Abstract:
The oligotrophic eastern Mediterranean Sea has always been considered poor regarding its cetacean fauna. Until recently, very little was known concerning the cetaceans that inhabit its northeastern part, i.e. the Greek Seas: east Ionian, Aegean,
north and south Cretan Seas. This work reveals that the Greek Seas present an unexpectedly high diversity in cetacean species and discusses preliminary information regarding their distribution and relative abundance. During the last ten years
(1991-2001), data from dedicated surveys, strandings, opportunistic sightings, and published or unpublished photographic and video documents have been systematically gathered in a database. Sightings from an older published work regarding the
cetaceans of the Aegean Sea, as well as all confirmed sightings and strandings that are found in the literature, have been also included in the database accounting for 618 sightings and 709 stranded cetaceans (in 668 stranding events).
From 1991 to 2001, dedicated surveys up to three months long have been organized every year in the summer and autumn. Surveys covered the north and south Ionian Sea, the sea area off south-west Crete, the Corinthian Gulf and in a lesser degree the
The oligotrophic eastern Mediterranean Sea has always been considered poor regarding its cetacean fauna. Until recently, very little was known concerning the cetaceans that inhabit its northeastern part, i.e. the Greek Seas: east Ionian, Aegean, north and south Cretan Seas. This work reveals that the Greek Seas present an unexpectedly high diversity in cetacean species and discusses preliminary information regarding their distribution and relative abundance. During the last ten years (1991-2001), data from dedicated surveys, strandings, opportunistic sightings, and published or unpublished photographic and video documents have been systematically gathered in a database. Sightings from an older published work regarding the cetaceans of the Aegean Sea, as well as all confirmed sightings and strandings that are found in the literature, have been also included in the database accounting for 618 sightings and 709 stranded cetaceans (in 668 stranding events).
From 1991 to 2001, dedicated surveys up to three months long have been organized every year in the summer and autumn. Surveys covered the north and south Ionian Sea, the sea area off south-west Crete, the Corinthian Gulf and in a lesser degree the sea area between the Northern Sporades Islands and the Chalkidiki Peninsula. Ferries with standard routes in the Aegean Sea have been used as platforms of opportunity for the surveys of Carpentieri et a/. (1999). Consequently, the distribution of sightings is seriously biased in favour of the above areas and routes. Conventional visual methods for detecting cetaceans have been used in all survey areas except off south-west Crete, south-west Ionian Sea and Northern Sporades - Chalkidiki area, where joint acoustic and visual methods have been used. Opportunistic sightings recorded up to the end of October 2001 in any other part of the Greek Seas have also been included in the database. We obtained stranding data mainly through the national network, which is organized and co-ordinated by the National Centre for Marine Research (since 2003). Hellenic Centre for Marine Research, HCMR) and the Pelagos Cetacean Research Institute. The network's data cover the period November 1991 - October 2001 and derived from standardised forms filled by local port-police authorities. This network cannot be considered complete since the number of unreported strandings (known through sources other than the network) is not negligible. After being meticulously checked, stranding reports were discarded (classified as "unidentified") if not accompanied by photos that could definitely allow unbiased species identification. For mass strandings and strandings of infrequent cetacean species additional information was gathered by contacting people who saw and photographed the stranded cetacean and/or by going in situ.
Only 41.1% of the total strandings were retained by those methods. Thirty-five old stranding records from the period 1840-1991 were also included in the database since they were accompanied by photos or were cited in scientific references. All stranding data refers to individuals and not to stranding events (mass strandings were rare and concerned mainly Cuvier's beaked whales). Our study revealed that twelve cetacean species have been recorded in the Greek Seas. Seven of them are permanently present and commonly observed in one or more of the Greek Seas: fin whale, sperm whale, Cuvier's beaked whale, Risso's dolphin, bottlenose dolphin, striped dolphin and common dolphin. In addition, the harbour porpoise that was considered absent from the entire Mediterranean is definitely present locally in the North Aegean, although its exact range and degree of residency have to be assessed. The false killer whale is an occasional species; the humpback whale has been sighted exceptionally once; the Sowerby's beaked whale and minke whale have been found floating dead only once. Four other species (beluga, Blainville's beaked whale, pilot whale, killer whale and blue whale) had been erroneously included in the Greek cetacean fauna in the past, due to a wrong assumption, two false identifications and lack of irrefutable evidence, respectively. Pilot and killer whales are permanently and occasionally present in the western Mediterranean, respectively. Although their occasional
occurrence in the Greek Seas cannot be refuted, it should still be regarded as unconfirmed.
It has to be noted that because of the variety of methods used in this study, the numbers of recorded sightings and strandings cannot be used as an index of relative abundance. Sightings are biased in favor of species and areas for which more effort has been dedicated during some surveys (e.g. sperm whales off south-west Crete). Similarly, standings are biased in favor of species that are easily identifiable (Cuvier's beaked whales and large whales) or species that draw the attention of people and press (sperm and fin whales). Keeping in mind the above remarks, we can however conclude the following. Considering the Greek Seas as a whole, there is no doubt that striped dolphins are the most abundant species in the pelagic waters, followed by bottlenose dolphins in the coastal waters. Both species can be encountered almost everywhere in Greece. Common dolphins are common only locally, in a few areas (coastal, internal Ionian Sea and north Aegean Sea). They are absent from some wide sea areas (Greek part of north Ionian Sea and off south-west Crete) and there are no sightings or strandings recorded southern than 36° 05' of latitude. Although Risso's dolphins are less frequent than the other dolphin species, they have been recorded in all geographical areas of the Greek Seas. Both sightings and strandings indicate that
Cuvier's beaked whales and sperm whales occur all along the Aegean Arc (the end of the continental shelf around the Aegean and Greek Ionian Seas), with sighting frequencies higher than anywhere else in the Mediterranean Sea. Both species are also present in the north and south Aegean Sea, mainly over deep basins. Finally, the fin whale is common in the pelagic waters of the Ionian Sea, but seems to rarely enter the Aegean Sea. Although still not complete, the existing image of the Greek cetacean fauna, in terms of species presence and distribution, is now close to the real situation. Nevertheless, there are no quantitative data regarding the absolute abundance and the population status of any species. Without such kind of data, there is no way to decide which is the proper conservation policy for cetaceans, and the effectiveness of any conservation measure cannot be monitored. Therefore, future effort has to focus on: i) the evaluation of abundance estimations for the population unit of each species, ii) the assessment of population status and trends for cetacean species that constitute conservation priorities at the local or regional level, iii) the definition of critical areas for these species, and iv) the establishment of a properly organised, national stranding network, in collaboration with the secretariat of ACCOBAMS. This network should be based on strictly scientific methods and rules, according to the international standards.
