Harbour seals were extensively hunted in Denmark, but have only been driven to local extinction in one larger area, the South Funen Archipelago and Little Belt, where the species has been absent throughout the 20th century. Despite high growth rates of the Danish harbour seal populations after protection from hunting in 1976, seals have only been observed sporadically in the South Funen Archipelago and Little Belt until recent years, where recolonisation now causes conflicts with fisheries. Here, we review historical sources documenting the local extinction of harbour seals in the area during the 19th century and report the results of aerial surveys of haul-out sites during moulting seasons of 2021–2023 and pupping seasons of 2022 and 2023. Historical sources reveal that seal hunting was a common practice in southern Denmark, but catches dwindled to rarities during the 19th century. During recent surveys, seals were detected at six of the identified potential haul-out sites. Around Aarø Island, an average of 141 (range: 92–186) harbour seals were recorded over four moulting season surveys, constituting the majority (90%) of the total counts of the surveyed area. During the pupping seasons, a total of five pups was encountered at two different haulouts. As none of the haulouts are protected during the pupping and breeding seasons, protective measures may support this recolonisation of the historic harbour seal breeding range.

Grey seals from both the Atlantic and Baltic Sea subspecies are recovering from dramatic declines and recolonising former ranges, potentially leading to overlapping distributions and an emerging subspecies transition zone in Kattegat between Denmark and Sweden. The two subspecies have asynchronous moulting and pupping seasons. We present aerial survey data from 2011 to 2023 in Danish Kattegat during the Atlantic subspecies' moulting (March–April) and pupping (December–January) seasons, as well as the Baltic subspecies' moulting season (May–June). During the Atlantic subspecies' peak moulting season, 82% of the grey seals were recorded north of the island of Læsø (N57°18′, E11°00′). In contrast, during the Baltic moulting season in those years, only 9% of the grey seals were recorded here. This indicates a predominance of Atlantic grey seals in the north and Baltic grey seals in central and southern Kattegat. In 2022 and 2023, three pups were recorded around Læsø during early January, which coincides with the pupping season of northern Wadden Sea grey seals. Previously, pups have been recorded in the same locations during the Baltic pupping season, which demonstrates overlapping breeding ranges. Grey seals are known to have plasticity in the timing of pupping indicated by a west to east cline of progressively later pupping in the eastern North Atlantic. Historical sources document that the Baltic pupping season in Kattegat was earlier than it has been in recent years. Thus, the expanding ranges may be associated with convergence of Atlantic and Baltic subspecies' pupping seasons and potential hybridisation in this emerging transition zone.

Les prélèvements de dérive en période de décrue réalisés conjointement dans le chenal principal et un chenal secondaire de la Durance ont mis en évidence l'importance de la dérive dans le repeuplement du lit principal. Une partie de cette dérive provient du champ d'inondation temporairement colonisé par les organismes benthiques dispersés, l'autre vient des chenaux latéraux.