Canyons are striking landscape features, providing habitat for a great diversity of wildlife. The same is true for marine canyons. One very remarkable underwater canyon is the Hellenic Trench in the eastern Mediterranean, which stretches across more than 50,000 km² along the Greek coasts from the Ionian Islands to south and east of Crete.
The Hellenic Trench consists of a continuous steep continental seaward slope, linear trenches, troughs and basins. It reaches a maximum depth of 5,267 m – the deepest area in the Mediterranean. This is one reason why it is a core habitat for deep-diving marine mammal species, in particular sperm whales and Cuvier’s beaked whales – because of the presence of their prey in the deep sea. Long lasting feeding dives have been repeatedly observed along the Hellenic Trench.
The area is an important feeding ground for sperm whales in the eastern Mediterranean and even appears to be their core habitat for calving and nursing. Calves were present in 79% of social unit encounters. Calves have also been observed during sightings of Cuvier’s beaked whales, including newborns, which shows that the Hellenic Trench constitutes a reproductive area for the species.
The Mediterranean subpopulation of sperm whale is classified as endangered, with declining numbers from significant anthropogenic threats. No more than 200-250 sperm whales are left in the eastern basin of the Mediterranean, with the Hellenic Trench as their key habitat. These whales are particularly threatened by ship strikes, i.e. the whales are hit by large vessels and suffer fatal wounds.
To counter this main threat to the sperm whales, OceanCare started the “SAvE Whales” project in the Peloponnese region. Further, OceanCare is working to prevent oil exploration in the Hellenic Trench.
As a key habitat for sperm whales and Cuvier’s beaked whales, and by featuring an outstanding diversity of marine mammals – including striped dolphins, common dolphins, Risso’s dolphins, bottlenose dolphins and Mediterranean monk seals – the Hellenic Trench qualifies as an ‘Important Marine Mammal Area’ (IMMA).
IMMAs are scientifically defined as discrete portions of habitat that are important to marine mammal species. The creation of a network of IMMAs represents a cost-effective approach to conservation by using the comparatively well-studied marine mammal species as indicators and umbrella species, meaning that a properly designed conservation plan would be beneficial to a wide range of wildlife and the broader ecosystem. Marine mammals are, in short, catalytic species. Thus, knowledge of areas that are important for them will facilitate the balancing of human uses of the sea with the imperative of conserving marine biodiversity.