Remote monitoring of the bycatch of demersal chondrichthyans using video imagery: a case study from a deep-water crustacean trawler

Effective monitoring and reporting of fisheries are crucial for successful management and are typically done by at-sea observers and fishers, respectively. However, this system can produce biased information due to economic and social limitations. Electronic monitoring and reporting systems (EMRs) are becoming more prevalent and are seen as a solution to combat illegal, unreported, and unregulated fishing. The present study aimed to test the effectiveness of an integrated EMR in identifying demersal and deep-sea sharks, skates, and chimaeras (hereafter chondrichthyans), which are bycatch in the Portuguese crustacean bottom trawl fishery. Footage (42 h) was thoroughly examined and provided identification of 2182 individuals representing 11 taxa. The majority were identified to the genus level, and some even to the species level. Only 0.9% of the chondrichthyans could not be identified. Furthermore, the highest bycatch rates of chondrichthyans were from the genera Etmopterus and Galeus. The limitations of the technology are discussed, and suggestions for improvement are made to enhance future research proposals and improve the overall design of the system. However, the successful implementation of the EMR in this study and other case studies worldwide demonstrates its potential for upscaling to other fisheries, contributing significantly to more sustainable fishing practices and better management of marine resources.