase vertebral deformities. Surprisingly, growth of low P animals, was comparable with regular P and high P animals, a finding discussed in terms of continuous feeding as a partial compensation for low dietary P. In low P conditions, bone formation continues but bone mineralisation is arrested discontinues, leading to the development of extended areas of non-mineralised bone (osteomalacia). The total Ca and P content in the vertebrae and opercula is reduced by about 50% in low P compared to regular and high P animals. In line with the reduced mineral content, vertebral centra stiffness is also reduced in low P animals. While the structural and functional integrity of the vertebral bodies in low P animals is maintained, animals show minor morphological alterations of the vertebral bodies. Low P animals develop a slight inward bending of the vertebral body endplates, intervertebral joints acquire an increased length and thickness, and ectopic cartilage develops at the interface between the vertebral body endplates and bone trabeculae. Importantly, this study provides supporting evidence that high dietary P does not benefit bone mineralisation and bone health compared with a regular dietary P. Regular and high P animals show a comparable extension of the osteoid (non-mineralised bone). Both groups have similar bone and opercula mineral content and vertebral centra stiffness.
Chapter III assesses if and how vertebral centra deformities develop over the course of 69 weeks. A total of 135 Atlantic salmon fed a low or high P in freshwater, followed by a regular diet prior to smoltification were PIT-tagged and subjected to long-term monitoring by means of x-ray imaging at three time points: prior to smoltification (50 g), at seawater stage (700 g), and at harvest (4.5 kg).
Four categories of vertebral deformity development can be identified: (1) recovery, (2) containment, (3) progression, and (4) late-onset. Deformities with a negative impact on the vertebral centra but with intact intervertebral joints can fully recover in seawater. Recovered deformities include both those following a low P diet history (low-mineralised and hyper-dense vertebrae), and deformities independent of the diet P history (mildly compressed and vertically shifted vertebrae). Stable vertebral fusions which affect two to three vertebral centra and the intervertebral spaces can be contained. Progressive vertebral fusions affect more than three vertebral centra and intervertebral spaces and worsen over time. Notably, this type of severe vertebral deformity can be observed as early as in freshwater stages. Vertical shifts, fusions, and compressions are also found to develop in late seawater stages of Atlantic salmon (late-onset deformities). The dietary P history was found not to be associated with contained, progressive, or late-onset deformities. This provides further evidence that low dietary P is not the main factor for the development of deformities in Atlantic salmon. The above analysis is important in the context of farming. Early detection of animals susceptible to develop severe deformities can prevent rearing of individuals with compromised bone health.
Chapter IV discusses the observed effect of elevated CO2 level on increased bone mineralisation under low P diet condition, which offers the possibility to reduce the P content in commercial salmon feeds. It complements studies on the effect of high dietary P on bone health in seawater stages of Atlantic salmon. Both high P and high CO2 result in a reduced feed intake and growth of the animals. Increased bone and scale mineralisation in animals reared in high CO2 water is only observed when the dietary P is low. The osteoblasts and osteocytes in low P animals are observed to downregulate the synthesis of fgf23, a hormone responsible for inhibition of renal phosphate reabsorption. It is hypothesised that in low P animals not only renal phosphate reabsorption but also intestinal phosphate absorption is increased. These findings provide the first insights on how to implement a reduction of dietary P use under high CO2 water conditions without jeopardizing bone mineralisation, an application which nevertheless requires further research and elaboration. To conclude, the hypothesis that high levels of dietary P are required to reduce the risk of vertebral deformities and to secure healthy bone formation and mineralisation must be rejected. Likewise, the hypothesis that high levels of CO2 are detrimental for the skeletal health of seawater stage Atlantic salmon is refuted by the observation that high CO2 levels in water increased bone mineralisation in animals fed a low P diet, a condition which leads to formation of non-mineralised bone.
Chapter V evaluates the use of low and high dietary P in the feeds for farmed Atlantic salmon. It discusses the increased mechanical load exerted by the axial musculature during handling stress as a potential factor inducing the development of vertebral deformities. A possibility to predict the prevalence and severity of vertebral deformities in the freshwater stages of Atlantic salmon to improve animal welfare in seawater is elaborated. Future prospects discuss the potential to reduce dietary P in aquaculture systems with a high level of CO2 and improved utilisation of P under regimes which involve periods of low dietary P feeding. This section furthermore considers alternative products to wild caught fishmeal and fish oil based products. These include insect meal, genetically modified terrestrial plants producing omega-3 long chain polyunsaturated fatty acids, and an increase in P availability with the application of phytase in a commonly used plant-based product.
