An index to differentiate megafauna entangled in operational fishing gears from abandoned, lost, or otherwise discarded fishing gears

Classifying entanglements of marine megafauna in certain anthropogenic items is challenging because many are found in fishing-related items, with the cause being either operational fishing gear (OFG) or abandoned, lost, or otherwise discarded fishing gear (ALDFG). The distinction between OFG and ALDFG is essential as each source requires different mitigation and remediation strategies. To reduce the uncertainty in sorting between these two distinct threats, we developed the Entanglement Source Assessment (ENSA) index. This index integrates a series of criteria related to the entangling item and the affected organism. It assess the likelihood that an entanglement was caused by an OFG or by an ALDFG using a Multi-Criteria Decision Analysis approach. The index was tested on 35 entanglement events involving various taxa, using video footage and photographs recorded in the Azores Archipelago (NE Atlantic). Overall, 57 % of the entanglements were classified as likely caused by ALDFG (ENSA scoring >60), indicating they resulted from marine debris. In comparison, 23 % were classified as likely from interactions with OFG (ENSA scoring ≤40). The remaining events were ambiguous and could not be confidently assigned to either source. ENSA is a valuable tool that integrates expert knowledge, transparently providing a clear view of the steps and reasoning behind the classification process. It will promote standardization when reporting the source (OFG vs. ALDFG), which is essential for implementing adequate policy measures to address the entanglement of marine megafauna in fishing-related items at national and global scales.