Research report: Distribution dataset of chondrichthyan species occurring in French metropolitan waters and across the North-East Atlantic

A quality-controlled occurrence dataset documents 86 chondrichthyan species recorded in French metropolitan marine waters and surrounding areas between 2003 and 2021. The harmonised, open-access resource provides records across the North-East Atlantic and Western Mediterranean Sea and was the foundation for the Atlas des Chondrichtyens de France métropolitaine. This is a data compilation, not a population assessment or systematic review.

The records cover the Greater North Sea, including the Kattegat, Skagerrak and English Channel; the Celtic Seas; the Bay of Biscay and Iberian Coast; and the Western Mediterranean Sea. Professional fisheries data came primarily from ObsMer, France’s observer programme for commercial fishing vessels. Observers sampled landings, discards and bycatches under a stratified design based on geography, quarterly season, vessel-size class and fleets.

Operations covered exclusive economic zones belonging to France, Great Britain, Spain, Belgium, Ireland and Norway, with some localised high-seas coverage. In Corsica, STARESO monitored small-scale fishing from 2009 to 2015 using a protocol described as comparable to ObsMer; programmes after 2015 were not included. Scientific sources included standardised bottom-trawl and acoustic-trawl surveys, MedSeaCan and CorSeaCan canyon expeditions, and Pelagis aerial and vessel-based observations.

Bottom trawls primarily detect benthic and demersal species and most such surveys did not sample beyond 500 metres. Acoustic trawl surveys target commercial pelagic fish and can record elasmobranchs as bycatch. The canyon campaigns used a remotely operated vehicle or two-seater submarine to collect photographs, videos and biological samples at depths of 90 to 700 metres across 13 selected areas in the Gulf of Lion and around Corsica.

Pelagis aerial surveys recorded observations of megafauna at the sea surface from an altitude of 180 metres while flying at 167 kilometres per hour. Two observers scanned a strip extending 200 metres to either side of the aircraft, documenting large fish and other megafauna without a distance limit. Weather and turbidity were also recorded because they can affect detection.

Vessel-based Pelagis observations were conducted aboard oceanographic vessels during several scientific surveys, with one or two dedicated observers recording conditions, megafauna and other objects encountered. Citizen-science records came from the ELASMED observatory, BioObs platform and APECS national basking-shark recording scheme. Unlike the scientific surveys, these submissions were opportunistic rather than collected under standardised sampling protocols.

ELASMED contributed records from the Western Mediterranean, while BioObs and APECS covered a broader group of marine sub-regions. BioObs applied geographic and feasibility checks and used photographs when available, while APECS retained only observations assigned reliability levels 1a, 1b or 2. Between two and five references were consulted for each species.

A record was geographically plausible when more than half of the relevant references confirmed the species’ presence in the ICES division where it was recorded. Both minimum and maximum thresholds were used for bathydemersal and bathypelagic species; only maximum thresholds were applied to other species. The validation thresholds were fixed to provide a consistent and reproducible framework.

The authors acknowledge that species can depart from known biological or ecological ranges, including during range shifts or in rare observations, and that expert judgement was applied when records were ambiguous. French taxonomic specialists assessed occurrences within their areas of expertise, and every retained occurrence was assigned one of four certainty levels. Spatial precision also varied: some records retained exact coordinates, fishing operations could use the centroid of deployment and retrieval positions, and sensitive ObsMer records were generalised to ICES statistical subrectangles measuring 0.16 degrees of latitude by 0.33 degrees of longitude.

The resource includes 86 species—seven Holocephali and 79 Elasmobranchii—rather than all 106 chondrichthyan species reported for French metropolitan waters. The difference reflects species not recorded in the compiled sources during 2003–2021, potentially because of rarity, limited detectability or their association with habitats that were not surveyed. Geographic coverage extends from 36.00° to 62.33° north and from −15.93° to 12.86° longitude, while the temporal range runs from 1 August 2003 to 21 December 2021.

Scientific names follow TAXREF version 18. Two linked data resources are provided: an event table describing sampling events and their characteristics, and an occurrence table listing species encounters linked to those events by event identifier. An event without a linked occurrence indicates that no species of interest was captured or observed.

The dataset is released under a Creative Commons Public Domain Waiver and is intended to support reuse in scientific analysis, conservation planning and reporting under national and European marine-biodiversity rules.

Subject of Research: A quality-controlled occurrence dataset of chondrichthyan species in French metropolitan waters and the North-East Atlantic and Western Mediterranean Sea, 2003–2021.

Article Title: Distribution dataset of chondrichthyan species occurring in French metropolitan waters and across the North-East Atlantic

Article References: Bisch, A., Stephan, P., Elliott, S., Barreau, T., Bousquet, C., Colombet, L., Dorémus, G., Marengo, M., Lapinski, M., Rohr, A., Sichel, F., Stephan, E., & Acou, A. (2026). Distribution dataset of chondrichthyan species occurring in French metropolitan waters and across the North-East Atlantic. Biodiversity Data Journal, 14, Article e191625. https://doi.org/10.3897/bdj.14.e191625

Image Credits: AI Generated

DOI: 10.3897/BDJ.14.e191625

Keywords: chondrichthyans, France, occurrence dataset, North-East Atlantic, Western Mediterranean, marine biodiversity, fisheries monitoring, citizen science, quality control, marine conservation, Distribution, dataset