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Sea lice cause substantial economic and environmental harm to Norway's aquaculture industry and wild salmonid populations. Rapid, accurate quantification of lice larval densities in coastal waters remains the greatest bottleneck for providing empirical data on infestation risk within wild salmon habitats and aquaculture production regions. We evaluated the capability of droplet digital PCR (ddPCR) as an absolute quantification method for the planktonic stages of two parasitic louse species, Lepeophtheirus salmonis (Krøyer) and Caligus elongatus (von Nordman). Results demonstrated linear relationships between the DNA quantity measured and the number of spiked larvae for both species and life stages. However, L. salmonis contained a significantly greater number of DNA copies than C. elongatus individuals and for C. elongatus, nauplii displayed a significantly higher number of DNA copies than copepodids. Our results suggest that ddPCR can effectively enumerate louse larvae, but interpreting ddPCR results differ between the two louse species. Obtaining larval abundance estimates from marine plankton samples will depend on the nauplii to copepodid ratio for C. elongatus, but not for L. salmonis. [ABSTRACT FROM AUTHOR]

It is hypothesized that in diadromous fish, migrations may occur because of differences in the availability of food in marine and freshwater habitats. The benefits of migration to sea may be increased growth opportunities and reproductive output, while the costs may be increased mortality and increased energy use. Here we examine mortality rates of anadromous Arctic char (Salvelinus alpinus) and brown trout (Salmo trutta) in fresh water and at sea over a 25-year period to test these hypotheses. Daily mortality rates were 5-15 times higher at sea than in fresh water, with highest rates for first-time migrants, inferring a clear trade-off between increased mass gain and mortality risk during the sea migration. Descending smolts were caught in a trap at the outlet of the river, individually tagged, and thereafter recorded each time they passed through the trap on their annual migration between the river and the sea. Brown trout females seemed to benefit to a higher degree from migrating to sea than did female Arctic char, probably because of the higher growth rate at sea, and hence higher reproductive output. Il est postule que, chez les poissons diadromes, des migrations peuvent avoir lieu en raison de differences de disponibilite de nourriture entre les habitats marins et d'eau douce. Les avantages de la migration vers la mer pourraient inclure des occasions de croissance accrues et une meilleure efficacite de la reproduction, alors que les couts peuvent comprendre une mortalite et une consommation d'energie accrues. Nous examinons les taux de mortalite d'ombles chevaliers (Salvelinus alpinus) et de truites brunes (Salmo trutta) en eau douce et en mer sur une periode de 25 ans afin de verifier ces hypotheses. Les taux de mortalite journaliers etaient de 5 a 15 fois plus eleves en mer qu'en eau douce, les poissons migrant pour la premiere fois presentant les taux les plus eleves, indiquant un compromis evident entre un plus grand gain de masse et un risque de mortalite accru durant la migration vers la mer. Des saumoneaux en devalaison ont ete pris dans un piege a l'emboucheur de la riviere et marques individuellement, puis chacun de leurs passages subsequents dans le piege durant leur migration annuelle entre la riviere et la mer a ete enregistre. La migration vers la mer semblait plus benefique aux truites brunes femelles qu'aux ombles chevaliers femelles, probablement en raison de leur taux de croissance plus grand en mer et donc d'une plus grande efficacite de la reproduction., Introduction Migratory behaviour can vary within species across a wide variety of taxa (Alerstam et al. 2003; Dingle and Drake 2007). The fitness consequences of different migratory strategies within the [...]

Data from a 25-year study of anadromous Arctic char (Salvelinus alpinus) and brown trout (Salmo trutta) in the River Halselva provided evidence that survival during winter was linked to marine growth during the previous summer. The study supported the 'critical size and critical period' hypothesis, which postulates that regulation of the abundance of adult salmonids occurs in two major phases. The first phase is marine mortality that occurs shortly after smolts enter salt water, and the second is during the following winter, when individuals that have not attained a critical size are unable to meet minimum metabolic requirements and die. In the present study, growth during summer appeared to be more important to winter survival than body size. Size-selective mortality occurred both at sea during summer and in fresh water during winter and was more evident for first-time migrants than repeat migrants. Les donnees d'une etude de 25 ans sur les ombles arctiques (Salvelinus alpinus) et les truites de mer (Salmo trutta) anadromes dans la riviere Halselva indiquent que la survie durant l'hiver est reliee a la croissance en mer durant l'ete precedent. L'etude appuie l'hypothese de << la taille critique et la periode critique >>, qui postule que la regulation de l'abondance des salmonides adultes se fait en deux grandes phases. La premiere de ces phases consiste en la mortalite en mer qui a lieu peu apres l'entree en eau salee des saumoneaux et la seconde se produit durant l'hiver suivant, alors que les individus qui n'ont pas atteint une certaine taille critique ne sont pas en mesure de repondre a leurs exigences metaboliques minimums et meurent. Dans la presente etude, la croissance durant l'ete semble etre plus importante pour la survie hivernale que la taille du corps. Une mortalite selective selon la taille se produit en mer durant l'ete et en eau douce durant l'hiver et est plus evidente pour les poissons qui migrent pour la premiere fois que pour les individus ayant deja effectue d'autres migrations. [Traduit par la Redaction], Introduction It is generally accepted that animals need to gain mass and store enough energy during periods of the year with rich food supplies to survive periods of the year [...]

This study found empirical evidence supporting the 'growth-survival' paradigm in the marine phase of Arctic char (Salvelinus alpinus) and brown trout (Salmo trutta). The paradigm postulates that larger or faster-growing individuals are more likely to survive than smaller or slower-growing conspecifics. The study employed long-term (25 year) capture data from a trap in the River Halselva in Norway during annual migration between marine and freshwater environments. Similar results were found for both species. Growth during the sea sojourn and return rates were positively correlated, linking increased survival with growth. Specific growth rate, survival, and duration of the sea sojourn of first-time migrants were correlated, suggesting that common environmental conditions at sea influence annual fish productivity. Freshwater and sea temperatures affected migration timing, whereas annual variation in marine growth and survival did not correlate with temperatures. This suggests that other factors such as variation in energy intake were the main source of annual growth variations. Moreover, the marine growth rate of the two species may signal annual overall fjord ecosystem production, especially related to their main prey. L'etude fait etat de preuves empiriques appuyant le paradigme de << croissance-survie >> chez les phases marines de l'omble chevalier (Salvelinus alpinus) et de la truite de mer (Salmo trutta). Ce paradigme postule que les individus plus grands ou a croissance plus rapide sont plus susceptibles de survivre que leurs conspecifiques plus petits ou a croissance plus lente. Nous avons utilise des donnees de capture de longue duree (25 ans) obtenues d'un piege dans la riviere Halselva, en Norvege, durant les migrations annuelles entre les milieux marins et d'eau douce. Des resultats semblables ont ete obtenus pour les deux especes. Il y a une correlation positive entre la croissance durant le sejour en mer et les taux de retour, temoignant d'un lien entre un taux de survie plus eleve et la croissance. Le taux de croissance, la survie et la duree du sejour en mer des individus migrant pour la premiere fois sont correles, ce qui donne a penser que des conditions ambiantes communes en mer influencent la productivite annuelle des poissons. Les temperatures de l'eau douce et de mer ont une incidence sur le moment de la migration, alors que les variations annuelles de la croissance et de la survie en mer ne sont pas correlees a la temperature. Cela porte a croire qu'un autre facteur, tel que la variation de l'apport energetique, constituerait la principale cause de variation de la croissance annuelle. En outre, le taux de croissance en mer des deux especes pourrait refleter la production annuelle globale de l'ecosysteme du fjord, particulierement en ce qui concerne leurs proies principales. [Traduit par la Redaction], Updated online 5 March 2018: The license for this article has been changed to the CC BY 4.0 license. The PDF and HTML versions of this article have been modified [...]

Photoplethysmography is a recent addition to physio‐logging in Atlantic salmon which can be used for pulse oximetry provided that the properties for light propagation in salmon tissues are known. In this work, optical properties of three constituents of Atlantic salmon blood have been characterized using a photo spectrometer in the VIS–NIR range (450–920 nm). Furthermore, Atlantic salmon blood cell size has been measured using a Coulter counter as part of light scattering property evaluations. Results indicate that plasma contributes little to scattering and absorption for wavelengths typically used in pulse oximetry as opposed to blood cells which are highly scattering. Extinction spectra for oxygenated and deoxygenated hemoglobin indicate that Atlantic salmon hemoglobin is similar to that in humans. Pulse oximetry sensors originally intended for human applications may thus be used to estimate blood oxygenation levels for this species. [ABSTRACT FROM AUTHOR]

A long-term study in the River Halselva in the Arctic region of Norway demonstrated that movements between watersheds were considerably higher in anadromous brown trout (Salmo trutta) than anadromous Arctic char (Salvelinus alpinus). Fourteen smolt year classes of both species were captured in a fish trap, individually tagged, and thereafter registered each time they passed the trap during their migration between the sea and fresh water every summer. Annual mean survival (i.e., recovery rate) after the first entry to sea as smolts was estimated as 31.4% in Arctic char and 26.6% in brown trout. Most surviving Arctic char returned to the River Halselva to overwinter after the same summer that they migrated to sea as smolts. However, several brown trout overwintered one to four times in other watersheds, mainly the considerably larger River Altaelva, before most eventually returned to the River Halselva upon maturation. The substantial difference in movement rate between watersheds between Arctic char (2.2%) and brown trout (39.6%) is expected to be a consequence of local geographic conditions combined with different habitat preferences of the two species. Une etude de longue duree de la riviere Halselva dans la region arctique de la Norvege a demontre que les deplacements entre bassins versants etaient considerablement plus importants pour la truite brune (Salmo trutta) anadrome que pour l'omble chevalier (Salvelinus alpinus) anadrome. Des saumoneaux de quatorze classes d'annee des deux especes ont ete captures dans un piege a poissons, marques individuellement, et subsequemment enregistres chaque fois qu'ils passaient par le piege durant leur migration entre la mer et l'eau douce chaque ete. Le taux de survie annuelle moyen (c.-a-d. le taux de recuperation) apres la premiere entree en mer comme saumoneaux a ete estime a 31,4 % pour les ombles chevaliers et 26,6 % pour les truites brune. La plupart des ombles chevaliers survivants retournaient a la riviere Halselva pour passer y l'hiver des l'ete ou ils avaient migre vers la mer en tant que saumoneaux. En revanche, plusieurs truites brune ont passe l'hiver d'une a quatre fois dans d'autres bassins versants, principalement celui de la riviere Altaelva, beaucoup plus grande, avant de finalement retourner ti la riviere Halselva a la maturite. La difference considerable des taux de deplacement entre bassins versants pour l'omble chevalier (2,2 %) et la truite brune (39,6 %) serait une consequence des conditions geographiques locales combinees a des preferences differentes des deux especes en matiere d'habitat. [Traduit par la Redaction], Introduction Anadromous salmonids return precisely to their natal river after ocean feeding migrations, which may last from a few weeks to several years (Thorpe 1988; Keefer and Caudill 2013). They [...]

Understanding the potential of natural populations to adapt to altered environments is becoming increasingly relevant in evolutionary research. Currently, our understanding of adaptation to human alteration of the environment is hampered by lack of knowledge on the genetic basis of traits, lack of time series, and little or no information on changes in optimal trait values. Here, we used time series data spanning nearly a century to investigate how the body mass of Atlantic salmon (Salmo salar) adapts to river regulation. We found that the change in body mass followed the change in waterflow, both decreasing to ~1/3 of their original values. Allele frequency changes at two loci in the regions of vgll3 and six6predicted more than 80% of the observed body mass reduction. Modeling the adaptive dynamics revealed that the population mean lagged behind its optimum before catching up approximately six salmon generations after the initial waterflow reduction. Our results demonstrate rapid adaptation mediated by large-effect loci and provide insight into the temporal dynamics of evolutionary rescue following human disturbance. [ABSTRACT FROM AUTHOR]

A study over a 22-year period of first-time migrants (smolts) of three sympatric salmonids (Atlantic salmon (Salmo salar), brown trout (Salmo trutta), and Arctic char (Salvelinus alpinus)) in a watercourse in northern Norway demonstrated that although there was considerable overlap in smolt migration timing among the species, Atlantic salmon migrated first, followed by Arctic char, and finally brown trout. The migration period of Arctic char had a smaller range and less annual variation than those of the two other species, possibly partly related to their more lake-dwelling habitat preference. For all species, water flow was important in explaining day-to-day variations in smolt runs. Water flow was most important for brown trout, change in flow for Atlantic salmon, whereas photoperiod was most important for Arctic char. These results suggest that both age and size of smolts and the timing of the smolt migration have been shaped by the different habitat preferences of these species both in fresh water and sea through local selection. Une etude sur une periode de 22 ans des saumoneaux qui migrent pour la premiere fois chez trois salmonides sympatriques (le saumon atlantique (Salmo salar), la truite brune (Salmo trutta)et l'omble chevalier (Salvelinus alpinus)) dans un cours d'eau du nord de la Norvege demontre que, bien qu'il y ait un important chevauchement dans la migration des saumoneaux des differentes especes, le saumon atlantique migre le premier, suivi de l'omble chevalier et ensuite de la truite brune. La periode de migration de l'omble chevalier a une etendue plus restreinte et une variation annuelle moindre que celles des deux autres especes, probablement en partie a cause de sa preference marquee pour les habitats lacustres. Chez toutes les especes, le debit est important pour expliquer les variations de jour en jour des migrations de saumoneaux. Le debit est le facteur le plus important pour la truite brune, le changement de debit l' est pour le saumon atlantique, alors que la photoperiode l'est pour l'omble chevalier. Nos resultats indiquent que tant l'age et la taille des saumoneaux que leur calendrier de migration ont ete faconnes par la selection locale compte tenu des preferences d'habitat differentes de ces especes, tant en eau douce qu' en mer. [Traduit par la Redaction], Introduction For diadromous fishes, habitat shifts between fresh water and the sea can be hazardous (Bell 2009; McDowall 2010), and for salmonids, smolt migration to the sea is a key [...]

Abstract: The physiological consequences of 'premature migratory return' to freshwater for wild sea-run brown trout (Salmo trutta) smolts infested with sea lice (Lepeophtheirus salmonis) were investigated in the laboratory. Osmoregulatory, [...]

Abstract: For wild, sea-run brown trout (Salmo trutta) smolts, the physiological consequences of abrupt transfer to seawater and simultaneous challenge with copepodid larvae of the sea louse, Lepeophtheirus salmonis (Kroyer, [...]

The timing of seaward migration is a key life‐history trait for many anadromous fish species, with growth and survival at sea depending on a match/mismatch scenario between the timing of the sea entry and optimal conditions. Based on a 25‐year study with 15,226 individually tagged brown trout (Salmo trutta) in a Norwegian river, we analysed how the within‐season timing of sea migration impacted growth and survival. In both first‐time and veteran migrants, marine growth was highest for early migrating individuals, large individuals, and those with a low condition factor when entering the sea. Survival was highest for individuals entering the sea early in the season. In first‐time migrants, survival increased with body length. Survival also increased with the number of other smolts migrating simultaneously. As the early smolts were the most successful, it may seem strange that many smolts migrate later in the season. We suggest that late‐migrating smolts may not be of a size and/or physiological state suitable for early marine conditions, and may make the best of a bad situation. [ABSTRACT FROM AUTHOR]