Marine Survival Of Atlantic Salmon Research Articles

Patterns of declining zooplankton energy in the northeast Atlantic as an indicator for marine survival of Atlantic salmon

Patterns of declining zooplankton energy in the northeast Atlantic as an indicator for marine survival of Atlantic salmon

Wild Atlantic salmon exposed to sea lice from aquaculture show reduced marine survival and modified response to ocean climate

Abstract Impacts on marine survival of Atlantic salmon Salmo salar include sea lice Lepeophtheirus salmonis infestation from coastal aquaculture, and ocean climate forcing. These effects may interact because infestation compromises smolt growth and body condition, and thus response to environmental conditions. We hypothesized that migrating smolts exposed to lice from salmon farms would show (i) reduced one sea-winter (1SW) returns to natal rivers and (ii) a shift in relationships between ocean climate and returns. Annual counts of 1SW fish were studied from ten rivers in Ireland, including five “control” systems without salmon aquaculture. Most counts showed a downward trend, consistent with declines in Atlantic salmon populations. Rivers with aquaculture showed lesser returns (mean 33%, range 19–46%) in years following high lice levels on nearby salmon farms. The level of likely lice pressure also modified how annual 1SW returns varied with ocean conditions. Returns to control rivers showed a weak negative relationship with the Atlantic Multi-decadal Oscillation (AMO) in the late summer (September) of the out-migrating year. This negative AMO effect became much stronger for fish migrating in low lice years but was not evident for high lice years. Smolts experiencing mild-to-moderate lice infestation may show greater sensitivity to ocean warming.

Estimating marine survival of Atlantic salmon using an inverse matrix approach.

The marine phase of anadromous Atlantic salmon (Salmo salar) is the least known yet one of the most crucial with regards to population persistence. Recently, declines in many salmon populations in eastern Canada have been attributed to changes in the conditions at sea, thus reducing their survival. However, marine survival estimates are difficult to obtain given that many individuals spend multiple winters in the ocean before returning to freshwater to spawn; therefore, multiple parameters need to be estimated. We develop a model that uses an age-structured projection matrix which, coupled with yearly smolt and return abundance estimates, allows us to resample a distribution of matrices weighted by how close the resulting return estimates match the simulated returns, using a sample-importance-resampling algorithm. We test this model by simulating a simple time series of salmon abundances, and generate six different scenarios of varying salmon life histories where we simulate data for one-sea-winter (1SW)-dominated and non-1SW dominated populations, as well as scenarios where the proportion returning as 1SW is stable or highly variable. We find that our model provides reasonable estimates of marine survival for the first year at sea (S1), but highly uncertain estimates of proportion returning as 1SW (Pr) and survival in the second year at sea (S2). Our exploration of variable scenarios suggests the model is able to detect temporal trends in S1 for populations that have a considerable 1SW component in the returns; the ability of the model to detect trends in S1 diminishes as the proportion of two-sea-winter fish increases. Variability in the annual proportion of fish returning as 1SW does not seem to impact model accuracy. Our approach provides an instructive stepping-stone towards a model that can be applied to empirical abundance estimates of Atlantic salmon, and anadromous fishes in general, and therefore improve our knowledge of the marine phase of their life cycles as well as examining spatial and temporal trends in their variability.

Disentangling the role of sea lice on the marine survival of Atlantic salmon

AbstractThe effects of sea lice on the marine survival of wild salmonids are widely debated. In Norway this debate has reached a crescendo as the Norwegian government has recently ratified a management system where the growth in the salmonid aquaculture industry will be conditional on regional estimated impact of salmon lice on wild fish. Sea lice have thus become the most prominent obstacle to the stated political aim of quintupling aquaculture production in Norway by 2050. Scientific documentation that salmon lice impact the marine survival of salmon is robust. However, it is also evident that marine survival of salmon is strongly impacted by other factors, and that the effect of salmon lice is most likely an integral part of these other mortality factors. In this paper, our goal is to discuss and give advice on how managers and policy makers should handle this complexity, and to identify the greatest challenges in using scientific results to construct robust management rules. Inadequate extrapolation from the scale of known effects to the scale of management implementation may initially give a false impression of scientific certainty, but will eventually fuel upsetting disagreements among stakeholders as they gradually uncover the shaky foundation of the implemented policy. Thus, using a single model and parameter to determine management advice is not warranted, as no single data point reflects the natural complexity of nature. Furthermore, robust management rules should be based on unambiguous definitions of key concepts. Finally, despite the scientific consensus that salmon lice are a risk to salmon, studies on wild populations in situ that accurately quantify the impact of salmon lice are still urgently needed. We give advice on how this can be accomplished.

Impacts of parasites on marine survival of Atlantic salmon: a meta‐analysis

AbstractParasites can, in theory, have large impacts on the survival of fish populations. One method to evaluate such impacts on anadromous species is to apply manipulative field experiments in which parallel groups of antiparasitically treated and non‐treated fish are simultaneously released and then subsequently recaptured as returning adults. A systematic review and meta‐analysis on all such Norwegian studies on Salmo salar provided a data set for the time period 1996 to 2011 on 118 release groups comprising 657 624 fish released and 3989 recaptured. The overall risk ratio (RR) was estimated to be 1.18 (95% CI: 1.07–1.30). The effect varied strongly between groups, (Higgins I2 = 40.1%). Over 70% of this heterogeneity could be explained by the release location, time period and baseline survival. The most important predictor variable was baseline survival. In groups with low recapture in the control group (low baseline survival), the effect of treatment was high (RR = 1.7), while in groups with high recapture in the control group (high baseline survival), there was no effect of treatment (RR ~ 1.00). The most prevalent parasite in the region affected by the drugs administered was Lepeophtheirus salmonis. Hence, the meta‐analysis supports the hypothesis that L. salmonis contributes to the mortality of S. salar during outward migration. However, the effect of treatment was not consistent, but was evidently strongly modulated by other risk factors. The results suggest that the population‐level effects of parasites cannot be estimated independently of other factors affecting the marine survival of S. salar.

Impact of parasites on salmon recruitment in the Northeast Atlantic Ocean

Parasites may have large effects on host population dynamics, marine fisheries and conservation, but a clear elucidation of their impact is limited by a lack of ecosystem-scale experimental data. We conducted a meta-analysis of replicated manipulative field experiments concerning the influence of parasitism by crustaceans on the marine survival of Atlantic salmon (Salmo salar L.). The data include 24 trials in which tagged smolts (totalling 283 347 fish; 1996-2008) were released as paired control and parasiticide-treated groups into 10 areas of Ireland and Norway. All experimental fish were infection-free when released into freshwater, and a proportion of each group was recovered as adult recruits returning to coastal waters 1 or more years later. Treatment had a significant positive effect on survival to recruitment, with an overall effect size (odds ratio) of 1.29 that corresponds to an estimated loss of 39 per cent (95% CI: 18-55%) of adult salmon recruitment. The parasitic crustaceans were probably acquired during early marine migration in areas that host large aquaculture populations of domesticated salmon, which elevate local abundances of ectoparasitic copepods-particularly Lepeophtheirus salmonis. These results provide experimental evidence from a large marine ecosystem that parasites can have large impacts on fish recruitment, fisheries and conservation.

Overview of the status of Atlantic salmon (Salmo salar) in the North Atlantic and trends in marine mortality

Abstract Chaput, G. 2012. Overview of the status of Atlantic salmon (Salmo salar) in the North Atlantic and trends in marine mortality. – ICES Journal of Marine Science, 69: 1538–1548. Since the early 1980s, the ICES Working Group on North Atlantic Salmon has collated and interpreted catch data, exchanged information on research initiatives, and provided advice to managers in support of conservation efforts for Atlantic salmon. During the past three decades, the annual production of anadromous Atlantic salmon from more than 2000 rivers draining into the North Atlantic has been less than 10 million adult-sized salmon. This represents a minor component, by number and biomass, of the pelagic ecosystem in the North Atlantic Ocean. Ideally, Atlantic salmon would be assessed and managed based on river-specific stock units, the scale that best corresponds to the spawner to recruitment dynamic. In reality, comparatively few river-specific assessments are available for either the Northwest or the Northeast Atlantic. The marine survival of Atlantic salmon is low and, based on return rates of smolts to adults from monitored rivers, has declined since the mid- to late 1980s. Abundance has declined more severely for the multi-sea-winter components, and especially in the southern areas of the species' range. Common patterns in abundance, inferred at the level of stock complex in the North Atlantic, suggest that broad-scale factors are affecting productivity and abundance and that they are acting throughout the salmon's time at sea.

Links between patterns of marine growth and survival of Atlantic salmon Salmo salar, L.

The hypothesis that marine survival of Atlantic salmon Salmo Salar is linked to marine growth was explored by using inter‐circuli distances and total numbers of circuli existing on scales from a population monitored over nearly four decades. The results suggest that marine growth controls survival, particularly during the late summer and early winter of the first year at sea. Recruitment is strongly linked to growth, described as the total number of circuli, but not to inter‐circuli distances. This highlights the potential of patterns of circuli number to be considered as proxies for growth. Indications that hatchery populations might be subject to other mortality events, in addition to those experienced by wild populations, are also presented.

Low concentrations of inorganic monomeric aluminum impair physiological status and marine survival of Atlantic salmon

Two strains of Atlantic salmon ( Salmo salar ) presmolts were exposed for 3 months to moderately acidic water (pH 5.8; 6±2 μg aluminum (Ali) l −1 inorganic monomeric aluminum-acid exposure group) or non-acid water (pH>6.5–6.9; <5 μg Ali l −1 —Good/control group) at NINA Research Station, Ims, Southern Norway. Exposure to low concentrations of Ali raised the gill-aluminum (gill-Al) concentration by 20–30 μg Al g −1 gill dry weight compared to control fish having <10 μg Al g −1 gill dry weight. The fish responded to the Al loading with elevated blood glucose, but retained more normal hematocrit and plasma chloride levels. Fish exposed under acid conditions grew significantly poorer than the control fish. After 3 months of exposure, 150 Carlin-tagged smolts from both Imsa treatments were released into the non-acidic River Imsa, 800 m upstream from a trap that caught all migrating smolts. Acid-exposed fish migrated downstream slightly later than the controls. At the same time, Carlin-tagged fish from all four treatments (Acid and Good, both strains; approximately 1000 fish group −1 ) were released downstream of the trap located 150 m above the river mouth. Based on the number of adult recaptures (by May 2001), marine survival was 20–30% lower for the acid-exposed fish than for the controls. There were no differences in marine growth between the treatments. The results suggest that even very low concentrations of Ali (6±2 μg l −1 ) can reduce seawater survival, thereby having effect on the population level. The physiological responses, reduced growth and reduced marine survival also suggest that the presmolts did not acclimate to the acid conditions.

Comparison of the marine survival of atlantic salmon, Salmo solar L. smolts vaccinated and nonvaccinated against vibriosis

The effect of vaccination against vibriosis on the marine survival of one-year-old smolts and two size-classes of two-year-old smolts of the short-migrating River Neva stock of Atlantic salmon ( Salmo salar L.) was studied through paired releases of Carlin-tagged fish in the Bothnian Sea (Baltic Sea) in 1991 and 1992. Vibriosis was supposed to contribute to the poor survival of post-smolts in the Bothnian Sea compared to the Gulf of Finland. Vaccinated groups were immunized with a single intraperitoneal injection the previous autumn with a commercial vaccine containing formalin-killed Vibrio anguillarum and V. ordalii bacteria incorporating aluminium sulphate as adjuvant. The experiment was designed in advance to detect a departure of 20–25% from the initial 50:50 stocking ratio of vaccinated and nonvaccinated fish at a 5% risk level and 90% power. The difference was substantial and could thus explain a significant proportion of the differences in stocking results between the Gulf of Finland and the Bothnian Sea. Tag recoveries were collected from the date of release until the end of 1995. In 1991, a total of 4000 two-year-old smolts were released, half of them vaccinated, with 588 (29.6%) tags returned from the vaccinated and 551 (27.6%) from the nonvaccinated groups. For two-year-old smolts in the 1992 year class, the corresponding numbers were 4200 released, with 347 (16.6%) and 327 (16.4%) recaptured, respectively. For one-year-old smolts in 1992, only 10 recoveries (0.5%) were obtained from both the vaccinated and nonvaccinated groups from the 4000 released, excluding the statistical analysis. For both year classes of two-year-olds, the distribution of recaptures over the years was homogeneous between vaccinated and nonvaccinated groups at a 5% risk level. The observed recapture ratios from the total number of recoveries did not differ statistically significantly ( G-test for goodness of fit) from the original stocking ratio of vaccinated and nonvaccinated fish at a 5% risk level. This indicates that vaccination did not affect survival statistically significantly.