Gulf of Corinth IMMA

Criterion A – Species or Population Vulnerability

The IUCN Red List classifies the Mediterranean subpopulation of common dolphin as Endangered, based on observed declines in the number of animals and extent of occurrence, as well as deterioration in the quality of habitat in large portions of the Mediterranean Sea. The population units of short-beaked common dolphins in the Gulf of Corinth, and the neighbouring inner Ionian Sea Archipelago, are the last representatives of this species in the entire Adriatic and Ionian Seas, while they are also absent in the largest portion of the eastern Mediterranean Sea. These animals in the Gulf of Corinth constitute a geographically distinct conservation unit that likely has little demographic and genetic exchange and faces a high risk of extinction. Due to its small population size, limited distribution, and suspected hybridization, could potentially qualify as Critically Endangered under standard criteria provided by the IUCN Red List to assess extinction risk. The Mediterranean subpopulations of striped dolphin are also listed as Vulnerable in the IUCN Red List of Threatened Species.

Criterion B: Distribution and Abundance

Sub-criterion B1: Small and Resident Populations

Both common dolphins and striped dolphins are resident and according to all evidence isolated in the semi-enclosed Gulf of Corinth. They are absent in the western shallow part of the gulf and the waters of the Gulf of Patras that separate them from the Ionian population units. The Ionian population unit of common dolphin’s number fewer than 100 individuals, therefore the estimated 22 individuals that inhabit the GOC are a large proportion of the animals inhabiting the adjacent Adriatic and Ionian. Although much more, the estimated approximately 1300 striped dolphins represent an unknown proportion of the eastern Mediterranean striped dolphin subpopulation.

Sub-criterion B2: Aggregations

The Gulf of Corinth is the permanent habitat of about 1300 isolated striped dolphins. Considering the relatively small surface of the sea area that they occupy, they likely represent the highest permanent concentration of the species in the entire Mediterranean Sea (likely to be >1.5 dolphin’s km²).

Criterion C: Key Life Cycle Activities

Sub-criterion C1: Reproductive Areas

Given that both the short-beaked common dolphin and the striped dolphin population units in the Gulf of Corinth are isolated, their entire life cycle is completed only inside the area. Striped dolphin newborns are commonly observed during summer with stranding data confirming this as the likely calving period. Newborn and young calf (total length <1 m) mortality is recorded from July to early September with a clear peak in late July to August, as in also observe for other areas in Greece. Sub-criterion C2: Feeding Areas

Due to their relative isolation from populations in the wider Mediterranean, both the likely short-beaked common dolphin and the striped dolphin population units in the Gulf of Corinth totally depend on the semi-enclosed ecosystem to feed. Cephalopods, particularly squid species, commonly observed at surface during surveys or during direct observations of dolphins and are a likely an important prey.

Criterion D: Special Attributes  

Sub-criterion D1: Distinctiveness

The dolphin societies in the Gulf of Corinth are distinct as a whole because of their unique behavioural and ecological characteristics. In addition, the mixed species dolphin societies in the gulf are unique in the world for three reasons: i) the striped dolphin population unit in the gulf is the only one known to inhabit a semi-enclosed gulf and be resident and isolated from other pelagic population units of this species, ii) the permanent three-species mixed pods of dolphins (common, striped, Risso’s dolphin)  in the Gulf of Corinth is a unique phenomenon of marine mammal symbiosis between species of different ecological needs and behavioural characteristics, iii) the gulf is the only known area in the world, where hybrids between the two different genus of Stenella and Delphinus are naturally and continuously produced and survive.