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  • 1
    Electronic Resource
    Electronic Resource
    Evidence of a genetic component in the seasonal return pattern of Atlantic salmon, Salmo salar L. (1991)
    Oxford, UK : Blackwell Publishing Ltd
    Journal of fish biology 38 (1991), S. 0 
    Details
    ISSN: 1095-8649
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: We tested the null hypothesis that differences in the seasonal return patterns between stocks of Atlantic salmon, Salmo salar L., are a result of a direct response to the environment, and not under genetic control. Two stocks were used in the experiments, originating from the R. Figga and R. Imsa, respectively. In their native habitat fish from the former are known to return to the home stream as adult salmon early in the summer, while from the latter return during late summer and autumn. By rearing these stocks in the same hatchery and releasing smolts of both stocks together at three sites in southern Norway, it was demonstrated that salmon from the R. Figga stock returned earlier to coastal Norway than salmon from the R. Imsa stock, as maturing adults. Thus, we reject the hypothesis that these stocks are genetically identical in this trait. Within both stocks, multi-sea-winter fish returned earlier than one-sea-winter fish. Within stocks, there was no significant difference in time of return between salmon released as 1- and 2-year-old smolts, or between fish reared from parents ascending the R. Imsa early or late in the season.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1095-8649.1991.tb03111.x
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  • 2
    Electronic Resource
    Electronic Resource
    Energetic cost of spawning in male and female Atlantic salmon (Salmo salar L.) (1991)
    Oxford, UK : Blackwell Publishing Ltd
    Journal of fish biology 39 (1991), S. 0 
    Details
    ISSN: 1095-8649
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Energetic expenditure during spawning of male and female 1 -sea-winter Atlantic salmon, Salmo salar L., was measured. Before spawning, the somatic energy content per unit weight did not differ between the sexes. The testes content offat was 0.24, of carbohydrate 8.89, of water 1.21 and of ash 1.61 times as high as that of the ovaries. Just prior to spawning, mean gonadosomatic index (GSI; wet weight, %) in males was 4.36 and in females 20.26, and expressed as energy ratios (kJ, %) 4.47 and 27.75, respectively. During spawning the energy loss of male soma was higher (35.57%) than that of females (25.00%). This was a result of higher loss of fat in males than in females. Total energy cost of spawning in males and females was on average 51.8 and 51.4%, respectively.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1095-8649.1991.tb04403.x
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  • 3
    Electronic Resource
    Electronic Resource
    Atlantic salmon straying from the River Imsa (2003)
    Oxford, UK : Blackwell Science Ltd
    Journal of fish biology 62 (2003), S. 0 
    Details
    ISSN: 1095-8649
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Mean estimated straying rate for Atlantic salmon Salmo salar L. leaving the River Imsa as smolts during 1976–1999 was 15% for hatchery fish and 6% for wild conspecifics. Hatchery Atlantic salmon selected for production traits during four or more generations strayed 〉50%. The straying rate was higher for Atlantic salmon staying 2 rather than 1 year at sea before attaining maturity. For spawning, 96% of the strays entered streams within 420 km from the River Imsa, and c. 80% entered streams within 60 km of the mouth of the River Imsa, whether the fish were wild or hatchery released. Within the 60 km zone, the number of strays caught in a river increased with the Atlantic salmon catch in that river, but there was no significant relationship between straying rate and water discharge or distance from the river to the River Imsa. The observed straying rate of hatchery Atlantic salmon decreased with increasing number of fish entering the River Imsa. Sexual maturation as parr did not influence the tendency to stray. The results suggest that the establishment of temporary zones, free of fish farms, outside important Atlantic salmon rivers by the fisheries authorities in Norway should be large, whole fjords, to be effective.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1095-8649.2003.00053.x
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  • 4
    Electronic Resource
    Electronic Resource
    Long-term study of the ecology of wild Atlantic salmon smolts in a small Norwegian river (1998)
    Oxford, UK : Blackwell Publishing Ltd
    Journal of fish biology 52 (1998), S. 0 
    Details
    ISSN: 1095-8649
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Backcalculated lengths at the end of the first growth season in wild Atlantic salmon Salmo salar differed significantly between parr smolting at age 1, 2 and 3 years over a period of 11 years (i.e. 1983–1993). Mean body lengths of the respective age groups at the end of the first growth period were 11·1, 6·2 and 4·7 cm, respectively. The mean percentage distribution of fish smolting at age 1, 2 and 3 was 14, 78 and 7%, and the mean smolt age was 1·95 years. Mean lengths at smolting of age groups 1, 2 and 3 were 13·6, 15·8 and 17·5 cm, respectively. Females outnumbered males among the downstream migrating smolts with a mean sex ratio (females/ males) estimated at 1·61, with a significant female surplus in 7 of the 11 years sampled. Of the smolts sampled, 14% exhibited enlarged gonads indicative of parr maturation, and all were males (37% of the parr males sampled). Mean annual smolt density from 1975 to 1996 was 13·4 individuals 100 m−2 ranging between 0·3–31 smolts 100 m−2. Mean densities (100 m−2) of the smolts aged 1, 2 and 3 years were 1·5, 9·3 and 0·9 fish, respectively. Mean annual biomass for the 22-year period (1975–1996) was estimated at 437 g 100 m−2, with a range of variation from 136 to 683 g 100 m−2. Smolt age 2 made up 81% of the mean annual biomass (355 g 100 m−2) and smolt age 1 and 3, 8% (35 g 100 m−2) and 11% (47 g 100 m−2), respectively.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1095-8649.1998.tb02023.x
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  • 5
    Electronic Resource
    Electronic Resource
    Potential for sea ranching rainbow trout, Oncorhynchus mykiss (Walbaum): evidence from trials in two Norwegian fjords (1993)
    Oxford, UK : Blackwell Publishing Ltd
    Aquaculture research 24 (1993), S. 0 
    Details
    ISSN: 1365-2109
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract. In total, 10014 hatchery-reared 1+ and 2+ rainbow trout, Oncorhynchus mykiss (Walbaum), were released near the mouth of the River Imsa, south-western Norway, and in the Oslofjord, south-eastern Norway. The reported recapture rate was significantly higher in the Oslofjord(15·4%) than at Ims(3·6%). Between 70 and 80% of the recaptures were made in the year of release. The fish were recaptured in rivers and the sea along the Norwegian coast, most of them near the release sites. In total, 60% were recaptured in salt water and 40% in fresh water. Fish released in the Oslofjord were largely captured with rod and line. Of those released at Ims most of the freshwater recaptures were made in a fish trap in the River Imsa. In salt water most fish were captured by nets. Specific growth rate varied inversely with body weight at release, decreased with time after release and decreased faster for fish released in the Oslofjord than at Ims. In general, the proportion of fish recaptured increased with mean fish weight at release. Recaptured biomass per 1000 fish released was higher when released in the Oslofjord (87·12kg) than at Ims (24·42kg). Stocking of rainbow trout in fjords is feasible and may contribute to local recreational fisheries. Yield was highest when relatively small (∼50g) fish were released. Economically, the best results may be obtained when the fish are released in nutrient rich fjords.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-2109.1993.tb00641.x
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  • 6
    Electronic Resource
    Electronic Resource
    Effect of smolt age on migratory behaviour of Baltic salmon, Salmo salar L., transplanted to the east Atlantic (1991)
    Oxford, UK : Blackwell Publishing Ltd
    Aquaculture research 22 (1991), S. 0 
    Details
    ISSN: 1365-2109
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract. This paper describes tests which were made to determine if smolt age at release influences the migratory pattern of three different stocks of salmon, Salmo salar L. The fish were hatchery-reared and released in two different rivers, the River Imsa and the River Akerselv. Based on the tag returns we found that Baltic salmon from the River Neva, USSR differed in migratory pattern from two Norwegian stocks from the River Lone and the River Imsa. A large proportion of the 2+ River Neva smolts stayed in the fjord during the summer and autumn after release. On the other hand, 2+ smolts of the Norwegian stocks left the fjord and migrated to the feeding areas in the Norwegian Sea within a short time after release. The 1+ smolts of all stocks showed the same migratory pattern as the 2+ smolts of Norwegian origin. We propose that the observed differences in migratory pattern are influenced by the developmental rate of the smolts. The effect of developmental rate on the migration may differ among stocks. Our results show that it is possible to develop a fjord fishery by releases of 2+ smolts of Neva salmon. However, such releases must be carried out with the utmost caution, preferably in fjords with no salmon rivers, so that the possibility of gene flow between populations is minimized.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-2109.1991.tb00527.x
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  • 7
    Electronic Resource
    Electronic Resource
    Estimates of the annual loss of Atlantic salmon, Salmo salar L., in Norway due to acidification (1991)
    Oxford, UK : Blackwell Publishing Ltd
    Aquaculture research 22 (1991), S. 0 
    Details
    ISSN: 1365-2109
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract. The pre-acidification level of Atlantic salmon, Salmo salar L., production in Norway was estimated from accessible rearing habitat, potential smolt production, smolt to adult survival, and mean adult weight. Atlantic salmon have been virtually lost in 25 rivers due to acidification. In total, 340.6km of river is affected, and this corresponds to a rearing area of 2044.8 ha. The total annual number of adult salmon lost was estimated to be between 92016 and 306720 individuals, weighing some 345-1150 tonnes.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-2109.1991.tb00497.x
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  • 8
    Electronic Resource
    Electronic Resource
    High numbers of farmed Atlantic salmon. Salmo salar L., observed in oceanic waters north of the Faroe Islands (1993)
    Oxford, UK : Blackwell Publishing Ltd
    Aquaculture research 24 (1993), S. 0 
    Details
    ISSN: 1365-2109
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract. To estimate the proportion of escaped fanned Atlantic salmon. Salmo salar L., at the feeding grounds in the north-east Atlantic Ocean, samples of salmon caught with long-lines north of the Faroe Islands were examined. Identification of reared fish was carried out using scale analysis. The proportion of fanned fish was estimated to range from 25 to 48% in the different samples, suggesting that high numbers of escaped farmed salmon occur in the Norwegian Sea. The farmed fish were significantly smaller in size than the wild salmon. Although it is suggested that most of the farmed fish are of Norwegian origin, farmed fish of Scottish, Faroese and Irish origin are also believed to be present. If not accounted for, high numbers of reared salmon in fisheries and stocks will seriously affect the assessments of fisheries and stocks of wild salmon.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-2109.1993.tb00657.x
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  • 9
    Electronic Resource
    Electronic Resource
    Migratory behaviour and growth of hatchery-reared post-smolt Atlantic salmon Salmo salar (1993)
    Oxford, UK : Blackwell Publishing Ltd
    Journal of fish biology 42 (1993), S. 0 
    Details
    ISSN: 1095-8649
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Individually lagged, 1+ and 2+ hatchery-reared smolts of Atlantic salmon were released in spring and early summer at the mouth of the R. Imsa, south-western Norway. The post-smolts moved mainly northwards in the sea with the coastal current. The estimated mean migratory speed (±s.d.) of those captured in the sea along the Norwegian coast was 7.45 (± 6.26) km day −1; in the fjords it was 1.63 (± 2.33) km day−2. Many of the post-smohs ascended rivers the same year as released; 37.3% of the total number recaptured were caught in R. Imsa, upstream from the site of release, and 5.8% were caught in other rivers throughout middle and southern parts of Norway. The fish recaptured in rivers was probably sexually mature and entered rivers to spawn. Mean specific growth rate for post-smolts caught in the sea was higher than for those caught in R. Imsa (P 〈0.001) but not for those caught in other rivers (P〉 0.05). Post-smolts ascending R. Imsa were smaller at release than those ascending other rivers. However, there was no size difference at release between post-smolts captured in the sea and those recaptured in rivers other than the R. Imsa.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1095-8649.1993.tb00346.x
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  • 10
    Electronic Resource
    Electronic Resource
    Is there a threshold size regulating seaward migration of brown trout and Atlantic salmon? (1993)
    Oxford, UK : Blackwell Publishing Ltd
    Journal of fish biology 42 (1993), S. 0 
    Details
    ISSN: 1095-8649
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: We investigated the influence of variation in body size and growth rate on age of smolting in Atlantic salmon and brown trout in four different Norwegian rivers. In Atlantic salmon smolt ages varied between 2 and 6 years, and in brown trout between 2 and 7 years. Smolt age was negatively correlated with parr growth, and positively correlated with smolt size. Age at smolting was more variable in the two northern than the two southern rivers. Smolt sizes and ages were also more variable in brown trout than in Atlantic salmon. Based on the observed variation in smolt size and age, we reject the hypothesis that a threshold size alone regulates age at smolting. Within populations smolt age depends on growth rate so that fast-growing parr smolted younger and smaller than slow-growing parr. We hypothesize that smolt size and age is a trade-off between expected benefits and costs imposed by differences in individual growth rate.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1095-8649.1993.tb00358.x
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