Spatial-Temporal Distribution of Megamouth Shark, Megachasma pelagios, Inferred from over 250 Individuals Recorded in the Three Oceans

First record of the megamouth shark Megachasma pelagios (Lamniformes: Megachasmidae), from the United Republic of Tanzania

The megamouth shark Megachasma pelagios (Lamniformes: Megachasmidae) was described in 1976 from a specimen caught off Hawaii (Taylor et al. 1983) and is the only extant member of its family and genus (Diez et al. 2022). From 1976 to 2010 M. pelagios was considered rare, with only 50 individuals recorded globally during that time (Nakaya 2010). In recent years it is apparent that it is more common and widespread than previously thought, with 273 confirmed records to date across 16 countries in the Atlantic, Indian and Pacific Oceans (Yu et al. 2021; Diez et al. 2022; Skelton et al. 2023). This species is classified as Least Concern on the IUCN Red List of Threatened Species, as it is globally distributed and does not appear to be heavily impacted by fisheries (Kyne et al. 2019).

To what extent are filter feeder elasmobranchs exposed to marine pollution? A systematic review

Filter feeding elasmobranchs may be considered as biological indicators of marine pollution, despite most of these species are under some degree of extinction risk. Among threats to this taxonomic group, marine pollution might represent an additional concern for their survival. In this review, a comprehensive systematic search of scientific literature on pollutants in filter feeding elasmobranchs was conducted to evaluate the bioaccumulation patterns, and risk for human consumers. We found that, despite an increasing trend in the number of published studies, the geographical coverage is still very limited and most of the studies focused solely on trace elements (70.8%). Among sharks, Rhincodon typus was the most represented species (66.7%), while Mobula mobular the most studied ray species (41.7%). Comparing the levels of pollutants in filter feeders between ocean basins, this review highlighted that Hg, As and Cd levels are mostly higher in those areas affected by both strong natural and anthropogenic source of emissions, such as the Indian Ocean. With regards to OCs, ΣPCB levels in muscle of C. maximus were between 4.3 and 50.5 μg kg^-1 ww, highlighting a persistent contamination of PCB in the Mediterranean Sea. Some species exceeded the maximum allowable limits for foodstuff consumption for As, Cd and Pb. A total of 77.8% of the analyzed species exceeded the Environmental Quality Standards for Hg, while they were always below the EQS_biota for HCB, PBDEs, PFOS and DDT. Given their feeding mechanism that continuously samples the marine environment, further investigations are urgently needed to determine not only the extent of contaminant exposure in different hotspot locations but also the risks posed to the elasmobranch health.