Potential Risk of Floating Marine Litter to Cetaceans and Sea Turtles: A Review of Spatial Risk Exposure Assessments

Marine litter is a main threat for marine life, although the assessment of the associated risks has not yet been fully incorporated into area‑based management tools. Floating litter is detrimental to cetaceans and sea turtles, and thus, these organisms are considered an effective indicator of areas where litter accumulates. Increasing our ability to predict high‑exposure risk locations, i.e., where and when marine megafauna is exposed to the potential negative impacts of litter, is important for prioritising smart‑conservation planning and is an essential first step in characterising the risk of real injury/damage. However, Risk Exposure Assessment (REA) is still underrepresented as a standardised procedure. Here, a literature review framed the state‑of‑the‑art of REA approaches for cetaceans and sea turtles from floating litter supporting the standardisation of metrics and procedures. Of the 415 papers resulting from the literature search, the 23 selected (2011–2022) showed that 57% of the studies were conducted in the Western‑Mediterranean Sea, evidencing inconsistent geographical applications. While a variety of REA methodological approaches revealed high informational heterogeneity, main limits and future recommendations were identified regarding raw data availability, information bias, geographical gaps, target species selection and lack of standard protocol needed to assess trends to evaluate the effectiveness of mitigation measures. Ultimately, the study showed that a spatial‑contextual approach (possibly functional trait‑based) is needed to effectively support long‑term year‑round monitoring programmes, especially in still un‑surveyed regions.