Thermal habitat of adult Atlantic salmon Salmo salar in a warming ocean

The year-round thermal habitat at sea for adult Atlantic salmon Salmo salar (n = 49) from northern Norway was investigated using archival tags over a 10 year study period. During their ocean feeding migration, the fish spent 90% of the time in waters with temperatures from 1.6–8.4°C. Daily mean temperatures ranged from −0.5 to 12.9°C, with daily temperature variation up to 9.6°C. Fish experienced the coldest water during winter (November–March) and the greatest thermal range during the first summer at sea (July–August). Trends in sea-surface temperatures influenced the thermal habitat of salmon during late summer and autumn (August–October), with fish experiencing warmer temperatures in warmer years. This pattern was absent during winter (November–March), when daily mean temperatures ranged from 3.4–5.0°C, in both colder and warmer years. The observations of a constant thermal habitat during winter in both warmer and colder years, may suggest that the ocean distribution of salmon is flexible and that individual migration routes could shift as a response to spatiotemporal alterations of favourable prey fields and ocean temperatures.     

Characterization of transferrin‐linked microsatellites in brown trout (Salmo trutta) and Atlantic salmon (Salmo salar)

The transferrin (TF) gene has recently received increased interest in fish given its fitness relevance as a resistance gene against pathogenic bacteria. In this study, we characterized five TF‐linked microsatellites in brown trout (Salmo trutta) and Atlantic salmon (Salmo salar). Interestingly, each marker amplified duplicated loci and linkage analysis revealed that the TF gene has most likely experienced a tandem duplication during salmonid evolution. In addition, the amplification of all five markers across a wide range of salmonid species suggests that they may be of general interest for the genetic analysis of the TF gene(s) in this teleost family.     

Territory size and distribution of newly-emerged Atlantic salmon (Salmo salar)

Newly emerged Atlantic salmon (Salmo salar) were observed from May to August 1981 at six isolated redds in Washington County, Maine, USA. Territorial size and distribution were measured. At the end of the emergence period (12 to 28 May), fish maintained positions (stations) at redds where water velocity did not exceed 52 cm s^–1 By 12 June, most salmon (80–96%) had moved off the redds of origin and had established territories 1 to 5 m from the redd. The area defended increased substantially after mid-June, but territorial aggression diminished by 15 July, and the fry dispersed downstream. All fish observed were territorial, and the percentage of time during which stations were held decreased from 89 in mid-May to as low as 40% in mid-June.Cooperators are the Maine Department of Inland Fisheries and Wildlife, University of Maine, U.S. Fish and Wildlife Service, and the Wildlife Management Institute     

Spawning behaviour of a farmed escaped female Atlantic salmon (Salmo salar)

Excavation of stranded redds revealed differences in spawning behaviour between farmed and wild Atlantic salmon. The redd of a farmed fish contained more egg pockets (nine v . average of two) and fewer eggs per pocket (averages: 459 v . 707). No other pocket measures differed.     

Residence time of the sea louse, Lepeophtheirus salmonis K., on Atlantic salmon, Salmo salar L., after immersion in fresh water

Returning adult salmon caught at the mouth of the River Dee, Aberdeenshire, were transferred to tanks in the laboratory. For fish placed in fresh water, sea lice remained attached for up to 6 days, though most lice were lost in the first 48 hours. Few lice were lost from salmon maintained in sea water. The experiments were conducted in water within a temperature range of 12·8 to 16° C, equivalent to summer river temperatures in the Aberdeenshire Dee.     

Overwintering and migration behaviour of post-spawned Atlantic salmon Salmo salar in a large hydropower-regulated river and reservoir

Tracking 47 post-spawned adult Atlantic salmon Salmo salar L. in a hydropower-regulated river through autumn, winter and spring revealed that winter survival was 56% and 75% in two study years, respectively, with higher mortality of males than females (50% vs. 33% and 100% vs. 13%, respectively). Some kelts (n = 7) displayed nondirected movements that were interpreted as a reconditioning period for an average of 9–17 days prior to directed downstream movements indicating the initiation of migration. Survival after the initiation of migration in spring was 83% and 94% to the hydropower dam in the first and second study years, and decreased to 60 and 63%, respectively, after dam passage. There were no further losses in the downriver reach in the second year, with the first year having a cumulative survival estimate of 53% to the river mouth. Kelts approached the dam when the spillway gates were available as a passage option most of the time (64%–75%), but some kelts arrived at the dam or had not yet passed when spillways were closed (n = 6) and the only remaining passage option was restricted to the turbines. However, all but one kelt that must have passed via turbine were successful in reaching the river mouth. Migratory delay presumably due to searching behaviour caused by low water flow was estimated at approximately 6 days as migration rates were significantly slower in the reservoir (median ± s.e. 8.5 ± 2.5 km day⁻¹) than up- (29.7 ± 5.0 km day⁻¹) or downriver (22.1 ± 3.1 km day⁻¹). The proportion of time (median 30%) that kelts spent swimming upstream (searching behaviour) in the reservoir was a significant variable for migration success.     

Vertical distribution of Atlantic salmon (Salmo salar) as a function of illumination

The vertical distribution of cultured Atlantic salmon larger than 1 kg was monitored by hydroacoustics in both a shallow (6 m) and a deep (20 m) cage. Surface light levels and fish distribution were registered for three periods throughout the year. The two fish groups were fed calculated rations twice a day. During the winter and spring (including vernal equinox), the fish were distributed at around 5 m depth in both cages when not feeding. Around summer solstice, the fish preferred deeper waters when not feeding. The light dependency of the vertical migration was pronounced, and indicates clearly that even a 20 m deep cage is not deep enough to meet the depth requirements of large Atlantic salmon during summer.     

Inclusion of water temperature in a fuzzy logic Atlantic salmon (Salmo salar) parr habitat model

As water temperature is projected to increase in the next decades and its rise is clearly identified as a threat for cold water fish species, it is necessary to adapt and optimize the tools allowing to assess the quantity and quality of habitats with the inclusion of temperature. In this paper, a fuzzy logic habitat model was improved by adding water temperature as a key determinant of juvenile Atlantic salmon parr habitat quality. First, salmon experts were consulted to gather their knowledge of salmon parr habitat, then the model was validated with juvenile salmon electrofishing data collected on the Sainte-Marguerite, Matapedia and Petite-Cascapedia rivers (Québec, Canada). The model indicates that when thermal contrasts exist at a site, cooler temperature offered better quality of habitat. Our field data show that when offered the choice, salmon parr significantly preferred to avoid both cold areas (<15 °C) and warm areas (>20.5 °C). Because such thermal contrasts were not consistently present among the sites sampled, the model was only validated for less than 60% of the sites. The results nevertheless indicate a significant correlation between median Habitat Quality Index and parr density for the Sainte-Marguerite River (R² = 0.38). A less important, albeit significant (F-test; p = 0.036) relationship was observed for the Petite-Cascapedia river (R² = 0.14). In all instances, the four-variable (depth, velocity, substrate size and temperature) model provided a better explanation of parr density than a similar model excluding water temperature.     

Experimental investigation of the effects of temperature and feeding regime on scale growth in Atlantic salmon Salmo salar post-smolts

Salmo salar post-smolts were reared in seawater under controlled laboratory conditions for 12 weeks. The fish were exposed to three constant temperature treatments (15, 10.5 and 6°C) and four feeding treatments (constant feeding, food withheld for 7 days, food withheld for 14 days and food withheld intermittently for four periods of 7 days). Scale growth was proportional to fish growth across all treatments, justifying the use of scale measurements as a proxy for growth during the early marine phase. The rate of circuli deposition was dependant on temperature and feeding regime and was generally proportional to fish growth but with some decoupling of the relationship at 15°C. Deposition rates varied from 4.8 days per circulus at 15°C (constant feeding) to 15.1 days per circulus at 6°C (interrupted feeding). Cumulative degree day (^°D) was a better predictor of circuli number than age, although the rate of circuli deposition ^°D⁻¹ was significantly lower at 6°C compared with 15 and 10.5°C. Inter-circuli distances were highly variable and did not reflect growth rate; tightly packed circuli occurred during periods without food when growth was depressed, but also during periods of rapid growth at 15°C. The results further current understanding of scale growth properties and can inform investigations of declining marine growth in S. salar based on interpretations of scale growth patterns.     

The effects of prior residence on behavior and growth rates in juvenile Atlantic salmon (Salmo salar)

It is well documented that prior residence confers advantagesin territorial disputes, but its impact on other aspects ofbehavior and fitness is less understood. We tested how priorresidence influences the subsequent feeding behavior and growthperformance of dispersing Atlantic salmon fry (Salmo salar)using experimental manipulations of residence in a seminaturalstream tank. In replicated trials, groups of seven "primary"fish were released into the stream tank 3 days ahead of seven"secondary" fish. Standardized behavioral observations were madeon each fish over the following 14 days, after which all fishwere removed and measured. Primaries and secondaries were initiallythe same size and body condition and exhibited the same degreeof site fidelity. However, primaries darted higher into thewater column to intercept prey items, fed at a higher rate,and subsequently grew faster. Larger fish (in terms of body length)tended to be more dominant, and dominants grew faster than subordinates.However, there was no difference in dominance between primaries andsecondaries. These results suggest that the well-documentedadvantage of early-emerging salmon fry over late-emerging frycannot be completely attributed to intrinsic differences andthat the advantage is partly mediated via a prior residenceeffect. Furthermore, prior residents gain foraging advantageswithout necessarily becoming more dominant.     

Effects of acute iron overload on Atlantic salmon (Salmo salar) and rainbow trout (Oncorhynchus mykiss)

Distribution of radioiron to various tissues after intraperitoneal injections was examined in Atlantic salmon and rainbow trout. Liver and spleen were found to be the major iron storage tissues. Injections of 1 or 5 mg iron as ferric ammonium citrate led to a fall in hemoglobin levels in both species after 2 d. Hemoglobin levels returned to normal levels in rainbow trout after 8 d, but Atlantic salmon had not recovered, and Hb levels fell below 3 g/100 mL. In both species, the fall in Hb was associated with a raise in iron levels in spleen and liver, suggesting damage to erythrocytes. Atlantic salmon liver ferritin showed a two- to threefold increase, while rainbow trout showed a sixfold increase, and a more rapid response. The toxic effect of iron in fish appears to be different from the effect in other vertebrates.     

An evaluation of the quality of fall-fingerling Atlantic salmon (Salmo salar L.) released to natural lacustrine nursery areas in Newfoundland,Canada

Results of experiments on controlled releases of fall-fingerling Atlantic salmon to lacustrine habitats in Newfoundland are reviewed in terms of survival during freshwater residence and smolt yield per unit of standing water habitat. Average survival from parr to smolt in three consecutive annual releases was 12.9% and we conclude that the quality of fall-fingerling salmon, produced from our semi-natural rearing techniques, was satisfactory. Year-class survival decreased progressively with consecutive releases. Rate of increase in juvenile salmon biomass remained stable over the duration of the study, suggesting that the average annual biomass of 1.6 kg ha^–1 of juvenile salmon released did not exceed habitat carrying capacity. Precocity did not appear to represent a significant deterrent to fall-fingerling survival. Annual smolt yield (by year-class) from stocking ranged from 53 to 130 ha^–1 (mean = 77 smolts ha^–1).     

Atlantic salmon (Salmo salar) of the Pigou and Bouleau Rivers,Quebec

Synopsis Juvenile Atlantic salmon of the Pigou and Bouleau Rivers, Quebec, were studied during the summer of 1972 and 1973. Growth increments for Pigou salmon averaged 36–50 mm yr^–1 and smolts averaged 2.9 yrs old. Bouleau salmon grew slower (26–41 mm yr^–1) and became smolts at a slightly older mean age (3.1 yrs). Mature male parr were more abundant in all age-groups from the Plgou River, possibly because of the faster growth. In terms of management, the Pigou River has little potential for increased salmon production because of limited habitat. On the other hand, the Bouleau River has considerable potential, and salmon production could be increased if the upper reaches were made accessible to migrating salmon.Contribution number 36 of the Matamek Research Station, Woods Hole Oceanographic Institute.     

Whole body elemental and proximate composition of Atlantic salmon (Salmo salar) during the life cycle

Atlantic salmon ( Salmo salar ) raised under production conditions were sampled periodically during their life cycle, in fresh and salt water, to determine their proximate and elemental composition. The parameters changed in relation to life cycle stage and fish size, and were influenced by whether the fish were in salt or freshwater. Measurements presented can be used to assist in the formulation of feeds, and to determine the health and nutritional status of commercially reared Atlantic salmon.     

Variation in the timing of river entry of Atlantic salmon (Salmo salar L.) in the Baltic

The timing of river entry in the Atlantic salmon is known to depend on genetic,demographic and environmental factors,but little is known about the relative magnitude of among population and among year variation and covariation in this respect in natural state Atlantic salmon rives.To investigate this,variability in the timing of river entry in three historical Finnish Atlantic salmon populations were analyzed using salmon trap data collected during 1870-1902.The analyses reveled that 1)the timing of river e...     

Beyond MHC: signals of elevated selection pressure on Atlantic salmon (Salmo salar) immune‐relevant loci

Using Atlantic salmon (Salmo salar) as a model system, we investigated whether 18 microsatellites tightly linked to immune‐relevant genes have experienced different selection pressures than 76 loci with no obvious association with immune function. Immune‐relevant loci were identified as outliers by two outlier tests significantly more often than nonimmune linked loci (22% vs. 1.6%). In addition, the allele frequencies of immune relevant markers were more often correlated with latitude and temperature. Combined, these results support the hypothesis that immune‐relevant loci more frequently exhibit footprints of selection than other loci. They also indicate that the correlation between immune‐relevant loci and latitude may be due to temperature‐induced differences in pathogen‐driven selection or some other environmental factor correlated with latitude.     

Spatial and temporal genetic structure of a river‐resident Atlantic salmon (Salmo salar) after millennia of isolation

The river‐resident Salmo salar (“småblank”) has been isolated from other Atlantic salmon populations for 9,500 years in upper River Namsen, Norway. This is the only European Atlantic salmon population accomplishing its entire life cycle in a river. Hydropower development during the last six decades has introduced movement barriers and changed more than 50% of the river habitat to lentic conditions. Based on microsatellites and SNPs, genetic variation within småblank was only about 50% of that in the anadromous Atlantic salmon within the same river. The genetic differentiation (F_ST) between småblank and the anadromous population was 0.24. This is similar to the differentiation between anadromous Atlantic salmon in Europe and North America. Microsatellite analyses identified three genetic subpopulations within småblank, each with an effective population size N_e of a few hundred individuals. There was no evidence of reduced heterozygosity and allelic richness in contemporary samples (2005–2008) compared with historical samples (1955–56 and 1978–79). However, there was a reduction in genetic differentiation between sampling localities over time. SNP data supported the differentiation of småblank into subpopulations and revealed downstream asymmetric gene flow between subpopulations. In spite of this, genetic variation was not higher in the lower than in the upper areas. The meta‐population structure of småblank probably maintains genetic variation better than one panmictic population would do, as long as gene flow among subpopulations is maintained. Småblank is a unique endemic island population of Atlantic salmon. It is in a precarious situation due to a variety of anthropogenic impacts on its restricted habitat area. Thus, maintaining population size and avoiding further habitat fragmentation are important.     

Expression of olfactory receptors in different life stages and life histories of wild Atlantic salmon (Salmo salar)

It has been hypothesized that salmonids use olfactory cues to return to their natal rivers and streams. However, the key components of the molecular pathway involved in imprinting and homing are still unknown. If odorants are involved in salmon homing migration, then olfactory receptors should play a critical role in the dissipation of information from the environment to the fish. Therefore, we examined the expression profiles of a suite of genes encoding olfactory receptors and other olfactory-related genes in the olfactory rosettes of different life stages in two anadromous and one non-anadromous wild Atlantic salmon populations from Newfoundland, Canada. We identified seven differentially expressed OlfC genes in juvenile anadromous salmon compared to returning adults in both populations of anadromous Atlantic salmon. The salmon from the Campbellton River had an additional 10 genes that were differentially expressed in juveniles compared to returning adults. There was no statistically significant difference in gene expression of any of the genes in the non-anadromous population (P < 0.01). The function of the OlfC gene products is not clear, but they are predicted to be amino acid receptors. Other studies have suggested that salmon use amino acids for imprinting and homing. This study, the first to examine the expression of olfactory-related genes in wild North American Atlantic salmon, has identified seven OlfC genes that may be involved in the imprinting and homeward migration of anadromous Atlantic salmon.