Villy Christensen

Villy Christensen
University of British Columbia - Vancouver | UBC · Institute for the Oceans and Fisheries

PhD, Cand. scient.

About

331
Publications
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34,729
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Additional affiliations
October 1999 - February 2016
University of British Columbia - Vancouver
Position
  • Professor (Full)

Publications

Publications (331)
Article
The salmon-eating Southern Resident killer whale (SRKW) (Orcinus orca) population currently comprises only 73 individuals, and is listed as ‘endangered’ under the Species at Risk Act in Canada. Recent evidence suggests that the growth of this population may be limited by food resources, especially Chinook salmon (Oncorhynchus tshawytscha). We prese...
Article
Ecosystem models, such as Ecopath with Ecosim (EwE), are useful tools for developing ecosystem-based management strategies. Model development, however, requires data for the estimation of input parameters including time series for calibration. Most small-scale fisheries lack such information, making it difficult to reliably use ecosystem models for...
Article
Full-text available
Marine Ecosystem Models (MEMs) provide a deeper understanding of marine ecosystem dynamics. The United Nations Decade of Ocean Science for Sustainable Development has highlighted the need to deploy these complex mechanistic spatial-temporal models to engage policy makers and society into dialogues towards sustainably managed oceans. From our shared...
Article
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Projections of climate change impacts on marine ecosystems have revealed long-term declines in global marine animal biomass and unevenly distributed impacts on fisheries. Here we apply an enhanced suite of global marine ecosystem models from the Fisheries and Marine Ecosystem Model Intercomparison Project (Fish-MIP), forced by new-generation Earth...
Article
The demand for fish maw (i.e., dried swim bladder) has apparently intensified during the past decades in Hong Kong and mainland China; currently, maw has similar annual import volumes but far higher mean unit values than other important seafood delicacies like shark fins and sea cucumber. Escalated demand for seafood delicacies can significantly co...
Article
Across publicly owned natural resources, the practice of recovering financial compensation, commonly known as resource rent, from extractive industries influences wealth distribution and general welfare of society. Catch shares are the primary approach adopted to diminish the economically wasteful race to fish by allocating shares of fish quotas-pu...
Article
The ecological system conformed by the islands of Tenerife and La Gomera (Canary Islands) is characterized though the trophic network. The indicators obtained by the Ecopath model show a stressed and still developing ecosystem, probably related to inadequate management of the fisheries that takes place in this area, focused on high trophic level sp...
Article
Full-text available
Growth and recruitment overfishing can co-occur when a fishery is subjecting small and immature fish in conjunction with adult fish to excessive exploitation rates such that it reduces the spawning biomass to the point where recruitment is significantly impaired. Such conditions are generally evident in open-access fisheries and are especially detr...
Article
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We have developed an approach that connects a complex and widely used scientific ecosystem modeling approach with a game engine for real-time communication and visualization of scientific results. The approach, OceanViz, focuses on communicating scientific data to non-scientific audiences to foster dialogue, offering experimental, immersive approac...
Article
Inland fisheries managers must account for multiple competing uses for aquatic resources; using methods such as ecosystem‐based management allows for different priorities for aquatic ecosystems to be accounted for. Declining abundance of kokanee salmon Oncorhynchus nerka (Walbaum) in Arrow Lakes Reservoir in the 1990s led to the use of large‐scale...
Article
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Dreissenid (zebra and quagga) mussels are spreading across North America and having an impact on freshwater ecosystems, through bottom-up impacts. Lakes in British Columbia are known to be at risk for mussel invasion due to favourable water chemistry and significant cross-border boat movements. This project uses Ecopath with Ecosim (EwE) to model a...
Article
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Mesopelagic fish, being in the middle of the trophic web, are important key species for the marine environment; yet limited knowledge exists about their biology and abundance. This is particularly true in the Mediterranean Sea where no regional assessment is currently undertaken regarding their biomass and/or distribution. This study evaluates spat...
Article
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Three Ecopath models were built to reproduce 3 experimental treatments carried out in earthen ponds located in Olhão, southern Portugal, to understand the energy transferred and the ecosystem state in integrated multi-trophic aquaculture (IMTA). These earthen ponds behave as simplified ecosystems or mesocosms, with well-defined borders, where the r...
Article
A new approach for estimating the fishing mortality benchmark F msy (fishing pressure that corresponds to maximum sustainable yield) is proposed. The approach includes density-dependent factors. The analysis considers 53 data-rich fish stocks in the Northeast Atlantic. The new F msy values are estimated from an ensemble of data sources: (i) applyin...
Article
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Considerable effort is being deployed to predict the impacts of climate change and anthropogenic activities on the ocean's biophysical environment, biodiversity, and natural resources to better understand how marine ecosystems and provided services to humans are likely to change and explore alternative pathways and options. We present an updated ve...
Article
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Climate-induced changes in the world’s oceans will have implications for fisheries productivity and management. Using a model ensemble from the Fisheries and Marine Ecosystem Model Intercomparison Project (Fish-MIP), we analyzed future trajectories of climate-change impacts on marine animal biomass and associated environmental drivers across the No...
Article
A mass balance model of the marine ecosystems is presented for the four prefectures of Japan prior to the Great East Japan earthquake. The Ecopath with Ecosim food web modelling approach and its Ecotracer routine were used to simulate the concentrations of ¹³⁷Cs in the ocean and the biota in order to serve as baseline, , and to estimate the initial...
Article
Predator recovery often leads to ecosystem change that can trigger conflicts with more recently established human activities. In the eastern North Pacific, recovering sea otters are transforming coastal systems by reducing populations of benthic invertebrates and releasing kelp forests from grazing pressure. These changes threaten established shell...
Article
The commercially, recreationally and culturally important Fraser River Sockeye Salmon Oncorhynchus nerka have experienced a productivity decline over the last three decades, which along with greater temporal variation in annual abundance (i.e. cyclic dominance) may at least partly be due to Steller Sea Lion Eumetopias jubatus (SSL) predation on ret...
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Aquaculture is the world's most diverse farming practice in terms of number of species, farming methods and environments used. While various organizations and institutions have promoted species diversification, overall species diversity within the aquaculture industry is likely not promoted nor sufficiently well quantified. Using the most extensive...
Article
When fish stocks migrate across multiple exclusive economic zones (EEZs), they compel managers to examine management at both national and international levels. A strategic interaction emerges when the fishing activity of one country impacts fishing opportunities available for other countries sharing the stock. Left unaddressed, strategic interactio...
Article
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Under climate change, species composition and abundances in high-latitude waters are expected to substantially reconfigure with consequences for trophic relationships and ecosystem services. Outcomes are challenging to project at national scales, despite their importance for management decisions. Using an ensemble of six global marine ecosystem mod...
Article
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Several studies have shown that mean length is only slightly biased and hence a robust indicator of the total mortality (fishing and natural mortalities). However, these studies use models that typically assume equilibrium conditions and are expected to predict a much stronger relationship between mean length and fishing mortality than would be obt...
Article
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This paper examines the structure and dynamics of the marine ecosystem surrounding Haida Gwaii (an archipelago in the southeastern Gulf of Alaska). Based on previous research, a set of improved mass-balanced models was constructed in Ecopath with Ecosim (EwE) to represent ecosystem states existing circa 1900, 1950, and currently. These models featu...
Article
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A mass balance model of trophic interactions among ten key functional producer and consumer groups in Lake Volta was constructed using the Ecopath model to study the energy flows and species interactions in the lake. The present study was based on secondary and primary data on fish catch, diet composition, phytoplankton and zooplankton biomasses, c...
Article
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While the physical dimensions of climate change are now routinely assessed through multimodel intercomparisons, projected impacts on the global ocean ecosystem generally rely on individual models with a specific set of assumptions. To address these single-model limitations, we present standardized ensemble projections from six global marine ecosyst...
Technical Report
Full-text available
Global fisheries catches can be increased in a sustainable way after rebuilding of fish populations, if ecosystem functioning is considered. A central biological reference point for fisheries management, Fmsy, the fishing pressure that gives the maximum sustainable yield, has been re-evaluated taking into account ecosystem functioning. This has bee...
Technical Report
Full-text available
The participants of the project “Ecosystem Based FMSY Values in Fisheries Management”, in short, the “FMSY project”, meet for the third time. The meeting took place at the facilities of the Bay Campus, University of Rhode Island, Narragansett, RI 02881, USA, 12-14 March 2018. An Agenda for the meeting was send out beforehand, and is given in Append...
Technical Report
Full-text available
The participants of the project “Ecosystem Based FMSY Values in Fisheries Management”, in short, the “MSY project”, meet for the first time. The meeting took place at the facilities of the Nordic Council of Ministers, Copenhagen, Denmark, 20-21 June 2017. An Agenda for the meeting was send out beforehand, and is given in Appendix 1. The list of par...
Technical Report
Full-text available
The participants of the project “Ecosystem Based FMSY Values in Fisheries Management”, in short, the “FMSY project”, meet for the first time. The meeting took place at the facilities of the University of British Columbia, Vancouver, Canada, 31 October to 2 November 2017. An Agenda for the meeting was send out beforehand, and is given in Appendix 1....
Technical Report
Full-text available
Global fisheries catches can be increased in a sustainable way after rebuilding of fish populations, if ecosystem functioning is considered.
Technical Report
Full-text available
Global fisheries catches can be increased in a sustainable way after rebuilding of fish populations, if ecosystem functioning is considered.
Article
In this paper we consider what may happen to the marine ecosystem of Gran Canaria Island within the 2030 horizon, if fishing strategies different from those currently in place were implemented and we evaluate the effect of, for example, reduction of recreational–artisanal fishing, limitation of catches (e.g. total allowable catches, TAC), or spatia...
Article
This study evaluated the socioeconomic benefits generated by the small-scale fisheries sector based on a socioeconomic modeling approach using the value chain plugin in the Ecopath with Ecosim (EwE) software system. Based on an EwE ecosystem model for the Baía Formosa area in Rio Grande do Norte State (Northeast Brazil), a value chain with 14 compo...
Article
Climate change, represented by ever-rising ocean temperatures, is a mounting threat to the marine ecosystem and its services. This is most evident in the longitudinal and depth-related migrations of the ectothermic species. Although the impacts of climate change on the marine ecosystem of the Arabian Gulf are expected to be exacerbated—owing to its...
Article
Coastal ecosystems are influenced by a suite of drivers and interactions, resulting in complex dynamics not captured by single species, single driver approaches. Kelp forest ecosystems of the California Current region are subject to extreme environmental variability as well as a suite of fishing pressures which remove organisms throughout the food...
Preprint
Full-text available
Climate change is shifting the abundance and distribution of marine species with consequences for ecosystem functioning, seafood supply, management and conservation. Several approaches for future projection exist but these have never been compared systematically to assess their variability. We conducted standardized ensemble projections including 6...
Article
In complex dynamic systems like fisheries, recognizing fishing-effort responses is as critical as understanding the biology of the exploited species for making sensible management decisions. In highly seasonal fisheries, it is theoretically possible for an “interannual bionomic equilibrium” to develop under open-access, where fleet dynamics may res...
Chapter
Coral reef and other tropical ecosystems together are the most productive and biologically diverse aquatic environments, yet they are also the most sensitive to human activities and ecological disturbance. The sustainability of coral reef and other tropical fisheries is challenged by growing population and poverty. The globalized trade market of fi...
Article
Full-text available
Model intercomparison studies in the climate and Earth sciences communities have been crucial to building credibility and coherence for future projections. They have quantified variability among models, spurred model development, contrasted within- and among-model uncertainty, assessed model fits to historical data, and provided ensemble projection...
Article
Full-text available
Sellafield marine discharges of 14C are the largest contributor to the global collective dose from the nuclear fuel industry. As such, it is important to understand the fate of these discharges beyond the limitations and scope of empirical analytical investigations for this highly mobile radioactive contaminant. Ecopath with Ecosim (EwE) is widely...
Article
Like fishing, natural regime shifts and human-induced environmental changes are often equally important factors in driving fish stock declines. In the Northwestern Arabian Gulf, many fish stocks are declining, raising questions about the reduction in the flow of Tigris-Euphrates rivers. Here we investigate the relationship between Tigris-Euphrates...
Article
Full-text available
Marine ecosystems evolve under many interconnected and area-specific pressures. To fulfil society's intensifying and diversifying needs while ensuring ecologically sustainable development, more effective marine spatial planning and broader-scope management of marine resources is necessary. Integrated ecological–economic fisheries models (IEEFMs) of...
Article
Full-text available
Ecotracer is a tool in the Ecopath with Ecosim (EwE) software package used to simulate and analyze the transport of contaminants such as methylmercury or radiocesium through aquatic food webs. Ecotracer solves the contaminant dynamic equations simultaneously with the biomass dynamic equations in Ecosim/Ecospace. In this paper, we give a detailed de...
Preprint
Full-text available
Model intercomparison studies in the climate and earth sciences communities have been crucial to build credibility and coherence for future projections. They have quantified variability among models, spurred model development, contrasted within- and among-model uncertainty, assessed model fits to historical data, and provided ensemble projections o...
Article
Full-text available
An important challenge for conserving and managing marine ecosystems is to advance our understanding of how multiple human stressors, environmental factors and marine resources interact and influence each other. The ecosystems of the Israeli Mediterranean coast have undergone significant ecological changes in recent decades, caused primarily by the...
Chapter
The effects of coastal hypoxia on fish biomass and fisheries landings in the northern Gulf of Mexico have been difficult to quantify. A main complicating factor is the fact that nutrient loading from freshwater discharge is not only the main contributor to the formation of the hypoxic zone, but also a driver of secondary productivity through bottom...
Article
Full-text available
The Mediterranean Sea has been defined “under siege” because of intense pressures from multiple human activities; yet there is still insufficient information on the cumulative impact of these stressors on the ecosystem and its resources. We evaluate how the historical (1950–2011) trends of various ecosystems groups/species have been impacted by cha...
Article
Peru is home to the world's biggest fishery with catches of over 95 million tonnes of anchoveta (Engraulis ringens), since 2000, yet one in six small children in Peru suffer from chronic malnutrition. This is not because anchoveta is unsuitable for human consumption—on the contrary, they are nutritious, tasty and available year-round, close to the...
Article
Since the 1950s, invertebrate fisheries catches have rapidly expanded globally to more than 10 million tonnes annually, with twice as many target species, and are now significant contributors to global seafood provision, export, trade and local livelihoods. Invertebrates play important and diverse functional roles in marine ecosystems, yet the ecos...
Article
Full-text available
Resource managers are often tasked with identifying and assessing the potential impacts of management actions on the biotic communities under their care. When the management activities directly influence a single species of interest, managers can turn to a variety of models to aid in their understanding of potential changes to that population. Howe...
Article
Simple predator-prey models make widely divergent predictions about impact on piscivores of harvesting forage fish species, depending on structural assumptions about the fine-scale spatial structure of trophic interactions (presence or absence of foraging arena structure in prey availability) and about limitation in predator or prey recruitment due...
Article
Simple predator-prey models make widely divergent predictions about impact on piscivores of harvesting forage fish species, depending on structural assumptions about the fine-scale spatial structure of trophic interactions (presence or absence of foraging arena structure in prey availability) and about limitation in predator or prey recruitment due...