Assessing Seafloor Litter Classification: Lessons from an Online Proficiency Test.

Seafloor litter is an applied indicator for the assessment of marine pollution. Harmonized seafloor litter categorization is essential for quality assured assessments. This study aimed to assess the quality of seafloor litter classification and the effectiveness of the International Council for Exploration of the Sea (ICES) seafloor litter categorization guidelines through an online proficiency test. Participants classified pictures of seafloor litter from trawls based on the ICES manual and photo guide. The test identified correlations between users' experience and classification accuracy. Findings demonstrated participants had a good ability to classify seafloor litter items based on the guidelines with an average accuracy rate of 83%. Some items were misclassified, but these errors could not be linked to the experience of the participants. Misclassifications during the proficiency test could be related to the nature of the picture-based assessment, a lack of participant knowledge of seafloor litter, and/or a lack of clarity in classification guidelines. The results of the test can be used as part of quality assurance measures to strengthen monitoring guidelines, future data collection and improve our understanding of potential human error in seafloor litter datasets.