Les échouages de mammifères marins en France en 2023: Réseau National Echouages (RNE)Rapport annuel Hexagone (incluant la Corse) et Outre-Mer

STRANDINGS OF MARINE MAMMALS ON THE FRENCH COASTLINE IN 2023France, Mainland and CorsicaThis report, for 2023, compiles all the reports received by the National Stranding Network (RNE), with a total of 3,005 marine mammals recorded. Previously, only animals found dead on the coast or taken in, as well as a few rare cases of erratic animals, were included in the reports; this year, animals considered in distress for which RNE intervention could not be performed, are also included. Among the 3,005 recorded cases, 2,681 dead animals were found stranded on the coasts, and 40 were found drifting at sea. Regarding live animals, 266 were reported in distress after stranding, and 18 were in difficulty in the water.The total number of animals observed in 2023 is significantly higher than in previous years, reaching a record high. This increase mainly affects the Atlantic coast, while reports remained relatively stable in the Channel-North Sea and the Mediterranean.Among the recorded species, 2,449 cetaceans (81%, with 15 different species) and 556 pinnipeds (18%, with 2 different species) were observed. The dominant species vary by region: the common dolphin contributed most to the rise in strandings in the Atlantic, the harbor porpoise remained predominant in the Channel-North Sea, and the striped dolphin in the Mediterranean. Notably, the bottlenose dolphin became the third most reported species in 2023, with a record number across all three coasts.A wide diversity of rarer species was also noted, including 2 pygmy sperm whales, a dwarf sperm whale, a Sowerby’s beaked whale, a Gervais’ beaked whale, and 5 Cuvier’s beaked whales. Several large cetaceans were also observed this year, including 3 fin whales, 3 minke whales, 4 humpback whales, and a sperm whale.The year 2023 was also marked by 9 mass stranding events, involving four species: the common dolphin (4 events, 18 individuals), the bottlenose dolphin (3 events, 24 individuals), the striped dolphin (1 event, 3 individuals), and Risso’s dolphin (1 event, 2 individuals). These strandings, involving 2 to 14 individuals, affected six departments across all three coasts. Grey seals account for the highest proportion of seal records (71%), mainly in northern France and Brittany. Harbour seals are mainly recorded on the coasts of northern France.Among the reports, 1,776 cetaceans and 403 pinnipeds were managed by the RNE. This year, significant effort was made to conduct more high-level examinations. Thus, for 5% of the cetaceans and seals, a level 4 veterinary necropsy was carried out. The representativity of the species examined is approximately respected, with the numbers of individuals examined generally proportional to the total number of stranded individuals per species, also respecting the spatial-temporal distribution. The results of high-level examinations corroborate those of lower-level examinations, indicating that bycatch is the main cause of mortality for the common dolphin. However, partial examinations reveal a higher proportion of deaths of indeterminate origin, often focusing causes around violent deaths and bycatch. On the other hand, complete examinations provide a better understanding of mortality causes, particularly by identifying more deaths due to natural causes resulting from pathological conditions and reducing the number of indeterminate cases. These detailed analyses are essential for improving the understanding of mortality factors in marine mammals.OverseasIn 2023, a total of 69 individuals belonging to 22 species were recorded across all overseas territories, including 16 species of cetaceans, 5 of pinnipeds, and 1 sirenian. This high diversity is explained by the geographical expanse of these dispersed territories and the variety of habitats they encompass. The archipelago of Saint-Pierre-and-Miquelon (n=20) and New Caledonia (n=18) reported the highest number of sightings this year, with Saint-Pierre-and-Miquelon also exhibiting the greatest diversity, featuring 8 different species.The survey of sightings in 2023 also revealed the first stranding of the Antarctic Minke Whale in Guyana, a species previously recorded only in New Caledonia. This year also saw the second mention of the Minke Whale in Saint-Pierre-and-Miquelon as well as the Pygmy Sperm Whale in Guadeloupe. Many species of deep-diving whales were reported along the overseas coastline, whether in distress or found dead.Two cases of mortality were reported this year in the Southern Ocean (subantarctic islands and Antarctica), unlike in Saint Martin and Saint Barthélemy, where no sightings were recorded, as well as in the Eparses Islands and Wallis and Futuna. The year 2023 was marked by three mass stranding events involving three different species. These incidents occurred in the Pacific Islands, a region regularly affected by such events that occur almost every year.Among the 69 marine mammals reported in 2023, 54 % were observed by the National Stranding Network. Of the animals examined whose state of decomposition allowed for a more advanced examination, 17 individuals underwent partial examinations by RNE correspondents in the overseas territories, but no complete examinations could be performed.In 2023, reported cases of captures were limited to Guyana, involving 2 Sotalia dolphins during partial examinations. Aside from the indeterminate cases, the most represented cause of death was natural, resulting from a pathological condition, notably with a common dolphin stranded in Saint-Pierre-and-Miquelon and a young humpback whale in distress in Martinique.

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