Phocoena phocoena relicta (Abel 1905) are the sub-species of harbour porpoise endemic in the Black Sea and neighbouring waters. Its population is separated from the nearest conspecifics (P. p. phocoena) in the north-eastern Atlantic by the Mediterranean Sea, from the northern Aegean Sea to the Strait of Gibraltar. Alexei Birkun (from the Brema Laboratory) has been studying them for many years and talks to WDCS about these endangered cetaceans ... and the geography of the region!! (You can find further information on the Brema Laboratory here however it may be good if you can speak Russian as most information on this website is in Russian).
Tell us more about the distribution of this sub-species. Where are the found?
The subspecies’ range encompasses the Black Sea proper and adjacent water bodies such as the Azov Sea, Kerch Strait, Turkish Straits System (Bosphorus, Marmara Sea, Dardanelles), and northern Aegean Sea. The occurrence in the Dardanelles Straits and Turkish Aegean Sea (Saroz Bay) was confirmed recently by findings of two stranded harbour porpoises there. Sporadic strandings (including live strandings) and sightings (including group sightings) of porpoises in the Greek northern Aegean have been known since 1993 (at least nine records were reported before 2008 for the Thracian Sea, Kavala Gulf, Strymonikos Gulf, Agiou Orous Gulf, and Thermaikos Gulf). Genetic studies have shown that it is possible that there may be separate subpopulations of the subspecies.
Occasionally, harbour porpoises have been sighted in the Danube, Dnieper, Don and Kuban rivers, their estuaries, deltas and tributaries (e.g., in the Danube in 1984-89 and 2003 or in the Ingulets, a confluent of the Dnieper, in 1999), and coastal freshwater, brackish and saline lakes and lagoons including the Yalpug and Sivash lakes, Berezansky and Grigorievsky lagoons, Tendrovsky, Yagorlytsky and Jarylgachsky bays, and the Gulf of Taganrog. All of these sites are situated on the northern and northwestern coasts of the Black Sea and round the Azov Sea.
Can you tell us a bit about their habitat preferences and their behaviour?
Harbour porpoises inhabit mainly shallow waters over the continental shelf around the entire perimeter of the Black Sea. Sometimes they also occur far offshore in deep water. During the warm season they venture into the Azov Sea through Kerch Strait as well as in the Marmara Sea and Bosphorus. Both of these small seas (as well as the northwestern Black Sea shelf zone) may represent geographically disjunct breeding-calving-feeding areas while the straits (Kerch and Bosphorus) serve as migration corridors. Harbour porpoises undertake annual migrations, leaving the Azov Sea and northwestern Black Sea before winter and returning in spring. Such movements also may occur between the Black Sea and Marmara Sea. In the latter (along with the Bosphorus) there were no records for January-March; during the period from March 2007 to June 2008, most sightings in the Bosphorus were recorded in spring and summer. The primary wintering areas are situated in the southeastern Black Sea including the southern Georgian territorial waters and perhaps the eastern Turkish territorial waters. Most of the Black Sea porpoise population may congregate there every year. These are also the well-known wintering grounds of Black Sea and Azov Sea populations of the anchovy, an important prey species for harbour porpoises during the cold season. At least 20 fish species have been recorded in the species’ stomachs, of which three are considered as the most important prey: anchovy, sprat and whiting. Black Sea harbour porpoises also occur in waters with low salinity and high turbidity; during the warm season they may visit brackish bays, lagoons, estuaries and rivers.
What can you tell us about their population numbers?
There are no current estimates of total population size. In the 20th century, the number of Black Sea harbour porpoises was dramatically reduced by massive direct killing for the cetacean-processing industry that continued until 1983. Line transect surveys were conducted during the last decade to estimate harbour porpoise abundance in different parts of the range. In particular, aerial surveys were conducted in the Azov Sea, Kerch Strait and northeastern shelf area of the Black Sea; vessel-based surveys were performed in the Kerch Strait, territorial waters of Ukraine and Russia in the Black Sea, Georgian territorial sea, and the central part of the Black Sea between Ukraine and Turkey. Survey results suggest that the present total population size is at least several 1,000s and possibly in the low 10,000s.
And their conservation status?
The Black Sea harbour porpoise has been assessed as Endangered (EN) in Resolution 3.19 of ACCOBAMS MoP3 (2007) and as EN (Endangered)in the IUCN Red List of Threatened Species (2008-10). Grounds for justification include: a) large directed kills in the past (at least 163,000-211,000 in 1976-83); b) ongoing incidental mortality in bottom-set gillnets (some 1000s per year); c) a mass mortality event in 1982 in the Azov Sea due to an explosion at a gas-extraction platform (>2,000 porpoises were found dead); d) two mortality events in 1989 and 1990 caused by the combined effects of parasitic and bacterial infections (several thousand individuals); e) a mortality event in 1993 caused by the ice entrapment of porpoises in the Azov Sea (at least several tens of porpoises); f) habitat degradation and decline in prey populations peaking in the late 1980s–early 1990s.
So what are the current major threats to these animals?
Incidental catch in fishing nets constitutes the most important threat and major source of human-induced mortality of Black Sea cetaceans. Numerous incidents of bycatch occur in the Azov Sea and Kerch Strait and throughout the Black Sea shelf area, including waters under the jurisdiction of all the riparian countries. Cetacean strandings with the obvious evidence of having been bycaught have been recorded in the Marmara Sea as well. All three Black Sea cetacean subspecies are known to be taken as bycatch, although incidental takes of endangered harbour porpoises evoke the greatest concern. Based on older records and on subsequent studies, during a 19-year period (1990-2008) a total of 1,126 incidentally caught cetaceans were reported for the Black Sea, including 1,089 harbour porpoises (96.7%), 17 common dolphins (1.5%) and 20 bottlenose dolphins (1.8%). Almost all (99.9%) recorded incidents were lethal.
Absolute numbers of population losses due to bycatch have not been estimated for Black Sea cetaceans, and the above figures are considered a gross underestimate. Preliminary indications suggest that the annual level of harbour porpoise bycatches may be numbered in the thousands per year and is unsustainable. The porpoises are caught in a variety of fisheries, although bottom-set gillnets with large mesh size (from 80-220 mm) are the most damaging, given that > 99% of the recorded bycatches occur in this gear. In 2006-2008, during an onboard examination of 3,604 bottom-set gillnets with an overall length of 278 km, a total of 484 bycaught cetaceans (480 harbour porpoises and four bottlenose dolphins) were found, whereas the catch of target fish species came to 4,751 Black Sea turbots and 1,830 spiny dogfishes. Aggregate bycatch indices of those fishing operations were evaluated as follows: 163 porpoises and two bottlenose dolphins per 100 km of turbot nets; 195 porpoises per 100 km of dogfish nets; 67 porpoises and one dolphin per 1000 turbots; and 88 porpoises per 1000 dogfishes. Peaks of harbour porpoise bycatches occurred in June (2.7/km of turbot nets) and August (7.6/km of dogfish nets). It should be underlined that such depressing statistics were obtained from just one fishing boat legally operating in small coastal area in Ukraine. In the meanwhile, hundreds of vessels are permitted annually to catch turbot and dogfish in the region. In addition, illegal, unreported or unregulated (IUU) fishing became widespread in the Black and Azov Seas in the past two decades suggesting that a significant share of cetacean bycatches takes place due to marine poaching.
Some sobering statistics there, and we wish Alexei all the best for his important and crucial work.