Are there cetaceans in the Black Sea?

The Black Sea, that semi-enclosed basin between Europe and Asia, does not immediately bring cetaceans to mind. Yet it is home to three endemic cetacean subspecies: that is, animals found nowhere else in the world. Isolated for several millennia, these populations have adapted to the very particular conditions of this less salty sea, which is subject to major human pressures.

A sea with unique conditions

The Black Sea is an almost enclosed sea, connected to the Mediterranean only by the Bosphorus and the Dardanelles straits. It receives enormous inputs of fresh water from the great rivers (Danube, Don, Dnieper, Dniester), which makes it a relatively low-salinity sea (17-18 g/L of salt against 38 g/L in the Mediterranean). Below about 150 metres its waters are anoxic: entirely devoid of oxygen, which makes the depths unsuitable for complex life. All the cetaceans there are therefore confined to the surface layers.

This geographical isolation and these particular conditions have favoured the evolution of distinct cetacean populations over thousands of years, long enough for science to regard them today as separate subspecies from their relatives in other seas.

The Black Sea common bottlenose dolphin

The first resident species is the Black Sea common bottlenose dolphin (Tursiops truncatus ponticus). Genetically and morphologically distinct from the common bottlenose dolphin elsewhere, this subspecies occupies the whole of the Black Sea, including the Kerch Strait and the Sea of Azov. Its mean size is slightly smaller than that of its Mediterranean relatives.

Its status is of serious concern. Listed as Endangered by the IUCN, its population is estimated at fewer than 1,000 individuals and has been in continuous decline for decades. The main causes: bycatch in fishing nets, the massive chemical pollution of the basin (industrial, agricultural and urban discharges), and the morbillivirus epidemics that killed several hundred individuals in the 1990s and the 2010s.

The Black Sea common dolphin

The second subspecies is the Black Sea common dolphin (Delphinus delphis ponticus). It lives in larger groups than the local bottlenose dolphin, several dozen and sometimes more than a hundred individuals, and frequents mainly offshore waters. Its diet rests chiefly on anchovy and sprat, two small pelagic fish that are crucial to the Black Sea ecosystem.

The Black Sea common dolphin population went through a historical collapse. In the 20^th century, commercial hunting (in particular from the 1930s to the 1960s) killed several hundred thousand individuals for their blubber and their meat. Current estimates are of the order of a few tens of thousands, a considerable figure compared with the local bottlenose dolphin, but one in constant retreat in the face of overfishing of their prey and of pollution.

The Black Sea harbour porpoise

The third subspecies, and probably the most threatened, is the Black Sea harbour porpoise (Phocoena phocoena relicta). Smaller (1.4 to 1.7 m), unobtrusive and living in very small groups, it occupies the coastal waters of the whole basin and even the Sea of Azov. It is the most emblematic of the three, and the one whose population has fallen most dramatically.

More than 10,000 porpoises a year once died in Turkish and Ukrainian gillnets, an extremely high figure for a population whose total size is today estimated at fewer than a few thousand. The morbillivirus epidemics of 1990 and 2014 also caused mass mortality. The subspecies is listed as Endangered by the IUCN.

A situation made worse by the war

Since 2022, the situation of the cetaceans of the Black Sea has deteriorated further because of the war in Ukraine. The military sonars used by the naval forces, underwater explosions, intense military traffic and increased pollution have caused abnormal mortality. The Ukrainian and Turkish authorities reported the stranding of hundreds of dolphins and porpoises in 2022-2023, on a scale never documented before. Necropsies showed acoustic trauma and internal lesions consistent with exposure to intense sound sources.

Conservation: a regional challenge

The conservation of the cetaceans of the Black Sea requires cooperation between six bordering countries (Russia, Ukraine, Romania, Bulgaria, Turkey, Georgia), cooperation that is particularly difficult today given the geopolitical context. The ACCOBAMS agreement (Agreement on the Conservation of Cetaceans of the Black Sea, Mediterranean Sea and Contiguous Atlantic Area) provides a legal framework, but its practical implementation remains fragile.

These three endemic subspecies, the product of an island-like evolution in an enclosed sea, illustrate both the little-known biological richness of the Black Sea and the extreme fragility of isolated cetacean populations in the face of accumulated human pressures. Their long-term survival remains uncertain.

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Further reading