Villy Christensen

Prospective Graduate Students / Postdocs

This faculty member is currently not actively recruiting graduate students or Postdoctoral Fellows, but might consider co-supervision together with another faculty member.


Relevant Thesis-Based Degree Programs

Research Options

I am available and interested in collaborations (e.g. clusters, grants).
I am interested in and conduct interdisciplinary research.

Research Methodology

Ecopath with Ecosim ecosystem modelling framework

Great Supervisor Week Mentions

Each year graduate students are encouraged to give kudos to their supervisors through social media and our website as part of #GreatSupervisorWeek. Below are students who mentioned this supervisor since the initiative was started in 2017.


Villy has always given me the freedom and encouragement to work on a broad set of topics beyond my thesis work, and I am trully thankful for his helpful guidance.

Abdulrahman Ben Hasan (2018)


Graduate Student Supervision

Doctoral Student Supervision

Dissertations completed in 2010 or later are listed below. Please note that there is a 6-12 month delay to add the latest dissertations.

Population dynamics and interactions of sockeye and kokanee salmon (Oncorhynchus nerka) with piscivorous char (Salvelinus sp.) and rainbow trout (O. mykiss) in the large lakes and reservoirs of British Columbia (2022)

Freshwater fisheries management is focused on a combination of economic, social and conservation objectives. One of the trade-offs among these objectives involves a balance between harvest and consistent ecosystem functions. There can be conflicts between recreational fisheries and conservation, which are exacerbated by other habitat uses, such as dam operations. This dissertation examines the tools used by managers; how strategies employed by managers interact with natural systems and each other; what are some of the unexpected consequences; and what impact these tools have on recreational freshwater fisheries objectives. First, the use of nutrient addition as a tool to increase fish production is examined. Ecosystem modelling is then used to look at the impact of nutrient addition on target fish species in combination with different flow regimes in a highly managed reservoir. A decision analysis table is used to compare effects of different nutrient addition scenarios under variable flow conditions. Nutrient addition was found to be the most important driver of the system, with constant nutrient addition resulting in higher biomasses of the target fish species. Next, the outcomes of different stocking programs in British Columbia are summarized. The potential effect of salmon reintroduction programs on native fish species was predicted using ecosystem modelling. These models indicated that higher stocking levels had negative effects on the native kokanee salmon, but resulted in variable effects on the predators, depending on the species being stocked. Finally, ecosystem modelling is used to look at the possible effects of invasive non-native mussels in a productive lake. The model predicted that fish species that remained in the lake would be affected the most, while the invasive mussels had less of an effect on anadromous sockeye salmon and rainbow trout that reared in streams. This dissertation shows that maintaining consistent ecosystem functions to support recreational fisheries objectives can be challenge in itself.

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On sustainability and financial return of fishery resources (2021)

Overexploitation and resource rent dissipation are some of the fundamental issues in fisheries management. The first undermines food security while the second implies a minimal economic return to the owning society. Sustainable fisheries are predominantly attained in conjunction with high management intensity, which keeps exploitation rates in check. Yet controlling exploitation becomes a daunting task under many complex fisheries contexts. Further, although profitability of fishing industry has improved after introducing quota-based systems, it is perceived that society is not receiving a fair share of the resource rent. In this dissertation, I focus on the Arabian Gulf region as a microcosm to examine various complex fisheries problems and underline, globally, the society’s compensation from the fishing industry. I begin by discussing situations where open access conditions are irreversible due to inherently poor management institutions or high dependency on fishing for livelihood. I show that well-designed size restriction—an easily implementable approach—can help avert overexploitation, rebuild depleted fish stocks and enhance yields without controlling exploitation rates. Next, I examine internationally shared fish stocks, whose sustainability requires managing exploitation rates at the international level rather than merely locally. I develop an age-structured model to evaluate bioeconomic trade-offs under alternative fishing scenarios. Harvesting a shared fish stock under cooperation or local but sustainable management provides much higher bioeconomic gains than competition. I then discuss the impacts of escalated market demand for dried swim bladder on fish, people and management in source countries. I highlight that while management interventions are required, the extremely high value of swim bladder would complicate regulatory efforts by stimulating black-market systems. Finally, I examine whether resource rent charges are imposed on catch share fisheries, and systematically compare that with forestry, oil, gas, and mining in 18 countries. I show that fishing is the only industry that consistently lacks resource rent charges, implying a forgoing stream of income in most countries. My dissertation contributes toward alleviating overfishing when exploitation rates are difficult to manage and underscores the need for national policies to consider the enhanced profitability of the fishing industry under catch share systems.

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Addressing questions on the social and economic outcomes of an individual transferable quota fishery (2020)

In Canada, fisheries are expected to contribute to prosperous coastal communities and the maintenance of stable and viable fishing fleets, alongside other objectives that include conservation and complying with legal obligations to Indigenous Peoples. Individual transferable quotas (ITQs) have been promoted as a management approach to improve the conservation and economic outcomes of fisheries. The use of ITQs in British Columbia (BC) groundfish fisheries is widespread, following successive introductions of ITQs into the fisheries since 1990. There has been no comprehensive evaluation of the social and economic outcomes of ITQ management in the BC fisheries during this time, despite more than a decade of fishery participants and Indigenous and coastal community representatives raising concerns about the negative impacts of quota ownership and leasing. With a focus on the BC Pacific halibut fishery, I construct a database for licences and quota, including ownership and leasing. I examine changes in the ownership profile of the fishery over a 25-year period and consider the extent to which processors exercise control over the quota market through leasing. I construct a financial enterprise model based on accounting principles to assess the impact of quota ownership and leasing prices on the financial performance of owner-operator halibut vessels. I compare the results of this research against objectives for fisheries in Canada, determined through an extensive search of the literature, including current and historical policy and legal documents, conference proceedings, testimony to Senate and House of Commons committees, speeches and briefing material dating from the 1970s. Owner-operators have been increasingly marginalized in the halibut fishery. Owner-operators that have entered the fishery since 2001 catch 15% but own less than 1% of the halibut quota. Lease fees for halibut have regularly exceeded 80% of the landed price, reducing lessee fishing enterprises to minimal earnings that do not support reinvestment or renewal of the fleet. The BC halibut fishery is not meeting objectives for fisheries in Canada with respect to fleet viability and the equitable distribution of benefits. I provide an overview of measures that can be used for a just and fair transformation of fisheries to achieve socio-economic objectives.

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Understanding, modeling and predicting trophic interactions between marine species (2015)

In this thesis, I explore and propose new methodologies and intend to provide new insights for understanding, modeling and predicting trophic interactions between marine species. I introduce the importance of trophic interactions in marine ecosystems and the common ecosystem modeling approaches applied to marine food webs. First, I present an attempt to synthetize information from all published Ecopath with Ecosim (EwE) models worldwide, gathered in the EcoBase digital repository. Through the compilation and standardization of a suite of metadata, I describe and discuss the usage of the EwE modeling approach and its evolution over time, since its very first application. I also present a meta-analysis of Ecopath models based on these metadata, where I select the models of potential interest, using a scoring method, and focus on one particular aspect of food web modeling, relating to the identification of keystone species. I propose a comprehensive and critical review of the ill-defined concept of keystone species and argue for a restored, exclusive and operational definition of the concept. The proposed definition is placed in a larger framework that considers different categories of ecologically important species. Then, a new functional index of keystoneness is derived from the EwE modeling approach, so as to identify potential keystone species in marine food webs. The proposed index addresses some of the biases observed in previously applied indices. Finally, I present an attempt to predict diet composition for predatory fish species. The intention is to build on existing large datasets, provided in the FishBase biodiversity information system, to identify predictors of fish feeding selectivity. The determination of clear or consistent pattern between biological and ecological species straits and diet composition is challenged by data restrictions, but some recommendations for future studies are provided. In conclusion, data availability may be a critical issue when considering some aspects of trophic interactions, especially for modeling and predictions at the species level. Data sharing within the scientific community, notably through the use of digital and open-access information repositories, is critical for the development of global meta-analyses in marine ecology.

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Mortality of migrating Pacific salmon smolts in southern British Columbia, Canada (2010)

No abstract available.

Master's Student Supervision

Theses completed in 2010 or later are listed below. Please note that there is a 6-12 month delay to add the latest theses.

Impact of environmental variability on Jack Mackerel (Trachurus murphyi) spawning grounds in the open sea of the Southeast Pacific (2021)

Jack mackerel (Trachurus murphyi) is a migratory species broadly distributed in the Pacific Ocean. Its main spawning grounds are located in the high seas zone off the Chilean coast. Several ichthyoplankton surveys have been conducted in this region, showing shifts in egg distribution, which have become more noticeable in the last decade. It is widely known that environmental conditions play an important role in determining the optimal conditions for development and survival for early life stages. However, the environmental drivers underlying changes in the egg distribution have been little studied. Yet, this knowledge is critical for understanding the effects of environmental forcing on spawning grounds and trends in this fish’s population. The aim of this research was to elucidate how eggs distribution is mediated by the environment and determine the impacts of climate variability on spawning grounds. Egg presence data from 14 ichthyoplankton surveys (1999-2018), as well as remote sensing data, were used to model egg-environment relationships using the Maxent species distribution model. Specifically, I analyzed the optimum temperature parameter, tolerance range and maps of habitat suitability index. The results suggest that temperature is the main driver of egg distribution, and its interannual variability has an impact on eggs by reducing the occurrence probability due to abnormally warmer or cooler conditions. Further, the tolerance range defined a thermal strip that varied spatially in the N-S and E-W directions as a function of the sea surface temperature variability. The latitudinal shift of the egg distribution and the thermal strip were in sync. Thus, the northerly and southerly egg displacements may indicate the species' adaptive response to environmental fluctuations. Other factors, such as wind and temperature anomalies, also shaped suitable conditions for spawning. Changes in these parameters due to climate variability, resulted in unsuitable conditions and restricted egg distribution. Based on these findings, adaptive boundaries in the sampling design are recommended in future ichthyoplankton surveys to prevent sampling bias.

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Fisheries in a changing environment: the impacts of the reduction in Shatt Al Arab flow on nearshore fish stocks in the Northern Persian Gulf (2017)

When fish catches decline, the standard recommended management solution is to reduce fishing mortality to allow stock recovery to more productive levels. This recommendation is based on the assumption that the most likely cause of the decline in the first place is fishing. Natural regime shifts and human-induced environmental changes are, however, often equally important factors in driving catch declines. In the Northern Persian Gulf, many commercial fish stocks are declining, raising questions about two main causes: overfishing and reduction in the flow of the major river, Shatt Al Arab. In Kuwait, the latter cause is strongly suspected of driving catch declines, especially with the implementation of high length limits and apparently good protection of juvenile nursery areas. Here I assess three case studies of Kuwait fish stocks and investigate the impact of reduced Shatt Al Arab flow on fish recruitment patterns. We found neutral and negative apparent capacity change in the green tiger shrimp stock and the orange-spotted grouper stock, respectively. These results suggest declining productivity in the nursery area of the orange-spotted grouper, but not in that of the tiger shrimp stock. In the case of the yellow-fin seabream assessment, the estimation of the relative recruitment was unreliable, hence the inability to examine the relationship between recruitment and the reduction in the flow rate of Shatt Al Arab. Our results demonstrate that reductions in Shatt Al Arab river flow are likely to impact fish recruitment patterns, causing changes in fish stock sizes. The findings presented here are expected to be a starting point for a more detailed investigation that tries to bring together data on what has been changing over time in the nearshore nursery environments, since most of the commercial fish stocks are inshore/estuarine dependent. Such investigation would be very critical for the fisheries management in deciding, for example, whether a reduction of fishing effort would be beneficial.

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In search of "effective management": Case study of the British Columbia dungeness crab (Cancer magister) fisery and lessions from domestic and international experience (2013)

Canadian fisheries such as the British Columbia Dungeness crab (Cancer magister) fishery face a number of complex economic, political, and ecological challenges. The situation has been compounded by the increased complexity of management frameworks and declining resources of the government body entrusted with the management of Canada’s fishery resources. This thesis looks for best practices to create effective management within Canadian fisheries through investigation of three key components of fisheries management: Maintaining an exploited stock’s biological sustainability; developing and maintaining industry-government relationships; and providing equitable financing for management activities. Chapter one provides a comparison of management strategies within the British Columbia Dungeness crab and Western Australia rock lobster fisheries. This investigation shows that effective management to address the current challenges within the Dungeness crab fishery can be developed but will require time, resources, and building of a strong industry- government relationship. The second chapter outlines many of the challenges impacting Canadian fisheries, highlighting the recent impacts of the “Larocque Decision”. A recent resolution to the Larocque Decision (Bill C-38) is then explored utilizing an analysis of the joint project agreement for the snow crab fishery in Area 19 in eastern Canada. This chapter shows that collaborative management to address the fallout from the “Larocque Decision” can be successfully developed under the current Canadian legislation. The chapter also demonstrates the limitations of current legislation in building such relationships and the fragility of collaborative frameworks built under the current regime. This thesis creates a list of the fundamental criteria needed to create effective management systems within fisheries, and concludes that collaborative management that creates a long-term true partnership between industry and government through a legislated process enhances the success of such management approaches.

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