Spatiotemporal modeling of bycatch data: methods and a practical guide through a case study in a Canadian Arctic fishery

Excess bycatch of marine species during commercial fishing trips is a challenging problem in fishery management worldwide. The aims of this paper are twofold: to introduce methods and provide a practical guide for spatiotemporal modelling of bycatch data, as well as to apply these methods and present a thorough examination of Greenland shark (Somniosus microcephalus) bycatch weight in a Canadian Arctic fishery. We introduce the spatially explicit two-part model and offer a step by step guide for applying the model to any form of bycatch data, from data cleaning, exploratory data analysis, variable and model selection, model checking, to results interpretation. We address various problems encountered in decision making and suggest that researchers proceed cautiously and always keep in mind the aims of the analysis when fitting a spatiotemporal model. Results identified spatiotemporal hotspots and indicated month and gear type were key drivers of high bycatch. The importance of onboard observers in providing robust bycatch data was also evident. These findings will help to inform conservation strategies and management decisions, such as limiting access to spatial hotspots, seasonal closures and gear restrictions.