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1.
Seven samples, each consisting of approximately 50 Atlantic salmon, were collected from five marine farms in Norway. These farms reported to rear fish originating from the same commercial breed; however, all samples followed a unique route of production from breeder to marine farm via egg, fry and smolt producers. A group of farmed escapees (n=50) were also captured. Following genotyping with 18 microsatellite loci, the global FST was 0.083, and pair‐wise values were as high as 0.158. Four clusters, with varying degrees of genetic differentiation, were identified among samples from the farms, and the source of the escapees was identified successfully. It is suggested that the genetic differences observed among samples from the farms were created through the process of genetic drift, facilitated by parallel sub‐strains, extensive within‐strain selection and low to moderate numbers of adults contributing to batches of eggs. In conclusion, this study has demonstrated that genetic identification of escaped Atlantic salmon, back to the farm of origin, may be possible even when farms rear fish reported to originate from a single breeder.  相似文献   

2.
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   

3.
Gilthead sea bream (Sparus aurata L.) aquaculture has rapidly spread around the Mediterranean Sea. Fish escapes from sea cages are one of the major problems for the industry and also represent a threat to the marine environment. Fishery catches are also influenced by escape events, being mirrored in increased landings of cultured species. However, within the Mediterranean, studies shedding light on the incidence of escaped individuals in fisheries landings are scarce. Firstly, the present study describes a simple scale‐examination methodology to distinguish escaped from wild S. aurata landed by coastal fisheries. Secondarily, the incidence of escapees is assessed within landings of the species in the western Mediterranean. The scale readings revealed a monthly incidence of escapees between 11.2 and 20.8%, representing 6.8% of the total income derived from these landings. Moreover, morphological differences between wild fish captured near and far from fish farms point towards escape events as a source of potential genetic admixture between cultured and wild genotypes. Socio‐economic and ecological implications of escapees are discussed, and a set of management guidelines proposed, to prevent and/or mitigate the negative influences of escaped fish on the ecosystem and traditional users of the coast such as fisheries.  相似文献   

4.
Meagre (Argyrosomus regius) is an emerging species in aquaculture considered a locally absent species in the Western Mediterranean. Little is known about meagre escape incidents from farms. To evaluate escape impacts and develop mitigation measures, knowledge about the behaviour of escaped meagre is necessary. In this study, a rapid dispersion of escaped meagre was observed following a simulated escape incident in a coastal Mediterranean farm, using acoustic telemetry (acoustic tag: AT) and mark‐and‐recapture techniques (external tag: ET). A small proportion of AT meagre (22.7%) remained within the farm boundaries 24 h after the simulated escape. A total of 84 meagre (9.2%) were captured by local trammel netters nearby the farm facility within the first 48 h after escape. Only two AT individuals (15.3%) were detected by acoustic receivers located in coastal areas within 2 days after dispersal from the farm and eight ET meagre (0.8%) were recaptured along the shoreline during the first week. Two AT individuals (15.3%) were considered to be dead by predation few hours after escape. The rest of the AT individuals (N = 6, 46.2%) left the facility alive, and they were never detected by receivers nor reported back by fishermen. Thus, our results highlight the necessity of establishing escape mitigation strategies at Mediterranean fish farms, i.e. recapture programmes 24–48 h after the escape incident in collaboration with local fishermen, to diminish potential impacts related to meagre escapees.  相似文献   

5.
To examine site fidelity and potential for ecosystem impacts, 20 escapee cod (Gadus morhua L.) from fjord‐based cod farms were tagged with acoustic transmitters, released in the vicinity of the same farm, and their subsequent behaviour and survival monitored using a fixed array of acoustic receivers. Most individuals demonstrated high fidelity to their farm where tagged, and this increased during the polar night. Only five individuals (25%) were occasionally detected at another farm (4 km distance), and only three cod (15%) migrated out of the fjord during the 6‐month study period. Vertical movements were consistently greater in the hours around noon than at night, a behaviour inconsistent with that observed for wild fish. A high mortality rate (40%) was observed during the first 4 months post‐release, and actual mortality may have been even higher, limiting the potential for negative ecosystem effects from cod escapees. Findings from this study are used to discuss the development of recapture strategies for minimising potential impacts from cod escapees to ensure sustainable farming activity.  相似文献   

6.
Cod bite on aquaculture net cages has resulted in damages like frayed netting and holes, which in part can explain why cultured cod have escaped more frequently than salmon over the last years. We describe damages found on various netting materials subjected to cod bite through field experiments at commercial cod farms. Further, a method to test local cod bite resistance of traditional netting structures is suggested and initial results from a test jig prototype are given. Results from field experiments indicated that cod may have been attracted by types of netting that made it possible to draw filaments out of the twine, while stiff, coated netting structures and thick filaments showed no sign of bite damage during the test period. We concluded that netting materials for cod aquaculture must be resistant to cod bite or be repellent or uninteresting for cod. Based on the present findings, the better choice among the traditional netting materials seemed to be hard-laid netting materials, preferably with a primer that glues the filaments together.  相似文献   

7.
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   

8.
Escapes of cod (Gadus morhua) from sea cages represent an economic problem for farmers and a potential environmental problem. We estimate that 0–6% of cod held in sea‐cage farms in Norway were reported to have escaped each year from 2000 to 2005, which is a high proportion compared with salmon. We interviewed employees at 19 coastal sea‐cage cod farms in Norway to investigate both how and why cultured cod escape and to document cage handling and management strategies that were effective in minimizing escapes. Based on the interviews, we describe five working hypotheses that may explain why a greater proportion of cod than salmon escape: (1) cod are more willing to escape than salmon; (2) cod bite the net cage and create wear and tear; (3) net cages have insufficient technical standards for cod culture; (4) cod are placed in sea cages at considerably smaller sizes than salmon; and (5) cod are more popular feed for predators. Preliminary testing of the hypothesis that cod bite netting and create holes was done by placing pre‐damaged net panels with cut twines and control panels inside sea cages. Holes in the pre‐damaged net panels increased in size over a period of 3 months. The type of damage indicated that biting of netting twines was the likely cause.  相似文献   

9.
Mature striped bass ( Morone saxatilis ) were collected from the spawning reaches of the Choptank River, Maryland for the purpose of evaluating stress effects associated with capture. Two commonly used capture devices were evaluated—gillnetting and electrofishing. Results indicated that stress, as measured by changes in plasma corticosteroid and chloride concentrations, was significantly lower and recovery time quicker in those fish captured by electrofishing compared to gillnetting. By the end of the study period (48 h), those fish captured by electrofishing had recovered from the initial capture shock as evidenced by corticosteroid levels returning to near baseline levels. Conversely, at 48 h post-capture, those fish captured by gillnetting exhibited severe hypochloremia and elevated corticosteroid levels approaching that of the initial stress associated with capture.  相似文献   

10.
Escape incidents in coastal aquaculture lead to economic losses for farmers and may have indirect socio‐economic effects on local fisheries. In this study, the relationship of meagre, Argyrosomus regius (Asso), production in open‐sea cages and coastal small‐scale fisheries was analysed through captures of escapes, which are easily detected because this species is considered locally absent in native communities in Western Mediterranean regions. Scale reading showed that 100% of captured meagre were escapees. The existence of a direct relationship, in terms of biomass, between the development of meagre coastal aquaculture and the increase of captures of this species by local fisheries was demonstrated. The spatial distribution of meagre captures suggested that there is a local environmental and economic interaction between meagre aquaculture and fisheries through escapees. Monitoring the presence of locally absent species such as meagre within landings might help to assess the magnitude of escapes, the potential economic effects on local aquaculture and fishery industries, and the potential adverse ecological impacts on local ecosystems.  相似文献   

11.
Abstract  Individually tagged farmed Atlantic salmon, Salmo salar L., were released from fish farms in simulated escapes in Scotland ( n  =   678) and Norway ( n  =   597) to compare migratory behaviour and dispersal. Large fish (510–870 mm fork length) were released to simulate the escape of aquaculture growers. Fish were released in spring and all recaptures of tagged fish were reported during summer and autumn of the year of release. Recapture rates were respectively 7.0 and 0.6% of the salmon released in Norway and Scotland, indicating a higher mortality or a lower exploitation or reporting rate for Scottish fish. Recaptures of Norwegian fish were all from Norway and mostly within 150 km of the release site; 64% were taken by anglers in fresh water. By contrast, the three salmon recaptured from the release in Scotland were reported from Norway (Hardangerfjord and Lofoten) and western Sweden (River Göta); two detached tags were found on beaches in Scotland north of the release site. These findings establish the capacity for long distance dispersal among escapees from aquaculture facilities and suggest a net easterly bias in long distance dispersal of salmon escaping from Scottish fish farms.  相似文献   

12.
A monitoring program for the prevalence and intensity of sea lice infestations of wild and escaped farmed salmon has been underway on the Magaguadavic River since 1992. Fish are screened in a fish ladder trap located in freshwater a short distance above the head of tide. No trends with time were evident in observed sea lice burdens, and in all years the majority of salmon, both wild and escapees, had no or low levels of infestation with sea lice. In the spring of 2002, 23 landlocked salmon moving to sea from the Magaguadavic River were acoustically tagged. Two fish returned to the river after a brief period of residence in Passamaquoddy Bay, with significant dermal damage from sea lice. These fish were tracked to areas close to commercial salmon farms.  相似文献   

13.
The effect of horizontal waves on flexible netting panels placed at angles to the wave direction is studied with the aim of evaluating the testing method of pre-tensioned mooring and radial systems and flexible netting structures. The netting was hung on a frame at a specific hanging ratio for ten types of polyethylene panels. Regular waves were experimentally generated with a wave period varying from 0.8 to 2.0 s and wave height ranging from 50 to 250 mm. The force on the netting structure was recorded by a tension transducer and a digital signal recorder. The results showed that the horizontal wave force on the netting panel changed periodically and asymmetrically when it was back and left or right declinate to the wave direction; similar results were found for the surface wave elevation. The opposite results were obtained when the sloping angle declinated front to the wave direction, with two obvious crests during each period. The horizontal wave force was related to the height and width of the netting panel, wave height, wave length, twine diameter, bar length of the mesh, and sloping angle relative to the wave direction. Using dual series relations, the least square approximation, and multiple stepwise regression analysis, the formula for estimating the maximum value of the wave force on the netting was obtained.  相似文献   

14.
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   

15.
Coastal aquaculture installations concentrate large numbers of wild fish species of both ecological and economic importance, including schools of bogue, Boops boops (L.), in high abundance and biomass. The aggregated species consume large quantities of the easily available pellets lost from cages. As a consequence, the physical condition of farm‐associated wild fish is increased and their physiology is altered. These changes may influence local fisheries as many of these aggregating species are targeted by fishers. We assess whether local fishers catch wild fish that have previously aggregated at fish farms by comparing the body condition, trophic indexes, diet overlap and the fatty acid (FA) composition of B. boops obtained from local fish markets and around fish farms. Bogue captured by trammel‐nets and around fish farms facilities presented a similar biological condition, as well as high quantities of pellets in the gut, and their FA profile was affected by vegetal‐derived FAs. In contrast, bogue captured by trawlers were not influenced by fish farms, as they consumed natural trophic resources. We conclude that artisanal fishers exploit these aggregated fish populations once they have dispersed away from farms, and benefit from a ‘biomass export’ from fish farms at a local scale.  相似文献   

16.
Salmon farms attract large amounts of wild fish, which prey on uneaten feed pellets. The modified diet of the wild fish aggregating at salmon farms may reduce the flesh quality of the fish, influencing the local fisheries. We compared the quality of saithe (Pollachius virens) captured near (farm associated—FA) or more than 5 km away (un‐associated—UA) from salmon farms in Norway. The fish were captured during summer, autumn and spring using two commercial fishing methods (jigging and bottom nets). Overall, the fillet quality of FA saithe was good, although it was clearly reduced for almost 10% of the catch. Moreover, the quality of the FA saithe was significantly reduced compared with UA saithe, but the differences were small. Our results also showed that fish caught with jigging had better quality than fish caught with nets, and that fish that died in the nets were of lower quality than fish that were alive after hauling. There was no clear variation among seasons in fillet quality. Although no major and overall differences in quality were found between FA and UA saithe, reduced quality for even a modest proportion of the fish may influence the value of the total catch.  相似文献   

17.
Abstract– Four quantitative (area-standardized electrofishing, trap nets, small-mesh [1.3 and 2-cm bar mesh] gill nets, large-mesh [2.5 and 5-cm bar mesh] gill nets) and two qualitative (non-standardized electrofishing, dip netting) sampling techniques were concurrently used to capture larval to adult fish in forested wetland habitats on seasonally inundated floodplains of two Alabama (USA) streams. Standardized area electrofishing appeared to be the best sampling technique for collecting and quantifying species because of high catch rate, broad species and size coverage, and rapid sampling. Electrofishing accounted for most fish (47 and 57% of pooled catch), almost all taxa, and a broad range of fish sizes. Large-mesh gill nets captured few fish (2% and 8%), a distinct subset of the species present, and the largest fish. Light traps were the most efficient and taxa-comprehensive sampling technique for larval fish. Light traps captured the vast majority of the pooled larval fish catch, including 6 of 7 families recorded at the sites. Larval fish dip netting captured larval fish of most families known to be present but in low numbers. For surveys of species composition and rapid bioassessments, nonstandardized electrofishing and larval fish dip netting appear adequate. For intensive research studies, the combination of area electrofishing, large-mesh (and in some cases small-mesh) gill nets, and light traps provide thorough and comprehensive data on wetland fish assemblages.  相似文献   

18.
Abstract Between 1994 and 1997, 508 pike, Esox lucius L., were tagged in Lower Lough Erne (LLE), Northern Ireland. By August 2000, 79 of these fish were recaptured. Ten of 27 pike recaptured and released a second time were then captured a third time. Distance from tagging to recapture site ranged from 0 to 16 km, with most recaptures within 10 km. Pike dispersed widely after spawning, an observation supported by netting survey data, and tended to return to the same spawning sites year after year. The usefulness of designated sanctuary areas free of commercial fishing, intended to maintain a stock of pike reserved for angling was evaluated. To protect angling stocks of pike from commercial fishing, sanctuary areas should be somewhat larger than at present.  相似文献   

19.
The health status of eight marine rainbow trout farms was followed from mid-June to mid-September 2006 by sampling both dead and healthy fish approximately every 2 weeks for bacteriological and virological investigation. No fish pathogenic viruses were detected, but all farms experienced disease and mortality as a result of various bacterial infections. Yersinia ruckeri was found on four and Renibacterium salmoninarum on five of the farms, but only during the first part of the surveillance period. This indicates that the fish carried the infection from fresh water, and cleared the infection in salt water. Aeromonas salmonicida subsp. salmonicida caused mortality on five farms, but persisted throughout the sampling period. Although A. salmonicida was probably carried from fresh water, the fish were not able to clear the infection in the sea. Vibrio anguillarum caused mortality on six of the farms throughout the sampling period, O1 being the dominant serovar, and Photobacterium damselae subsp. damselae was found on seven farms as a cause of disease. During the period of highest water temperatures Vibrio parahaemolyticus and Vibrio vulnificus were detected in dead fish in five and two farms, respectively, although their significance as causative pathogens is questionable. Vibrio vulnificus has not previously been found in rainbow trout in Denmark. Both mortality and number of antimicrobial treatments during the period were considerably higher in unvaccinated compared with vaccinated fish. Resistance to commonly used antimicrobials was low or absent.  相似文献   

20.
  • 1. Artificial structures are becoming increasingly important in conserving biodiversity in urban ecosystems, by providing habitat for endangered or rare species. Their role in providing habitat for such species has, however, been largely unexplored.
  • 2. In Sydney Harbour, Australia, seahorses were observed among the netting used to keep sharks out of swimming enclosures. Over a 2‐year period, the relative densities of two species of seahorses observed on netting was measured at swimming enclosures with permanent netting and at swimming areas that were only enclosed with netting during the summer months.
  • 3. The rate of colonization by seahorses to new netting was also examined over a period of 10 months.
  • 4. Numbers of seahorses on permanent swimming enclosures were 10 to 100 times greater than numbers present on swimming enclosures that were only set up during the summer months.
  • 5. This large difference may have been attributed to the slow rate of colonization of seahorses to new habitat. Seahorses were not observed at experimental nets that were deployed in two areas in the harbour until at least 4 months after the netting was deployed.
  • 6. Swimming pool nets are a habitat for species of seahorses in Sydney Harbour and, consequently, the removal or disturbance of swimming nets may impact the survival of these fish. Management of these artificial habitats may therefore best be focused on providing a permanent habitat that may help to compensate for the loss of netting during winter months.
Copyright © 2007 John Wiley & Sons, Ltd.  相似文献   

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