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1.
The migratory behaviour of adult wild and escaped farmed Atlantic salmon, Salmo salar L., before, during after spawning in the River Namsen, Norway, was analysed using radio telemetry. The fish were caught, radio tagged and released into the fjord between 7 and 25 km from the river mouth. A significantly higher proportion of wild (74%) than farmed (43%) salmon was subsequently recorded in the river. Wild salmon (33%) were more frequently captured in the sea and in rivers than farmed salmon (14%). The migration speed from release to passing a data logger 11 km upstream from the river mouth was not significantly different between wild (20.6 km day?1) and farmed (19.8 km day?1) salmon. Wild salmon tagged when water flow in the river was increasing had a significantly higher migration speed than wild salmon tagged when water flow was decreasing. This was not true for farmed salmon. Farmed salmon were distributed significantly higher up the river than wild salmon during spawning, although both types of fish were found together in spawning areas. Thus, there was no geographical isolation to prevent spawning between wild and escaped farmed salmon. Farmed salmon had significantly more and longer up- and downstream movements than wild salmon during the spawning period. Unlike farmed salmon, the number of riverine movements by wild salmon increased significantly when variation in water flow increased. A smaller proportion of wild (9%) than farmed (77%) salmon survived through the winter after spawning.  相似文献   

2.
This study explores the ecological and economic impacts of interactions between escaped farmed and wild Atlantic salmon (Salmo salar, Salmonidae) over generations. An age‐ and stage‐structured bioeconomic model is developed. The biological part of the model includes age‐specific life‐history traits such as survival rates, fecundity and spawning successes for wild and escaped farmed salmon, as well as their hybrids, while the economic part takes account of use and non‐use values of fish stock. The model is simulated under three scenarios using data from the Atlantic salmon fishery and salmon farming in Norway. The social welfare is derived from harvest and wild salmon while the economic benefits of fishing comprise both sea and river fisheries. The results reveal that the wild salmon stock is gradually replaced by salmon with farmed origin, while the total social welfare and economic benefit decline, although not at the same rate as the wild salmon stock.  相似文献   

3.
Abstract  Isomeric ratios of astaxanthin in eggs and alevins of Atlantic salmon, Salmo salar L., have proven useful in identifying female spawners of farmed origin, but the method underestimates the proportion of fish of farmed origin. The rate of underestimation was studied by analysing astaxanthin content in tissue of 55 farmed Atlantic salmon ascending two Norwegian rivers in the autumn of 1991. The astaxanthin content fell into two distinct classes. Fifty-one per cent of the adult escaped salmon had isomeric ratios similar to salmon fed synthetic astaxanthin, whereas all the remaining fish had ratios similar to wild fish. Discriminant analysis classified 96.4% of the fish with known astaxanthin content into the correct astaxanthin class on basis of tail-fin erosion, length, weight and gill-cover damage. This discriminant function was used to estimate the astaxanthin classification of 1017 farmed salmon caught in nine rivers during 1989–1991. The classification success varied among years from 52 to 64%. Corresponding numbers for females and males were 45–48% and 54–70%, respectively. Thus, estimates of spawning rates of farmed female salmon via astaxanthin content in eggs or alevins from redds should be adjusted accordingly. The observed isomeric ratios of astaxanthin in the escaped farmed salmon and the relationship with morphology indicates that a significant proportion of the escapees ascending rivers have spent more than 1 year in the wild after escape.  相似文献   

4.
In several areas along the Norwegian coast local fishermen claim that wild migrating Atlantic cod (Gadus morhua L.) have changed their spawning migratory behaviour following establishment of salmon farms, and no longer enter their natural spawning grounds in the fjords. This has created a heated debate in Norway and, in some areas, passed down a moratorium on establishing new salmon farms. Research has so far not been able to show a causal connection, but it has been suggested that water-soluble odorants from high density salmon stocks in commercial fish farms might be responsible for the avoidance of areas with fish farming and abandonment of nearby traditional spawning grounds. The aim of this study was to test this hypothesis by studying the spatiotemporal distribution of wild migrating cod tagged with acoustic transmitters using an array of automatic listening stations in Øksfjord, a Norwegian fjord with intensive fish farming and traditional spawning grounds for cod. The tagged cod were released either in the outer parts of Øksfjord, i.e. in the area they were caught, or in the inner part of the fjord close to their traditional spawning areas. The olfactory sense was physically blocked for 50% of the fish. Only one cod released in the outer part of the fjord visited the traditional spawning grounds. The majority of the cod that were released in the inner part of the fjord remained in this area for approximately three weeks before they left the fjord. There were no differences in spatiotemporal distribution between cod with intact and cod with blocked olfactory sense. Thus, the results provided no evidence that migrating wild cod avoid areas with fish farming as a response to odorants, but the results do not per se contradict the fishermen's observation that coastal cod have changed their migratory pattern in this fjord.  相似文献   

5.
Local fishermen in several areas of Norway assert that salmon farms have caused the wild migrating cod to change their migratory behaviour, so that they no longer enter their natural spawning grounds in the fjords. If the asserted changes in behaviour of wild cod populations can be linked to establishment of salmon farms, water-soluble odorants are then possible candidates to explain such a connection. Chemical stimulants are important to the individual fish's conception of the surrounding environment. High density stocks of fish in a farm are expected to release large amounts of waterborne information. The present laboratory experiments were conducted to test behavioural responses in Atlantic cod exposed to water containing metabolites and waste from farmed salmon. The trials were conducted on single fish in a multiple chamber preference system. The results show that migrating wild Atlantic cod chose to spend more time in chambers without addition of water from the salmon tank, regardless of their maturation status, and even at very low concentrations (0.2%). The avoidance is probably due to presence of chemical compounds with olfactory properties from salmon, since anosmic cod did not elicit such response. Farmed cod, on the other hand, does not avoid water from the salmon tank, and stationary wild cod caught nearby a fish farm had a less pronounced response as compared to wild migrating cod. The response seen is not species specific, as wild migrating cod responded similar to water from a tank holding farmed cod as to water from salmon. These results do not preclude fishermen's observations that cod change their behaviour in areas with fish farming activity. Such a change in behaviour could be a response to water-soluble odorants, but needs to be validated and detailed in further laboratory experiments as well as in nature before any conclusions can be made.  相似文献   

6.
The migration patterns of wild and released farmed Atlantic salmon, Salmo salar L., were studied by radio-telemetry during migration from entering a river to after spawning. The wild salmon were caught during return migration in bagnets and the farmed salmon were produced in a near by fish farm. Both groups were tagged and released at sea near the river mouth of the River Alta, North Norway. A pronounced individual variation in migration pattern was observed. No significant differences was found between wild and farmed salmon in the distance from entering the river mouth to the place of the first stop (recorded in the same pool for 5 days or longer) and the days from entering the river mouth to arrival at the first stop. For both wild and farmed salmon, mean migration speed was 2.6 km day1, varying from 0.4 to 11.0 km day-1. A larger proportion of farmed salmon distributed to the upper part of the river at spawning; mean distances from the river mouth were 30.1 and 19.1 km. respectively. Farmed salmon spent a significantly longer time from entering the river to reaching the area occupied during spawning.  相似文献   

7.
This is the first comprehensive study on the occurrence and distribution of piscine reovirus (PRV) in Atlantic salmon, Salmo salar L., caught in Norwegian rivers. PRV is a newly discovered reovirus associated with heart and skeletal muscle inflammation (HSMI), a serious and commercially important disease affecting farmed Atlantic salmon in Norway. A cross‐sectional survey based on real‐time RT‐PCR screening of head kidney samples from wild, cultivated and escaped farmed Atlantic salmon caught from 2007 to 2009 in Norwegian rivers has been conducted. In addition, anadromous trout (sea‐trout), Salmo trutta L., caught from 2007 to 2010, and anadromous Arctic char, Salvelinus alpinus (L.), caught from 2007 to 2009, were tested. PRV was detected in Atlantic salmon from all counties included in the study and in 31 of 36 examined rivers. PRV was also detected in sea‐trout but not in anadromous Arctic char. In this study, the mean proportion of PRV positives was 13.4% in wild Atlantic salmon, 24.0% in salmon released for stock enhancement purposes and 55.2% in escaped farmed salmon. Histopathological examination of hearts from 21 PRV‐positive wild and one cultivated salmon (Ct values ranging from 17.0 to 39.8) revealed no HSMI‐related lesions. Thus, it seems that PRV is widespread in Atlantic salmon returning to Norwegian rivers, and that the virus can be present in high titres without causing lesions traditionally associated with HSMI.  相似文献   

8.
Run timing of escaped farmed Atlantic salmon Salmo salar vs. wild fish was compared by the use of video camera surveillance in 15 rivers over several years, covering 1600 km of the Norwegian coastline (from 58°N to 69°N). Annual runs of wild salmon varied among rivers from <200 fish to more than 10 000. During the surveillance period that for most rivers extended from late May to early October, larger‐sized salmon (fish ≥ 65 cm) generally entered the rivers earlier than small fish. The percentage of salmon identified as escaped farmed fish ranged from 0.1% to 17% across rivers with an average of 4.3%. Estimates of escapees are, however, assumed to represent minimum values because an unknown number of farmed fish passing the video cameras may have been misclassified as wild fish. By the use of a linear mixed model and generalised additive mixed models, it was found that the relationship between run timing and fish length differed significantly between farmed and wild salmon. While small‐sized farmed and wild fish (<65 cm) entered the river at about the same time, wild large salmon returned on average 1–2 weeks earlier than similarly sized escapees. The proportion of large‐sized farmed escapees also increased until late August and decreased thereafter. In contrast, there was a relatively constant and lower proportion of small‐sized escapees throughout the season. Within the surveillance period, there was no evidence of any exceptionally late runs of fish classified as escaped farmed salmon.  相似文献   

9.
External morphological characteristics were used to identify escaped farmed Atlantic salmon, Salmo salar L., in a coastal salmon fishery in County Antrim, Northern Ireland during four fishing seasons and at an adjacent freshwater location (R. Bush) during a 5-year period. Out of a total of 36 326 adult salmon examined in the fishery, 883 (2.4%) were identified as having escaped from sea cages. Annual average values ranged from 0.26% to 4.04% of the fish caught. Occurrence of escapees entering an adult trap in fresh water averaged 0.88%, with a range of 0.13–2.62%, depending on year. No correlation between presence in the marine fishery and in fresh water was evident, the latter year-round figures probably being more indicative of presence of escapees in spawning stocks. Entry to fresh water was significantly later on average for escaped farmed salmon, compared with wild salmon.  相似文献   

10.
A previous study described genetic changes in a wild Atlantic salmon , Salmo salar L., population resulting from the spawning of escaped farmed salmon in the Glenarm River, Northern Ireland, in 1990. This study reports an extension of the original investigation with a further follow-up sample that was taken from the river in 1997 to assess the genetic status of the wild population two generations after the original hybridization between the wild population and the farmed strain. Overall genetic variation across eight polymorphic allozyme loci indicated that the wild population remains significantly different from the pre-escape population and from the immediate post-escape population, the presence of an allele not having been previously detected in this population ( GPI-1,2*140 ), suggesting that further incursion(s) of farmed salmon may have taken place.  相似文献   

11.
Wild and farmed Atlantic salmon ( Salmo salar L.) and Atlantic cod ( Gadus morhua L.) were collected to assess changes in mercury with size in wild vs. farmed fish. Mercury concentrations were compared with Health Canada and United States Environmental Protection Agency consumption guidelines. Lipid dilution of mercury was examined by comparing lipid-extracted (LE) and non-lipid-extracted (NLE) flesh samples in both farmed and wild fish. Mercury concentrations in the flesh and liver of farmed salmon were significantly lower than concentrations in wild salmon of similar fork length ( P <0.001), possibly due to growth dilution in rapidly growing farmed fish. Mercury concentrations were higher in LE tissue compared with NLE ( P <0.05), suggesting lipid dilution of mercury in farmed fish with a high lipid content. Farmed cod, which do not grow more rapidly than wild cod, did not have significantly different flesh and liver concentrations compared with wild cod of similar fork length ( P >0.05). Between species of farmed fish, cod had significantly higher mercury concentrations than salmon ( P <0.05), but neither farmed nor wild salmon mercury concentrations exceeded federal consumption guidelines. These results suggest that rapid growth rates and a high lipid content may play important roles in regulating concentrations of contaminants such as mercury.  相似文献   

12.
The role of escaped farmed salmon in spreading infectious agents from aquaculture to wild salmonid populations is largely unknown. This is a case study of potential disease interaction between escaped farmed and wild fish populations. In summer 2012, significant numbers of farmed Atlantic salmon were captured in the Hardangerfjord and in a local river. Genetic analyses of 59 of the escaped salmon and samples collected from six local salmon farms pointed out the most likely source farm, but two other farms had an overlapping genetic profile. The escapees were also analysed for three viruses that are prevalent in fish farming in Norway. Almost all the escaped salmon were infected with salmon alphavirus (SAV) and piscine reovirus (PRV). To use the infection profile to assist genetic methods in identifying the likely farm of origin, samples from the farms were also tested for these viruses. However, in the current case, all the three farms had an infection profile that was similar to that of the escapees. We have shown that double-virus-infected escaped salmon ascend a river close to the likely source farms, reinforcing the potential for spread of viruses to wild salmonids.  相似文献   

13.
Microsatellite DNA loci and the Pantophysin locus (Pan I) were used to investigate levels of genetic diversity within farmed strains of Atlantic cod Gadus morhua and to compare them with the wild source population. A total of 282 farmed samples originating from a spawning ground off the south-west coast of Iceland were sampled in the years 2002 and 2003, and 258 wild cod were collected at the same spawning ground in the same years. The farmed strains exhibited a lower mean number of alleles and allelic diversity than the wild samples at the microsatellite loci. Significant differences were observed between wild and farmed samples both in allele and genotype frequencies at the Pan I locus. We argue that the genetic divergence of wild and farmed samples of Atlantic cod may be due to a small number of effective founding breeders contributing to the genetic variation of the farmed strains, inducing a reduction in allelic diversity. We discuss the potential effect of breeding practices on the genetic diversity of Atlantic cod.  相似文献   

14.
Studies of contest competition between wild and farmed fish have mostly focused on fish with strongly territorial behaviour. Little is known about species with more plastic social behaviour, such as Atlantic cod (Gadus morhua L.), a species that can either aggressively defend territories or shoal. There is also concern that cod that escape from farms will compete with wild populations. We examined dyadic contest competition between wild and farmed juvenile cod using an intruder–resident experimental set‐up in the laboratory. No prior residency advantage was observed, but the differences between farmed and wild cod were clear. Farmed cod were more submissive than wild cod and fled earlier during contests, which suggests that wild fish often out‐compete farmed intruders. Both fish types initiated aggression earlier against fish of the same background. A multivariate analysis of 11 different behavioural traits indicated that a group of 59% of farmed fish were behaviourally very similar to the 55% most submissive wild fish. These results suggest that wild juvenile cod may be quite robust towards competition for food and shelter from juvenile farmed cod, but further research is needed to verify this pattern.  相似文献   

15.
Farming of Atlantic cod makes it possible to supply cod throughout the year. The aim of this study was to investigate the effects of season and postmortem ice storage on the quality parameters of farmed cod. Farmed Atlantic cod were sampled from the same pen in the period February 2006–March 2007. Cod whole body and somatic weight, condition factors and hepatosomatic index were all affected by season, all decreasing during maturation and spawning in the winter. Muscle pH and water were influenced by season, increasing during maturation and spawning and then decreasing after spawning. Season also affected the colour of the fillet. There was a significant increase in whiteness post‐spawning and a decrease during the second maturation. Water‐holding capacity (WHC), levels of trimethylamine oxide and trimethylamine, as well as microbiological data, did not vary due to season. Muscle pH, water content, WHC and microbial counts increased during storage for all samplings.  相似文献   

16.
Abstract. The frequency of escaped farmed salmon in the River Polla, Scotland was estimated at spawning in 1990, the second year after the escape of 184000 fish from a sea-cage site nearby. Fourteen of 73 spawners examined were of farmed origin. In only six of these fish were scale growth patterns consistent with their being part of the documented escape. All of these fish carried the pigment canthaxanthin. Fifty-nine redds were constructed at spawning. Five of 54 redds sampled contained embryos or alevins bearing canthaxanthin. The frequency of fry bearing canthaxanthin was determined in samples obtained from the neighbouring Rivers Hope and Dionard following spawning in both 1989 and 1990. There was no evidence of substantial returns of salmon from the documented escape to these rivers. These findings and those of a previous study suggest that more than 95% of those fish which returned to rivers near the site of the documented loss did so in the first year after escape and that fewer than 0·5% of those fish which escaped returned within the 2 years of study.  相似文献   

17.
Trimethylamine oxide (TMAO) is found at high levels in wild Atlantic cod. Trimethylamine oxide is reduced to trimethylamine (TMA) during iced storage. In this study, the levels of TMAO and TMA in wild and farmed cod and the impact of storage, gender and season on these levels were investigated. Wild cod had higher levels of TMAO than farmed cod. Wild cod also had higher levels of TMA after 15 days of iced storage. Farmed cod were found to have levels of TMA‐N <5 mg/100 g after 15 days of iced storage, which is below the maximum permitted level for fresh fish. Therefore, TMA appears to be an unsuitable measure of freshness in farmed cod. Female farmed cod had higher levels of TMAO than male farmed cod; no such difference between genders was found in wild cod. Female and male farmed cod had similar levels of TMA after post‐mortem iced storage. The hepatosomatic index (HSI) of female farmed cod was higher than that seen in male cod and this may be the underlying reason for the differences in muscle TMAO. Levels of TMAO in male farmed cod were higher during the autumn and were correlated with a larger HSI during the same period.  相似文献   

18.
Laffaille P. Impact of stocked Atlantic salmon (Salmo salar L.) on habitat use by the wild population.
Ecology of Freshwater Fish 2011: 20: 67–73. © 2010 John Wiley & Sons A/S Abstract – We investigated the summer habitat occupied by populations of young‐of‐the‐year wild and stocked (farmed populations released into the native range) Atlantic salmon under allopatric and sympatric conditions. Under allopatric conditions, farmed and wild salmon occupied habitats with the same characteristics. The salmon preferentially occupied the riffle areas. However, under sympatric conditions, the fish occupied meso‐ and micro‐habitats with different characteristics. Wild salmon avoided habitats used by farmed salmon and preferred glide areas with considerable vegetation cover. This study suggests that differences in the pattern of habitats used by young Atlantic salmon were both size‐ and origin‐dependent and may result from intra‐species competition between farmed and wild populations. Given that stocking with farmed Atlantic salmon is carried out intensively to enhance recreational angling or to conserve salmon populations, this study warns that this can have a negative impact on the extant wild Atlantic salmon population.  相似文献   

19.
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.  相似文献   

20.
Farmed Atlantic salmon, Salmo salar, frequently escape from the aquaculture industry and interact with wild populations. The impact of these interactions on the wild populations will depend, in part, on differences in their performances. This study compared the swimming and cardiac performance of farmed salmon (Aquagen) with their founder population from the River Namsen both before and after gamete stripping. Cardiac output (CO), heart rate (HR), and stroke volume (SV), which were measured by placing Doppler flow probes around the ventral aorta of the fish, increased with exercise, but the response did not significantly differ between farmed and wild salmon. Similarly, the swimming performance of wild salmon never significantly differed from the farmed salmon. The overall similarity in swimming and cardiac performance between farmed and wild Atlantic salmon observed in the present study suggests that cultured salmon may have the ability to be competitive with the wild salmon in native waters.  相似文献   

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