Fish harvest and replacement of top piscivorous predators in aquatic food webs: implications for restoration and fisheries management

  • Author / Creator
    McGregor, Andrea M
  • The potential for walleye (<i>Sander vitreus</i>) restoration at Lac la Biche, Alberta, Canada is a social-ecological question that requires understanding of changes to ecosystem integrity and historical fidelity resulting from disturbance. This study explored variability in fisheries-induced disturbance across time, examined the effects of disturbance on ecosystem structure and functioning, characterized the system during different eras from pre-European settlement to the present, and assessed walleye restoration potential based on conceptual models describing the system response to disturbance. An anthropological assessment of historical harvest was conducted (1800 to 1900) to estimate the magnitude of subsistence lake whitefish (<i>Coregonus clupeaformis</i>) harvest during rapid settlement of the Lac la Biche area. The results were compared to more recent harvest estimates (1900 to 2009) reflecting combined commercial, subsistence and recreational harvest, to describe the relative variability in the magnitude of fishing disturbances during the 200 years preceding the current restoration project. Ecosystem models for 1800 and 1900 were used to examine how historical fisheries affected the structure, functioning, and resilience of the system, and to assess if targeting system conditions in 1900 would satisfy the restoration goal of a walleye-dominated ecosystem. Results suggest little change in ecosystem structure and function between 1800 and 1900, though the trend in the analyses is towards declining system maturity and resilience. Parameters and state variables used as model inputs provide plausible values for guiding the restoration program. Potential success of the walleye restoration program was addressed using a series of models representing four eras (1800, 1900, 1965, 2005) to test the for multiple ecosystem states, specifically a walleye-dominated equilibrium and a double-crested cormorant (<i>Phalacrocorax auritus</i>) dominated equilibrium. Identification of alternate stable attractors would influence the predictability of system recovery following a disturbance. Results from over 900 model simulations suggest both walleye and cormorant attractors existed in historical (1800, 1900) models but a single cormorant-dominated equilibrium is present in contemporary models (1965, 2005). Differential size-selective foraging of walleye and cormorants on yellow perch (Perca flavescens) provides a negative feedback stabilizing each state. Recovery of a walleye population seems possible but restoration of a walleye-dominated ecosystem was not predicted.

  • Subjects / Keywords
  • Graduation date
  • Type of Item
  • Degree
    Doctor of Philosophy
  • DOI
  • 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.
  • Language
  • Institution
    University of Alberta
  • Degree level
  • Department
    • Department of Renewable Resources
  • Specialization
    • Wildlife Ecology and Management
  • Supervisor / co-supervisor and their department(s)
    • Sullivan, Michael (Renewable Resources, Adjunct)
    • Foote, A. Lee (Renewable Resources)
  • Examining committee members and their departments
    • Davis, Chris (Non-voting)
    • Vinebrook, Rolf (Biological Sciences)
    • Poesch, Mark (Renewable Resources)
    • Pereira, Don (External - Fisheries, Wildlife and Conservation Biology)
    • Schindler, David (Biological Sciences)