Object-oriented migration modelling for biological impact assessment

We present a general animal migration model based on field data and driven by stochastic movement routines. This approach avoids the inaccuracies of random or uniform animal distribution assumptions and circumvents the causal modelling of complex migratory mechanisms, such as guiding or navigation, to reproduce detailed movement patterns of individuals within a population. The general migration model, MIGMOD, exploits the object-oriented programming paradigm (OOP) to efficiently model both general migratory behaviors and those that vary across species and age/sex classes. MIGMOD couples to a model of the behavior and fate of petroleum and chemical spills, thus producing quantitative measures of potential biological impacts. This paper presents MIGMOD-generated impact assessments of ringed seal and polar bear populations for several hypothetical oil spills in the Barents sea. By varying the oil-release date and the migration speeds of the animals, different exposure data are generated. In particular, spill timing affects certain developmental classes of ringed seals more than others, and migration speed has a drastic positive effect upon the exposure incidents of polar bears. These differences indicate both (a) the sensitivity of the model to these parameters and (b) the advantages of migration modelling over simpler approaches that fail to incorporate factors such as large-scale seasonal movements, denning, foraging and other idiosyncratic behaviors of different species and age/sex classes of animals.