Villy Christensen

 
Prospective Graduate Students / Postdocs

This faculty member is currently not looking for graduate students or Postdoctoral Fellows. Please do not contact the faculty member with any such requests.

Professor

Research Classification

Ecosystem (Aquatic and Terrestrial)
Ecological Trends
Fishery Resources
Marine Environment

Relevant Degree Programs

 

Postdoctoral Fellows

  • Vijay Kumar (Oceans and Inland Waters, Prediction and Climatic Modeling)

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 (Jan 2008 - Mar 2019)
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.

View record

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

No abstract available.

Master's Student Supervision (2010-2017)
Characterizing the knowledge and attitudes towards sharks and the domestic use of shark meat and fins in Peru (2017)

Shark populations show evidence of declines at a global scale. Knowledge of the socio-economic consequences of changes in their abundance is limited. Furthermore, research on the status of peoples’ knowledge and attitudes towards sharks and how these affect their values, behaviours and actions is lagging behind the pursuit of biological and ecological concerns.Framed within Peru’s National Plan of Action for the Conservation and Management of Sharks, Rays and Chimeras, the present study sought to: (1) characterize coastal Peruvian’s general knowledge and attitudes towards sharks and shark meat consumption; (2) describe the domestic market and trade flows of shark commodities; (3) estimate the apparent consumption of shark meat and fins in Peru; and (4) reconstruct the catches required to maintain the estimated local levels of shark consumption.Using data from over 2000 surveys provided by OCEANA Peru, I determined that a limited proportion of the Peruvian coastal population was aware of sharks’ presence in the country’s waters, and of these, only a minor subset was capable of naming shark species found locally. Furthermore, Peruvians have very negative attitudes towards sharks, driven by fear and prevalent misconceptions regarding their feeding habits and behaviour, which are reinforced by mass media.Using public data, provided by various organizations within the Peruvian government, I determined that shark meat consumption in Peru is high and growing, although its contribution to national food security remains low. Nonetheless, most shark meat consumers are not aware that they are eating sharks due to deceptive advertising. Improvements on seafood traceability have only been observed on exports, as data associated with landings, local markets and imports remains highly aggregated. Moreover, official statistics severely underestimate the catches required to maintain the Peruvian supply (by 39%) and demand (by 85%) of shark products.These findings can be used to inform the design of communications campaigns and government policies seeking to: (i) improve people’s knowledge and attitudes towards sharks in Peru, (ii) increase seafood traceability, (iii) protect seafood consumers, and (iv) advance towards the incorporation of these dimensions in the quantitative evaluation of policy outcomes for achieving sustainable shark fisheries.

View record

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.

View record

 
 

If this is your researcher profile you can log in to the Faculty & Staff portal to update your details and provide recruitment preferences.