Novel approach to studying marine fauna: using long-life remote underwater video cameras to assess occurrence and behaviour of threatened and data-deficient elasmobranch species in southern Mozambique

Understanding the behaviour and ecological role of elasmobranchs is essential for their conservation, particularly in regions harbouring threatened and data-deficient species like the Inhambane coastline in southern Mozambique, southwestern Indian Ocean. This study employed long-life remote underwater video cameras (LL-RUV) to observe elasmobranch occurrence and behaviour at a rocky reef near Praia do Tofo known for frequent elasmobranch sightings. Between 2021 and 2024, 524 hours of LL-RUV data were collected, revealing the presence of 14 threatened and data-deficient elasmobranch species. Reef manta rays ( Mobula alfredi ), small eye stingrays ( Megatrygon microps ), and oceanic manta rays ( Mobula birostris ) were identified as the primary elasmobranch users of the studied cleaning stations (n = 81, n = 72 and n = 61 respectively), engaging in mutualistic interactions with cleaner fish and spending significant amounts of time at the studied reef. In contrast, spotted eagle rays ( Aetobatus ocellatus ) and blacktip sharks ( Carcharhinus limbatus ) were solely observed cruising over the reef without engaging in cleaning interactions (n = 40 and n = 27 respectively). In addition, this study provides evidence of intra- and inter-specific interactions between reef and oceanic manta rays, small eye stingrays and bowmouth guitarfish ( Rhina ancylostoma ) and co-occurrences of both manta ray species and smalleye stingrays with “hitchhiker” species including cobia ( Rachycentron canadum ) and remoras ( Echeneis spp.). The use of LL-RUV cameras represents a significant advancement in marine research. These cameras enable continuous, non-intrusive, long-term monitoring of marine environments, capturing natural behaviours, while minimising disturbances caused by divers. As a result, more accurate observations of elasmobranch behaviour and cleaning station dynamics can be recorded, which might be missed during short-term surveys. This research highlights the potential of LL-RUV cameras as powerful tools for advancing our understanding of elasmobranch occurrence and behaviour and underscores their value in informing targeted and effective conservation strategies. Beyond elasmobranch research, LL-RUVs hold tremendous potential for studying a wide range of marine species and habitats, offering a versatile tool for ecological monitoring and conservation efforts across diverse marine ecosystems.