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

• Author / Creator

  Peacock, Stephanie J

• 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.

• Subjects / Keywords

  • Aquaculture
  • Social ecological
  • Host-parasite
  • Sea lice
  • Models
  • Salmon
  • Predation

• Graduation date

  Fall 2015

• Type of Item

  Thesis

• Degree

  Doctor of Philosophy

• DOI

  https://doi.org/10.7939/R3QV3CF6D

• License

  This thesis is made available by the University of Alberta Libraries with permission of the copyright owner solely for non-commercial purposes. This thesis, or any portion thereof, may not otherwise be copied or reproduced without the written consent of the copyright owner, except to the extent permitted by Canadian copyright law.