Canadian Tax Dollars going to good use...fish farm bailouts...

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Journal of Applied Ecology doi: 10.1111/j.1365-2664.2010.01889.x

Coho salmon productivity in relation to salmon lice from infected prey and salmon farms
Brendan M. Connors1*, Martin Krkosˇ ek2,3, Jennifer Ford4 and Lawrence M. Dill1
1Earth to Ocean and Evolutionary and Behavioural Ecology Research Groups, Department of Biological Sciences,
Simon Fraser University, 8888 University Drive, Burnaby, BC V5A 1S6, Canada; 2School of Aquatic and Fishery
Sciences, University of Washington, 1122 NE Boat St, Seattle, WA 98105, USA; 3Department of Zoology, University
of Otago, PO Box 56, Dunedin 9054, New Zealand; and 4Oceans and Coastal Management Division, Bedford Institute
of Oceanography, Fisheries and Oceans Canada, Dartmouth, NS B2Y 4A2, Canada

Summary
1. Pathogen transmission from open net-pen aquaculture facilities can depress sympatric wild fish populations. However, little is known about the effects of pathogen transmission from farmed fish on species interactions or other ecosystem components. Coho salmon Oncorhynchus kisutch smolts are susceptible hosts to the parasitic salmon louse Lepeophtheirus salmonis as well as a primary predator of juvenile pink Oncorhynchus gorbuscha salmon, a major host species for lice.
2. We used a hierarchical model of stock-recruit dynamics to compare coho salmon population dynamics across a region that varies in salmon louse infestation of juvenile coho and their pink salmon prey.
3. During a period of recurring salmon louse infestations in a region of open net-pen salmon farms, coho salmon productivity (recruits per spawner at low spawner abundance) was depressed approximately sevenfold relative to unexposed populations. Alternate hypotheses for the observed difference in productivity, such as declines in coho prey, perturbations to freshwater habitat or stochasticity, are unlikely to explain this pattern.
4. Lice parasitizing juvenile coho salmon were likely to be trophically transmitted during predation on parasitized juvenile pink salmon as well as directly transmitted fromsalmon farms.
5. Synthesis and applications. The finding that species interactions may cause the effects of pathogen transmission from farmed to wild fish to propagate up a marine food web has important conservation implications: (i) the management of salmon aquaculture should consider and account for species interactions and the potential for these interactions to intensify pathogen transmission from farmed to wild fish, (ii) the ecosystem impact of louse transmission from farmed to wild salmon has likely to have been previously underestimated and (iii) comprehensive monitoring of wild salmon and their population dynamics in areas of intensive salmon aquaculture should be a priority to determine if open net-pen salmon aquaculture is ecologically sustainable.
Key-words: aquaculture, Pacific salmon, parasite, predator–prey, trophic transmission

 

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Can. J. Fish. Aquat. Sci. 61: 147–157 (2004) doi: 10.1139/F04-016 © 2004 NRC Canada

Sea lice (Lepeophtheirus salmonis) infection rates on juvenile pink (Oncorhynchus gorbuscha) andchum (Oncorhynchus keta) salmon in the nearshore marine environment of British Columbia, Canada
Alexandra Morton, Richard Routledge, Corey Peet, and Aleria Ladwig

Abstract: This study compared sea lice (Lepeophtheirus salmonis) infestation rates on juvenile pink (Oncorhynchus gorbuscha) and chum (Oncorhynchus keta) salmon in five nearshore areas of the British Columbia coast selected on the basis of proximity to salmon farms. A 10-week study in the Broughton Archipelago found sea lice were 8.8 times more abundant on wild fish near farms holding adult salmon and 5.0 times more abundant on wild fish near farms holding smolts than in areas distant from salmon farms. We found that 90% of juvenile pink and chum salmon sampled near salmon farms in the Broughton Archipelago were infected with more than 1.6 lice•(g host mass)–1, a proposed lethal limit when the lice reach mobile stages. Sea lice abundance was near zero in all areas without salmon farms. Salinity and temperature differences could not account for the higher infestation rates near the fish farms. The most immature life stages dominated the lice population throughout the study, suggesting the source of lice was a stationary, local salmonid population. No such wild population could be identified. The evidence from this control–impact study points to a relationship between salmon farms and sea lice on adjacent, wild, juvenile salmon.

 

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PATTERNS OF SEA LICE INFESTATIONS
ON SCOTTISH WEST COAST SEA TROUT:
SURVEY RESULTS, 1997 - 2000
September 2001
J.R.A. Butler
Wester Ross Fisheries Trust, The Harbour Centre, Gairloch, Wester Ross, IV21 2BQ
S. Marshall
West Sutherland Fisheries Trust, Gardener’s Cottage, Scourie, by Lairg, Sutherland, IV27 4SX
J. Watt
Lochaber & District Fisheries Trust, Arieniskill Cottage, Lochailort, Inverness-shire, PH38 4LZ
A. Kettlewhite, C. Bull
Argyll Fisheries Trust, Old Schoolhouse, Ardchonnel, Eredine, Dalmally, Argyll, PA33 1BU
M. Bilsby, H. Bilsby
Western Isles Fisheries Trust, Creed Lodge, Marybank, Stornoway, Isle of Lewis, HS2 9JN
J. Ribbens, C.A. Sinclair
West Galloway Fisheries Trust, Fisheries House, Station Industrial Estate, Newton Stuart, DG8 6ND
R.C. Stoddart, D.W.T. Crompton
Institute of Biomedical and Life Sciences, Graham Kerr Building, University of Glasgow, G12 8QQ

In response to the need for a collaborative approach to sea lice management between salmon farming and wild salmonid interests on the west coast of Scotland, the Association of West Coast Fisheries Trusts has initiated a monitoring programme of lice infestations on sea trout (Salmo trutta L.). Up to 17 river estuaries were sampled annually in June 1998-2000 to target premature-returning sea trout. Data from four of these sites were also collected in June 1997. This paper presents the results of the programme, and draws comparisons with previous surveys undertaken in 1991-1992, 1994 and 1996, and also with marine salmon farm production cycles. No fish were caught at the two sites outside the salmon farming zone, and therefore all data related to rivers £ 26 km from active salmon farms. Between 76% and 92% of fish were post-smolts, ranging from 10 cm to 35 cm fork length. Only Lepeophtheirus salmonis (Krøyer) were found. Infestations were characterised by localised epizootics and wide variation between sites sampled simultaneously, and within sites sampled in consecutive years. A maximum lice abundance of 187.4 was recorded at the Dundonnell River in June 2000, and the highest individual infestation was 500, recorded at the River Laxford in June 1998. Sites on the periphery of the salmon farming zone had generally low infestations, and an absence of prematurely-returning fish. Overall, the minimum proportion of fish infected with a potentially lethal level of ³ 30 lice was 37.4% in 1998, 13.5% in 1999 and 39.5% in 2000. Moribund, lice-infested post-smolts and older sea trout were found in the Rivers Ewe, Gruinard and Dundonnell. Lice stages on post-smolts were dominated by chalimus, while preadults were most common on older sea trout. Heavy settlements of chalimus caused tissue damage to dorsal fins. The results parallel those of previous surveys in western Scotland, and the characteristics of the lice epizootics mirror those identified in western Ireland and Norway. Time series of three or more years’ data at five rivers demonstrated that inter-year variations in infestations were related to salmon farm production cycles in the local hydrographic area. In areas of single year class production lice abundance fluctuated from low, background levels in the first spring of production (when ovigerous female lice were absent) to high levels in the second spring (when ovigerous lice were present). In areas of mixed year class production lice levels usually fluctuated above background levels, since one or other farm harboured ovigerous lice every spring. Aggregated data for six sites in 1998-2000 showed that abundance for mixed year class areas (89.2) was significantly higher than single year class areas (13.8). This was reflected by lice demography: in mixed year class areas lice stages were dominated by juveniles, but in single year class areas mobile lice were more common, reflecting a more stable population. There is some evidence that with the doubling of salmon farm production between 1994 and 2000 lice infestations on sea trout have intensified. Recommendations are made for the use of synchronised, single year class production to improve lice control on both farmed and wild salmonids.

 

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North American Journal of Fisheries Management 28:523–532, 2008
! Copyright by the American Fisheries Society 2008
DOI: 10.1577/M07-042.1

Sea Louse Infestation in Wild Juvenile Salmon and Pacific Herring Associated with Fish Farms off the East-Central Coast of Vancouver Island, British Columbia
ALEXANDRA MORTON
Raincoast Research Society, Simoom Sound, British Columbia V0P 1S0, Canada
RICK ROUTLEDGE
Department of Statistics and Actuarial Science, Simon Fraser University,
8888 University Drive, Burnaby, British Columbia V5A 1S6, Canada
MARTIN KRKOSˇ EK
Centre for Mathematical Biology, Department of Biological Sciences, 632 Central Academic Building,
University of Alberta, Edmonton, Alberta T6G 2G1, Canada

Abstract.—Reports of infestations of sea lice Lepeophtheirus salmonis and Caligus clemensi in juvenile salmonids in Pacific Canada have been restricted to pink salmon Oncorhynchus gorbuscha and chum salmon O. keta from one salmon-farming region, the Broughton Archipelago of British Columbia. Here, we report on 2 years of sea louse field surveys of wild juvenile pink and chum salmon, as well as wild sockeye salmon O. nerka and larval Pacific herring Clupea pallasii, in another salmon farming region, he Discovery Islands region of British Columbia. For pink and chum salmon we tested for the dependency of sea louse abundance on temperature, salinity, sampling period, host species, and farm exposure category. For both louse species, farm exposure was the only consistently significant predictor of sea lice abundance. Fish exposed to salmon farms were infected with more sea lice than those in the peripheral category. Sea louse abundance on sockeye salmon and Pacific herring followed the same trends, but sample sizes were too low to support formal statistical analysis. The Pacific herring were translucent and lacked scales, and they were primarily parasitized by C. clemensi. These results suggest that the association of salmon farms with sea lice infestations of wild juvenile fish in Pacific Canada now extends beyond juvenile pink and chum salmon in the Broughton Archipelago. Canada’s most abundant and economically valuable salmon populations, as well as British Columbia’s most valuable Pacific herring stock, migrate through the Discovery Islands; hence, parasite transmission from farm to wild fish in this region may have important economic and ecological implications.

 

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Aquaculture Research, 2001, 32, 947±962
Salmon lice infection of wild sea trout and Arctic char in marine and freshwaters: the effects of salmon farms
P A Bjùrn1, B Finstad2 & R Kristoffersen1
1The Norwegian College of Fishery Science. Breivika. N-9037 Tromsù, Norway
2The Norwegian Institute for Nature Research, Tungasletta 2, N-7485 Trondheim, Norway
Correspondence: P A Bjùrn, Norwegian Institute of Fisheries and Aquaculture, N-9291 Tromsù, Norway.
E-mail: paal-arne.bjorn@®skforsk.norut.no

Abstract
The abundance of salmon lice and the physiological effects of infection were examined in two stocks of sympatric sea trout and anadromous Arctic char in northern Norway. One stock feed in a coastal area with extensive salmon farming (exposed locality), while the other feed in a region with little farming activity (unexposed locality). The results showed that the lice infection was significantly higher at the exposed locality, at which the mean intensity of infection peaked in June and July at over 100 and 200 lice larvae per fish respectively. At the exposed locality we also observed a premature return to freshwater of the most heavily infected fish. Such behaviour has previously been interpreted as a response by the fish to reduce the stress caused by the infection and/or to enhance survival. Blood samples taken from sea trout at sea at the exposed locality showed a positive correlation between intensity of parasite infection and an increase in the plasma cortisol, chloride and blood glucose concentrations, while the correlations from sea trout in freshwater were more casual. Several indices pointed towards an excessive mortality of the heaviest infected fish, and 47% of the fish caught in freshwater and 32% of those captured at sea carried lice at intensities above the level that has been shown to induce mortality in laboratory experiments. Furthermore, almost half of all fish from the exposed locality had lice intensities that would probably cause osmoregulatory imbalance. High salmon lice infections may therefore have profound negative effects upon wild populations of sea trout. At the unexposed location, the infection intensities were low, and few fish carried more than 10 lice. These are probably within the normal range of natural infection and such intensities are not expected to affect the stock negatively.

 

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www.pnas.org cgi doi 10.1073 pnas.0603525103
15506–15510 # PNAS # October 17, 2006 # vol. 103 # no. 42
Epizootics of wild fish induced by farm fish
Martin Krkosˇek*†, Mark A. Lewis*, Alexandra Morton‡, L. Neil Frazer§, and John P. Volpe¶
*Centre for Mathematical Biology, Departments of Mathematical and Statistical Sciences and Biological Sciences, University of Alberta, Edmonton, AB,
Canada T6G 1G1; ‡Raincoast Research Society, Simoom Sound, BC, Canada V0P 1S0; §Department of Geology and Geophysics, School of Ocean and Earth
Science and Technology, University of Hawaii, 2525 Correa Road, Honolulu, HI 96822; and ¶School of Environmental Studies, University of Victoria,
3800 Finnerty Road, Victoria, BC, Canada V8P 5C2
Edited by Stephen R. Carpenter, University of Wisconsin, Madison, WI, and approved August 24, 2006 (received for review April 29, 2006)

The continuing decline of ocean fisheries and rise of global fish consumption has driven aquaculture growth by 10% annually over the last decade. The association of fish farms with disease emergence in sympatric wild fish stocks remains one of the most controversial and unresolved threats aquaculture poses to coastal ecosystems and fisheries. We report a comprehensive analysis of the spread and impact of farm-origin parasites on the survival of wild fish populations. We mathematically coupled extensive data sets of native parasitic sea lice (Lepeophtheirus salmonis) transmission and pathogenicity on migratory wild juvenile pink (Oncorhynchus gorbuscha) and chum (Oncorhynchus keta) salmon. Farm-origin lice induced 9–95% mortality in several sympatric wild juvenile pink and chum salmon populations. The epizootics arise through a mechanism that is new to our understanding of emerging infectious diseases: fish farms undermine a functional role of host migration in protecting juvenile hosts from parasites associated with adult hosts. Although the migratory life cycles of Pacific salmon naturally separate adults from juveniles, fish farms provide L. salmonis novel access to juvenile hosts, in this case raising infection rates for at least the first 2.5 months of the salmon’s marine life ( 80 km of the migration route). Spatial segregation between juveniles and adults is common among temperate marine fishes, and as aquaculture continues its rapid growth, this disease mechanism may challenge the sustainability of coastal ecosystems and economies.

 

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www.pnas.org cgi doi 10.1073 pnas.0607419103
PNAS October 17, 2006 vol. 103 no. 42 15277
Salmon-farming impacts on wild salmon
Ray Hilborn*
School of Aquatic and Fishery Sciences, University of Washington, Box 355020, Seattle, WA 98195

Concerns have been raised about the impact of farmed fish on wild fish through a range of mechanisms including disease and the impact of fish that escape from farms (1). Although Alaska has banned salmon farming and Washington has developed only a very small industry, British Columbia, with an extensive network of protected inlets, has developed a very large salmon-farming industry, now considerably bigger in terms of tons produced than the wild salmon production there. The salmonfarming industry is a significant and growing part of the local economy with the potential to grow to the scale that has occurred in Norway and Chile. In this issue of PNAS, Krkosˇek et al. (2) present data to show that migrating juvenile salmon are infected by sea lice as they pass salmon farms and that such sea lice infestations cause significant mortality. Their article provides support for those who oppose net-pen aquaculture of salmon within the range of wild hotspots of infection as wild salmon pass the farms. The three principal elements of the experimental method are replication, control, and randomization. From previous work (3), we now have replication of the basic observation that migrating juvenile salmon become infected with sea lice as they pass salmon farms. A better control would be to follow salmon down migration paths where there are no salmon farms; if the model of Krkosˇek et al. (2) is correct, there should be only background infection rates along such migratory corridors.

However, the concept of controls is inexorably tied into the issue of randomization of treatments. It seems unlikely that salmon farms are located randomly; rather, some sites in the inlets of British Columbia are probably better for salmon farms than others. If the habitats that are preferred for salmon farms are also habitats that contain naturally high sea lice concentrations, then the infection rates landward of salmon farms, and indeed migration corridors without any salmon farms, may not be appropriate controls. The obvious next step in understanding the impact of salmon farms on sea lice infection is to monitor wild populations migrating down corridors without salmon farms. Population-Level Impacts The bigger policy question is the population- level impact of salmon farms on the wild salmon in British Columbia.

More broadly, this impact would likely also occur in other countries such as Norway, Scotland, and Ireland that have both large salmon-farming operations and wild salmon. Beamish et al. (4) have shown that wild pink salmon in central British Columbia had an exceptionally high ocean survival rate in 2003 despite the presence of a large number of salmon farms in their migration corridor. They argue that this finding means that salmon farms and wild salmon can coexist without significant impact on the wild salmon. Krkosˇek et al. (2) make no specific claims or calculations regarding population-level impacts, but they state, ‘‘as aquaculture continues its rapid growth, this disease mechanism may challenge the sustainability of coastal ecosystems and economies.’’ The larger scale impacts of salmon farming on wild populations have not been answered by Krkosˇek et al. (2), but given the intensity of salmon farming in central British Columbia and the high infection and mortality rates they observed, their data would seem to support an important population-level impact.

The next step will be (i) to analyze the number of wild salmon migrating past salmon farms and the number that do not and (ii) to use the mortality estimates weighted by the proportion of the total wild populations that are exposed to salmon farms to estimate theoretical population- level impacts. These calculations would need to be reconciled with the observations in ref. 4. One possibility is that the mortality impact of sea- lice infestation depends on the condition of the juvenile salmon, which likely varies widely from year to year. Beamish et al. (4) showed that the survival of juvenile salmon migrating in 2003 was much higher than in other recent years. The mortality experiments of Krkosˇek et al. (2) were done in 2004 and 2005. Levin et al. (5) showed that the competitive impact of hatchery salmon on wild salmon was much stronger in years of poor ocean condition, which may be true for the impact of sea-lice infestation. The results of Levin et al. could potentially reconcile the conflicting observations of high mortality caused by sea lice in 2004 and 2005 and the very high survival rates of wild salmon juveniles in 2003.

There is little doubt that salmon netpen farming and other forms of net-pen aquaculture will continue to grow around the world. Political responses have been highly variable, ranging from outright banning to wholesale support. The article by Krkosˇek et al. (2) is an important step in providing better scientific information for such policy decisions.

 

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Effects of parasites from salmon farms on productivity of wild salmon
Martin Krkošeka,b,1, Brendan M. Connorsb,c, Alexandra Mortonb,d, Mark A. Lewise, Lawrence M. Dillc, and Ray Hilbornf
aDepartment of Zoology, University of Otago, Dunedin, New Zealand, 9016; bSalmon Coast Field Station, Simoom Sound, BC, Canada V0P 1S0; cEarth to Ocean
Research Group, Department of Biological Sciences, Simon Fraser University, Burnaby, BC, Canada V5A 1S6; dRaincoast Research Society, Simoom Sound,
BC, Canada V0P 1S0; eCentre for Mathematical Biology, Department of Mathematical and Statistical Sciences, Department of Biological Sciences, University of
Alberta, Edmonton, AB, Canada T6G 2G1; and fSchool of Aquatic and Fishery Sciences, University of Washington, Seattle, WA 98105
Edited by William C. Clark, Harvard University, Cambridge, MA, and approved July 27, 2011 (received for review February 2, 2011)

The ecological risks of salmon aquaculture have motivated changes to management and policy designed to protect wild salmon populations and habitats in several countries. In Canada, much attention has focused on outbreaks of parasitic copepods, sea lice (Lepeophtheirus salmonis), on farmed and wild salmon in the Broughton Archipelago, British Columbia. Several recent studies have reached contradictory conclusions on whether the spread of lice from salmon farms affects the productivity of sympatric wild salmon populations. We analyzed recently available sea lice data on farms and spawner–recruit data for pink (Oncorhynchus gorbuscha) and coho (Oncorhynchus kisutch) salmon populations in the Broughton Archipelago and nearby regions where farms are not present. Our results show that sea lice abundance on farms is negatively associated with productivity of both pink and coho salmon in the Broughton Archipelago. These results reconcile the contradictory findings of previous studies and suggest that management and policy measures designed to protect wild salmon from sea lice should yield conservation and fishery benefits.

 

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Proc. R. Soc. B (2009) 276, 3385–3394
doi:10.1098/rspb.2009.0771
Published online 8 July 2009

How sea lice from salmon farms may cause wild salmonid declines in Europe and North
America and be a threat to fishes elsewhere
Mark J. Costello*
Leigh Marine Laboratory, University of Auckland, PO Box 347, Warkworth, New Zealand

Fishes farmed in sea pens may become infested by parasites from wild fishes and in turn become point sources for parasites. Sea lice, copepods of the family Caligidae, are the best-studied example of this risk. Sea lice are the most significant parasitic pathogen in salmon farming in Europe and the Americas, are estimated to cost the world industry E300 million a year and may also be pathogenic to wild fishes under natural conditions. Epizootics, characteristically dominated by juvenile (copepodite and chalimus) stages, have repeatedly occurred on juvenile wild salmonids in areas where farms have sea lice infestations, but have not been recorded elsewhere. This paper synthesizes the literature, including modelling studies, to provide an understanding of how one species, the salmon louse, Lepeophtheirus salmonis, can infest wild salmonids from farm sources. Three-dimensional hydrographic models predicted the distribution of the planktonic salmon lice larvae best when they accounted for wind-driven surface currents and larval behaviour. Caligus species can also cause problems on farms and transfer from farms to wild fishes, and this genus is cosmopolitan. Sea lice thus threaten finfish farming worldwide, but with the possible exception of L. salmonis, their host relationships and transmission adaptations are unknown. The increasing evidence that lice from farms can be a significant cause of mortality on nearby wild fish populations provides an additional challenge to controlling lice on the farms and also raises conservation, economic and political issues about how to balance aquaculture and fisheries resource management.
Keywords: Caligus; Lepeophtheirus; trout; epizootics; aquaculture; ectoparasites

 

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Proc. R. Soc. B (2007) 274, 3141–3149
doi:10.1098/rspb.2007.1122
Published online 17 October 2007

Effects of host migration, diversity and aquaculture on sea lice threats to Pacific salmon populations
Martin Krkosˇek1,*, Allen Gottesfeld2, Bart Proctor3, Dave Rolston3,Charmaine Carr-Harris3 and Mark A. Lewis1

1Centre for Mathematical Biology, Departments of Mathematical and Statistical Sciences and Biological Sciences,
University of Alberta, Edmonton, Alberta, Canada T6G 2G1
2Skeena Fisheries Commission, Hazelton, British Columbia, Canada V0J 1Y0
3Oona River Resources Association, Oona River, British Columbia, Canada V0V 1E0

Animal migrations can affect disease dynamics. One consequence of migration common to marine fish and invertebrates is migratory allopatry—a period of spatial separation between adult and juvenile hosts, which is caused by host migration and which prevents parasite transmission from adult to juvenile hosts. We studied this characteristic for sea lice (Lepeophtheirus salmonis and Caligus clemensi ) and pink salmon (Oncorhynchus gorbuscha) from one of the Canada’s largest salmon stocks. Migratory allopatry protects juvenile salmon from L. salmonis for two to three months of early marine life (2–3% prevalence). In contrast, host diversity facilitates access for C. clemensi to juvenile salmon (8–20% prevalence) but infections appear ephemeral. Aquaculture can augment host abundance and diversity and increase parasite exposure of wild juvenile fish. An empirically parametrized model shows high sensitivity of salmon populations to increased L. salmonis exposure, predicting population collapse at one to five motile L. salmonis per juvenile pink salmon. These results characterize parasite threats of salmon aquaculture to wild salmon populations and show how host migration and diversity are important factors affecting parasite transmission in the oceans.
Keywords: migration; host diversity; parasite transmission; aquaculture; salmon; sea lice

 

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Proc. R. Soc. B (2009) 276, 2819–2828
doi:10.1098/rspb.2009.0317
Received 23 February 2009
Accepted 16 April 2009 2819 This journal is q 2009 The Royal Society
Published online 6 May 2009

Sea lice and salmon population dynamics: effects of exposure time for migratory fish
Martin Krkosˇek1,2,*, Alexandra Morton3, John P. Volpe4
and Mark A. Lewis1,2

1Centre for Mathematical Biology, Department of Mathematical and Statistical Sciences, and
2Department of Biological Sciences, University of Alberta, Edmonton, Alberta T6G 2R3, Canada
3Salmon Coast Field Station, Simoom Sound, British Columbia V0P 1S0, Canada
4School of Environmental Studies, University of Victoria, Victoria, British Columbia V8P 5C2, Canada

The ecological impact of parasite transmission from fish farms is probably mediated by the migration of wild fishes, which determines the period of exposure to parasites. For Pacific salmon and the parasitic sea louse, Lepeophtheirus salmonis, analysis of the exposure period may resolve conflicting observations of epizootic mortality in field studies and parasite rejection in experiments. This is because exposure periods can differ by 2–3 orders of magnitude, ranging from months in the field to hours in experiments. We developed a mathematical model of salmon–louse population dynamics, parametrized by a study that monitored naturally infected juvenile salmon held in ocean enclosures. Analysis of replicated trials indicates that lice suffer high mortality, particularly during pre-adult stages. The model suggests louse populations rapidly decline following brief exposure of juvenile salmon, similar to laboratory study designs and data. However, when the exposure period lasts for several weeks, as occurs when juvenile salmon migrate past salmon farms, the model predicts that lice accumulate to abundances that can elevate salmon mortality and depress salmon populations. The duration of parasite exposure is probably critical to salmon–louse population dynamics, and should therefore be accommodated in coastal planning and management where fish farms are situated on wild fish migration routes.
Keywords: salmon; sea lice; aquaculture; conservation; reservoir host; host–parasite dynamics

 

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Characteristics of the sea trout, Salmo trutta L., stocks from the Owengowla and Invermore Fisheries, Connemara, Western Ireland, and recent trends in marine survival.
Gargan, P. G., Roche, W. K., Forde, & G.P. Ferguson, A.

ABSTRACT
The Owengowla and Invermore sea trout fisheries, situated in Connemara, Western Ireland, have historically been important sea trout angling fisheries. Like other midwestern sea trout fisheries, both suffered a sea trout stock collapse in 1989. Upstream and downstream traps were installed on both fisheries and data on sea trout smolt and kelt runs, age and length frequency of migrants, and marine survival over the 1991 – 2003 period are presented. The trapping data indicates that substantial runs of sea trout smolts were derived from an extremely small spawning escapement of sea trout, implying that the freshwater trout stock contribute significantly to sea trout smolt runs in both systems. Exceptionally low sea trout finnock (0-sea winter) marine survival rates were recorded annually for the Owengowla fishery over a ten year period, with the exception of one year when prolonged whole-bay spring fallowing of marine salmon farms took place in Bertraghboy Bay, into which the Owengowla discharges. Wholebay spring fallowing did not take place in the neighbouring Kilkieran Bay, into which the Invermore enters, and annual sea trout finnock marine survival was consistently poor over this period. These data demonstrate that the practice of whole-bay spring fallowing of marine salmon farms has a positive effect on sea trout finnock marine survival in fisheries within such bays. The data also strongly supports the view that the sea trout stock collapse on Irelands west coast was contributed to by sea lice infestation from marine salmon farms.

 

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Proc. R. Soc. B (2005) 272, 689–696
doi:10.1098/rspb.2004.3027
Published online 1 April 2005

Transmission dynamics of parasitic sea lice from farm to wild salmon
Martin Krkosˇek1,2*, Mark A. Lewis1,2 and John P. Volpe2†
1Center for Mathematical Biology, Department of Mathematical and Statistical Sciences, and 2Department of Biological Sciences,
University of Alberta, Edmonton, Alberta, Canada T6G 2E7

Marine salmon farming has been correlated with parasitic sea lice infestations and concurrent declines of wild salmonids. Here, we report a quantitative analysis of how a single salmon farm altered the natural transmission dynamics of sea lice to juvenile Pacific salmon. We studied infections of sea lice (Lepeophtheirus salmonis and Caligus clemensi ) on juvenile pink salmon (Oncorhynchus gorbuscha) and chum salmon (Oncorhynchus keta) as they passed an isolated salmon farm during their seaward migration down two long and narrow corridors. Our calculations suggest the infection pressure imposed by the farm was four orders of magnitude greater than ambient levels, resulting in a maximum infection pressure near the farmthat was 73 times greater than ambient levels and exceeded ambient levels for 30 km along the two wild salmon migration corridors. The farm-produced cohort of lice parasitizing the wild juvenile hosts reached reproductive maturity and produced a second generation of lice that re-infected the juvenile salmon. This raises the infection pressure from the farm by an additional order of magnitude, with a composite infection pressure that exceeds ambient levels for 75 km of the two migration routes. Amplified sea lice infestations due to salmon farms are a potential limiting factor to wild salmonid conservation.
Keywords: salmon conservation; aquaculture; sea lice; reservoir host; macroparasite; emergent disease

 

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Biol. Lett. (2010) 6, 548–551
doi:10.1098/rsbl.2009.0872
Published online 17 February 2010

Temporal and spatial patterns of sea lice levels on sea trout in western Scotland in relation to fish farm production cycles
S. J. Middlemas1,*, J. A. Raffell2, D. W. Hay1,
M. Hatton-Ellis2 and J. D. Armstrong1
1Marine Scotland Science, Freshwater Laboratory, Faskally,
Pitlochry PH16 5LB, UK
2Marine Scotland Science, Shieldaig Field Station, Shieldaig,
Strathcarron IV54 8XJ, UK
*Author for correspondence (s.middlemas@marlab.ac.uk).

The relationship between aquaculture and infestations of sea lice on wild sea trout (Salmo trutta) populations is controversial. Although some authors have concluded that there is a link between aquaculture and lice burdens on wild fish, others have questioned this interpretation. Lice levels have been shown to be generally higher on Atlantic salmon farms during the second years of two-year production cycles. Here we investigate whether this pattern relates to lice burdens on wild fish across broad temporal and spatial axes. Within Loch Shieldaig across five successive farm cycles from 2000 to 2009, the percentage of sea trout with lice, and those above a critical level, were significantly higher in the second year of a two-year production cycle. These patterns were mirrored in 2002–2003 across the Scottish west coast. The results suggest a link between Atlantic salmon farms and sea lice burdens on sea trout in the West of Scotland.
Keywords: Lepeophtheirus; Salmo trutta; aquaculture

 

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Sea lice dispersion and salmon survival in relation to salmon farm activity in the Broughton Archipelago
Alexandra Morton1, Rick Routledge2, Amy McConnell3, and Martin Krkosˇek1,4*†
1Salmon Coast Field Station, Simoom Sound, BC, Canada
2Department of Statistics and Actuarial Science, Simon Fraser University, Burnaby, British Columbia, Canada
3Department of Biology, Simon Fraser University, Burnaby, British Columbia, Canada
4School of Aquatic and Fishery Sciences, University of Washington, Seattle, Washington, USA
*Corresponding Author: tel: +1 250 974 7177; fax: +1 206 685 7471; e-mail:mkrkosek@u.washington.edu.
†Present address: Department of Zoology, University of Otago, Dunedin, Otago, New Zealand.
Morton, A., Routledge, R., McConnell, A., and Krkosˇek, M. 2011. Sea lice dispersion and salmon survival in relation to salmon farm activity in the Broughton Archipelago. – ICES Journal of Marine Science, 68: 144–156.
Received 21 October 2009; accepted 3 August 2010; advance access publication 11 October 2010.

The risk of salmon lice (Lepeophtheirus salmonis) transmission to wild juvenile Pacific salmon has spurred management change to reduce lice on salmon farms. We studied the abundance of planktonic lice preceding the juvenile salmon outmigration as well as the abundance of lice on juvenile pink (Oncorhynchus gorbuscha) and chum (Oncorhynchus keta) salmon in two distinct migration routes, one containing only fallow farms and the other active farms that applied a parasiticide. Results indicate that fallowing reduces the abundance and flattens the spatial distribution of lice relative to that expected in areas without farms. Active farms remained the primary source of lice, but transmission was reduced 100-fold relative to previous epizootics in the study area. On the migration route containing active farms, 50% of the juvenile salmon showed evidence of louse damage to surface tissues and the estimated direct louse-induced mortality was ,10%, not including indirect effects of infection on predation risk or competition. The survival of the pink salmon cohort was not statistically different from a reference region without salmon farms. Although repeated use of a single parasiticide can lead to resistance, reducing louse transmission from farmed salmon may help conserve some wild Pacific salmon populations.
Keywords: aquaculture, conservation, salmon, sea lice.

Introduction
An increase in sea lice (Lepeophtheirus salmonis) infestations of wild juvenile pink (Oncorhynchus gorbuscha) and chum (Oncorhynchus keta) salmon above those typically observed in nature have been linked with salmon farms in Pacific Canada (Morton and Williams, 2003; Morton et al., 2004, 2008; Krkosˇek et al., 2005a, 2006). The infestations are associated with high mortality of wild juvenile salmon (Morton and Routledge, 2005; Krkosˇek et al., 2006) and depressed populations of wild salmon (Krkosˇek et al., 2007a; Ford and Myers, 2008). The sea louse is a native marine ectoparasitic copepod that commonly infects adult wild and farmed salmonids, feeding on host surface tissues and causing morbidity and mortality (Pike and Wadsworth, 2000; Costello, 2006). Although adult Pacific salmon are commonly infested (Nagasawa, 2001; Beamish et al., 2005), juvenile Pacific salmon tend to be protected from lice because they enter the ocean uninfested and are spatially separated from large adult salmon populations for the first 2–3 months of marine life (Krkosˇek et al., 2007b). Because lice are found on juvenile Pacific salmon at prevalences typically ,5% in areas without salmon farms, it is likely that the elevation—or bioamplification— of the numbers of sea lice by salmon farms leads to infestations (Krkosˇek, 2010). Lice have a direct life cycle, with non-infectious nauplii and infectious copepodites that disperse in the plankton, followed by a developmental progression of parasitic stages from copepodites, to chalimi, and then motiles. Motiles include adult lice that sexually reproduce on host fish, with females extruding eggstrings from which planktonic nauplii hatch. Transmission of lice among host fish and between wild and farmed salmon is predominantly via the planktonic stages as well as through motile lice, which can move among fish (Ritchie, 1997; Connors et al., 2008). The threat of sea-louse transmission to wild Pacific salmon is likely mediated by siting and management of farms as well as biotic and abiotic factors (Krkosˇek, 2010). Two possible management options to reduce louse exposure of wild juvenile salmon are removing salmon farms from wild salmon migration routes and treating farmed salmon with chemical therapeutants (Morton et al., 2005; Orr, 2007). In Canada, fallowing salmon farms during the juvenile outmigration is not practical yearly because farmed salmon require more than a year in the marine pens to reach harvest size. In one year, a British Columbia management plan that emptied salmon farms on one route was associated with reduced abundance of sea lice on juvenile pink and chum salmon in the Broughton Archipelago (Morton et al., 2005), and the cohort of juvenile pink salmon subjected to the fallow experienced exceptionally high marine survival (Beamish et al., 2006). As it is not practical to fallow farms every year during the salmon outmigration, there has been a movement towards the coordinated
# 2010 International Council for the Exploration of the Sea. Published by Oxford Journals. All rights reserved.
For Permissions, please email: journals.permissions@oxfordjournals.org

ICES Journal of Marine Science (2011), 68(1), 144–156. doi:10.1093/icesjms/fsq146

 

[agentaqua]

Pa°l Arne Bjørn and Bengt Finstad Bjørn, P. A., and Finstad, B. 2002. Salmon lice, Lepeophtheirus salmonis (Krøyer), infestation in sympatric populations of Arctic char, Salvelinus alpinus (L.), and sea trout, Salmo trutta (L.), in areas near and distant from salmon farms. – ICES Journal of Marine Science, 59: 131–139.

The abundance of salmon lice was examined in two stocks of sympatric anadromous Arctic char and sea trout in sub-Arctic regions in northern Norway in June, July, and August 1992 and 1993. One stock feeds in a coastal area exposed to moderate salmon farming activity (exposed area), while the other feed in a region without salmon farms (unexposed area). The salmon lice infestation on both species differed significantly between the exposed and unexposed area as well as between years and also between weeks within the same year. We did not detect, however, any clear significant differences in salmon lice abundance between sympatric populations of Arctic char and sea trout, or between different size groups of the species. The 1992 and 1993 infestation pattern in the exposed area showed an epidemic tendency in both Arctic char and sea trout, characterised by a sudden increase in both prevalence and abundance of lice larvae in July 1992 (23.6 25.7 lice/fish) and August 1993 (19.9 20.8 lice/fish). We therefore suggest that salmon lice epidemics, previously only observed on sea trout, may also occur in populations of Arctic char, and that fish farming contributes to the elevated lice level in wild fish. The fish in the unexposed area were also infested, although at significantly lower levels than fish from the exposed area. The infestation peaked in August 1992 at 13.0 18.1 lice/fish and August 1993 at 3.9 4.5 lice/fish, suggested that lice originating on ascending wild Atlantic salmon, or lice larvae drifting from farming areas, may infest Arctic char and sea trout also in unexposed localities in Subarctic areas.
2002 International Council for the Exploration of the Sea
Keywords: Arctic char, fish farming, salmon lice, sea trout, Subarctic regions.
Received 24 January 2000; accepted 19 September 2001.

 

[agentaqua]

So - there's 33 peer-reviewed studies from all over the globe - indicating an impact of farm-origin lice on adjacent salmonids. I don't see your published rebuttals to any of them CK - except that you don't personally like the authors because they part their hair on the wrong side, or their uncle is an American...

 

[ClayoquotKid]

Every single one of the papers cited has a fatal flaw - Without knowing the values of all the other impacts and factors involved in the survival of wild salmon you can never put one on the theorized impact of aquaculture.

Peer-reviewed speculation.

Could, Might, May - None of those ever show a DOES.

I'm sure this is where the tobacco industry comparison will come in, as every time it is pointed out that there is no instance of an impact being measured, it is always used to deflect away from that fact.

Populations of wild salmon go up and down, regardless of the presence of aquaculture, and so far every paper theorizing impacts from it has had to ignore the ups in order to explain the downs.

I'm pretty sure I have never claimed zero impact on wild stocks from salmon aquaculture, but what I have said is that since it has not been able to be measured - it must be small.

Put into context, it would likely pale in comparision to known impacts. (And BTW, putting something into context is not "deflection" - it is rational thought.)

Dragging in every other reason you don't like something after you've failed to realistic show support for one is, well.... I wish I had that hairbrush waving kid GIF to put up, because IMO it is perfect.

You guys can prop up your views with whatever you like, but don't expect the rest of us to share them, or see it the same way.

There are plenty of aquaculture workers who share the same passion for wild salmon, the companies themselves support enhancement and there are lots of people out there working hard to ensure that their day-to-day jobs aren't negatively impacting the things that make their lives on the coast so great.

I'm not about to "take my ball and go home" because of a few anonymous posters on here, and net-pen aquaculture is not about to leave the coast either.

Everything people do has impacts, and quite honestly I find the objections of some of the sportfishing community towards aquaculture ridiculously hypocritical and, at times, absurd.

 

[fogged in]

Every single one of the papers cited has a fatal flaw - Without knowing the values of all the other impacts and factors involved in the survival of wild salmon you can never put one on the theorized impact of aquaculture.

Peer-reviewed speculation.

Could, Might, May - None of those ever show a DOES.

I'm sure this is where the tobacco industry comparison will come in, as every time it is pointed out that there is no instance of an impact being measured, it is always used to deflect away from that fact.

Populations of wild salmon go up and down, regardless of the presence of aquaculture, and so far every paper theorizing impacts from it has had to ignore the ups in order to explain the downs.

I'm pretty sure I have never claimed zero impact on wild stocks from salmon aquaculture, but what I have said is that since it has not been able to be measured - it must be small.

Put into context, it would likely pale in comparision to known impacts. (And BTW, putting something into context is not "deflection" - it is rational thought.)

Dragging in every other reason you don't like something after you've failed to realistic show support for one is, well.... I wish I had that hairbrush waving kid GIF to put up, because IMO it is perfect.

You guys can prop up your views with whatever you like, but don't expect the rest of us to share them, or see it the same way.

There are plenty of aquaculture workers who share the same passion for wild salmon, the companies themselves support enhancement and there are lots of people out there working hard to ensure that their day-to-day jobs aren't negatively impacting the things that make their lives on the coast so great.

I'm not about to "take my ball and go home" because of a few anonymous posters on here, and net-pen aquaculture is not about to leave the coast either.

Everything people do has impacts, and quite honestly I find the objections of some of the sportfishing community towards aquaculture ridiculously hypocritical and, at times, absurd.

I think you are off topic Kid
"Canadian Tax Dollars going to good use...fish farm bailouts... "
Why don't you start your own thread?
You could call it
"Why I love fish farms" and see how many posts you get.

 

[ClayoquotKid]

So - there's 33 peer-reviewed studies from all over the globe - indicating an impact of farm-origin lice on adjacent salmonids. I don't see your published rebuttals to any of them CK - except that you don't personally like the authors because they part their hair on the wrong side, or their uncle is an American...

You're really getting a workout today 'Aqua.

So, how is all the work done by Morton and Krkosek actually playing out in the Broughton?