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The decline of common dolphins and other marine megafauna east of Lefkada, Greece

 
     
 

The waters east of Lefkada, western Greece - a Natura 2000 Site of Community Importance - are one of the last places where common dolphins can be found in the central Mediterranean Sea.

In 2002 ACCOBAMS recognised that pilot conservation and management actions should be developed and implemented immediately to preserve common dolphin habitat in this area. In the Conservation Plan for Mediterranean common dolphins (ACCOBAMS, 2004), the waters east of Lefkada and around Kalamos were identified as area of high conservation importance.

The significance of protecting common dolphins east of Lefkada and around Kalamos was also highlighted in the IUCN 2002-2010 Conservation Action Plan for the World’s cetaceans.

Notwithstanding these designations, the immediate risk of complete eradication from the area of common dolphins was documented by intensive research.

 

Common dolphin numbers decreased from 150 to only 15 animals in ten years.

 

Abundance trend of common dolphins east of Lefkada and around the island of Kalamos in 1995-2007:

 

Occurrence of common dolphins east of Lefkada and around the island of Kalamos in 1997-2007 (red lines) indicate the extent of the decline:

GPS tracks of research vessels closely following common dolphin groups are shown as a proxy of common dolphin relative abundance in the area. Effort was uniformly distributed throughout the time of the study.

 

The observed negative trends are not considered a consequence of emigration or long-range movements of common dolphins. This area has been one of the few remaining pockets of high-density occurrence in the central and eastern Mediterranean, and there are virtually no reports of common dolphins in surrounding areas, notwithstanding substantial dedicated effort by several research groups, totalling tens of thousands of kilometres and covering large portions of the eastern Ionian Sea, as well as waters west of the Peloponnese.

Common dolphins appear to be rare in, or absent from, the adjacent central Mediterranean areas explored so far, including the Hellenic Trench, other neritic and pelagic portions of the Ionian Sea, and the Adriatic Sea, the only exception being the inner Gulf of Corinth where a few common dolphins remain.

 

   

Research indicates a high risk of local disappearance of common dolphins in the near future unless fishery management measures are implemented immediately.

   

 

Sightings of large tuna also declined dramatically east of Lefkada and around Kalamos:

 

 

Why did common dolphins and tuna decline ?

Evidence shows that the decline of common dolphins and tuna was caused primarily by prey depletion resulting from overfishing. The impact of fishing on the local ecosystem has been tremendous, and resulted in significant ecosystem damage and loss of biodiversity.

 

 

Fishery landings in Greece increased until 1994 due to the fleet modernisation and geographic expansion of the fisheries over this period. However, declining trends since the mid 1990s suggest that such effects have ceased and fisheries have become unsustainable (Papathanassiou & Zenetos 2005, Stergiou et al. 2007a,b).

 

 

Ecosystem services have been seriously compromised by overfishing, and the sustainability of fisheries is no at stake.

 

 

Total fish biomass removed by common dolphins and by fisheries east of Lefkada and around Kalamos in 2007: 

The red part of the fisheries bars shows removal of species representing key prey for common dolphins, as well as for other top predators such as tuna and swordfish.

 

Most of the impact is caused by a relatively small number of industrial boats, particularly purse seiners. Trawlers and beach seiners are also relatively few, but are known to cause significant ecosystem damage.

 

Composition of the fishing fleet and number of boats operating east of Lefkada and around Kalamos: