Villy Christensen

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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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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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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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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No abstract available.