Temporal variation in abundance, return rate and life histories of previously spawned Atlantic salmon in a large subarctic river

The 30 year time series analyses revealed large temporal variation in the return rates and a recent increase in abundance of previous spawning Atlantic salmon Salmo salar in the River Teno, northern Scandinavia. The mean proportion of repeat spawners was 7 and 4% in the total Atlantic salmon catch and 9 and 22% in multi‐sea‐winter (MSW) catch component for females and males, respectively. Previous spawners constituted on the average 7% of the catch in mass but up to 20%(31 t) and 30%(19 t) in 2003 and in 2004, respectively. In 1975–2000, the proportion of previous spawners varied between 1 and 6%(3–12% of MSW Atlantic salmon), whereas in 2001–2004, they accounted for 8–21%(16–35% of MSW Atlantic salmon) of the total Atlantic salmon catch. The number of previous spawners in the catch correlated significantly with the preceding numbers of respective 1–3 sea‐winter (SW) maiden Atlantic salmon 2 years earlier. The recent increase in the numbers of 1S1 and 2S1 (1 or 2 years at sea followed by first spawning and 1 year reconditioning period at sea) alternate spawning Atlantic salmon was a consequence of higher numbers of maiden 1SW and 2SW Atlantic salmon in the catches and increased sea temperatures. Similarly, the return rate of 1SW Atlantic salmon to second spawning has improved in recent years. Most previous spawners ascended and were captured early in the fishing season. The smolt and sea‐age combinations of repeat spawners comprised 68 age groups contributing with the annual mean of 15 age groups to the great diversity of the River Teno Atlantic salmon population complex.     

Quantifying the ocean, freshwater and human effects on year-to-year variability of one-sea-winter Atlantic salmon angled in multiple Norwegian rivers

Many Atlantic salmon, Salmo salar, populations are decreasing throughout the species' distributional range probably due to several factors acting in concert. A number of studies have documented the influence of freshwater and ocean conditions, climate variability and human impacts resulting from impoundment and aquaculture. However, most previous research has focused on analyzing single or only a few populations, and quantified isolated effects rather than handling multiple factors in conjunction. By using a multi-river mixed-effects model we estimated the effects of oceanic and river conditions, as well as human impacts, on year-to-year and between-river variability across 60 time series of recreational catch of one-sea-winter salmon (grilse) from Norwegian rivers over 29 years (1979-2007). Warm coastal temperatures at the time of smolt entrance into the sea and increased water discharge during upstream migration of mature fish were associated with higher rod catches of grilse. When hydropower stations were present in the course of the river systems the strength of the relationship with runoff was reduced. Catches of grilse in the river increased significantly following the reduction of the harvesting of this life-stage at sea. However, an average decreasing temporal trend was still detected and appeared to be stronger in the presence of salmon farms on the migration route of smolts in coastal/fjord areas. These results suggest that both ocean and freshwater conditions in conjunction with various human impacts contribute to shape interannual fluctuations and between-river variability of wild Atlantic salmon in Norwegian rivers. Current global change altering coastal temperature and water flow patterns might have implications for future grilse catches, moreover, positioning of aquaculture facilities as well as the implementation of hydropower schemes or other encroachments should be made with care when implementing management actions and searching for solutions to conserve this species.     

Previously spawned Atlantic salmon ascend a large subarctic river earlier than their maiden counterparts

Spawning migration timing of maiden Atlantic salmon Salmo salar and previous spawners was analysed in the catches in 1989–2004 in the large subarctic River Teno in the northernmost parts of Finland and Norway. The hypothesis was that the migration timing of previous spawners and their maiden counterparts is similar, with the migration timing similar between sexes. In most cases, however, previous spawners were observed to migrate into the River Teno and its tributaries earlier than their maiden counterparts. The difference in run timing was especially evident between maiden one-sea-winter (1SW) Atlantic salmon and the corresponding group of previous spawners [1S1, 1 year at sea (1) followed by first spawning (S) and reconditioning period of 1 year (1) at sea and second spawning run] for both sexes in the River Teno and in its two tributaries. The same was also evident between 2SW maiden and 2S1 previous spawning female Atlantic salmon in the River Teno. Females showed earlier spawning migration than males both in previous spawners and maiden Atlantic salmon. Different maiden sea-age classes also showed differences in run timing as multi-sea-winter fish (2–4SW) ascended earlier than 1SW fish but the timing of 1S1 and 2S1 previous spawning females coincided. The results suggest that run timing of Atlantic salmon may not be strictly genetically fixed as previous spawners ascend earlier than they did on their first spawning migration as maiden fish, and indicated that the closeness of the reconditioning area of postspawners to the river of origin resulted in an early ascent. Run timing of different sea-age groups has major management implications if the populations are heavily exploited with numerous fishing methods in different periods of the fishing season, as in the River Teno system.     

Effect of origin, sex and sea age of Atlantic salmon on their recapture rate after river ascent

The recapture rate of Atlantic salmon (Salmo salar L.) after river ascent was examined by the trapping and tagging of ascending spawners in the lower reaches of the Simojoki River, which flows into the northern Baltic Sea. In 1997 and 1998, altogether 825 Carlin‐tagged salmon were released to continue their upstream migration. Of these, 800 could be sexed and categorized as reared (91%) or wild (9%) salmon. In 1997, most of the ascending salmon were multi‐sea‐winter (MSW) fish, whereas in 1998 almost all were one‐sea‐winter (1SW) male grilse due to the late trapping season. About 10% of all tagged fish were recaptured, two‐thirds of which were caught in the river before their descent to the sea. There was no difference in the recapture rate between salmon of wild (8.5%) or reared (9.5%) origin, or between females (11.6%) and males (9.3%). Generalized linear models for data from 1997 showed that the recapture rate increased with length and age of females, but that the opposite was true for males. River fishing did not seem to remove proportionally more early ascending salmon than fish that ascended later.     

Contemporary ocean warming and freshwater conditions are related to later sea age at maturity in Atlantic salmon spawning in Norwegian rivers

Atlantic salmon populations are reported to be declining throughout its range, raising major management concerns. Variation in adult fish abundance may be due to variation in survival, growth, and timing of life history decisions. Given the complex life history, utilizing highly divergent habitats, the reasons for declines may be multiple and difficult to disentangle. Using recreational angling data of two sea age groups, one‐sea‐winter (1SW) and two‐sea‐winter (2SW) fish originated from the same smolt year class, we show that sea age at maturity of the returns has increased in 59 Norwegian rivers over the cohorts 1991–2005. By means of linear mixed‐effects models we found that the proportion of 1SW fish spawning in Norway has decreased concomitant with the increasing sea surface temperature experienced by the fish in autumn during their first year at sea. Furthermore, the decrease in the proportion of 1SW fish was influenced by freshwater conditions as measured by water discharge during summer months 1 year ahead of seaward migration. These results suggest that part of the variability in age at maturity can be explained by the large‐scale changes occurring in the north‐eastern Atlantic pelagic food web affecting postsmolt growth, and by differences in river conditions influencing presmolt growth rate and later upstream migration.     

Selective exploitation of early running fish may induce genetic and phenotypic changes in Atlantic salmon

Genetic evidence for the selective exploitation by anglers of early running fish was examined in four Iberian Atlantic salmon populations using protein and mtDNA markers. The populations studied had been exploited exclusively by anglers since 1949 during a fixed fishing season that ran approximately from March to July. Genetic variation at six protein loci was small and was accounted for by the MEP‐2 * and MDH‐3,4 * polymorphisms, which generally remained stable over time and were in Castle–Hardy–Weinberg equilibrium during the fishing season. Early running fish that had spent multiple winters at sea (MSW) generally had higher frequencies of the common MEP‐2 *(100) allele than did late running, one sea winter (1SW) grilse that were significantly smaller and tended to escape the fishery. Spawners differed from angler caught fish in their mtDNA frequencies and consistently had a lower sea‐age and a smaller body size. Spawners also smolted at an older age and displayed lower frequencies of the MEP‐2 *(100) allele in three of the four populations studied. These results suggest that in these rivers anglers selectively exploit a distinct component of the population and inadvertently cause a differential mortality of genetic types that is likely to be detrimental to population viability.     

Age, sex ratio and timing of the catch of kelts and ascending Atlantic salmon in the subarctic River Teno

By 15 June, 82% of the catch of Atlantic salmon Salmo salar kelts had been taken from the middle part of River Teno, northern Scandinavia. The median date of capture was 4 June for males and 8 June for females. Salmon of 1–4 sea–winters (SW) of both sexes survived spawning to return to sea as kelts. Among males, 1 SW kelts were caught earliest in the spring and 3 SW latest, but among females 4 SW were earliest, then 3 SW and finally 1 and 2 SW. There were 17 river and sea–age combinations among the kelts compared with 23 among the ascending salmon. The smolt age distribution and the mean smolt age differed significantly only between female 2 SW ascending salmon (3·97 years) and kelts (4·14 years). The proportion of 1 SW females was higher and that of 3 SW males lower among kelts than among ascending salmon. The proportion of males among 1 SW ascending salmon was 80% but among kelts only 57%. Similarly, the proportion of males among 3 SW fish was 21% for ascending salmon but only 7% for kelts. Hence overwinter mortality was higher among males. Male and female kelts of 1 and female kelts of 2 SWhad a greater mean length than ascending salmon in corresponding groups indicating a better survival of larger fish within an age group. Grilse ascend rivers after most kelts have left, but the main catch of ascending 2–3 SW salmon takes place concurrently with kelts leaving the river, inadvertently targeting kelts in the fishery.     

Anadromous red-spotted masu salmon (Oncorhynchus masou ishikawae), a southernmost sea-migration form of salmonid,displays low variation in both age at seaward migration and sea age

We examined variations in age at seaward migration and sea age for the anadromous form of red-spotted masu salmon (Oncorhynchus masou ishikawae) in two Japanese rivers. The anadromous form of red-spotted masu salmon expressed only two sea migration patterns in the two rivers: (a) the majority of the salmon (95%, n = 81) were of age-0, and age-1 migrants were rare (n = 4); and (b) all the salmon examined (n = 22) made a return migration within a year, with 23% of the salmon exhibiting potamodromy in the river. Owing to low variation in their sea migratory patterns, the anadromous form of red-spotted masu salmon is likely vulnerable to environmental fluctuations.     

The timing, sex and age composition of the wild and reared Atlantic salmon ascending the Simojoki River, northern Finland

In the Simojoki River in the northern Gulf of Bothnia, reared salmon stocked as smolts produced considerable numbers of ascending one‐sea‐winter (1 SW) males, whereas the proportion of male 1 SW salmon was low among spawning migrants of wild or reared parr origin. The sex ratio among ascending wild fish and reared salmon stocked as parr was similar, with females predominating, while reared salmon stocked as smolts were mainly males. The multi‐sea‐winter (MSW) salmon entered the river annually within a fairly short time period from the beginning of the migration season, independent of their sex or origin. 1 SW males migrated into the river significantly later in the season than MSW males. The results indicate that the delayed opening of the fishing season in the Gulf of Bothnia is effective in reducing the harvest of MSW salmon at sea. However, as the timing of the ascent may vary by several weeks from year to year, the effect of this regulation bound to certain calendar days may also vary considerably from year to year.     

The effect of acclimation upon the survival of Ptinus tectus and Tenebrio molitor when exposed to low temperatures

Ptinus tectus and Tenebrio molitor adults were acclimated for 24 hours to 15°, 25° and 35°. Evidence of acclimation was given by measurement of the chill coma point, heart beat and respiration rates. The respective chill coma points for insects acclimated to 15°, 25° and 35° were 2.9°, 3.7° and 4.7° for P. tectus, and 5.4°, 6.9° and 8.3° for T. molitor. The rates of heart beat and oxygen intake showed that P. tectus could acclimate from 25° to 15° but not to 35°, whilst T. molitor could acclimate from 25° to 35° but not to 15°. Acclimation also affected the undercooling point and fat content, but not the water content. The acclimated insects were exposed to a range of low temperatures for varying periods of time and allowed to recover at 15°, 25° or 35°. The dosage mortality data produced were subjected to probit analyses. In both species mortality varied with the time and temperature of exposure. In P. tectus there was a zone of resistance to freezing extending from 0° (L.D.₅₀=1820h) to -9° (L.D.₅₀=49–76h) and acclimation affected the terminal region (-9° to-12°) of this zone by altering the undercooling point. Resistance to freezing was minimal in T. molitor and was unaffected by acclimation. The time taken to recover in both species varied with the recovery temperature and the quantity and intensity of cold, but was unaffected by acclimation.

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Résumé Ptinus tectus et Tenebrio molitor furent maintenus pendant 24 h à des températures de 15°, 25° et 35°, puis testés quant à leur résistance au froid, par la détermination de la température provoquant le coma et par les variations de leur rythme cardiaque ou de leur consommation d'oxygène. Dans les deux espèces on observe que le coma se manifeste pour une température d'autant moins basse que la température d'acclimatation était plus élevée. Les adultes de ces mêmes insectes ont été exposés à des températures sub-létales inférieures à 0°, pendant des durées variables, puis ramenés à des températures de 15°, 25° et 35°. La mortalité est alors estimée et comparée entre des lots préalablement acclimatés à tem températures de 15°, 25° et 35°. Chez les deux espèces étudiées la mortalité augmente avec la durée d'action de la température sub-létale (facteur quantité) et avec la baisse de température subie (facteur intensité). La température d'acclimatatio ppréalable n'affecte pas, chez Tenebrio molitor la D.L. 50, alors que chez Ptinus tectus il se révèle qu'une acclimatation à la plus basse température, diminue la mortalité après action de températures sub-létales comprises entre-9° et-12°. On a également comparé le taux de mortalité pour des températures égales ou supérieures à 0° (6°-15°-25°-29°-35°) chez des insectes acclimatés à 25° et ramenés à cette température après action du froid. La mortalité minimun s'observe alors pour une température de restauration de 15°. Les températures de surfusion, la teneur en eau et en lipides furent précisées pour chacun de ces insectes, en rapport avec la température d'acclimatation à laquelle ils avaient été préalablement soumis.

     

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.     

The North Atlantic subpolar gyre and the marine migration of Atlantic salmon Salmo salar: the ‘Merry‐Go‐Round’ hypothesis

One model for marine migration of Atlantic salmon Salmo salar proposes that North American and southern European stocks (<62° N) move directly to feeding grounds off west Greenland, then overwinter in the Labrador Sea, whereas northern European stocks (>62° N) utilize the Norwegian Sea. An alternate model proposes that both North American and European stocks migrate in the North Atlantic Subpolar Gyre (NASpG) where S. salar enter the NASpG on their respective sides of the Atlantic, and travel counterclockwise within the NASpG until returning to natal rivers. A review of data accumulated during the last 50 years suggests a gyre model is most probable. Freshwater parr metamorphose into smolts which have morphological, physiological and behavioural adaptations of epipelagic, marine fishes. Former high‐seas fisheries were seasonally sequential and moved in the direction of NASpG currents, and catches were highest along the main axis of the NASpG. Marking and discrimination studies indicate mixed continental origin feeding aggregations on both sides of the Atlantic. Marked North American smolts were captured off Norway, the Faroe Islands, east and west Greenland, and adults tagged at the Faroes were recovered in Canadian rivers. Marked European smolts were recovered off Newfoundland and Labrador, west and east Greenland, and adults tagged in the Labrador Sea were captured in European rivers. High Caesium‐137 (¹³⁷Cs) levels in S. salar returning to a Quebec river suggested 62·3% had fed at or east of Iceland, whereas levels in 1 sea‐winter (SW) Atlantic Canada returnees indicated 24·7% had fed east of the Faroes. Lower levels of ¹³⁷ Cs in returning 1SW Irish fish suggest much of their growth occurred in the western Atlantic. These data suggest marine migration of S. salar follows a gyre model and is similar to other open‐ocean migrations of epipelagic fishes.     

Marine post-smolt growth and age at maturity of Atlantic salmon

The annual variation in sea-age of maturation for a hatchery dependent stock of Atlantic salmon was compared to variation in post-smolt growth as evidenced by circuli spacing patterns. The proportion of returns of 1-seawinter (1 SW) and 2 SW salmon and the fraction of the smolt year class or cohort that maturated as 1 SW fish, were compared to seasonal growth indices determined from circuli spacing on the scales of smolt class survivors returning as 1 SW and 2 SW spawners. Using image processing techniques, we extracted inter-circuli distances from scales from 2244 recaptured fish. Spacing data for the first year at sea were collected and then expressed as seasonal growth indices for the spring period, when post-smolts first enter the ocean; the summer, when growth appears maximal; and winter, when growth appears to be at a minimum. In general, circuli spacings were wider for 1 SW than for the 2 SW returns of the same smolt cohort. The 1 SW fraction was significantly and positively correlated with late summer growth, suggesting that growth during this season is pivotal in determining the proportion of a smolt class that matures early.     

The environmental requirements of Atlantic salmon, Salmo salar L., during their passage through the Thames Estuary, 1982–1989

An examination of data on both water quality in the Thames Estuary and on the count of salmon. Salmo salar L . trapped in fresh water above the head of the tide in 1982–1989, was carried out to establish statistical correlations. The annual and monthly return of salmon as 1-sea-winter fish (grilse) in June to September was negatively correlated with water temperature, a nil catch being associated with a maximum value of 24.2° C, coupled with lower values maintained over substantial lengths of the estuary (e.g. 21.5° C over a distance of no more than 50 km). The annual return was negatively related to the extent to which the estuary was predicted to be lethal from the combination of low concentration of dissolved oxygen (DO) and high temperature, a reduction in DO of 1 mg 1 ¹ being equivalent to an increase in temperature of 4° C. The annual return for the whole year was directly related to the return in July to September. Depending upon the year, the monthly returns were related to both DO and temperature; they were reduced to a tenth at a 95 percentile DO of 2.7 mg 1 ¹, whilst the weekly catches were reduced to zero at 2.4 mg 1⁻¹. Weekly catches increased with river flow and daily catches increased with both river flow and tidal height. The few mortalities observed in the estuary in July are generally related to the quality of the water as predicted from the combination of high temperature and low DO.     

La diapause facultative dePimpla instigator [Hym.: Ichneumonidae] II. Rôle de la température

Résumé La diapause larvaire facultative de l'ichneumonidePimpla instigator F. est sous la dépendance de la photopériode et de la température. Les courbes de la réponse photopériodique sont établies pour plusieurs températures. Les basses températures augmentent le pourcentage de larves en diapause, tandis que les hautes tendent à annuler l'effet des photopériodes inductrices de la diapause. A 30°C aucun animal ne diapause, quelle que soit la photopériode. Les larves males entrent plus facilement en diapause que les larves femelles.

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Summary Larval diapause ofPimpla instigator is dependent on photoperiod and temperature. The photoperiodic induction response curves are compared at different levels of constant temperature. Low temperatures enhance the diapause-inducing effect of photoperiods, whereas high temperatures reduce it. The larval diapause was not induced at any photoperiod when the insects were reared at 30°C.

     

Infestations of Atlantic salmon, Salmo salar, by Gyrodactylus salaris in Norwegian rivers

Over the 6 years 1980–85, 212 Norwegian rivers have been examined for occurrence of Gyrodactylus salaris: it was found in 26 rivers and six salmon hatcheries scattered throughout the country from Troms county in the north to Sogn og Fjordane in western Norway. The distribution of G. salaris is connected with the stocking of fish from infected salmon hatcheries. The populations of salmon parr have been drastically reduced in the infected rivers. In later years catches of ascending salmon in these rivers have also sharply declined: in 1984 salmon fishery losses were estimated at 250–500 t.
Gyrodactylus salaris is most probably a recent introduction to Norwegian rivers. A primary aim is to exterminate this parasite from all infected rivers and hatcheries: so far this has been accomplished in one river and one hatchery.     

Increasing temperature associated with increasing grilse proportion and smaller grilse size of Atlantic salmon

Effects of temperature on Atlantic salmon (Salmo salar) were analysed using Carlin tag recovery data (1985–2014), and mixed-stock catch data (smolt years from 2001 to 2012) in northern parts of the Baltic Sea. During warmer summers, the mean smolt length of the recaptured salmon tended to be smaller, and salmon were recaptured more frequently in feeding grounds closer to the home rivers in the Gulf of Bothnia, while colder summers were associated with more recaptures further south, in the Baltic Main Basin. Moreover, a warmer spring in the smolt year was associated with decreased weight of male grilses in mixed stock data. Further, warmer spring temperatures during the smolt year were associated with a higher proportion of one-sea-winter (1SW) males during the return migration in mixed stock data. These results suggest that the increasing global temperature may affect Atlantic salmon life history demographics.     

Experimental comparison of laboratory-reared vs. wild-typeTrichogramma chilonis [Hym.: Trichogrammatidae] II. Tolerance of non-optimal temperatures

A comparative study was made of the tolerance of wild-type (WT) vs. laboratory-reared (LR)Trichogramma chilonis Ishii (=T. confusum Vigg.) for low (2°C) and high (35°C) temperatures. The wild-type populations orginated from two geographical regions viz., Vijayapura (near Bangalore) and Hyderabad. Probit analysis of the data to determine the precise LT₅₀ showed that the WT populations survived high and low temperatures better than the LR populations.

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Résumé Une étude comparative a été effectuée sur la tolérance à des températures basses (2°C) et élevées (35°C) deTrichogramma chilonis Ishii provenant de la nature par rapport à une souche de laboratoire. Les populations sauvages provenaient de 2 régions: Vijayupara (près de Bangalore) et Hyderabad. Une analyse probit des données destinée à déterminer le temps létal 50 a montré que les populations sauvages survivent mieux aux températures extrêmes que la population d'élevage.

     

Seasonality and heterogeneity of live fish movements in Scottish fish farms

Movement of live animals is a key contributor to disease spread. Farmed Atlantic salmon Salmo salar, rainbow trout Onchorynchus mykiss and brown/sea trout Salmo trutta are initially raised in freshwater (FW) farms; all the salmon and some of the trout are subsequently moved to seawater (SW) farms. Frequently, fish are moved between farms during their FW stage and sometimes during their SW stage. Seasonality and differences in contact patterns across production phases have been shown to influence the course of an epidemic in livestock; however, these parameters have not been included in previous network models studying disease transmission in salmonids. In Scotland, farmers are required to register fish movements onto and off their farms; these records were used in the present study to investigate seasonality and heterogeneity of movements for each production phase separately for farmed salmon, rainbow trout and brown/sea trout. Salmon FW-FW and FW-SW movements showed a higher degree of heterogeneity in number of contacts and different seasonal patterns compared with SW-SW movements. FW-FW movements peaked from May to July and FW-SW movements peaked from March to April and from October to November. Salmon SW-SW movements occurred more consistently over the year and showed fewer connections and number of repeated connections between farms. Therefore, the salmon SW-SW network might be treated as homogeneous regarding the number of connections between farms and without seasonality. However, seasonality and production phase should be included in simulation models concerning FW-FW and FW-SW movements specifically. The number of rainbow trout FW-FW and brown/sea trout FW-FW movements were different from random. However, movements from other production phases were too low to discern a seasonal pattern or differences in contact pattern.     

Atlantic salmon colonization of the Russian Arctic coast: pioneers from North America

Previous studies of the ESTD * isozyme locus in the Atlantic salmon show the * 80 allele to be absent across the species' European range, with the exception of northern Russia, whereas the allele is nearly fixed in North American populations. The allele was found in samples from 15 out of 18 rivers on the Kola Peninsula and White sea coast and had frequencies that ranged from 0·017 to 0·363. Typing of fish in nine of these rivers for mtDNA variation in the ND1 gene region found variation characteristic of North American salmon in three Kola Peninsula populations and is the only part of Europe where such variants have been detected. The study area was completely glaciated during the late Pleistocene period and the restriction of the European distribution of these ESTD * and mtDNA variants to this area suggests that salmon that colonized the Russian Arctic coast rivers included fish of North American origin after the Pleistocene glacier had retreated.