New Publication: Harbour Porpoise distribution modelling techniques

Ocean Science Consulting Limited (OSC) is excited to report the publication of our newest peer-reviewed paper in Ecological Modelling. The paper, titled ‘Comparing distribution of harbour porpoise using generalized additive models and hierarchical Bayesian models with integrated nested laplace approximation’ was authored by OSC’s Senior Analyst, Dr Laura Williamson, Prof Beth Scott, Megan Laxton, Prof Janine Illian, OSC’s Managing Director Dr Victoria Todd, Dr Peter Miller, and Dr Kate Brookes.

Species Distribution Models are used regularly to develop management strategies for anthropogenic disturbance in the marine environment, but many modelling techniques ignore the spatial nature of data. This can lead to a poor understanding of key marine species in the area. To address this, we compared predictions of two different modelling approaches on the fine-scale spatial distribution of harbour porpoise (Phocoena phocoena). We used aerial-video-survey data of porpoise, collected along the east coast of Scotland in August and September, 2010 and 2014. Environmental variables were also included in statistical models, to represent porpoise habitat preference and the presence of prey species. We compared the traditional and commonly implemented Generalized Additive Model (GAM) with two Hierarchical Bayesian Modelling (HBM) approaches which used an Integrated Nested Laplace Approximation (INLA) model-fitting methodology. 

Predicted harbour porpoise densities on the Scottish east coast, from each modelling technique. (See publication for full description)

Overall, predicted porpoise distributions were similar between the two models; however, HBMs had twice the level of certainty, and also identified some areas of high relative porpoise density that were not apparent in the GAM. For large-scale analysis (>5–10 km resolution), such as initial impact assessments, there was little difference between results, but the HBM model (using LGCP) provided greater insight into the fine-scale (<1 km) distribution of porpoise. While the HBM requires more computational power than GAMs to implement, our new publication demonstrates its potential benefits; we recommend the use of HBM modelling approaches to refine harbour porpoise conservation, management, and mitigation measures within offshore developments or protected areas. 

At OSC, we are proud of our record in publishing scientific articles in peer-reviewed journals, and contributing to the wider scientific understanding of the marine environment. This paper, which focusses heavily on complex statistical approaches, demonstrates our ability to conduct ambitious, highly specialised data analysis and modelling techniques. These skills ensure we provide the best possible data services for clients, and in turn also help to inform industry practices and future scientific research. Dr Laura Williamson would like to extend her thanks to all authors involved in this research and looks forward to working with them again in the future. 

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