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


Other title
Double-crested cormorant
Alternate stable states
Ecopath with Ecosim
restoration ecology
Ecosystem Modelling
Lake whitefish
Fisheries Management
Historical fish harvest
Type of item
Degree grantor
University of Alberta
Author or creator
McGregor, Andrea M
Supervisor and department
Foote, A. Lee (Renewable Resources)
Sullivan, Michael (Renewable Resources, Adjunct)
Examining committee member and department
Vinebrook, Rolf (Biological Sciences)
Pereira, Don (External - Fisheries, Wildlife and Conservation Biology)
Poesch, Mark (Renewable Resources)
Davis, Chris (Non-voting)
Schindler, David (Biological Sciences)
Department of Renewable Resources
Wildlife Ecology and Management
Date accepted
Graduation date
Doctor of Philosophy
Degree level
The potential for walleye (Sander vitreus) 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 (Coregonus clupeaformis) 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 (Phalacrocorax auritus) 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.
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. Where the thesis is converted to, or otherwise made available in digital form, the University of Alberta will advise potential users of the thesis of these terms. 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.
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