Common dolphins around Kalamos, Greece
The species’ precipitous decline in eastern Ionian Sea coastal waters was documented by researchers who studied a population living around the island of Kalamos, near Lefkada, Greece.
Seeing common dolphins was a frequent event around the Greek island of Kalamos until the late 1990s.
Today, common dolphins have become a rare sight in this EC Site of Community Importance. Their numbers dropped by one order of magnitude in only ten years.
Large marine predators like tuna and swordfish have also become rare, and fishermen lament a decline in landings.
The main reason behind ecosystem collapse is fishery mismanagement resulting in overfishing.
Main threats: overfishing and mortality in fishing gear.
Management solution: reduce fishing effort and ban detrimental fishing gear (used by a relatively small number of boats).
Benefits: ecosystem recovery, increased biodiversity, increased aesthetic and cultural value of the area, survival of artisanal fishing, nature tourism.
Dolphins declined dramatically across the 13 years of the study (1995-2007).
While 150 animals were present in the study area (about 1000 km2) in 1996, only 15 were observed in 2007.
The decline of common dolphins around Kalamos, western Greece.
The movements of common dolphins tracked by the researchers based on individual photo-identification (an entirely benign, non-intrusive method) are shown below.
Movements of common dolphins around Kalamos between 1997 and 2007.
Evidence shows that the decline was caused primarily by prey depletion resulting from overfishing.
The impact of fishing on the local ecosystem has been tremendous, and resulted in the almost complete disappearance of common dolphins and in the decline of tuna and other large marine predators.
Estimate of total fish biomass removed by common dolphins and fisheries. The red part of the fisheries bars shows removal of species representing key prey for common dolphins.
Cetacean Alliance investigators:
For more information, see:
Bearzi G., Politi E., Agazzi S., Azzellino A. 2006. Prey depletion caused by overfishing and the decline of marine megafauna in eastern Ionian Sea coastal waters (central Mediterranean). Biological Conservation 127(4):373-382. (444 Kb)
Bearzi G., Agazzi S., Gonzalvo J., Costa M., Bonizzoni S., Politi E., Piroddi C., Reeves R.R. 2008. Overfishing and the disappearance of short-beaked common dolphins from western Greece. Endangered Species Research 5:1-12. (1.0 Mb)