Tracing Time's Footprints: Exploring Feeding Ecology and Historical Changes of Mediterranean Common Dolphin (Delphinus delphis) Over Two Centuries

The Mediterranean common dolphin (Delphinus delphis) presents an enigmatic natural history during the past centuries. Widely prevalent in the 19th and early 20th centuries, it faced a significant decline across most of the basin by the late 1960s caused by multiple anthropogenic threats, including culling, bycatch, prey depletion, and habitat degradation. The IUCN has designated the Inner Mediterranean population of common dolphins as Endangered. Here, we analyzed stable isotopes of nitrogen and carbon (δ15N and δ13C) on skeletal remains collected in Mediterranean natural history museums to investigate spatio-temporal trophic shifts and niche partitioning of the Mediterranean common dolphin over the past 200 years. Results indicate that before the 1970s common dolphins occupied a higher trophic level, while after their population decline, they shifted their ecology, overlapping with the striped dolphin, reflecting changes in prey and habitat use. This study provides the first long-term evidence of trophic and ecological shifts in the Mediterranean common dolphin, offering insights into the potential drivers of its decline. Understanding these changes is crucial for conservation efforts, as the species' past and present ecological roles may inform strategies to mitigate further population losses.