Bottlenose Dolphins (Tursiops truncatus) Along the Coast of Israel: Abundance and Social Structure

The dynamics of cetacean populations profoundly shape the survival and well-being of their members, particularly in nutrient-deficient and anthropogenically impacted regions like the eastern Mediterranean Sea. The common bottlenose dolphin (Tursiops truncatus), one of the most extensively studied cetaceans, exhibits complex and diverse social behaviours worldwide. In Israel, common bottlenose dolphins have been observed and studied since 1993, yet no comprehensive analysis has been made of the derived data to unravel their abundance and social structure. Using photographic sightings collected between 2005 and 2020, this study employs mark-recapture models and social network analysis to uncover the population's dynamics. Observations along the entire Israeli coastline revealed an average group size of 5.9 dolphins, 3.8 of which had clearly marked dorsal fins. Abundance estimates indicated a stable population of 68–88 individuals present at any time, forming part of a larger superpopulation of approximately 343 dolphins. Within this, 42 mature individuals presented higher site fidelity to the study area and exhibited a fluid fission-fusion social structure characterized by frequent group changes and short-term associations. Most identified individuals were observed foraging around fishing trawlers, forming significantly smaller groups and exhibiting lower association indices than those observed in the absence of trawlers. These findings emphasize the existence of a small, partially resident population in the easternmost Mediterranean Sea, highlighting the urgent need for coordinated, region-wide conservation efforts to protect this vulnerable population, mitigate the impact of fishing trawlers and preserve their dynamic habitat.