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People, predators and parasites: Unexpected dynamics of sea lice in Pacific Canada Open Access


Other title
social ecological
sea lice
Type of item
Degree grantor
University of Alberta
Author or creator
Peacock, Stephanie J
Supervisor and department
Martin Krkošek (Ecology and Evolutionary Biology, University of Toronto)
Mark Lewis (Biological Sciences and Mathematical and Statistical Sciences)
Examining committee member and department
Troy Day (Biology and Mathematics and Statistics)
Jens Roland (Biological Sciences)
Rolf Vinebrook (Biological Sciences)
Subhash Lele (Mathematical and Statistical Sciences)
Department of Biological Sciences
Date accepted
Graduation date
Doctor of Philosophy
Degree level
The current rate and extent of human-induced changes to the environment are unprecedented. There is an urgent need to understand and predict the dynamics of coupled human and natural systems so that we can maintain the ecosystem services on which we depend. Temperate coastal regions have experienced a rapid expansion of open-net salmon farming in recent decades. The success of aquaculture depends on maintaining a healthy coastal environment in which to grow fish, but the transition to aquaculture has changed the structure of coastal fish populations and lead to the unexpected emergence of disease in both farmed and wild populations. In particular, sea louse parasites are a persisting problem that threaten the long-term sustainability of salmon farming. In this thesis, I consider the reciprocal interactions between people and parasites and between parasites and predators that mediate sea louse dynamics on farmed salmon and impacts on wild fish populations. Analysis of a simple model for parasites on adjacent salmon farms coupled by dispersal suggested that strict thresholds for parasite abundance requiring management intervention may actually hinder efforts to eradicate sea lice at the regional scale. Model analysis and examination of long-term data on sea lice of farmed and wild salmon from the Broughton Archipelago of British Columbia show that coordinated timing of treatments among farms is more effective at reducing sea lice on farmed salmon for the betterment of wild salmon populations. But assessing the effects of sea lice on migrating wild juvenile salmon is much more complex than accounting for transmission from farms as wild salmon are embedded in an ecosystem and subject to interacting pressure from predation and competition. In the second part of my thesis, I consider how predators may mediate the effect of parasites in multi-host systems. Model analysis and field-based experiments suggest that selective predation on pink salmon and on parasitized prey may result in a parasite-mediated release from predation for chum salmon, a less-desirable prey species. This is contrary to previous research suggesting that parasites increase the predation susceptibility of both juvenile pink and chum salmon and may explain why chum salmon population appear unaffected by sea louse epizootics in the early 2000s while pink salmon populations declined. Throughout this work, I have found that unexpected behaviour can emerge from a combination of factors -- people, predators and parasites -- even when each part seems well understood in isolation. The complexity ecosystems and our role in them is important for ecologists and policy makers to consider as we enter an era of unprecedented human growth and impacts on natural ecosystems.
Permission is hereby granted to the University of Alberta Libraries to reproduce single copies of this thesis and to lend or sell such copies for private, scholarly or scientific research purposes only. The author reserves all other publication and other rights in association with the copyright in the thesis and, except as herein before provided, neither the thesis nor any substantial portion thereof may be printed or otherwise reproduced in any material form whatsoever without the author's prior written permission.
Citation for previous publication
Peacock, S. J., Krkošek, M., Proboszcz, S., Orr, C. & Lewis, M. A. 2013. Cessation of a salmon decline with control of parasites. Ecological Applications 23: 606–620.Peacock, S. J., Connors, B. M., Krkošek, M., Irvine, J. R. & Lewis, M. A. 2014. Can reduced predation offset negative effects of sea louse parasites on chum salmon? Proceedings of the Royal Society B: Biological Sciences 281: 20132913.Peacock, S.J., Krkošek, M., Bateman, A.W., Lewis, M. A. Parasitism and food web dynamics of juvenile Pacific salmon. Ecosphere. In Press.

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