Uncovering the global status of plastic presence in marine chondrichthyans

Plastic pollution represents a global environmental issue. Awareness of plastic pollution in marine organisms increased strongly during the last decades, including chondrichthyans. Due to a lack of a broad and comprehensive view of this global issue in chondrichthyans, we synthesized the 48 publications covering 54 species since 2002, and employed bibliometric analysis and data exploration to summarize the historical progression of the development, characteristics of plastics in chondrichthyans and evaluate their potential impacts across various regions, habitats, and Red List categories. The bibliometric analysis revealed that the investigation of plastic distribution in demersal sharks inhabiting the nearshore areas of the Mediterranean and northeastern Atlantic Ocean is a major research focus. Based on the current evaluation, plastics have been ubiquitously discovered within sharks, skates, and rays; however, only less than 5% of chondrichthyans worldwide have been investigated. Among these, 25 species are classified under one of the three threatened categories (critically endangered, endangered or vulnerable), according to IUCN Red List. The average abundance (all specimens) and load (specimens that contained plastics) in chondrichthyans were 2.86 +/- 7.71 items/individual and 4.91 +/- 9.39 items/individual, respectively. Plastic abundance/load is not influenced by the sampling regions, habitats, or Red List categories; however, higher records were found in the endangered and near threatened species. The plastics are predominantly fibrous in shape, with blue and black being the predominant colors, along with polypropylene and polyethylene in polymer type. Notably, inconsistencies in sampling, processing, and identification methods across studies might impeded the integration and comparison of data. This review highlights the potential implications of plastic pollution from chondrichthyans on biodiversity conservation and emphasizes the necessity to consider intra- and inter-specific variations in biometric and ecological characteristics, as well as establish standardized protocols to facilitate effective comparisons in contamination dynamics between studies of chondrichthyans.