Sperm whale
  Case studies
    Hellenic Trench, Greece
  Other Mediterranean species



Sperm whales in the western Hellenic Trench, Greece


Based on opportunistic sightings of “large whales” by fishermen in SW Crete and on the favourable underwater relief in that area, the Pelagos Cetacean Research Institute initiated a research programme in 1998, which led to the discovery of one of the most important population units of sperm whales in the entire Mediterranean Sea.

The first acoustic and visual surveys revealed the year-round presence of sperm whales off W-SW Crete. Solitary or small groups of mature and immature males, as well as social units (females with their offspring) showed later to be seasonally resident, since they were photo-identified in consecutive years. Some social units are regularly observed since 1999. Members of a social unit first photographed opportunistically in 1994 were still observed 13 years later, in 2007.

If not unique, SW Crete and the Hellenic Trench turned to be one of the very few known areas in the world where both social units and solitary males co-exist all year round. Both feeding and breeding are taking place along the Hellenic Trench. Newborns and calves as well as reproductive activity have been observed repeatedly.

The study area was significantly enlarged in 2002 to cover a large portion of the Hellenic Trench, from the island of Lefkada in the Ionian Sea to the south-eastern edge of Crete. Research methods include passive acoustics, visual surveys, photo-identification, photogrammetry, sloughed skin collection, and underwater observation.

Research by the Pelagos Institute has shown that the number of the sperm whales that inhabit the area is very low (less than 200 individuals in total) and makes this population unit very vulnerable to human impact.


Proposed Marine Protected Area in Southwest Crete / Hellenic Trench, as adopted by the Parties to ACCOBAMS.


A diving sperm whale photographed in the Hellenic Trench.


At least one sperm whale dies every year in Greece after a collision with a large vessel. Several individuals have been seen bearing severe collision/propeller marks and injuries on their body. The rate of mortality due to collisions appears high and is likely unsustainable.

Although driftnet fishing is uncommon in the Greek Seas, individual sperm whales have been observed entangled or carrying driftnet pieces around their flukes. Plastic bags and debris are often found in the stomach of stranded animals and in some cases constitute the cause of their death.

Underwater explosions from illegal dynamite fishing activities occur very often within the sperm whale habitat, especially in SW Crete, although their impact on sperm whales cannot be assessed. Military sonar has also been used repeatedly within the limits of their habitat.


A sperm whale stranded in West Peloponnese (April 2005), showing deep wounds likely caused by a ship propeller.


A sperm whale photographed in SW Crete (August 2000), with its flukes entangled in a driftnet.


Cetacean Alliance investigators:

For more information see:

Frantzis A., Alexiadou P., Paximadis G., Politi E., Gannier A., Corsini-Foka M. 2003. Current knowledge of the cetacean fauna of the Greek Seas. The Journal of Cetacean Research Management 5(3): 219-232. (1.1 Mb)

Frantzis A., Swift R., Gillespie D., Menhennett C., Gordon J., Gialinakis S. 1999. Sperm whale presence off south-west Crete, Greece, western Mediterranean. European Research on Cetaceans 13:214-217. (1.24 Mb)

Information presented here also based on:

Frantzis A., Alexiadou P. In preparation. Sperm whale occurrence, site fidelity and social organization along the Hellenic Trench (Greece, Mediterranean Sea).

Frantzis A., Matthiopoulos J., Alexiadou P. In preparation. Using combined acoustic and visual data to estimate sperm whale abundance in the Hellenic Trench (Greece, Mediterranean Sea).