Marine turtles are traditionally restricted to tropical and subtropical waters, where temperature regimes support their thermoregulation, navigation, and migratory behaviour. Despite this, rare strandings have historically occurred in northern European regions, including Denmark. Here, we present the first century-scale consolidation of marine turtle stranding records in Denmark (1926-2025), revealing a sharp rise in strandings since 2020-particularly between 2024 and early 2025-exceeding all events recorded in the previous 94 years. We conducted mitochondrial DNA analysis on stranded loggerhead (Caretta caretta), leatherback (Dermochelys coriacea), and green turtles (Chelonia mydas) collected over the past 26 years. D-loop haplotypes indicate that most individuals carried lineages previously reported from rookeries in the North Atlantic and Greater Caribbean, with some haplotypes also documented in West Africa. One C. mydas carried a distinct Omani haplotype associated with the northwestern Indian Ocean lineage, consistent with anthropogenic introduction. Environmental parameters, including sea surface temperature, wind speed, and storm frequency, were analysed alongside the stranding records, suggesting associations between stranding events and seasonal climatic conditions, particularly during winter months. Our results suggest that oceanographic conditions and cold-stunning during winter months may contribute to the increasing number of strandings observed in temperate waters. The recent rise in turtle strandings in Denmark highlights the importance of monitoring marine turtle occurrences at the northern limits of their distribution. Integrating genetic data with environmental observations provides a useful framework for understanding how marine turtle movements and strandings may respond to changing marine conditions.
Nielsen et al. (Wed,) studied this question.