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Projects - dr.ir. GM (Geert) Aarts

  • Student research projects

    For those students who are interested in pursuing a career in marine mammal science (and/or statistical ecology), we sometimes offer the opportunity to carry out a practical training or MSc/BSc thesis project at IMARES. Unfortunately, the available placements are limited, but please send an e-mail if you are interested.

    Some topics available are:

    • Photo ID on grey seals
    • The influence of available forage habitat on the size and distribution of seal colonies
    • Spatial distribution and habitat selection of marine mammals in the North Sea
    • Day-night rhythms in harbour porpoises based on passive acoustic monitoring
    • Small scale distribution of marine mammals based on photogrammetric methods applied to camera recordings. This method can also be used to estimate detection probabilities for passive acoustic monitoring.
    • The effect of underwater explosions on grey seals.

    Since I have a strong interest in (spatial) statistical methods, I’m particularly interested in accepting students with a similar interest in more quantitative ecological research.

     

     

  • Brief summary of research interest

    My research is focussed on three main themes: Marine mammals, fish & fisheries, and statistical ecology.

    After completion of my PhD at the Sea Mammal Research Unit (St. Andrews University, Scotland), I worked for two years part-time at IMARES (Wageningen UR), and part-time at the Mathematics and Statistics Department of Wageningen University, teaching statistics. At the fishery department of IMARES, my research was focussed on statistical age- and size-structured population models, which were applied in stock assessments for commercial flatfish species. In 2009, I continued working on marine mammals at IMARES on Texel, and in 2011 I started a NWO-ZKO Postdoc on the effect of sound on marine mammals.

    Over the years, I have studied several marine mammal species, such as harbour seal, grey seal, harbour porpoise, stellar sea lion and Risso dolphin. I have a strong interest in statistical ecological problems and for example worked on spatial point process models, state-space models for animal movement, distance sampling, Bayesian population models, mixed-effect models, likelihood-based inference, and statistical models for species distributions. I have several years of experience with R, and taught R-courses within the Netherlands and abroad. 

    Currently my research focusses on understanding the spatial distribution of marine mammals. In future years, I hope to spend more time studying how formation of colonies on land is shaped by the surrounding resource landscape. See below for more details.

     

  • The size and distribution of animal colonies and of human settlements: Balancing group advantage and resource depletion.

    Although most organisms (including humans) have a natural tendency to aggregate because of group benefits, it often leads to increase food competition and local resource depletion. If resource availability declines, it may cause a sudden population collapse or even species extinction. The fact that animal aggregations or human settlements of different sizes occur within a landscape indeed suggests the existence of a balance between group benefits and spatially-varying resource availability. There is however an gap in understanding of how resource availability effects the size and distribution of such settlements. Hence, our ability to predict whether those aggregating species are able to cope with ongoing environmental changes is limited.

    In this research we aim to estimate and predict how animal aggregations and human settlements respond to changes in resource availability. Using extensive simulations, we will try to assess how the size and location of aggregations and settlements emerges from different resource landscapes and biological mechanisms. The developed models will be validated using real data. More specifically, we will focus on two central-place foragers, seals (the grey seal Halichoerus grypus and harbour seal Phoca vitulina) and fishermen. These study groups aggregate in well-defined sites, namely colonies and harbours, and forage within the relatively unobstructed marine environment, allowing for free movement. Furthermore, there is ample individual movement data, which can be used to define how they operate in the surrounding seascape, and which resources and types of habitats they select. Data on seals and fishermen helps us to formulate more generic rules describing how the size and distribution of aggregations and settlements change in response to the environment. The resulting framework has the potential to highlight impending collapse of wildlife populations, it may also elucidate which groups of humans are at risk.