Stomach contents of three deep-diving toothed whale species stranded in Greece, eastern Mediterranean

Abstract

Understanding trophic ecology is essential for assessing the role of top predators in marine food webs. In the Mediterranean Sea, toothed whales are key components of megafauna and for this reason, we investigated the diets of nine deep-diving odontocetes stranded along the Greek coastline: five Risso’s dolphins (Grampus griseus), three goose-beaked whales (Ziphius cavirostris) and one sperm whale (Physeter macrocephalus). A total of 17 cephalopod species were identified and quantified via percentage by number (%Ν) and by weight (%W). For Risso’s dolphins, Histioteuthis reversa was the most important prey item (%N=24.7, %W=27.3), while Histioteuthis bonnellii dominated the diets of goose-beaked whales (%N=32.3, %W=34.1) and the sperm whale (%N=86.8, %W=99.8). We report, for the first time for G. griseus in the eastern Mediterranean, Illex coindetii as a rather important prey and the beltfish Trichiurus lepturus as an unusual prey. Our findings underscore the ecological importance of the Histioteuthis genus in the diets of deep-diving toothed whales in the Mediterranean. Risso’s dolphins exhibited the most diverse diet, indicative of a generalist foraging strategy, whereas goose beaked whales and the single sperm whale displayed more specialized feeding habits focusing on mesopelagic and bathypelagic prey. The finding of macroplastics in the sperm whale highlights a widespread threat to this species in the region. Despite the small sample size and the opportunistic nature of stranding events, our findings align with previous evidence of species-specific dietary patterns and emphasize the importance of conserving deep-sea foraging habitats in the eastern Mediterranean.

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