Mapping Marine Debris Risk Using Expert Elicitation, Empirical Data, and Spatial Modelling

Anthropogenic debris is a widespread and prevalent component of aquatic systems. Organisms are increasing exposed to debris, leading to detrimental impacts through pathways such as entanglement, ingestion, and bio-accumulation. Multiple taxa interact with debris, and while the consequences to individual organisms are known in principle, their impacts at scales relevant to management are poorly understood. Despite uncertainties, decision-makers are tasked with addressing issues associated with debris and require an estimate of risks. Here, we provide a methodology to estimate the risk posed by specific debris items to a range of organisms within a management area. Risk was determined as a function of both (1) the consequence of an interaction, and (2) the likelihood of exposure, estimated through expert elicitation and empirical debris data, respectively. Using the New South Wales (NSW) Marine Estate as a case study, the methodology identified specific debris items posing risks to seven biological 'assets' (benthic assemblages, cetaceans, fish and sharks, planktonic assemblages, shorebirds, seabirds, turtles) through several pathways. Items posing 'high risk' to these biological groups included fishing-related items (fishing line, nets, traps and pots) through pathways of ingestion and entangle-ment. Microplastics and hard-plastic fragments also posed high risk via ingestion and bioaccumulation. The values were then assessed spatially, using marine debris databases, identifying variability in risk across the Marine Estate and thus, priority areas for management. By identifying the prominent debris items causing risks to specific and multiple assets, resources may be better allocated to maximise the efficacy of interventions.