Journal articles: 'Sea lice; Salmon farms'

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Morton, Alexandra, Richard Routledge, Corey Peet, and Aleria Ladwig. "Sea lice (Lepeophtheirus salmonis) infection rates on juvenile pink (Oncorhynchus gorbuscha) and chum (Oncorhynchus keta) salmon in the nearshore marine environment of British Columbia, Canada." Canadian Journal of Fisheries and Aquatic Sciences 61, no. 2 (February 1, 2004): 147–57. http://dx.doi.org/10.1139/f04-016.

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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 controlimpact study points to a relationship between salmon farms and sea lice on adjacent, wild, juvenile salmon.

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Middlemas, S. J., J. A. Raffell, D. W. Hay, M. Hatton-Ellis, and J. D. Armstrong. "Temporal and spatial patterns of sea lice levels on sea trout in western Scotland in relation to fish farm production cycles." Biology Letters 6, no. 4 (February 17, 2010): 548–51. http://dx.doi.org/10.1098/rsbl.2009.0872.

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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.

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Morton, Alexandra B., and Rob Williams. "First Report of a Sea Louse, Lepeophtheirus salmonis, Infestation on Juvenile Pink Salmon, Oncorhynchus gorbuscha, in Nearshore Habitat." Canadian Field-Naturalist 117, no. 4 (October 1, 2003): 634. http://dx.doi.org/10.22621/cfn.v117i4.834.

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High infestation rates of the Sea Louse (Lepeophtheirus salmonis) have been reported on juvenile salmonids in Europe since 1989; however, this species has not been reported on juvenile Pacific salmonids until now. Magnitude of Sea Lice infestation was examined in 2001 on juvenile Pink Salmon (Oncorhynchus gorbuscha) migrating through a British Columbia archipelago. On average, the 751 juvenile Pink Salmon sampled weighed 2.25 g (± 0.039 SE), were infected with 11.3 (± 0.41 SE) Sea Lice per fish and 6.1 (± 0.24SE) Sea Lice per gram host weight. Fully 75.0% of fish were infected at loads equivalent to or higher than the lethal limit reported for much larger Sea Trout (Salmo trutta) post-smolts. Abundance (Kruskal-Wallis statistic = 100.95, p<0.0001) and intensity (KW= 70.05, p<0.0001) of lice, and mean number of lice/g host weight (K-W= 112.23, p<0.0001) were significantly higher in juvenile Pink Salmon in close proximity to salmon farms, than in Pink Salmon distant from salmon farms.

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Morton, Alexandra, Rick Routledge, Amy McConnell, and Martin Krkošek. "Sea lice dispersion and salmon survival in relation to salmon farm activity in the Broughton Archipelago." ICES Journal of Marine Science 68, no. 1 (October 11, 2010): 144–56. http://dx.doi.org/10.1093/icesjms/fsq146.

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Abstract Morton, A., Routledge, R., McConnell, A., and Krkošek, 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. 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.

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Peacock, Stephanie J., Martin Krkošek, Andrew W. Bateman, and Mark A. Lewis. "Estimation of spatiotemporal transmission dynamics and analysis of management scenarios for sea lice of farmed and wild salmon." Canadian Journal of Fisheries and Aquatic Sciences 77, no. 1 (January 2020): 55–68. http://dx.doi.org/10.1139/cjfas-2019-0036.

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Parasite transmission between farmed and wild salmon affects the sustainability of salmon aquaculture in Pacific Canada. Understanding and managing parasites in aquaculture is challenged by spatial and temporal variation in transmission dynamics. We developed a mechanistic model that connects sea louse (Lepeoptheirus salmonis) outbreak and control on farmed salmon (Salmo salar) to spatiotemporal dynamics of sea lice on migrating wild juvenile salmon (Oncorhynchus keta and Oncorhynchus gorbuscha). We fitted the model to time series of sea lice on farmed salmon and spatial surveys of juvenile wild salmon in the Broughton Archipelago. We used the parameterized model to evaluate alternative management scenarios based on the resulting sea louse infestations and predicted mortality of wild salmon. Early and coordinated management of sea lice on salmon farms was most effective for controlling outbreaks in wild salmon, while uncoordinated treatments led to a resurgence of sea lice on salmon farms during the juvenile salmon migration. This study highlights the importance of incorporating spatiotemporal variability when considering infectious disease dynamics shared by farmed and wild hosts, particularly when migratory wildlife are involved.

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Vollset, Knut Wiik, Elina Halttunen, Bengt Finstad, Ørjan Karlsen, Pål Arne Bjørn, and Ian Dohoo. "Salmon lice infestations on sea trout predicts infestations on migrating salmon post-smolts." ICES Journal of Marine Science 74, no. 9 (June 1, 2017): 2354–63. http://dx.doi.org/10.1093/icesjms/fsx090.

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Abstract Impacts of sea lice (Lepeophtheirus salmonis or Caligus spp.) on wild salmonids is currently one of the most important issues facing management of fish farms in salmon producing countries in the northern hemisphere. Surveillance of sea lice on wild Atlantic salmon (Salmo salar) is often hampered by the ability to catch enough migrating post-smolts. Therefore, sea lice abundance on anadromous trout (Salmo trutta) is often used to infer sea lice abundance on migrating salmon post-smolt. However, the assumption that there is a relationship between the abundance of lice on salmon and trout has never been tested. Here we use a dataset of sea lice on salmon post-smolt and sea trout that have been caught simultaneously in trawl hauls, to evaluate the correlation in abundance of sea lice between the two species using various statistical models. We demonstrate that trout generally has higher abundances of sea lice than salmon. Average lice per gram fish on sea trout (log transformed) predicted the abundance of lice on salmon best. Negative binomial models of lice counts were preferable to using trout lice counts as direct estimates of salmon lice abundance, and they had better predictive ability than logit models of high (vs. low) lice counts. Including the size of the salmon increased the predictive ability of the model, but these data are not generally available. The effect of salmon weight may have been a direct effect of body size, or an indirect effect of time spent in marine waters. Finally, we predict lower salmon lice counts on migrating salmon with our selected binomial model than with the current method of using trout lice counts as a direct estimator on salmon lice counts, and demonstrate that management advice would change considerably depending on the chosen method.

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Price, M. H. H., A. Morton, and J. D. Reynolds. "Evidence of farm-induced parasite infestations on wild juvenile salmon in multiple regions of coastal British Columbia, Canada." Canadian Journal of Fisheries and Aquatic Sciences 67, no. 12 (December 2010): 1925–32. http://dx.doi.org/10.1139/f10-105.

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Salmon farms are spatially concentrated reservoirs of fish host populations that can disrupt natural salmonid host–parasite dynamics. Sea lice frequently infect farm salmon and parasitize sympatric wild juvenile salmonids, with negative impacts on survival in Europe and Pacific Canada. We examined louse parasitism of wild juvenile chum salmon ( Oncorhynchus keta ) and pink salmon ( Oncorhynchus gorbuscha ) from three salmon farming regions in British Columbia (Finlayson, Broughton Archipelago, and Georgia Strait). We compared sites of low and high exposure to farms and included an area without farms (Bella Bella) to assess baseline infection levels. Louse prevalence and abundance were lowest and most similar to natural baseline levels at low-exposure sites and highest at high-exposure sites in all farm regions. A significantly greater proportion of the lice were Lepeophtheirus salmonis at high-exposure sites. Exposure to salmon farms was the only consistently significant factor to explain the variation in prevalence data, with a secondary role played by salinity. Our results support the hypothesis that salmon farms are a major source of sea lice on juvenile wild salmon in salmon farming regions and underscore the importance of using management techniques that mitigate threats to wild stocks.

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Krkošek, Martin, and Ray Hilborn. "Sea lice (Lepeophtheirus salmonis) infestations and the productivity of pink salmon (Oncorhynchus gorbuscha) in the Broughton Archipelago, British Columbia, Canada." Canadian Journal of Fisheries and Aquatic Sciences 68, no. 1 (January 2011): 17–29. http://dx.doi.org/10.1139/f10-137.

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The spread of salmon lice ( Lepeophtheirus salmonis ) from salmon farms may threaten some wild salmon populations. Infestations of wild juvenile pink salmon ( Oncorhynchus gorbuscha ) have been associated with high mortality and population decline. Using stock–recruit data for pink salmon from the central coast of British Columbia, we analyzed how fishing mortality and spatial covariation combine with louse infestation to affect pink salmon population dynamics. The results indicate substantial coherence in survival at nested spatial scales — large-scale regional covariation and smaller scale covariation within management areas. Populations exposed to salmon farms (those from the Broughton Archipelago) show a sharp decline in productivity during sea lice infestations relative to pre-infestation years. Unexposed populations (comprising four management areas) did not experience a change in productivity during infestation years and had similar productivity to exposed populations before infestations. Our results suggest that sea lice infestations may result in declines of pink salmon populations and that management and policy of salmon farms should consider protecting wild juvenile salmon from exposure to sea lice.

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Riddell, Brian E., Richard J. Beamish, Laura J. Richards, and John R. Candy. "Comment on "Declining Wild Salmon Populations in Relation to Parasites from Farm Salmon"." Science 322, no. 5909 (December 19, 2008): 1790.2–1790. http://dx.doi.org/10.1126/science.1156341.

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Krkošek et al. (Reports, 14 December 2007, p. 1772) claimed that sea lice spread from salmon farms placed wild pink salmon populations “on a trajectory toward rapid local extinction.” Their prediction is inconsistent with observed pink salmon returns and overstates the risks from sea lice and salmon farming.

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Shinn, A. P., B. A. Banks, N. Tange, J. E. Bron, C. Sommerville, T. Aoki, and R. Wootten. "Utility of 18S rDNA and ITS sequences as population markers for Lepeophtheirus salmonis (Copepoda: Caligidae) parasitising Atlantic salmon (Salmo salar) in Scotland." Contributions to Zoology 69, no. 1-2 (2000): 89–98. http://dx.doi.org/10.1163/18759866-0690102010.

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Genetic differentiation within the salmon louse Lepeophtheirus salmonis (Krøyer, 1837), was investigated by the sequencing of specific nucleotide regions. Partial sequences of the 18S ribosomal RNA gene and the ribosomal internal transcribed spacer (ITS-1) region from single sea lice were amplified by the polymerase chain reaction (PCR). Lice were collected from wild and farmed Atlantic salmon (Salmo salar L., 1758) from nine selected localities around the Scottish coastline. A 0.9kb fragment of the 18S ribosomal RNA gene was amplified and compared for several samples of lice which showed no observable differences between the lice from different collection sites confirming the absence of cryptic species. The 454 nucleotide ITS-1 sequence showed differences between derived sequences from 13 sea lice samples from 4 collection sites which included 2 farm sites and 2 sites where lice were taken from wild fish. Across all samples, there was a 92.14% similarity in the ITS-1 sequence. The percentage similarity in the ITS-1 sequence in samples office from two fish farms were 99.71% (site A) and 95.72% (site D) but only 86.90% (site B) and 86.03% (site C) similarity was shown in lice samples taken from sites where wild salmonids were caught. The greater similarity between the ITS-1 sequence within farm sites may be attributed to a restricted gene flow within lice populations in Atlantic salmon cage sites.

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Cantrell, Danielle, Ramón Filgueira, Crawford W. Revie, Erin E. Rees, Raphael Vanderstichel, Ming Guo, Michael G. G. Foreman, Di Wan, and Jon Grant. "The relevance of larval biology on spatiotemporal patterns of pathogen connectivity among open-marine salmon farms." Canadian Journal of Fisheries and Aquatic Sciences 77, no. 3 (March 2020): 505–19. http://dx.doi.org/10.1139/cjfas-2019-0040.

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Warming waters are changing marine pathogen dispersal patterns and infectivity worldwide. Coupled biological–physical modelling has been used in many systems to determine the connectivity of metapopulations via infectious disease particles. Here we model the connectivity of sea lice larvae (Lepeophtheirus salmonis) among salmon farms in the Broughton Archipelago, British Columbia, Canada, using a coupled biological–physical model. The physical model simulated pathogen dispersal, while the biological component influenced the survival and developmental rates of the sea lice. Model results predicted high temporal variability in connectivity strength among farms, an emergent effect from the interacting parts of the simulation (dispersion versus survival and development). Drivers of temporal variability were disentangled using generalized additive modeling, which revealed the variability was most strongly impacted by the spring freshet, which can act as a natural aid for sea lice control in the Broughton Archipelago. Our results suggest that farm management strategies can benefit by accounting for short-term spikes in regional pathogen connectivity among farms. Additionally, future scenarios of a warming climate with reduced snowpack can make sea lice control more challenging.

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Contreras, Marinela, Marius Karlsen, Margarita Villar, Rolf Olsen, Lisa Leknes, Anette Furevik, Karine Yttredal, et al. "Vaccination with Ectoparasite Proteins Involved in Midgut Function and Blood Digestion Reduces Salmon Louse Infestations." Vaccines 8, no. 1 (January 19, 2020): 32. http://dx.doi.org/10.3390/vaccines8010032.

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Infestation with the salmon louse Lepeophtheirus salmonis (Copepoda, Caligidae) affects Atlantic salmon (Salmo salar L.) production in European aquaculture. Furthermore, high levels of salmon lice in farms significantly increase challenge pressure against wild salmon populations. Currently, available control methods for salmon louse have limitations, and vaccination appears as an attractive, environmentally sound strategy. In this study, we addressed one of the main limitations for vaccine development, the identification of candidate protective antigens. Based on recent advances in tick vaccine research, herein, we targeted the salmon louse midgut function and blood digestion for the identification of candidate target proteins for the control of ectoparasite infestations. The results of this translational approach resulted in the identification and subsequent evaluation of the new candidate protective antigens, putative Toll-like receptor 6 (P30), and potassium chloride, and amino acid transporter (P33). Vaccination with these antigens provided protection in Atlantic salmon by reducing adult female (P33) or chalimus II (P30) sea lice infestations. These results support the development of vaccines for the control of sea lice infestations.

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Connors, B. M., M. Krkošek, and L. M. Dill. "Sea lice escape predation on their host." Biology Letters 4, no. 5 (June 17, 2008): 455–57. http://dx.doi.org/10.1098/rsbl.2008.0276.

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Parasites seldom have predators but often fall victim to those of their hosts. How parasites respond to host predation can have important consequences for both hosts and parasites, though empirical investigations are rare. The exposure of wild juvenile salmon to sea lice ( Lepeophtheirus salmonis ) from salmon farms allowed us to study a novel ecological interaction: the response of sea lice to predation on their juvenile pink and chum salmon hosts by two salmonid predators—coho smolts and cut-throat trout. In approximately 70% of trials in which a predator consumed a parasitized prey, lice escaped predation by swimming or moving directly onto the predator. This trophic transmission is strongly male biased, probably because behaviour and morphology constrain female movement and transmission. These findings highlight the potential for sea lice to be transmitted up marine food webs in areas of intensive salmon aquaculture, with implications for louse population dynamics and predatory salmonid health.

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Gargan, Patrick, Egil Karlsbakk, John Coyne, Carys Davies, and William Roche. "Sea lice (Lepeophtheirus salmonis and Caligus elongatus) infestation levels on sea trout (Salmo trutta L.) around the Irish Sea, an area without salmon aquaculture." ICES Journal of Marine Science 73, no. 9 (April 1, 2016): 2395–407. http://dx.doi.org/10.1093/icesjms/fsw044.

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Abstract Sea trout are parasitized by two species of caligid copepod sea lice, Lepeophtheirus salmonis and Caligus elongatus. Generally, levels of lice infestation are low and few adverse effects on the host have been reported. However, with the advent of marine salmon farming since the 1980s, there have been many published accounts of L. salmonis sea lice epizootics on salmonids in aquaculture areas. Few large-scale studies are available on levels of sea lice infestation of sea trout in areas without salmon farms or before their development. Understanding natural background lice levels on sea trout is important to interpret lice levels on trout in aquaculture areas. The Celtic Sea Trout Project, an INTERREG IVA Ireland Wales EU funded project, examined the status, distribution, genetics, and ecology of sea trout around the Irish Sea and provided an opportunity to assess levels of lice on sea trout spatially and temporally in an area without marine salmon farming. The prevalence of L. salmonis remained constant over the 3 years (63–69%), whereas the prevalence of C. elongatus was lower (20–40%). The mean abundance of L. salmonis ranged from 3.6 to 3.8 and that of C. elongatus ranged from 0.6 to 4.3 (n = 850). There was a significant variation in L. salmonis abundance between marine areas. However, the relative stability in the prevalence and mean intensity of both lice species observed and the low mean abundances and very small proportion of juvenile life stages of L. salmonis reported here are similar to those reported from other studies in areas without salmon farming and likely represent natural background salmon lice levels on sea trout. This 3-year study, conducted over a wide geographic area, represents one of the largest studies of sea lice infestation patterns on sea trout in an area distant from finfish aquaculture influences.

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Stige, LC, KO Helgesen, H. Viljugrein, and L. Qviller. "A statistical mechanistic approach including temperature and salinity effects to improve salmon lice modelling of infestation pressure." Aquaculture Environment Interactions 13 (August 26, 2021): 339–61. http://dx.doi.org/10.3354/aei00410.

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Salmon lice Lepeophtheirus salmonis pose a major threat to the sustainable development of salmonid farming. To investigate effects of farm-origin salmon lice on wild salmonids, salmon lice dynamics are typically simulated using models that depend on experimentally determined rates of development, reproduction, mortality and infestation. Several recent studies provide new estimates of how these demographic rates depend on temperature and salinity. Here, we review and synthesize these studies and test if updating a salmon lice infestation model based on the new insights improves predictions of salmon lice infestations on salmon post-smolts in experimental cages in the sea. This model predicts spatiotemporal variation in infestation pressure based on weekly monitoring data of salmon lice and sea temperature in all salmonid fish farms in Norway, here supplemented by temperature and salinity data from a regional ocean model. Using data from 2012-2017 to select model formulation, we found the largest improvement in explanatory power by incorporating a salinity-dependent infestation rate. Updating functions for temperature-dependent egg production and infestation rates led to smaller improvements. Moreover, results suggest additional effects of temperature and a possible temperature-salinity interaction effect, not captured by the modelled processes. Out-of-sample predictions for experimental cage data from 2018-2020 confirmed that the uncertainty was realistically quantified, but also showed that associations of salmon lice infestations with salinity and temperature had changed. These results provide a field evaluation of experimental data and point to a knowledge gap regarding the combined effects of temperature and salinity on salmon lice infestations.

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Bron, J. E., and J. W. Treasurer. "Sea lice (Caligidae) on wrasse (Labridae) from selected British wild and salmon-farm sources." Journal of the Marine Biological Association of the United Kingdom 72, no. 3 (August 1992): 645–50. http://dx.doi.org/10.1017/s0025315400059415.

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The occurrence and intensity of infection of caligid species on the five species of wrasse commonly found in British waters are reported from twelve localities in the British Isles and from seven fish-farms in Scotland where wrasse are used to remove sea lice from salmon (Salmo salar L.). A low prevalence of infection was recorded for all wrasse species except ballan. Chalimus of Caligus centrodonti Baird were identified from fins of ballan, rock cook and goldsinny wrasse, this being the first host record for the latter two species. Single chalimus stages of Caligus elongatus Nordmann were identified from a ballan wrasse and a goldsinny wrasse and are similarly first records from these host species. No C. centrodonti were found on farmed salmon and conversely no Lepeophtheirus salmonis (Krøyer) were identified from wrasse kept in contact with infected salmon. This suggests that transfer of caligids between wrasse and salmon and vice versa does not pose problems for fish health on sea-farms.

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Gentry, K., S. Bui, F. Oppedal, and T. Dempster. "Sea lice prevention strategies affect cleaner fish delousing efficacy in commercial Atlantic salmon sea cages." Aquaculture Environment Interactions 12 (February 27, 2020): 67–80. http://dx.doi.org/10.3354/aei00348.

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Over the last 2 decades, cleaner fishes have been employed to remove external sea lice parasites from Atlantic salmon Salmo salar in sea cages. Norway, Scotland, Ireland, and the Faroe Islands combined now use ~60 million cleaner fish per year. While small-scale experiments demonstrate the efficacy of cleaner fishes, industrial-scale sea cages have multiple structures and conditions that create different environments, which may impact cleaner fish efficacy and welfare. Here, in commercial sea cages, we investigated if 4 different anti-lice strategies impacted the delousing efficacy, physical condition, and behaviour of cleaner fish (corkwing wrasse Symphodus melops). The strategies tested were: (1) cleaner fishes only; (2) cleaner fishes and functional feed; (3) cleaner fishes, functional feed, and deep lights and feeding; and (4) cleaner fishes, functional feed, deep lights and feeding, and lice skirts. Corkwing wrasse were sampled from 3 cage-level replicates of each anti-lice strategy 3 times over 2 mo. Lice levels on salmon were recorded every 3 to 4 wk. Only 11% of corkwing wrasse had salmon lice in their gut, with individual wrasse having up to 72 lice in their stomach. Wrasse in cages encircled by lice skirts consumed one-ninth as many lice as those in other anti-lice treatments and had less overall impact on the number of lice per salmon. Fin, skin, mouth and eye condition, K factor, and observed cleaning behaviours of corkwing wrasse were similar across all anti-lice strategies. Our results demonstrate that different in-cage anti-lice strategies altered the magnitude of lice consumption in corkwing wrasse at this site and for this production period. Moreover, while a small proportion of corkwing wrasse appear to target lice as prey, most individual corkwing wrasse were ineffective biological control agents in a full-scale farm setting.

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Groner, Maya L., Luke A. Rogers, Andrew W. Bateman, Brendan M. Connors, L. Neil Frazer, Sean C. Godwin, Martin Krkošek, et al. "Lessons from sea louse and salmon epidemiology." Philosophical Transactions of the Royal Society B: Biological Sciences 371, no. 1689 (March 5, 2016): 20150203. http://dx.doi.org/10.1098/rstb.2015.0203.

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Effective disease management can benefit from mathematical models that identify drivers of epidemiological change and guide decision-making. This is well illustrated in the host–parasite system of sea lice and salmon, which has been modelled extensively due to the economic costs associated with sea louse infections on salmon farms and the conservation concerns associated with sea louse infections on wild salmon. Consequently, a rich modelling literature devoted to sea louse and salmon epidemiology has been developed. We provide a synthesis of the mathematical and statistical models that have been used to study the epidemiology of sea lice and salmon. These studies span both conceptual and tactical models to quantify the effects of infections on host populations and communities, describe and predict patterns of transmission and dispersal, and guide evidence-based management of wild and farmed salmon. As aquaculture production continues to increase, advances made in modelling sea louse and salmon epidemiology should inform the sustainable management of marine resources.

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Morton, Alexandra, and Rob Williams. "Response of the Sea Louse Lepeophtheirus salmonis Infestation Levels on Juvenile Wild Pink, Oncorhynchus gorbuscha, and Chum, O. keta, Salmon to Arrival of Parasitized Wild Adult Pink Salmon." Canadian Field-Naturalist 120, no. 2 (April 1, 2006): 199. http://dx.doi.org/10.22621/cfn.v120i2.288.

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Recent recurring infestations of Sea Lice, Lepeophtheirus salmonis, on juvenile Pacific salmon (Oncorhynchus spp.) and subsequent annual declines of these stocks have made it imperative to identify the source of Sea Lice. While several studies now identify farm salmon populations as sources of Sea Louse larvae, it is unclear to what extent wild salmonid hosts also contribute Sea Lice. We measured Sea Louse numbers on adult Pink Salmon (Oncorhynchus gorbuscha) migrating inshore. We also measured Sea Louse numbers on wild juvenile Pink and Chum salmon (Oncorhynchus keta) migrating to sea before the adults returned, and as the two age cohorts mingled. Adult Pink Salmon carried an average of 9.89 (SE 0.90) gravid lice per fish, and thus were capable of infecting the adjacent juveniles. Salinity and temperature remained favourable to Sea Louse reproduction throughout the study. However, all accepted measures of Sea Louse infestation failed to show significant increase on the juvenile salmon, either in overall abundance of Sea Lice or of the initial infective-stage juvenile lice, while the adult wild salmon were present in the study area. This study suggests that even during periods of peak interaction, wild adult salmon are not the primary source of the recent and unprecedented infestations of Sea Lice on juvenile Pacific Pink and Chum salmon in the inshore waters of British Columbia.

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Kristoffersen, A. B., E. E. Rees, H. Stryhn, R. Ibarra, J. L. Campisto, C. W. Revie, and S. St-Hilaire. "Understanding sources of sea lice for salmon farms in Chile." Preventive Veterinary Medicine 111, no. 1-2 (August 2013): 165–75. http://dx.doi.org/10.1016/j.prevetmed.2013.03.015.

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Heuch, Peter A., George Gettinby, and Crawford W. Revie. "Counting sea lice on Atlantic salmon farms — Empirical and theoretical observations." Aquaculture 320, no. 3-4 (November 2011): 149–53. http://dx.doi.org/10.1016/j.aquaculture.2011.05.002.

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Harvey, A. C., M. Quintela, K. A. Glover, Ø. Karlsen, R. Nilsen, Ø. Skaala, H. Sægrov, S. Kålås, S. Knutar, and V. Wennevik. "Inferring Atlantic salmon post-smolt migration patterns using genetic assignment." Royal Society Open Science 6, no. 10 (October 2019): 190426. http://dx.doi.org/10.1098/rsos.190426.

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Understanding migratory patterns is important for predicting and mitigating unwanted consequences of environmental change or anthropogenic challenges on vulnerable species. Wild Atlantic salmon undergo challenging migrations between freshwater and marine environments, and the numbers of salmon returning to their natal rivers to reproduce have declined over several decades. Mortality from sea lice linked to fish farms within their seaward migration routes is proposed as a contributing factor to these declines. Here, we used 31 microsatellite markers to establish a genetic baseline for the main rivers in the Hardangerfjord, western Norway. Mixed stock analysis was used to assign Atlantic salmon post-smolts caught in trawls in 2013–2017 back to regional reporting units. Analyses demonstrated that individuals originating from rivers located in the inner region of the fjord arrived at the outer fjord later than individuals from middle and outer fjord rivers. Therefore, as post-smolts originating from inner rivers also have to migrate longer distances to exit the fjord, these data suggest that inner fjord populations are more likely to be at risk of mortality through aquaculture-produced sea lice, and other natural factors such as predation, than middle or outer fjord populations with earlier exit times and shorter journeys. These results will be used to calibrate models estimating mortality from sea lice on wild salmon for the regulation of the Norwegian aquaculture industry.

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Marty, G. D., S. M. Saksida, and T. J. Quinn. "Relationship of farm salmon, sea lice, and wild salmon populations." Proceedings of the National Academy of Sciences 107, no. 52 (December 13, 2010): 22599–604. http://dx.doi.org/10.1073/pnas.1009573108.

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Frazer, L. Neil, Alexandra Morton, and Martin Krkošek. "Critical thresholds in sea lice epidemics: evidence, sensitivity and subcritical estimation." Proceedings of the Royal Society B: Biological Sciences 279, no. 1735 (January 4, 2012): 1950–58. http://dx.doi.org/10.1098/rspb.2011.2210.

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Host density thresholds are a fundamental component of the population dynamics of pathogens, but empirical evidence and estimates are lacking. We studied host density thresholds in the dynamics of ectoparasitic sea lice ( Lepeophtheirus salmonis ) on salmon farms. Empirical examples include a 1994 epidemic in Atlantic Canada and a 2001 epidemic in Pacific Canada. A mathematical model suggests dynamics of lice are governed by a stable endemic equilibrium until the critical host density threshold drops owing to environmental change, or is exceeded by stocking, causing epidemics that require rapid harvest or treatment. Sensitivity analysis of the critical threshold suggests variation in dependence on biotic parameters and high sensitivity to temperature and salinity. We provide a method for estimating the critical threshold from parasite abundances at subcritical host densities and estimate the critical threshold and transmission coefficient for the two epidemics. Host density thresholds may be a fundamental component of disease dynamics in coastal seas where salmon farming occurs.

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Gharbi, Karim, Louise Matthews, James Bron, Ron Roberts, Alan Tinch, and Michael Stear. "The control of sea lice in Atlantic salmon by selective breeding." Journal of The Royal Society Interface 12, no. 110 (September 2015): 20150574. http://dx.doi.org/10.1098/rsif.2015.0574.

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Sea lice threaten the welfare of farmed Atlantic salmon and the sustainability of fish farming across the world. Chemical treatments are the major method of control but drug resistance means that alternatives are urgently needed. Selective breeding can be a cheap and effective alternative. Here, we combine experimental trials and diagnostics to provide a practical protocol for quantifying resistance to sea lice. We then combined quantitative genetics with epidemiological modelling to make the first prediction of the response to selection, quantified in terms of reduced need for chemical treatments. We infected over 1400 young fish with Lepeophtheirus salmonis , the most important species in the Northern Hemisphere. Mechanisms of resistance were expressed early in infection. Consequently, the number of lice per fish and the ranking of families were very similar at 7 and 17 days post infection, providing a stable window for assessing susceptibility to infection. The heritability of lice numbers within this time window was moderately high at 0.3, confirming that selective breeding is viable. We combined an epidemiological model of sea lice infection and control on a salmon farm with genetic variation in susceptibility among individuals. We simulated 10 generations of selective breeding and examined the frequency of treatments needed to control infection. Our model predicted that substantially fewer chemical treatments are needed to control lice outbreaks in selected populations and chemical treatment could be unnecessary after 10 generations of selection. Selective breeding for sea lice resistance should reduce the impact of sea lice on fish health and thus substantially improve the sustainability of Atlantic salmon production.

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McEwan, Gregor F., Maya L. Groner, Danielle L. Burnett, Mark D. Fast, and Crawford W. Revie. "Managing aquatic parasites for reduced drug resistance: lessons from the land." Journal of The Royal Society Interface 13, no. 125 (December 2016): 20160830. http://dx.doi.org/10.1098/rsif.2016.0830.

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Atlantic salmon farming is one of the largest aquaculture industries in the world. A major problem in salmon farms is the sea louse ectoparasite Lepeophtheirus salmonis , which can cause stress, secondary infection and sometimes mortality in the salmon host. Sea lice have substantial impacts on farm economics and potentially nearby wild salmonid populations. The most common method of controlling sea louse infestations is application of chemicals. However, most farming regions worldwide have observed resistance to the small set of treatment chemicals that are available. Despite this, there has been little investigation of treatment strategies for managing resistance in aquaculture. In this article, we compare four archetypical treatment strategies inspired by agriculture, where the topic has a rich history of study, and add a fifth strategy common in aquaculture. We use an agent-based model (ABM) to simulate these strategies and their varying applications of chemicals over time and space. We analyse the ABM output to compare how the strategies perform in controlling louse abundance, number of treatments required and levels of resistance in the sea louse population. Our results indicated that among the approaches considered applying chemicals in combination was the most effective over the long term.

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Núñez-Acuña, Gustavo, Constanza Sáez-Vera, Valentina Valenzuela-Muñoz, Diego Valenzuela-Miranda, Gabriel Arriagada, and Cristian Gallardo-Escárate. "Tackling the Molecular Drug Sensitivity in the Sea Louse Caligus rogercresseyi Based on mRNA and lncRNA Interactions." Genes 11, no. 8 (July 27, 2020): 857. http://dx.doi.org/10.3390/genes11080857.

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Caligus rogercresseyi, commonly known as sea louse, is an ectoparasite copepod that impacts the salmon aquaculture in Chile, causing losses of hundreds of million dollars per year. This pathogen is mainly controlled by immersion baths with delousing drugs, which can lead to resistant traits selection in lice populations. Bioassays are commonly used to assess louse drug sensitivity, but the current procedures may mask relevant molecular responses. This study aimed to discover novel coding genes and non-coding RNAs that could evidence drug sensitivity at the genomic level. Sea lice samples from populations with contrasting sensitivity to delousing drugs were collected. Bioassays using azamethiphos, cypermethrin, and deltamethrin drugs were conducted to evaluate the sensitivity and to collect samples for RNA-sequencing. Transcriptome sequencing was conducted on samples exposed to each drug to evaluate the presence of coding and non-coding RNAs associated with the response of these compounds. The results revealed specific transcriptome patterns in lice exposed to azamethiphos, deltamethrin, and cypermethrin drugs. Enrichment analyses of Gene Ontology terms showed specific biological processes and molecular functions associated with each delousing drug analyzed. Furthermore, novel long non-coding RNAs (lncRNAs) were identified in C. rogercresseyi and tightly linked to differentially expressed coding genes. A significant correlation between gene transcription patterns and phenotypic effects was found in lice collected from different salmon farms with contrasting drug treatment efficacies. The significant correlation among gene transcription patterns with the historical background of drug sensitivity suggests novel molecular mechanisms of pharmacological resistance in lice populations.

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Shinn, A. P., J. E. Bron, D. J. Gray, and C. Sommervill. "Elemental analysis of Scottish populations of the ectoparasitic copepod Lepeophtheirus salmonis." Contributions to Zoology 69, no. 1-2 (2000): 79–87. http://dx.doi.org/10.1163/18759866-0690102009.

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Conventional nebulisation ICPMS (Inductively Coupled Plasma Mass Spectrometry), was used to determine the concentration of a broad range of elements in the salmon louse Lepeophtheirus salmonis. Lice samples were collected from Atlantic salmon in seven localities (4 fish farms and 3 wild salmon fisheries) on two separate sampling occasions and prepared for analysis. Sixty six elements were measured, 35 of these were found to be variable and were subjected to univariate and multivariate statistical analysis. The results of the single element comparisons showed that not all individual sites could be discriminated from each other. Sea lice collected from cultured salmonids could be discriminated from those on wild salmonids at the same site using the elements magnesium (<0.05%), vanadium (<0.01%) and uranium (<0.05%). Using discriminant analysis based on 28 elements, the separation of all sampled sea lice localities from each other was clear (100% correct classification) giving each an individual signature. Further analysis examined the effects of sequentially removing elements from the discrimination model in order to determine the minimum number of elements required to obtain satisfactory discrimination of populations. It was found that 16 elements could still provide 100% correct classification, whilst 12 elements still provided 97.30% correct classification. This pilot study has shown elemental analysis to be a potentially successful method for the discrimination of populations of L. salmonis, although the biological basis of the elemental signatures derived remains to be established.

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Gislason, H. "Statistical modelling of sea lice count data from salmon farms in the Faroe Islands." Journal of Fish Diseases 41, no. 6 (November 17, 2017): 973–93. http://dx.doi.org/10.1111/jfd.12742.

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30

Westcott, Jillian D., K. Larry Hammell, and John F. Burka. "Sea lice treatments, management practices and sea lice sampling methods on Atlantic salmon farms in the Bay of Fundy, New Brunswick, Canada." Aquaculture Research 35, no. 8 (July 2004): 784–92. http://dx.doi.org/10.1111/j.1365-2109.2004.01101.x.

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31

Elmoslemany, A., S. K. Whyte, C. W. Revie, and K. L. Hammell. "Sea lice monitoring on Atlantic salmon farms in New Brunswick, Canada: comparing audit and farm staff counts." Journal of Fish Diseases 36, no. 3 (January 13, 2013): 241–47. http://dx.doi.org/10.1111/jfd.12051.

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32

Murray, AG, and M. Hall. "Treatment rates for sea lice of Scottish inshore marine salmon farms depend on local (sea loch) farmed salmon biomass and oceanography." Aquaculture Environment Interactions 5, no. 2 (May 20, 2014): 117–25. http://dx.doi.org/10.3354/aei00099.

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Krkošek, Martin, Jennifer S. Ford, Alexandra Morton, Subhash Lele, and Mark A. Lewis. "Response to Comment on "Declining Wild Salmon Populations in Relation to Parasites from Farm Salmon"." Science 322, no. 5909 (December 19, 2008): 1790.3–1790. http://dx.doi.org/10.1126/science.1156578.

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We evaluated the effect of sea lice (Lepeophtheirus salmonis) infestations on wild pink salmon (Oncorhynchus gorbuscha) populations in the Broughton Archipelago, British Columbia. Riddell et al. suggest that we ignored factors and selectively used data. Here, we clarify misunderstandings and provide analysis to test the strength of our conclusions.

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34

Beamish, Richard J., Simon Jones, Chrys-Ellen Neville, Ruston Sweeting, Grace Karreman, Sonja Saksida, and Elysha Gordon. "Exceptional marine survival of pink salmon that entered the marine environment in 2003 suggests that farmed Atlantic salmon and Pacific salmon can coexist successfully in a marine ecosystem on the Pacific coast of Canada." ICES Journal of Marine Science 63, no. 7 (January 1, 2006): 1326–37. http://dx.doi.org/10.1016/j.icesjms.2006.04.011.

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Abstract Juvenile pink salmon that entered a marine ecosystem along the eastern margin of Queen Charlotte Strait in 2003 and returned as adults in 2004 had very high marine survival. The early seaward migration and midsummer rearing in 2003 were in an area containing 16 active Atlantic salmon farms. Two species of sea louse, Lepeophtheirus salmonis and Caligus clemensi, were commonly found on farmed salmon and juvenile Pacific salmon during the early rearing period of the pink salmon. Mobile L. salmonis and C. clemensi were most abundant on farmed Atlantic salmon from February to May and on pink salmon in June. Chalimus stages were the dominant stages on pink salmon to the end of May. Mobile stages of C. clemensi were the dominant stages and species of sea louse on farmed Atlantic salmon and pink salmon at about the same time in June. DNA studies showed that local juvenile pink salmon were in the area until August. The exceptional returns of the brood year suggest that pink salmon populations and farmed Atlantic salmon coexisted successfully during 2003 within an environment that included sea lice and farmed Atlantic salmon. The processes responsible for the high marine survival cannot be identified with certainty, but they could include increased freshwater discharge in 2003, which may have resulted in lower salinity less favourable to sea louse production, increased inflow of nutrient-rich water to the study area, and the introduction of a Provincial Action Plan that required mandatory louse monitoring and established a fallowed migration corridor for pink salmon.

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Taranger, Geir Lasse, Ørjan Karlsen, Raymond John Bannister, Kevin Alan Glover, Vivian Husa, Egil Karlsbakk, Bjørn Olav Kvamme, et al. "Risk assessment of the environmental impact of Norwegian Atlantic salmon farming." ICES Journal of Marine Science 72, no. 3 (September 2, 2014): 997–1021. http://dx.doi.org/10.1093/icesjms/fsu132.

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Abstract Norwegian aquaculture has grown from its pioneering days in the 1970s to be a major industry. It is primarily based on culturing Atlantic salmon and rainbow trout and has the potential to influence the surrounding environment and wild populations. To evaluate these potential hazards, the Institute of Marine Research initiated a risk assessment of Norwegian salmon farming in 2011. This assessment has been repeated annually since. Here, we describe the background, methods and limitations of the risk assessment for the following hazards: genetic introgression of farmed salmon in wild populations, regulatory effects of salmon lice and viral diseases on wild salmonid populations, local and regional impact of nutrients and organic load. The main findings are as follows: (i) 21 of the 34 wild salmon populations investigated indicated moderate-to-high risk for genetic introgression from farmed escaped salmon. (ii) of 109 stations investigated along the Norwegian coast for salmon lice infection, 27 indicated moderate-to-high likelihood of mortality for salmon smolts while 67 stations indicated moderate-to-high mortality of wild sea trout. (iii) Viral disease outbreaks (pancreas disease, infectious pancreatic necrosis, heart and skeletal muscle inflammation, and cardiomyopathy syndrome) in Norwegian salmon farming suggest extensive release of viruses in many areas. However, screening of wild salmonids revealed low to very low prevalence of the causal viruses. (iv) From ∼500 yearly investigations of local organic loading under fish farms, only 2% of them displayed unacceptable conditions in 2013. The risk of eutrophication and organic load beyond the production area of the farm is considered low. Despite several limitations, especially limited monitoring data, this work represents one of the world’s first risk assessment of aquaculture. This has provided the Norwegian government with the basis upon which to take decisions for further development of the Norwegian aquaculture industry.

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COSTELLO, M. J. "Development of the use of wrasse to control sea lice on salmon farms in Ireland." Aquaculture Research 25, no. 1 (January 1994): 130. http://dx.doi.org/10.1111/j.1365-2109.1994.tb00679.x.

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Jeong, Jaewoon, and Crawford W. Revie. "Appropriate sampling strategies to estimate sea lice prevalence on salmon farms with low infestation levels." Aquaculture 518 (March 2020): 734858. http://dx.doi.org/10.1016/j.aquaculture.2019.734858.

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Bjørn, P. A., B. Finstad, and R. Kristoffersen. "Salmon lice infection of wild sea trout and Arctic char in marine and freshwaters: the effects of salmon farms." Aquaculture Research 32, no. 12 (December 2001): 947–62. http://dx.doi.org/10.1046/j.1365-2109.2001.00627.x.

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Laurin, E., M. Stormoen, C. Revie, and J. Sanchez. "A stepwise integrated risk-assessment framework in aquaculture: the case of sea lice tolerance to freshwater treatments on salmon farms." Aquaculture Environment Interactions 12 (October 22, 2020): 417–28. http://dx.doi.org/10.3354/aei00373.

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Aquaculture studies are often faced with data limitations when carrying out a quantitative risk assessment. Consolidating results from a literature search of potentially applicable methods, we propose a stepwise integrated methods approach that incorporates foundations from an antimicrobial resistance framework, the Office International Epizooties risk model, quantitative microbial risk assessment and infectious disease transmission models. We suggest that an initial ranking profile can be used to prioritize more in-depth qualitative and quantitative risk assessments, when data are available. The ranking method was done using a software that provides practical and interactive graphics for visualizing the impact of different factors and their respective weights on the likelihood of undesirable events (hazards) occurring. For this step, we illustrate how to include available data to obtain ranking results for decision makers using information from a recent sea lice freshwater tolerance literature review (Groner et al. 2019) that identified a gap in quantitative data. In our case example, for copepodid sea lice life stages, hypothetically changing how much experts believe that location and time are important factors revealed the most impact on the ranking for different degrees of freshwater tolerance evolution (no evolution, various partial options, known evolution). The factors ‘location’ and ‘time’, as well as ‘freshwater treatment’, have the greatest impact on the ranking for the preadult sea lice life-stages model. Results from our proposed ranking method can help to drive decisions around interpreting the various factors as they apply to mitigation planning and prioritizing those that should be included in further research. Additionally, we identify where quantitative data could be incorporated, as they become available, into a full risk assessment model with suggested models for a freshwater tolerance risk analysis framework.

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40

Roth, Myron. "The availability and use of chemotherapeutic sea lice control products." Contributions to Zoology 69, no. 1-2 (2000): 109–18. http://dx.doi.org/10.1163/18759866-0690102012.

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An international survey revealed that eleven compounds representing five pesticide types are currently being used on commercial salmon farms for sea lice control. These include two organophosphates (dichlorvos and azamethiphos); three pyrethrin/pyrethroid compounds (pyrethrum, cypermethrin, deltamethrin); one oxidizing agent (hydrogen peroxide); three avermectins (ivermectin, emamectin and doramectin) and two benzoylphenyl ureas (teflubenzuron and diflubenzuron). The number of compounds available in any one country is highly variable, ranging from 9 (Norway) to 6 (Chile, United Kingdom) to 4 (Ireland, Faeroes, Canada) to 2 (US)). Dichlorvos, Azamethiphos and cypermethrin were the most widely used compounds (5 countries) followed by, hydrogen peroxide, ivermectin and emamectin (4 countries each), teflubenzuron (3 countries), diflubenzuron (2 countries), and deltamethrin, pyrethrum and doramectin (1 country each). Although, like trichlorfon, dichlorvos use is being discontinued in several countries notably Norway and the Faeroes. In most instances the availability of sea lice chemotherapeutants is limited, many being used under extra-label veterinary prescription or exemption, and special investigation permits. Access to a broad range of compounds with different modes of action, as well as application methods, has only recently been acquired making assessment of chemotherapy, and therefore integrated pest management, difficult.

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Willis, K. J., P. A. Gillibrand, C. J. Cromey, and K. D. Black. "Sea lice treatments on salmon farms have no adverse effects on zooplankton communities: a case study." Marine Pollution Bulletin 50, no. 8 (August 2005): 806–16. http://dx.doi.org/10.1016/j.marpolbul.2005.02.001.

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42

Robbins, Chris, George Gettinby, Fiona Lees, Mark Baillie, Chris Wallace, and Crawford W. Revie. "Assessing topical treatment interventions on Scottish salmon farms using a sea lice (Lepeophtheirus salmonis) population model." Aquaculture 306, no. 1-4 (August 2010): 191–97. http://dx.doi.org/10.1016/j.aquaculture.2010.05.006.

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43

Elghafghuf, Adel, Raphael Vanderstichel, Larry Hammell, and Henrik Stryhn. "Estimating sea lice infestation pressure on salmon farms: Comparing different methods using multivariate state-space models." Epidemics 31 (June 2020): 100394. http://dx.doi.org/10.1016/j.epidem.2020.100394.

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44

Krkošek, Martin, Mark A. Lewis, and John P. Volpe. "Transmission dynamics of parasitic sea lice from farm to wild salmon." Proceedings of the Royal Society B: Biological Sciences 272, no. 1564 (April 2005): 689–96. http://dx.doi.org/10.1098/rspb.2004.3027.

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Taccardi, EY, IR Bricknell, and HJ Hamlin. "Seasonal progression of embryo size and lipid reserves in sea lice Lepeophtheirus salmonis collected from salmon farms." Marine Ecology Progress Series 664 (April 15, 2021): 79–86. http://dx.doi.org/10.3354/meps13664.

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Sea liceLepeophtheirus salmonisare marine copepods that are the primary parasitic threat to Atlantic salmonSalmo salaraquaculture. Prior to infecting a host,L. salmonisembryos and larvae rely entirely on maternally derived lipid reserves, offering a unique lens for investigation of energetic trade-offs and reproductive investment. In the current study, we combined histology and image processing to assessL. salmonisembryo size, number of lipid droplets per egg, and lipid area across monthly collections (2018-2019) fromS. salarfarms in Maine, USA. Results indicate consistent embryo areas from season to season, peak lipid metrics in May, and minima in lipid quantities from October-December. Therefore, gravid females appear to invest the highest lipid levels in their embryos under biologically favorable conditions, when future larvae may thrive in the plankton and infection typically begins to surge on farms. In contrast, maternal lice likely allocate proportionately more energy into metabolizing their own lipid stores for vertical migration and survival through the winter. A detailed understanding of seasonal lipid reserves is fundamental for the improvement of infection models. These indicators at the earliest developmental stage partially encode recruitment of subsequent planktonic larvae, enabling unique forecasting potential to inform pest management on salmon farms.

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Faust, Ellika, Kim Tallaksen Halvorsen, Per Andersen, Halvor Knutsen, and Carl André. "Cleaner fish escape salmon farms and hybridize with local wrasse populations." Royal Society Open Science 5, no. 3 (March 2018): 171752. http://dx.doi.org/10.1098/rsos.171752.

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The genetic impact of farmed fish escaping aquaculture is a highly debated issue. However, non-target species, such as cleaner fish used to remove sea lice from farmed fish, are rarely considered. Here, we report that wild corkwing wrasse ( Symphodus melops ), which are transported long distances to be used as cleaner fish in salmon farms, escape and hybridize with local populations. Recently, increasing numbers of corkwing wrasse have been reported in Flatanger in Norway, north of its described distribution range, an area heavily relying on the import of cleaner fish from Skagerrak. Using genetic markers identified with 2bRAD sequencing, we show that, although the Flatanger population largely is a result of a northward range expansion, there is also evidence of considerable gene flow from southern populations in Skagerrak and Kattegat. Of the 40 corkwing wrasses sampled in Flatanger, we discovered two individuals with clear southern genotypes, one first-generation hybrid, and 12 potential second-generation hybrids. In summary, we provide evidence that corkwing wrasse escape from fish farms and hybridize with local populations at the leading edge of an ongoing range expansion. Although the magnitude and significance of escapees warrant further investigation, these results should be taken into consideration in the use of translocated cleaner fish.

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Krkošek, Martin, Mark A. Lewis, John P. Volpe, and Alexandra Morton. "Fish Farms and Sea Lice Infestations of Wild Juvenile Salmon in the Broughton Archipelago—A Rebuttal to." Reviews in Fisheries Science 14, no. 1-2 (January 2006): 1–11. http://dx.doi.org/10.1080/10641260500433531.

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Revie, CW, G. Gettinby, JW Treasurer, and C. Wallace. "Identifying epidemiological factors affecting sea lice Lepeophtheirus salmonis abundance on Scottish salmon farms using general linear models." Diseases of Aquatic Organisms 57 (2003): 85–95. http://dx.doi.org/10.3354/dao057085.

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49

Deady, Sandra, Sarah J. A. Varian, and Julie M. Fives. "The use of cleaner-fish to control sea lice on two Irish salmon (Salmo salar) farms with particular reference to wrasse behaviour in salmon cages." Aquaculture 131, no. 1-2 (March 1995): 73–90. http://dx.doi.org/10.1016/0044-8486(94)00331-h.

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Sackville, M., S. Tang, L. Nendick, A. P. Farrell, and C. J. Brauner. "Pink salmon (Oncorhynchus gorbuscha) osmoregulatory development plays a key role in sea louse (Lepeophtheirus salmonis) tolerance." Canadian Journal of Fisheries and Aquatic Sciences 68, no. 6 (June 2011): 1087–96. http://dx.doi.org/10.1139/f2011-037.

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Sea lice ( Lepeophtheirus salmonis ) of fish-farm origin have been implicated in reducing populations of pink salmon ( Oncorhynchus gorbuscha ) in British Columbia’s Broughton Archipelago. Owing to the physically disruptive nature of louse attachment to fish skin in a hyperosmotic environment, we hypothesize that the impacts on fish performance are ionoregulatory in origin. Therefore, ionoregulatory status was measured in juvenile pink salmon artificially infected in the laboratory and naturally infected in the wild. Body [Na+] of laboratory-infected fish (∼1 week seawater (SW); 0.2–0.4 g) increased significantly by 12% with a single chalimus-4 louse, and by 23% with 2–3 chalimus-3 lice. Mortality over this 24-day trial was 2.4% for fish initially infected with 1–3 lice. Body [Na+] for fish caught with natural infections (∼4–12 weeks SW; 0.5–1.5 g) did not differ from uninfected controls. Combining data sets revealed a “no effect” threshold of 0.5 g for body [Na+] of fish infected with one chalimus-4 louse. We propose that this size-related louse tolerance is associated with hypo-osmoregulatory development, adding to a previously suggested multifactorial mechanism based on epidermal and immune system development. We suggest management bodies consider this fish-mass threshold when planning to minimize risk to wild fish populations.

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Journal articles on the topic 'Sea lice; Salmon farms'

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