Exploring the temporal dynamics of cetaceans strandings in the Mediterranean Sea

Identifying temporal trends in cetacean strandings and factors affecting their mortality is crucial to provide supporting information on mitigation and conservation actions. Analysis of stranding data collected from multiple databases, shows that a total of 3816 stranding events of six cetacean species were recorded between 2000 and 2021 in the Mediterranean Sea. The main evidence is that in 87.7% of stranding events the cause of death was unknown, while bycatch resulted to be the most frequent identified cause (N=321, 8.4%). Significant positive trends in annual strandings events were detected for the striped dolphin Stenella coeruleoalba, the common bottlenose dolphin Tursiops truncatus, and the common dolphin Delphinus delphis. Bycatch showed different trends at the species level, with a significant reduction in striped dolphins strandings and an increase for common bottlenose dolphins. Results suggest that juvenile striped dolphins appear to be significantly more vulnerable to both bycatch and collision compared to other life stages, while in common bottlenose dolphins these impacts are more evenly distributed across all age classes, with no significant differences between life stages. Additionally, juveniles of common bottlenose dolphins showed significantly lower natural mortality compared to other age classes. Although stranding events are considerable sources of data and offer cost-effective tools for monitoring these species, the lack of strong Mediterranean coordination still prevents the collection of information in a systematic and uniform way, limiting the possibility to conduct robust assessments at Mediterranean scale.