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Are bottlenose dolphins starving in eastern Ionian Greece?

Giovanni Bearzi and Elena Politi / Tethys Research Institute

Based on a study that has been presented at the last European Cetacean Society conference in Cork, Ireland, bottlenose dolphins (
Tursiops truncatus) photo-identified in eastern Ionian Greece coastal waters show clear signs of malnutrition. An estimated 39% of the photo-identified adults had inter-rib spaces that were distinctively hollowed in the visible part of the thorax.

This small bottlenose dolphin community has been consistently studied since 1993 by the Tethys Research Institute, and includes 44 photo-identified individuals showing high levels of site fidelity. These dolphins share the area with a community of common dolphins (
Delphinus delphis).

As the lack of sufficient food to maximise reproductive potential may be the most important regulator of population size in animals, the reported findings may be indicative of the potential threats affecting this coastal bottlenose dolphin community. The high percentage of individuals showing signs of malnutrition suggests that the community is experiencing feeding-related difficulties.

Bottom trawling is seasonally intensive in the area, and has reportedly reduced local demersal fish resources. Since 1985, it has been acknowledged that the hake in this area has been "heavily overfished", local stocks being largely composed of immature individuals. As bottlenose dolphins in the Mediterranean Sea largely rely on demersal food prey, the species may be negatively affected by local overfishing, particularly as far as trawling fisheries are concerned.

Potential "food-web competition" with the sympatric community of short-beaked common dolphins may also occur. However, this is unlikely to account for the dramatic level of bottlenose dolphin malnutrition recorded in the area, also considering that the two species seem to have rather diverse food preferences and strategies.

The small size of the bottlenose dolphin community and its degree of genetic isolation suggest that this community may have undergone a substantial decline, and may be currently under threat. Critical habitat requirements - particularly as far as prey availability is concerned - must be assessed to ensure the survival of this coastal bottlenose dolphin community.