Salmon Coast Field Station

Simoom Sound, Canada

Salmon Coast Field Station

Simoom Sound, Canada
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Krkosek M.,University of Toronto | Krkosek M.,University of Otago | Ashander J.,University of Alberta | Ashander J.,University of California at Davis | And 3 more authors.
American Naturalist | Year: 2013

The exchange of native pathogens between wild and domesticated animals can lead to novel disease threats to wildlife. However, the dynamics of wild host-parasite systems exposed to a reservoir of domesticated hosts are not well understood. A simple mathematical model reveals that the spill-back of native parasites from domestic to wild hosts may cause a demographic Allee effect in the wild host population. A second model is tailored to the particulars of pink salmon (Oncorhynchus gorbuscha) and salmon lice (Lepeophtheirus salmonis), for which parasite spill-back is a conservation and fishery concern. In both models, parasite spill-back weakens the coupling of parasite and wild host abundance-particularly at low host abundance-causing parasites per host to increase as a wild host population declines. These findings show that parasites shared across host populations have effects analogous to those of generalist predators and can similarly cause an unstable equilibrium in a focal host population that separates persistence and extirpation. Allee effects in wildlife arising from parasite spill-back are likely to be most pronounced in systems where the magnitude of transmission from domestic to wild host populations is high because of high parasite abundance in domestic hosts, prolonged sympatry of domestic and wild hosts, a high transmission coefficient for parasites, long-lived parasite larvae, and proximity of domesticated populations to wildlife migration corridors. © 2013 by The University of Chicago.

Krkosek M.,University of Alberta | Krkosek M.,University of Washington | Krkosek M.,University of Otago | Connors B.M.,Simon Fraser University | And 9 more authors.
Ecological Applications | Year: 2011

For some salmon populations, the individual and population effects of sea lice (Lepeophtheirus salmonis) transmission from sea cage salmon farms is probably mediated by predation, which is a primary natural source of mortality of juvenile salmon. We examined how sea lice infestation affects predation risk and mortality of juvenile pink (Oncorhynchus gorbuscha) and chum (O. keta) salmon, and developed a mathematical model to assess the implications for population dynamics and conservation. A risk-taking experiment indicated that infected juvenile pink salmon accept a higher predation risk in order to obtain foraging opportunities. In a schooling experiment with juvenile chum salmon, infected individuals had increased nearest-neighbor distances and occupied peripheral positions in the school. Prey selection experiments with cutthroat trout (O. clarkii ) predators indicated that infection reduces the ability of juvenile pink salmon to evade a predatory strike. Group predation experiments with coho salmon (O. kisutch) feeding on juvenile pink or chum salmon indicated that predators selectively consume infected prey. The experimental results indicate that lice may increase the rate of prey capture but not the handling time of a predator. Based on this result, we developed a mathematical model of sea lice and salmon population dynamics in which parasitism affects the attack rate in a type II functional response. Analysis of the model indicates that: (1) the estimated mortality of wild juvenile salmon due to sea lice infestation is probably higher than previously thought; (2) predation can cause a simultaneous decline in sea louse abundance on wild fish and salmon productivity that could mislead managers and regulators; and (3) compensatory mortality occurs in the saturation region of the type II functional response where prey are abundant because predators increase mortality of parasites but not overall predation rates. These findings indicate that predation is an important component of salmon-louse dynamics and has implications for estimating mortality, reducing infection, and developing conservation policy. © 2011 by the Ecological Society of America.

Price M.H.H.,University of Victoria | Price M.H.H.,Raincoast Conservation Foundation | Morton A.,Salmon Coast Field Station | Reynolds J.D.,Simon Fraser University
Canadian Journal of Fisheries and Aquatic Sciences | Year: 2010

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.

Williams J.,St. Francis Xavier University | Polk Z.C.S.,Salmon Coast Field Station | Smit L.A.,British Columbia Ministry of forests | Macinnis G.,Antigonish
Journal of Shellfish Research | Year: 2015

In the spring of 2007, a small number of empty valves from the bay scallop, Argopecten irradians irradians (Lamarck), were observed at several locations in Pomquet Harbour, Nova Scotia, Canada. Snorkeling surveys at selected sites in the harbor were carried out in spring 2007, summer 2007, and spring 2008. Scallop densities were very low in all sampling times, ranging between 0.04 and 0.053 scallops/m2. The size distributions from 2007 suggested a single cohort of 0 + individuals, with one 1 + scallop. The 2008 samples were predominantly 1 + scallops, with five 0 + individuals. Four marked scallops from 2007 were collected alive in 2008, demonstrating their ability to overwinter. These scallops had an average daily growth rate of 0.08 mm/day from July 2007 to May 2008. A thermistor deployed in the same eelgrass beds indicated that the scallops survived extended periods of time with temperatures below 0°C. In 2013, four of the sites were surveyed again, and dramatic increases in density were recorded, averaging 1.713 scallops/m2. The bay scallops in Pomquet Harbour probably represent an incidental introduction, as larvae, from aquaculture operations ∼80 km to the north.

Groner M.L.,University of Prince Edward Island | Rogers L.A.,University of Toronto | Bateman A.W.,University of Toronto | Bateman A.W.,University of Alberta | And 12 more authors.
Philosophical Transactions of the Royal Society B: Biological Sciences | Year: 2016

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. © 2016 The Author(s) Published by the Royal Society. All rights reserved.

PubMed | University of Alberta, ESSA Technologies Ltd., Salmon Coast Field Station and University of Toronto
Type: Journal Article | Journal: Ecology | Year: 2016

The global expansion of aquaculture has changed the structure of fish populations in coastal environments, with implications for disease dynamics. In Pacific Canada, farmed salmon act as reservoir hosts for parasites and pathogens, including sea lice (Lepeophtheirus salmonis and Caligus clemensi) that can transmit to migrating wild salmon. Assessing the impact of salmon farms on wild salmon requires regular monitoring of sea-louse infections on both farmed and wild fish. Since 2001, we have collected juvenile pink (Oncorhynchus gorbuscha) and chum (O.keta) salmon annually at three sites in the Broughton Archipelago in British Columbia, Canada, during the annual juvenile salmon migration from fresh water to the open ocean. From sampled fish, we recorded counts of parasitic copepodid-, chalimus-, and motile-stage sea lice. We report louse abundances as well as supplementary observations of fish size, development, and health.

Krkosek M.,University of Otago | Connors B.M.,Salmon Coast Field Station | Connors B.M.,Simon Fraser University | Lewis M.A.,Center for Mathematical Biology | And 2 more authors.
American Naturalist | Year: 2012

Allee effects are thought to mediate the dynamics of population colonization, particularly for invasive species. However, Allee effects acting on parasites have rarely been considered in the analogous process of infectious disease establishment and spread. We studied the colonization of uninfected wild juvenile Pacific salmon populations by ectoparasitic salmon lice (Lepeophtheirus salmonis) over a 4-year period. In a data set of 68,376 fish, we observed 85 occurrences of precopular pair formation among 1,259 preadult female and 613 adult male lice. The probability of pair formation was dependent on the local abundance of lice, but this mate limitation is likely offset somewhat by mate-searching dispersal of males among host fish. A mathematical model of macroparasite population dynamics that incorporates the empirical results suggests a high likelihood of a demographic Allee effect, which can cause the colonizing parasite populations to die out. These results may provide the first empirical evidence for Allee effects in a macroparasite. Furthermore, the data give a rare detailed view of Allee effects in colonization dynamics and suggest that Allee effects may dampen the spread of parasites in a coastal marine ecosystem. © 2012 by The University of Chicago.

Neil Frazer L.,University of Hawaii at Manoa | Morton A.,Salmon Coast Field Station | Krkosek M.,University of Otago
Proceedings of the Royal Society B: Biological Sciences | Year: 2012

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. © 2011 The Royal Society.

Morton A.,Salmon Coast Field Station | Routledge R.,Simon Fraser University | McConnell A.,Simon Fraser University | Krkosek M.,Salmon Coast Field Station | And 2 more authors.
ICES Journal of Marine Science | Year: 2011

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. © 2010 International Council for the Exploration of the Sea. Published by Oxford Journals. All rights reserved.

Connors B.M.,Simon Fraser University | Braun D.C.,Simon Fraser University | Peterman R.M.,Simon Fraser University | Cooper A.B.,Simon Fraser University | And 5 more authors.
Conservation Letters | Year: 2012

Climate, competition, and disease are well-recognized drivers of population dynamics. These stressors can be intertwined by animal migrations, leading to uncertainty about the roles of natural and anthropogenic factors in conservation and resource management. We quantitatively assessed the four leading hypotheses for an enigmatic long-term decline in productivity of Canada's iconic Fraser River sockeye salmon: (1) delayed density-dependence, (2) local oceanographic conditions, (3) pathogen transmission from farmed salmon, and (4) ocean-basin scale competition with pink salmon. Our findings suggest that the long-term decline is primarily explained by competition with pink salmon, which can be amplified by exposure to farmed salmon early in sockeye marine life, and by a compensatory interaction between coastal ocean temperature and farmed-salmon exposure. These correlative relationships suggest oceanic-scale processes, which are beyond the reach of current regulatory agencies, may exacerbate local ecological processes that challenge the coexistence of fisheries and aquaculture-based economies in coastal seas. © 2012 Wiley Periodicals, Inc.

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