Evidence of changing migratory patterns of wild Atlantic salmon Salmo salar smolts in the River Bush,Northern Ireland,and possible associations with climate change

The migration patterns, timing and biological characteristics of wild Atlantic salmon Salmo salar smolts in the River Bush, Northern Ireland, were examined over the period 1978–2008. A distinct change in the timing of the smolt run was detected with progressively earlier emigration periods evident across the time series. The shift in run timing ranged from 3·6 to 4·8 days 10 years^?1 for a range of standard migratory audit points. The timing of smolt emigration has been linked to ambient river temperature patterns. Distinct seasonal patterns were evident for biological characteristics of River Bush smolts with mean age and fork length decreasing throughout the emigration period. Marine survival patterns in 1 sea winter River Bush S. salar were strongly influenced by the run timing of the preceding smolt year such that later emigrating cohorts demonstrated increased survival. Possible mechanisms for this relationship based on local climatic variation have been explored, including the effect of potential thermal mismatch between freshwater and marine environments.     

The pre‐spawning migratory behaviour of Atlantic salmon Salmo salar in a large lacustrine catchment

The movements of adult Atlantic salmon Salmo salar were determined as they migrated to spawning habitats in a large lacustrine catchment, Lough Neagh, in Northern Ireland. The minimum average ground speed of S. salar through the lake was 2·1 km day^?1 and the mean residence time was 11 days. Tagged S. salar tended to actively migrate through the lake which represented a transitory habitat for adult S. salar. Migration time from the release site, through the lake, to a spawning tributary decreased during the migratory period. During the 4 year study period between 20·5 and 41·6% of tagged S. salar which entered the lake each year, explored at least one other channel before ascending the final spawning tributary. Exploratory behaviour was more likely in S. salar which spawned in the tributaries furthest from the sea. Exploratory behaviour was also more likely to occur during periods of reduced discharge in the natal stream. The fishery management implications of complex pre‐spawning behaviour in a mixed stock lacustrine system, are discussed.     

The relationship between a summer fry (0+) abundance index, derived from semi-quantitative electrofishing, and egg deposition of Atlantic salmon, in the River Bush, Northern Ireland

Atlantic salmon survival in the R. Bush (N. Ireland) from egg to summer 0+ was inversely density-dependent on egg deposition ( P <0.05). A stock-recruitment relationship derived from egg deposition and summer 0+ abundance index data was compared to that derived from adult and smolt counts based on total trapping. Fitted Ricker curves indicated maximum recruitment at around 2.35 million eggs and 2.46 million eggs for 0+ index and smolt count methods, respectively. Salmon 0+ abundance index data from semi-quantitative electrofishing could be obtained with relatively little effort, and used to derive whole-river stock-recruitment relationships on rivers where only adult count or some other estimator of parental stock is available. The derivation and expression of spawning targets from stock/recruitment relationships is discussed with reference to the R. Bush data.     

Size‐dependent growth of individual Atlantic salmon Salmo salar alevins from hatch to first feeding

Variation in egg size, hatch timing and size at hatch, and their influence on individual growth rates of Atlantic salmon Salmo salar alevins up to first feeding were examined in pure strain and hybrid crosses of fish from Scotland and Canada. At the intra‐female, intra‐cross type and inter‐cross type levels, specific growth rates prior to first feed were strongly size dependent, with smaller and later hatching alevins growing significantly faster. The magnitude of this size‐dependent growth was greatest in the hybrid crosses. This resulted in a 40% reduction in the coefficient of variation (c.v. ) in alevin size from post‐hatch to first feeding at the intra‐female level, and a reduction of both intra‐ and inter‐cross differences in alevin sizes in the same period.     

Application of a fry (0+;) abundance index, based on semi-quantitative electrofishing, to predict Atlantic salmon smolt runs in the River Bush, Northern Ireland

An abundance index for 0+ Atlantic salmon was based on semi-quantitative electrofishing estimates at 137 sites in typical juvenile habitat throughout the River Bush (N. Ireland). 0 + abundance was linearly related to total smolt numbers migrating through a downstream trap in subsequent years ( r ²= 0.716, P <0.001), suggesting a high degree of predictive ability. This predictive ability decreased as smolt age increased, suggesting influence of density-independent mortality. Potential application of the technique to estimate smolt production from rivers having no trapping facilities is discussed, together with sources of variability potentially affecting estimates.     

A study of temporal genetic variation in a natural population of Atlantic salmon in the River Bush, Northern Ireland

Temporal genetic variation in River Bush Atlantic salmon was low and much less than among geographically discrete samples reported from elsewhere.     

Water discharge affects Atlantic salmon Salmo salar smolt production: a 27 year study in the River Orkla,Norway

A model that explains 48% of the annual variation in Atlantic salmon Salmo salar smolt production in the River Orkla, Norway, has been established. This variation could be explained by egg deposition, minimum daily discharge during the previous winter and minimum weekly discharge during the summer 3 years before smolt migration. All coefficients in the model were positive, which indicates that more eggs and higher minimum discharge levels during the winter before smolt migration and the summer after hatching benefit smolt production. Hence, when the spawning target of the river is reached, the minimum levels of river discharge, in both winter and summer, are the main bottlenecks for the parr survival, and hence for smolt production. The River Orkla was developed for hydropower production in the early 1980s by the construction of four reservoirs upstream of the river stretch accessible to S. salar. Although no water has been removed from the catchment, the dynamics of water flow has been altered, mainly by increasing discharges during winter and reducing spring floods. In spite of the higher than natural winter discharges, minimum winter discharge is still a determinant of smolt production. Hence, in regulated rivers, the maintenance of discharges to ensure that they are as high as possible during dry periods is an important means of securing high S. salar smolt production.     

Spatial distribution correspondence of a juvenile Atlantic salmon Salmo salar cohort from age 0+ to 1+ years

The spatial distribution of Atlantic salmon Salmo salar young-of-the-year (0+) and 1 year old parr (1+) from the 2006 spawning cohort in a 5125 m reach of the River Skauga in central Norway was documented. A high degree of similarity was found between the distribution of 0+ and 1+ parr based on catches at 205 transects sampled in both years. Cross-correlations and partial cross-correlations (correcting for habitat variables) confirmed significant positive association between the two distributions on a small spatial scale (within 100 m) and a clear pattern of decreasing correlation with distance.     

Passing a seawater challenge test is not indicative of hatchery‐reared Atlantic salmon Salmo salar smolts performing as well at sea as their naturally produced conspecifics

Despite satisfactory reactions to seawater challenge tests indicative of appropriate physiological state, hatchery‐reared Atlantic salmon Salmo salar smolts stocked in the Eira River in Norway between 2001 and 2011 performed less well at sea in terms of growth, age at maturity and survival than smolts of natural origin. The mean rates of return to the river for hatchery‐reared and naturally produced S. salar were 0·98 and 2·35%. In the Eira River, c. 50 000 hatchery‐reared S. salar smolts of local origin were stocked annually to compensate for reduced natural smolt production following regulation for hydroelectric purposes, while a mean of 17 262 smolts were produced naturally in the river. This study demonstrates that, although captive S. salar perform well in seawater challenge tests, hatchery‐reared smolts are not necessarily as adaptable to marine life as their naturally produced counterparts. These findings suggest that production of hatchery‐reared smolts more similar to naturally produced individuals in morphology, physiology and behaviour will be necessary to improve success of hatchery releases. Where possible, supplementary or alternative measures, including habitat restoration, could be implemented to ensure the long‐term viability of wild stocks.     

The effect of intragastric transmitters on feeding behaviour of Atlantic salmon, Salmo salar; parr during autumn

The proportion of Atlantic salmon parr (146 265 mm total length) that fed in laboratory tanks during autumn was 0% in fish filled with intragastric transmitters compared with 78 100% in controls.     

Increases in benthic community production and metabolism in response to marine‐derived nutrients from spawning Atlantic salmon (Salmo salar)

相似文献   

No evidence of kin bias in dispersion of young‐of‐the‐year Atlantic salmon Salmo salar L. in a natural stream

Ninety‐one young‐of‐the‐year Atlantic salmon Salmo salar were captured using a non‐invasive snorkelling technique in a 38 m section of Catamaran Brook, New Brunswick, Canada, to test whether related fish settle closer to one another than unrelated fish. A maximum likelihood estimate of parentage relationships assessed by genotyping eight microsatellite loci revealed five half‐sibling families in the sample of fish. Related juvenile S. salar were not found closer to one another than unrelated fish in three analyses at two spatial scales: a comparison of the relatedness of focal fish to their nearest neighbour and to their four nearest neighbours, and a correlation of the pair‐wise relatedness and distance matrices for all fish in the sample. The lack of a kin‐biased dispersion pattern may be related to the lower density of fish or the scarcity of full‐siblings at the study site compared to laboratory conditions.     

Amount and distribution of biochemical-genetic variation among wild populations and a hatchery stock of Atlantic salmon, Salmo salar L., from north-east Ireland

The effects of tributyltin (TBT) compounds on gill morphology were examined in the mummichog, Fundulus heteroclitus , in 96-h LC50 and 6-week sublethal exposures. Morphometry was used for the identification and quantification of effects with the light microscope. A 96-h LC50 of 17.2 μg 1 ¹ was determined. Morphometric analysis of gill tissues revealed hypertrophy of the lamellar epithelium in fish exposed to 17.2 μg 1–1. Relative diffusing capacity was significantly decreased (−41 %); ( P <0.05, ANOVA, Bonferroni t -test). At 35.6 μg 1⁻¹, TBT exposure resulted in a significant reduction (− 40%) in the volume of the lamellar blood channels. Both of these observations occurred in fish that showed signs of acute poisoning including loss of equilibrium. In fish exposed to sublethal concentrations of 0.105–2.000 μg TBT 1⁻¹ for 6 weeks, there were no pathological changes in the gill. There were no treatment-related changes in the surface morphology of the gills of fish from both experiments upon scanning electron microscopic examination. Although gill pathology was observed in acutely toxic exposures, it does not appear to be a major mechanism of TBT toxicity.     

Microsatellite DNA markers for the study of Atlantic salmon (Salmo salar) kinship,population structure,and mixed‐fishery analyses

Eleven microsatellite DNA loci were identified and characterized for Atlantic salmon (Salmo salar) collected from the Penobscot River, Maine, USA and the River Nith, Scotland, UK. The markers revealed high levels of genetic diversity (seven to 48 alleles per locus), heterozygosity (to 100%), and allelic heterogeneity (all comparisons). Considerable differentiation was observed as the genetic distance (chord) between the two collections was 0.680 and the pairwise F_ST, 0.12, was highly significant. These findings are consistent with patterns of continental‐level differentiation observed previously using an alternate suite of microsatellite loci. Locus‐by‐locus analyses of molecular variance suggested that most markers were suitable for delineating kinships and population genetic structure.     

The effect of catch‐and‐release angling at high water temperatures on behaviour and survival of Atlantic salmon Salmo salar during spawning migration

In this study, behaviour and survival following catch‐and‐release (C&R) angling was investigated in wild Atlantic salmon Salmo salar (n = 75) angled on sport fishing gear in the River Otra in southern Norway at water temperatures of 16·3–21·1° C. Salmo salar were tagged externally with radio transmitters and immediately released back into the river to simulate a realistic C&R situation. The majority of S. salar (91%) survived C&R. Most S. salar that were present in the River Otra during the spawning period 3–4 months later were located at known spawning grounds. Downstream movements (median furthest position: 0·5 km, range: 0·1–11·0 km) during the first 4 days after release were recorded for 72% of S. salar, presumably stress‐induced fallback associated with C&R. Individuals that fell back spent a median of 15 days before commencing their first upstream movement after release, and 34 days before they returned to or were located above their release site. Mortality appeared to be somewhat elevated at the higher end of the temperature range (14% at 18–21° C), although sample sizes were low. In conclusion, C&R at water temperatures up to 18° C had small behavioural consequences and was associated with low mortality (7%). Nevertheless, low levels of mortality occur due to C&R angling and these losses should be accounted for by management authorities in rivers where C&R is practised. Refinement of best practices for C&R may help to reduce mortality, particularly at warmer temperatures.     

A study of variability in the MHC class II β1 and class I α2 domain exons of Atlantic salmon, Salmo salar L.

Variability in the most extracellular exons of Atlantic salmon MHC-Sasa class I and class II was studied by polymerase chain reaction (PCR) amplification followed by sequencing. The domains studied were class I α2 and class II β1. The material used was genomic DNA of fish, mainly derived from the major Norwegian breeding pool, supplemented with some material from a minor breeder and a local river strain. The analysis revealed extensive variation, most individuals being heterozygous with at least two variants.     

Reservoir to river passage of age‐0+ year fishes,indication of a dispersion pathway for a non‐native species

This study demonstrates passage of age‐0+ year individuals of pikeperch Sander lucioperca, common bream Abramis brama and non‐native tubenose goby Proterorhinus semilunaris from the Nové Mlýny Reservoir into the River Dyje (Danube River basin, Czech Republic) through the turbine of a hydropower facility. Most fishes had standard length (L_S) in the range 12–33 mm. Seasonal patterns corresponded with spawning activity, i.e. an early single spawning event for S. lucioperca, multiple spawning events for A. brama and continuous spawning with a later start and prolonged duration for P. semilunaris. Sander lucioperca, P. semilunaris and larger A. brama (>22 mm) drifted almost exclusively during the dark; smaller A. brama displayed no preference for light or dark. Proterorhinus semilunaris displayed significantly lower mortality than other species when passing through the turbine (3% compared to 18%). The passage of high numbers of P. semilunaris from the reservoir (estimated at 473 000 individuals per year), and their subsequent mass downstream drift, may have contributed to rapid population establishment along the River Dyje and the quick downstream expansion.     

Establishment and characterization of a new cell line (SSP‐9) derived from Atlantic salmon Salmo salar that expresses type I if n

In the present work, the establishment and biological characterization of a new cell line, SSP‐9, derived from the pronephros of the Atlantic salmon Salmo salar, are reported. These cells grew well in Leibovitz's (L15) medium supplemented with 10% foetal calf serum at temperatures from 15 to 25° C, and they have been sub‐cultured over 100 passages to produce a continuous cell line with an epithelial‐like morphology. The SSP‐9 cells attached and spread efficiently at different plating densities, retaining 80% of cell viability after storage in liquid nitrogen. When karyotyped, the cells had 40–52 chromosomes, with a modal number of 48. Viral susceptibility tests showed that SSP‐9 cells were susceptible to infectious pancreatic necrosis virus and infectious haematopoietic necrosis virus, producing infectious virus and regular cytopathic effects. Moreover, these cells could be stimulated by poly I:C, showing significant up‐regulation in the expression of the genes that regulate immune responses, such as ifn and mx‐1. SSP‐9 cells constitutively express genes characteristic of macrophages, such as major histocompatibility complex (mhc‐II) and interleukin 12b (il‐12b), and flow cytometry assays confirmed that SSP‐9 cells can be permanently transfected with plasmids expressing a reporter gene. Accordingly, this new cell line is apparently suitable for transgenic manipulation, and to study host cell–virus interactions and immune processes.     

An analysis of genetic stock identification on a small geographical scale using microsatellite markers,and its application in the management of a mixed‐stock fishery for Atlantic salmon Salmo salar in Ireland

A genetic stock identification (GSI) study was undertaken in a fishery for Atlantic salmon Salmo salar to determine the effects of restrictive fishery management measures on the stock composition of the fishery, and if accurate and precise stock composition estimates could be achieved on the small geographical scale where this fishery operates, using a suite of only seven microsatellite loci. The stock composition of the Foyle fishery was shown to comprise almost exclusively of Foyle origin fish in the 3 years after restrictive measures were introduced in 2007, compared to 85% the year before. This showed that the restrictive measures resulted in the Foyle fishery being transformed from a mixed‐stock fishery to an almost exclusively single‐stock fishery, and showed how GSI studies can guide and evaluate management decisions to successfully manage these fisheries. Highly accurate and precise stock composition estimates were achieved in this study, using both cBAYES and ONCOR genetic software packages. This suggests accurate and precise stock composition is possible even on small geographical scales.     

The influence of broad scale climatic phenomena on long term trends in Atlantic salmon population size: an example from the River Foyle, Ireland

The effect of marine climatic conditions in the North Atlantic on the abundance of returning migrant Atlantic salmon Salmo salar in the River Foyle, Ireland was examined. Catches of Atlantic salmon from commercial netting stations significantly predicted a measure of population size independent of catches over a 48 year period, thus commercial net catches were used as a measure of relative population size over a longer period in this study. The North Atlantic Oscillation index in winter (wNAOI) provides a generalized measure of climate variation for the northern hemisphere and between 1875 and 2001, the wNAOI was a highly significant predictor of the 5 year running mean of catches of migrant Atlantic salmon returning to the River Foyle. When the index was <0·151, the wNAOI correlated significantly and negatively with Atlantic salmon catches, with 70% of the variance in population size explained by variation in conditions in the marine environment between 1875 and 2001. When the wNAOI was >0·151, however, this relationship uncoupled. The probability of catches exceeding the long‐term median was 2·34 times lower in years where the wNAOI was above the 0·151 breakpoint than for years when it was <0·151. The wNAOI exceeded the 0·151 threshold on 8 out of the 10 years prior to 2001. Models of climate change indicated that the NAOI is likely to increase significantly with time. If these models are correct, this study would lead to the conclusion that a decoupling of these broad scale climate effects on Atlantic salmon population size will become the norm. Data presented here suggests two consequences of this. Firstly that the value of the NAOI as a predictive tool for forecasting adult Atlantic salmon population size will be limited and secondly that the median population size will become lower in the future.