Pål Bjørn - Academia.edu (original) (raw)
Papers by Pål Bjørn
NINAs publikasjoner NINA Rapport Dette er en ny, elektronisk serie fra 2005 som erstatter de tidl... more NINAs publikasjoner NINA Rapport Dette er en ny, elektronisk serie fra 2005 som erstatter de tidligere seriene NINA Fagrapport, NINA Oppdragsmelding og NINA Project Report. Normalt er dette NINAs rapportering til oppdragsgiver etter gjennomført forsknings-, overvåkings-eller utredningsarbeid. I tillegg vil serien favne mye av instituttets øvrige rapportering, for eksempel fra seminarer og konferanser, resultater av eget forsknings-og utredningsarbeid og litteraturstudier. NINA Rapport kan også utgis på annet språk når det er hensiktsmessig.
Human Ecology, 2007
Environmental effects of salmon farming are controversial issues. In Northern Norway, cod fishers... more Environmental effects of salmon farming are controversial issues. In Northern Norway, cod fishers argue that the location of salmon pens in fjords results in the cessation of local cod spawning. Research supporting or rejecting such statements is scant. There is an absence of both short-term and long-term studies on the effects that salmon farming may have on wild fish stocks. There are few studies of local ecosystem relationships in general. This article explores fishers’ arguments about the effects of salmon farming. It discusses methods of assessing the reliability and validity of fisher knowledge, and contributes to the discussion on assets and limitations of narrative data and experiential knowledge.
Journal of Fish Biology, 2007
ABSTRACT A synthesis of results from two projects was assessed to analyse possible influence of s... more ABSTRACT A synthesis of results from two projects was assessed to analyse possible influence of sea lice Lepeophtheirus salmonis on marine Atlantic salmon Salmo salar survival. During the years 1992–2004, trawling for wild migrating post-smolts was performed in Trondheimsfjord, a fjord in which no Atlantic salmon aquaculture activity is permitted. Prevalence and intensity of sea lice infections on migrating wild post-smolts differed between years. A correlation analysis between 1 sea-winter (SW) Atlantic salmon catch statistics from the River Orkla (a Trondheimsfjord river) and sea lice infections on the migrating smolts in the Trondheimsfjord was not significant. Up to 2% reduction in adult returns due to sea-lice infection was expected. In addition, experimental releases from 1996 to 1998 with individually tagged groups of hatchery-reared Atlantic salmon smolts given protection against sea-lice infection was performed. Higher recaptures of adult Atlantic salmon from 1998 treated smolts compared to the control group may correspond to high abundance of sea lice found on the wild smolt, and may indicate influence on post-smolt mortality. These studies indicate that post-smolt mortality in Trondheimsfjord is marginally influenced by sea lice infection; however, the methods for assessing wild smolt mortality might be insufficient. Higher infections of sea lice farther out in the fjord may indicate more loss in Atlantic salmon returns in some years.
Journal of Fish Biology, 2010
Groups of mature (5+ year old) Arctic charr Salvelinus alpinus held in sea water were exposed for... more Groups of mature (5+ year old) Arctic charr Salvelinus alpinus held in sea water were exposed for 34 days to either a high (mean ± s.e. 0·15 ± 0·01 sea lice Lepeophtheirus salmonis g −1 fish mass) (HI), medium (0·07 ± 0·00 sea lice g −1 fish mass) (MI) or no [control (C)] sea-lice infection during early stages of gonad development (June to July). Infection with sea lice resulted in increased plasma cortisol concentrations and this was related to intensity of infection; females tended to have higher cortisol concentrations than males at high infection intensities (HI group: female c. 130 ng ml −1 ; male c. 80 ng ml −1 ). Plasma osmolality (C c. 330, MI c. 350 and HI c. 415 mOsm) and chloride concentrations (C c. 135, MI c. 155 and HI c. 190 mM) increased significantly with infection intensity, indicating osmoregulatory problems in infected fish. A strong positive relationship between plasma osmolality and cortisol concentration was recorded. Plasma sex-steroid concentrations were influenced negatively by sea-lice infection, particularly in the HI group, and were inversely related to plasma cortisol concentrations. The most heavily infected fish postponed the initiation of reproductive development until exposed to fresh water and timing of ovulation tended to be delayed in these fish. Growth rate and condition were negatively influenced by sea-lice infection and growth rate was inversely related to plasma cortisol concentrations. Sea-lice infection resulted in mortality among females in the HI group, and the proportion of maturing females was lower in the MI group (46%) than in the controls (85%). Egg production in the MI and HI groups was c. 50 and 30% of the C group. Egg size, embryonic survival and fry mass did not differ across groups. Sea lice influence reproductive development and egg production in S. alpinus, and consequently these parasites may influence populations via sublethal effects on broodfish, affecting growth and condition, and their reproductive output.
Hydrobiologia, 2007
Effects of artificial salmon lice infection and pharmaceutical salmon lice prophylaxis on surviva... more Effects of artificial salmon lice infection and pharmaceutical salmon lice prophylaxis on survival and rate of progression of Atlantic salmon (n = 72) and brown trout post-smolts (n = 72) during their fjord migration, were studied by telemetry. The infected groups were
Hydrobiologia, 2007
The behaviour of wild (n = 43, mean L T = 152 mm) and hatchery-reared (n = 71, mean L T = 198 mm)... more The behaviour of wild (n = 43, mean L T = 152 mm) and hatchery-reared (n = 71, mean L T = 198 mm) Atlantic salmon and wild anadromous brown trout (n = 34, mean L T = 171 mm) post-smolts with acoustic transmitters was compared in a Norwegian fjord system. There was no difference in survival between wild and hatchery reared salmon from release in the river mouth to passing receiver sites 9.5 km and 37.0 km from the release site. Mortality approached 65% during the first 37 km of the marine migration for both groups. There was no difference between wild and hatchery-reared salmon either in time from release to first recording at 9.5 km (mean 135 and 80 h), or in the rate of movement through the fjord (mean 0.53 and 0.56 bl s -1 ). Hatchery-reared salmon reached the 37 km site sooner after release than the wild salmon (mean 168 and 450 h), but rate of movement in terms of body lengths per second did not differ (mean 0.56 and 0.77 bl s -1 ). The brown trout remained a longer period in the inner part of the fjord system, with much slower rates of movement during the first 9.5 km (mean 0.06 bl s -1 ).
Estuarine, Coastal and Shelf Science, 2010
Fish-farming structures are widespread in coastal waters and are highly attractive to wild fish. ... more Fish-farming structures are widespread in coastal waters and are highly attractive to wild fish. Several studies have estimated that tons to tens of tons of wild fish aggregate around fish farms. These estimates assumed that the majority of wild fish are concentrated immediately beneath farms, although this assumption has never been explicitly tested. We tested the hypothesis that abundances of
Canadian Journal of Zoology, 1998
nina.no
Other publishing In addition to reporting in NINA's own series, the institute's employe... more Other publishing In addition to reporting in NINA's own series, the institute's employees publish a large proportion of their scientific results in international journals, popular science books and magazines. ... CONTACT DETAILS NINA head office NO-7485 Trondheim Norway ...
Aquatic Living Resources, 1993
ala as J. A., T. G. Heggberget, P. A. Bj$rn, O. Rcitan, Aquat. Living Resour., 1993, 6, 31-38. Fo... more ala as J. A., T. G. Heggberget, P. A. Bj$rn, O. Rcitan, Aquat. Living Resour., 1993, 6, 31-38. Foraging activities of goosanders (Anatidae, Mergus merganser) were studied in relation to seaward migration of smolt in the River Halselva in northern Norway, 1987Norway, -1989. Birds aggrcgatcd in the estuary in June, during mass migration of smolts. Whcn present in the estuary males and females spent 28.7 and 35.6% of their time feeding. Only 15% of dives resulted in birds' bringing prey to the surface and about 25% of prey found in goosander stomachs wcrc salmonids. For hatchery-reared smolts released in the estuary, average length taken did not differ from that available; for wild smolts of Arctic char, however, smaller fishes than those available were takcn. For 1989, we estimate that goosanders took 1 % of the hatchcry-reared smolts released in the estuary, and 2% of the wild smolts whcn smolts passed the estuary during seaward migration. As it is likely that less fit smolts (e. g. sick, injured, small) are most pronc to predation, we argue that such a level of predation on migrating smolts from goosanders has only a minor impact on salmonid production. Suggestions to reduce predation are discussed.
Aquaculture Research, 2008
Commercial farming of Atlantic cod (Gadus morhua L.) is now being developed in several countries.... more Commercial farming of Atlantic cod (Gadus morhua L.) is now being developed in several countries. The ecological consequences of cod culture are poorly understood, but recent research suggests that Atlantic cod are more prone to escape from net pens than Atlantic salmon. Here, we describe the movements and the spatiotemporal distribution of farmed cod after escape relative to wild cod, both during and outside the natural spawning season. The experimental design included simulating escape incidents of farmed cod tagged with acoustic transmitters and using an array of automatic listening stations to monitor their dispersal and distribution. For comparison, local wild cod were monitored using the same array of receivers. The farmed cod dispersed rapidly after a simulated escape, they randomly distributed over large areas and their distribution overlapped with local wild cod. Moreover, escaped farmed ¢sh were found at local cod spawning areas during the spawning season. The study also indicated that the recapture rate of escaped farmed cod was high compared with that of escaped farmed salmon. Thus, while our results showed that there is a considerable potential for ecosystem e¡ects caused by escaped farmed cod, mitigating actions such as an e⁄cient recapture ¢shery for escapees may be possible.
Aquaculture Research, 1995
The survival of salmon lice. Lepeophtheirus salmonis (Kreyer) on Arctic charr. Salvelinus alpinus... more The survival of salmon lice. Lepeophtheirus salmonis (Kreyer) on Arctic charr. Salvelinus alpinus (L). in fresh water was studied. The results showed that salmon lice were able to survive for up to 3 weeks, in contrast with previous published information that the parasite is quickly shed when the fish enters fresh water.
Aquaculture Research, 2008
Cultured ¢sh escaping from farms represent an economic loss as well as a potential problem for wi... more Cultured ¢sh escaping from farms represent an economic loss as well as a potential problem for wild ¢sh populations. This study investigated the escape-related behaviour of farmed Norwegian coastal and northeast Arctic cod (NEAC), Gadus morhua L. Six groups of ¢sh were observed during three replicate trials in a large tank that was split into two equal parts by a net wall. The ¢sh could move freely through an opening in the net during the trials. Three groups were not fed during the trials. The ¢rst escape occurred shortly after producing the net opening (11 AE 10.5 min; mean AE standard deviation). Norwegian coastal cod were more prone to escape than the NEAC. A starvation period of 9 days increased the number of ¢sh on the escape side of the tank. Net biting and net inspection by the ¢sh were frequently observed, irrespective of whether the ¢sh were fed or not. The same ¢sh were repeatedly found on the escape side of the tank, but the propensity for recurrent escape behaviour was not related to genotype, feeding status or size. The results suggest that other factors, such as individual variation in boldness or exploration behaviour, could a¡ect the willingness to escape.
Aquaculture, 2012
Acidification is acknowledged as a cause for extinction or catch reductions in numerous rivers su... more Acidification is acknowledged as a cause for extinction or catch reductions in numerous rivers supporting Atlantic salmon (Salmo salar L.) populations in Norway. In freshwater, labile (cationic/inorganic) forms of Al (LAl) accumulate onto and in fish gills, where high concentrations can result in mortality due to respiratory and ionoregulatory dysfunction. At lower concentrations, Al may still have major population effects, mainly through the inhibition of gill Na + ,K + -ATPase activity, reducing hypo-osmoregulatory capacity and thereby affecting marine survival. Following episodic exposure, normal smolt properties are expected to be restored. In 2006 and 2007 we exposed groups of 1100 to 1200 one-year old hatchery reared, Carlin tagged Atlantic salmon smolts of the Imsa strain (South-Western Norway) to moderately acidified water (pH 5.6-5.7; 10-15 μg L Al l −1 ) for 2 to 14 days whereupon they were transferred to a water quality assumed to be satisfactory for smolt (good water; pH 6.8-7.2 and b 6 μg L Al l −1 ) for 2 to 14 days to monitor recovery from the prior exposure. Control fish had gill-Al concentrations in the range of 5 to 10 μg Al g − 1 gill dry weight (dw) while Al-exposed fish had gill-Al concentrations exceeding 30 μg Al g − 1 gill dw. Following transfer to good water, gill-Al did not return to control levels within a time span of 14 days. The physiological responses measured as blood ions (Na + , Cl − ), blood acid-base balance (pH, pCO 2 and HCO 3 − ), and blood glucose improved relative to the acid/aluminum (Al) exposed groups, but not to levels measured in the control fish. Mortality was elevated in all Al-exposed/recovery groups following transfer to seawater (34 ppt) and gill Na + ,K + -ATPase was reduced. The results suggest that smolts had not fully recovered 14 days after a short-term acid/Al exposure, where recovery depends on what traits are used as indicators of healthy fish. An Al-exposure experienced by presmolt several weeks prior to the smolt spring migration can have negative population effects, both by reducing hypo-osmoregulatory capacity and by making the fish more vulnerable to secondary stressors in the marine environment.
Aquaculture, 2012
Acid rain has reduced several salmonid stocks in Norway and salmon lice have been identified as a... more Acid rain has reduced several salmonid stocks in Norway and salmon lice have been identified as a major population regulation factor. The combination of these two factors has also been seen to reduce postsmolt survival. In the present study, we have addressed the effects of an episodic exposure to acidic water and later recovery in good freshwater quality (Acid/Recovery groups) followed by salmon lice infestation in seawater in more detail. The ecological perspective of this can be directly addressed to changes over the last decades from chronic acidification over Norway and Europe, to more episodic spring acidification of rivers prior to or during downstream migration of smolts. The results showed that salmon lice-induced mortality increased in all episodic Acid/Rec groups. However, the group given the longest recovery period experienced the lowest mortality compared to the other treatment groups. A period of recovery after acid exposure may eventually restore the fish back to normal physiological level, but in the present experiment a period of 14 days of recovery after a 2 day exposure to acid water was too short to fully restore the fish back to normal levels. Even short-time episodic acidification followed by recovery during springtime and the vulnerable smoltification process, may therefore have negative and often unnoticed effects in wild salmonids until the postsmolts meet other stressors in the marine phase such as salmon lice and other fish diseases.
Aquaculture, 2007
Salmon populations on the western coast of Norway may experience both moderately acidified rivers... more Salmon populations on the western coast of Norway may experience both moderately acidified rivers and salmon lice (Lepeophtheirus salmonis Krøyer) attacks. The present study addresses the question of interactive effects of acidification and salmon lice infestation on postsmolt survival. Three groups each of approximately 1500 one-year old Atlantic salmon smolts of the Imsa strain, South-Western Norway, were exposed to one of three suboptimal water qualities (high acid, moderate acid and episodic acid) and experienced acidic water (pH 5.6-5.9 and 7-45 μg Ali/l) with different exposure duration (3 to 10 days). A fourth group exposed to pH N 6.6 and b 9 μg Ali/l acted as control (reference group). After freshwater exposure, smolts (n = 150) from each group were moved into tanks containing brackish water (16‰) and after 8 h they were given full strength seawater (33‰) and given 1 day of recovery before being infected with salmon lice copepodids. Four non-infected groups (n = 100) from the same exposures acted as controls. Over a 42 day period, postsmolts were regularly inspected and sampled for mortality, lice density and physiological status in seawater. The lice per smolt density were highest in the episodic acid group, followed by the high acid, moderate acid and the reference groups. Mortality was low in the four non-infected control groups, and significantly elevated in the lice infected groups (high acid N moderate acid N episodic acid N reference). Plasma chloride levels were within the normal range in the non-infected groups, while fish in the infected high acid and moderate acid groups had elevated plasma chloride levels. High gill aluminium was seen in the three exposure groups in freshwater.
![Research paper thumbnail of Corrigendum to “A review of the Norwegian ‘National Action Plan Against Salmon Lice on Salmonids’: The effect on wild salmonids” [Aquaculture 246 (2005) 79–92]](https://attachments.academia-assets.com/43097756/thumbnails/1.jpg)
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Aquaculture, 2011
Norway has the largest salmon-farming industry in the world, an industry that is still growing, a... more Norway has the largest salmon-farming industry in the world, an industry that is still growing, and in recent years production of marine species like Atlantic cod has also increased. At the same time, Norway has the world's largest wild stock of Atlantic salmon and has fjord systems and ocean areas rich in wild marine fish species which form the basis of a large fishing industry. As the aquaculture industry grows and diversifies, there is concern about the potential effects of pathogens spreading from farmed fish to wild populations. The overall health situation in Norwegian aquaculture is good, but some pathogens are not controlled effectively. In particular, salmon lice produced in farms may cause problems for wild salmonids and other parasites may be abundant too. Also, viral diseases in Atlantic salmon and bacterial diseases in Atlantic cod give rise to several disease outbreaks annually. The open design of most aquaculture systems allows the transmission of pathogens from the environment or from wild fish to the farmed fish. The objective of this review is to provide an overview of current knowledge of disease interaction and pathogen exchange between farmed and wild fish populations, with emphasis on Norwegian condition. In addition, the paper contains an evaluation of research methods that would be useful in expanding knowledge of pathogen exchange between wild and farmed fish, and in surveys of diseases in wild fish populations. The impact of pathogen transfer from farmed fish to economically important wild fish populations is assessed together with risk analysis considering possible consequences of pathogen exchange between farmed and wild fish. Finally, the review contains suggestions for future research that will increase the knowledge in the field.
NINAs publikasjoner NINA Rapport Dette er en ny, elektronisk serie fra 2005 som erstatter de tidl... more NINAs publikasjoner NINA Rapport Dette er en ny, elektronisk serie fra 2005 som erstatter de tidligere seriene NINA Fagrapport, NINA Oppdragsmelding og NINA Project Report. Normalt er dette NINAs rapportering til oppdragsgiver etter gjennomført forsknings-, overvåkings-eller utredningsarbeid. I tillegg vil serien favne mye av instituttets øvrige rapportering, for eksempel fra seminarer og konferanser, resultater av eget forsknings-og utredningsarbeid og litteraturstudier. NINA Rapport kan også utgis på annet språk når det er hensiktsmessig.
Human Ecology, 2007
Environmental effects of salmon farming are controversial issues. In Northern Norway, cod fishers... more Environmental effects of salmon farming are controversial issues. In Northern Norway, cod fishers argue that the location of salmon pens in fjords results in the cessation of local cod spawning. Research supporting or rejecting such statements is scant. There is an absence of both short-term and long-term studies on the effects that salmon farming may have on wild fish stocks. There are few studies of local ecosystem relationships in general. This article explores fishers’ arguments about the effects of salmon farming. It discusses methods of assessing the reliability and validity of fisher knowledge, and contributes to the discussion on assets and limitations of narrative data and experiential knowledge.
Journal of Fish Biology, 2007
ABSTRACT A synthesis of results from two projects was assessed to analyse possible influence of s... more ABSTRACT A synthesis of results from two projects was assessed to analyse possible influence of sea lice Lepeophtheirus salmonis on marine Atlantic salmon Salmo salar survival. During the years 1992–2004, trawling for wild migrating post-smolts was performed in Trondheimsfjord, a fjord in which no Atlantic salmon aquaculture activity is permitted. Prevalence and intensity of sea lice infections on migrating wild post-smolts differed between years. A correlation analysis between 1 sea-winter (SW) Atlantic salmon catch statistics from the River Orkla (a Trondheimsfjord river) and sea lice infections on the migrating smolts in the Trondheimsfjord was not significant. Up to 2% reduction in adult returns due to sea-lice infection was expected. In addition, experimental releases from 1996 to 1998 with individually tagged groups of hatchery-reared Atlantic salmon smolts given protection against sea-lice infection was performed. Higher recaptures of adult Atlantic salmon from 1998 treated smolts compared to the control group may correspond to high abundance of sea lice found on the wild smolt, and may indicate influence on post-smolt mortality. These studies indicate that post-smolt mortality in Trondheimsfjord is marginally influenced by sea lice infection; however, the methods for assessing wild smolt mortality might be insufficient. Higher infections of sea lice farther out in the fjord may indicate more loss in Atlantic salmon returns in some years.
Journal of Fish Biology, 2010
Groups of mature (5+ year old) Arctic charr Salvelinus alpinus held in sea water were exposed for... more Groups of mature (5+ year old) Arctic charr Salvelinus alpinus held in sea water were exposed for 34 days to either a high (mean ± s.e. 0·15 ± 0·01 sea lice Lepeophtheirus salmonis g −1 fish mass) (HI), medium (0·07 ± 0·00 sea lice g −1 fish mass) (MI) or no [control (C)] sea-lice infection during early stages of gonad development (June to July). Infection with sea lice resulted in increased plasma cortisol concentrations and this was related to intensity of infection; females tended to have higher cortisol concentrations than males at high infection intensities (HI group: female c. 130 ng ml −1 ; male c. 80 ng ml −1 ). Plasma osmolality (C c. 330, MI c. 350 and HI c. 415 mOsm) and chloride concentrations (C c. 135, MI c. 155 and HI c. 190 mM) increased significantly with infection intensity, indicating osmoregulatory problems in infected fish. A strong positive relationship between plasma osmolality and cortisol concentration was recorded. Plasma sex-steroid concentrations were influenced negatively by sea-lice infection, particularly in the HI group, and were inversely related to plasma cortisol concentrations. The most heavily infected fish postponed the initiation of reproductive development until exposed to fresh water and timing of ovulation tended to be delayed in these fish. Growth rate and condition were negatively influenced by sea-lice infection and growth rate was inversely related to plasma cortisol concentrations. Sea-lice infection resulted in mortality among females in the HI group, and the proportion of maturing females was lower in the MI group (46%) than in the controls (85%). Egg production in the MI and HI groups was c. 50 and 30% of the C group. Egg size, embryonic survival and fry mass did not differ across groups. Sea lice influence reproductive development and egg production in S. alpinus, and consequently these parasites may influence populations via sublethal effects on broodfish, affecting growth and condition, and their reproductive output.
Hydrobiologia, 2007
Effects of artificial salmon lice infection and pharmaceutical salmon lice prophylaxis on surviva... more Effects of artificial salmon lice infection and pharmaceutical salmon lice prophylaxis on survival and rate of progression of Atlantic salmon (n = 72) and brown trout post-smolts (n = 72) during their fjord migration, were studied by telemetry. The infected groups were
Hydrobiologia, 2007
The behaviour of wild (n = 43, mean L T = 152 mm) and hatchery-reared (n = 71, mean L T = 198 mm)... more The behaviour of wild (n = 43, mean L T = 152 mm) and hatchery-reared (n = 71, mean L T = 198 mm) Atlantic salmon and wild anadromous brown trout (n = 34, mean L T = 171 mm) post-smolts with acoustic transmitters was compared in a Norwegian fjord system. There was no difference in survival between wild and hatchery reared salmon from release in the river mouth to passing receiver sites 9.5 km and 37.0 km from the release site. Mortality approached 65% during the first 37 km of the marine migration for both groups. There was no difference between wild and hatchery-reared salmon either in time from release to first recording at 9.5 km (mean 135 and 80 h), or in the rate of movement through the fjord (mean 0.53 and 0.56 bl s -1 ). Hatchery-reared salmon reached the 37 km site sooner after release than the wild salmon (mean 168 and 450 h), but rate of movement in terms of body lengths per second did not differ (mean 0.56 and 0.77 bl s -1 ). The brown trout remained a longer period in the inner part of the fjord system, with much slower rates of movement during the first 9.5 km (mean 0.06 bl s -1 ).
Estuarine, Coastal and Shelf Science, 2010
Fish-farming structures are widespread in coastal waters and are highly attractive to wild fish. ... more Fish-farming structures are widespread in coastal waters and are highly attractive to wild fish. Several studies have estimated that tons to tens of tons of wild fish aggregate around fish farms. These estimates assumed that the majority of wild fish are concentrated immediately beneath farms, although this assumption has never been explicitly tested. We tested the hypothesis that abundances of
Canadian Journal of Zoology, 1998
nina.no
Other publishing In addition to reporting in NINA's own series, the institute's employe... more Other publishing In addition to reporting in NINA's own series, the institute's employees publish a large proportion of their scientific results in international journals, popular science books and magazines. ... CONTACT DETAILS NINA head office NO-7485 Trondheim Norway ...
Aquatic Living Resources, 1993
ala as J. A., T. G. Heggberget, P. A. Bj$rn, O. Rcitan, Aquat. Living Resour., 1993, 6, 31-38. Fo... more ala as J. A., T. G. Heggberget, P. A. Bj$rn, O. Rcitan, Aquat. Living Resour., 1993, 6, 31-38. Foraging activities of goosanders (Anatidae, Mergus merganser) were studied in relation to seaward migration of smolt in the River Halselva in northern Norway, 1987Norway, -1989. Birds aggrcgatcd in the estuary in June, during mass migration of smolts. Whcn present in the estuary males and females spent 28.7 and 35.6% of their time feeding. Only 15% of dives resulted in birds' bringing prey to the surface and about 25% of prey found in goosander stomachs wcrc salmonids. For hatchery-reared smolts released in the estuary, average length taken did not differ from that available; for wild smolts of Arctic char, however, smaller fishes than those available were takcn. For 1989, we estimate that goosanders took 1 % of the hatchcry-reared smolts released in the estuary, and 2% of the wild smolts whcn smolts passed the estuary during seaward migration. As it is likely that less fit smolts (e. g. sick, injured, small) are most pronc to predation, we argue that such a level of predation on migrating smolts from goosanders has only a minor impact on salmonid production. Suggestions to reduce predation are discussed.
Aquaculture Research, 2008
Commercial farming of Atlantic cod (Gadus morhua L.) is now being developed in several countries.... more Commercial farming of Atlantic cod (Gadus morhua L.) is now being developed in several countries. The ecological consequences of cod culture are poorly understood, but recent research suggests that Atlantic cod are more prone to escape from net pens than Atlantic salmon. Here, we describe the movements and the spatiotemporal distribution of farmed cod after escape relative to wild cod, both during and outside the natural spawning season. The experimental design included simulating escape incidents of farmed cod tagged with acoustic transmitters and using an array of automatic listening stations to monitor their dispersal and distribution. For comparison, local wild cod were monitored using the same array of receivers. The farmed cod dispersed rapidly after a simulated escape, they randomly distributed over large areas and their distribution overlapped with local wild cod. Moreover, escaped farmed ¢sh were found at local cod spawning areas during the spawning season. The study also indicated that the recapture rate of escaped farmed cod was high compared with that of escaped farmed salmon. Thus, while our results showed that there is a considerable potential for ecosystem e¡ects caused by escaped farmed cod, mitigating actions such as an e⁄cient recapture ¢shery for escapees may be possible.
Aquaculture Research, 1995
The survival of salmon lice. Lepeophtheirus salmonis (Kreyer) on Arctic charr. Salvelinus alpinus... more The survival of salmon lice. Lepeophtheirus salmonis (Kreyer) on Arctic charr. Salvelinus alpinus (L). in fresh water was studied. The results showed that salmon lice were able to survive for up to 3 weeks, in contrast with previous published information that the parasite is quickly shed when the fish enters fresh water.
Aquaculture Research, 2008
Cultured ¢sh escaping from farms represent an economic loss as well as a potential problem for wi... more Cultured ¢sh escaping from farms represent an economic loss as well as a potential problem for wild ¢sh populations. This study investigated the escape-related behaviour of farmed Norwegian coastal and northeast Arctic cod (NEAC), Gadus morhua L. Six groups of ¢sh were observed during three replicate trials in a large tank that was split into two equal parts by a net wall. The ¢sh could move freely through an opening in the net during the trials. Three groups were not fed during the trials. The ¢rst escape occurred shortly after producing the net opening (11 AE 10.5 min; mean AE standard deviation). Norwegian coastal cod were more prone to escape than the NEAC. A starvation period of 9 days increased the number of ¢sh on the escape side of the tank. Net biting and net inspection by the ¢sh were frequently observed, irrespective of whether the ¢sh were fed or not. The same ¢sh were repeatedly found on the escape side of the tank, but the propensity for recurrent escape behaviour was not related to genotype, feeding status or size. The results suggest that other factors, such as individual variation in boldness or exploration behaviour, could a¡ect the willingness to escape.
Aquaculture, 2012
Acidification is acknowledged as a cause for extinction or catch reductions in numerous rivers su... more Acidification is acknowledged as a cause for extinction or catch reductions in numerous rivers supporting Atlantic salmon (Salmo salar L.) populations in Norway. In freshwater, labile (cationic/inorganic) forms of Al (LAl) accumulate onto and in fish gills, where high concentrations can result in mortality due to respiratory and ionoregulatory dysfunction. At lower concentrations, Al may still have major population effects, mainly through the inhibition of gill Na + ,K + -ATPase activity, reducing hypo-osmoregulatory capacity and thereby affecting marine survival. Following episodic exposure, normal smolt properties are expected to be restored. In 2006 and 2007 we exposed groups of 1100 to 1200 one-year old hatchery reared, Carlin tagged Atlantic salmon smolts of the Imsa strain (South-Western Norway) to moderately acidified water (pH 5.6-5.7; 10-15 μg L Al l −1 ) for 2 to 14 days whereupon they were transferred to a water quality assumed to be satisfactory for smolt (good water; pH 6.8-7.2 and b 6 μg L Al l −1 ) for 2 to 14 days to monitor recovery from the prior exposure. Control fish had gill-Al concentrations in the range of 5 to 10 μg Al g − 1 gill dry weight (dw) while Al-exposed fish had gill-Al concentrations exceeding 30 μg Al g − 1 gill dw. Following transfer to good water, gill-Al did not return to control levels within a time span of 14 days. The physiological responses measured as blood ions (Na + , Cl − ), blood acid-base balance (pH, pCO 2 and HCO 3 − ), and blood glucose improved relative to the acid/aluminum (Al) exposed groups, but not to levels measured in the control fish. Mortality was elevated in all Al-exposed/recovery groups following transfer to seawater (34 ppt) and gill Na + ,K + -ATPase was reduced. The results suggest that smolts had not fully recovered 14 days after a short-term acid/Al exposure, where recovery depends on what traits are used as indicators of healthy fish. An Al-exposure experienced by presmolt several weeks prior to the smolt spring migration can have negative population effects, both by reducing hypo-osmoregulatory capacity and by making the fish more vulnerable to secondary stressors in the marine environment.
Aquaculture, 2012
Acid rain has reduced several salmonid stocks in Norway and salmon lice have been identified as a... more Acid rain has reduced several salmonid stocks in Norway and salmon lice have been identified as a major population regulation factor. The combination of these two factors has also been seen to reduce postsmolt survival. In the present study, we have addressed the effects of an episodic exposure to acidic water and later recovery in good freshwater quality (Acid/Recovery groups) followed by salmon lice infestation in seawater in more detail. The ecological perspective of this can be directly addressed to changes over the last decades from chronic acidification over Norway and Europe, to more episodic spring acidification of rivers prior to or during downstream migration of smolts. The results showed that salmon lice-induced mortality increased in all episodic Acid/Rec groups. However, the group given the longest recovery period experienced the lowest mortality compared to the other treatment groups. A period of recovery after acid exposure may eventually restore the fish back to normal physiological level, but in the present experiment a period of 14 days of recovery after a 2 day exposure to acid water was too short to fully restore the fish back to normal levels. Even short-time episodic acidification followed by recovery during springtime and the vulnerable smoltification process, may therefore have negative and often unnoticed effects in wild salmonids until the postsmolts meet other stressors in the marine phase such as salmon lice and other fish diseases.
Aquaculture, 2007
Salmon populations on the western coast of Norway may experience both moderately acidified rivers... more Salmon populations on the western coast of Norway may experience both moderately acidified rivers and salmon lice (Lepeophtheirus salmonis Krøyer) attacks. The present study addresses the question of interactive effects of acidification and salmon lice infestation on postsmolt survival. Three groups each of approximately 1500 one-year old Atlantic salmon smolts of the Imsa strain, South-Western Norway, were exposed to one of three suboptimal water qualities (high acid, moderate acid and episodic acid) and experienced acidic water (pH 5.6-5.9 and 7-45 μg Ali/l) with different exposure duration (3 to 10 days). A fourth group exposed to pH N 6.6 and b 9 μg Ali/l acted as control (reference group). After freshwater exposure, smolts (n = 150) from each group were moved into tanks containing brackish water (16‰) and after 8 h they were given full strength seawater (33‰) and given 1 day of recovery before being infected with salmon lice copepodids. Four non-infected groups (n = 100) from the same exposures acted as controls. Over a 42 day period, postsmolts were regularly inspected and sampled for mortality, lice density and physiological status in seawater. The lice per smolt density were highest in the episodic acid group, followed by the high acid, moderate acid and the reference groups. Mortality was low in the four non-infected control groups, and significantly elevated in the lice infected groups (high acid N moderate acid N episodic acid N reference). Plasma chloride levels were within the normal range in the non-infected groups, while fish in the infected high acid and moderate acid groups had elevated plasma chloride levels. High gill aluminium was seen in the three exposure groups in freshwater.
Aquaculture, 2011
Norway has the largest salmon-farming industry in the world, an industry that is still growing, a... more Norway has the largest salmon-farming industry in the world, an industry that is still growing, and in recent years production of marine species like Atlantic cod has also increased. At the same time, Norway has the world's largest wild stock of Atlantic salmon and has fjord systems and ocean areas rich in wild marine fish species which form the basis of a large fishing industry. As the aquaculture industry grows and diversifies, there is concern about the potential effects of pathogens spreading from farmed fish to wild populations. The overall health situation in Norwegian aquaculture is good, but some pathogens are not controlled effectively. In particular, salmon lice produced in farms may cause problems for wild salmonids and other parasites may be abundant too. Also, viral diseases in Atlantic salmon and bacterial diseases in Atlantic cod give rise to several disease outbreaks annually. The open design of most aquaculture systems allows the transmission of pathogens from the environment or from wild fish to the farmed fish. The objective of this review is to provide an overview of current knowledge of disease interaction and pathogen exchange between farmed and wild fish populations, with emphasis on Norwegian condition. In addition, the paper contains an evaluation of research methods that would be useful in expanding knowledge of pathogen exchange between wild and farmed fish, and in surveys of diseases in wild fish populations. The impact of pathogen transfer from farmed fish to economically important wild fish populations is assessed together with risk analysis considering possible consequences of pathogen exchange between farmed and wild fish. Finally, the review contains suggestions for future research that will increase the knowledge in the field.