Conservation status:
In Bulgaria: Red book – Vulnerable VU [A1acde + 2ce]; Biological diversity act – Appendices II and III. International: Red list of IUCN – EN (Endangered); Bern convention – Appendix II; CITES – Appendix II; Bonn convention – Appendix II; Habitats directive 92/43/EEC – Appendices II and IV.
The Black Sea harbour porpoise is separated as subspecies (Phocoena phocoena relicta) with morphological and genetic diversities from the population of Ph. phocoena in other parts of the world. The Black Sea and Aegean harbour porpoises possibly are separate subpopulations of the subspecies.
Distribution:
The species is found in the coastal areas of the Arctic Ocean, the coastal areas of the north parts of the Atlantic and Pacific Oceans, the Black Sea and the Sea of Azov. In the Mediterranean (including the Aegean Sea) there are few registered cases. The distribution area of the Black Sea subspecies includes the Black Sea and the Sea of Azov, the Kerch strait, the Sea of Marmara, the Bosphorus, the north Aegean Sea and most probably the Dardanelles. The Black Sea population is totally isolated from the nearest population of Ph. phocoena in the northeast Atlantic Ocean by the Mediterranean Sea. Although it is still not agreed on when it happened it is clear that the harbour porpoise has come to the Black Sea through the Mediterranean Sea, where it is considered that has had population in the past.
The area of the Black Sea subspecies includes the territorial waters and the exclusive economic areas of Bulgaria, Georgia, Romania, Rusia, Turkey and Ukraine in the Black Sea; the territorial waters of Greece in the north Aegean Sea and probably the Turkish territorial waters in the northeast Aegean Sea. Sometimes the harbour porpoises are observed in the estuaries, the deltas and the tributaries of the rivers Danube, Dnieper, Don and Kuban and the coastal freshwater, brackish and saline lakes and lagoons including Yalpug and Sivash, Berezanski and Grigorievska lagoons, the bays Tendrovsky, Yagorlytski and Jarylgachsky and Taganrog. All these places are located in Ukraine and Russia on the north and northwest shores of the Black Sea and around the Sea of Azov.
The population of Ph. ph. relicta consists of three or more subpopulations including these, which spend larger part of the year in regions with geographic and ecological diversities, for example the Sea of Azov, the northwest Black Sea and the Sea of Marmara. The Bosphoruus, the Sea of Marmara and the Dardanelles serve as relation between the Black Sea and the Aegean Sea. Population: The total number of the population of the subspecies is indeterminate which makes the entire exploration of the Black Sea extremely important. The common opinion is that in the larger part of the 20th century the number of the harbour porpoise in the Black Sea is higher than the bottlenose dolphin (Tursiops truncatus ponticus) and lower than the common dolphin (Delphinus delphis ponticus). Line transect surveys by aircraft and vessel have been conducted in the last 15 years to assess the size of the population of the harbour porpoise in the separate parts of the area. The results from these studies suggest that the current total population size is about several thousands and probably some tens of thousands of individuals (over 50 000).
Biology and ecology:
The harbour porpoise is the smallest representative of the cetaceans in the Black Sea with body length of 1,3-1,5 m, maximum 1,8 m and average weight 30 kg. The females are a bit larger than the males. The head is short and round, the rostrum (the beak) is not distinctive, the dorsal fin is short, triangular and round. The back is colored in dark grey to black, which gradually converts into white underneath. The teeth are small, 40-56 on the lower and upper jaws. In shape teeth of the porpoises are distinctively different compared to teeth of dolphins being flat spade-shaped unlike dolphins’ conic shape.
The harbour porpoise is a marine mammal with relatively short life, but with higher level of reproduction in comparison with the rest of the cetaceans in the Black Sea. The males and females reach sexual maturity probably at the age of 3-4 years. The breeding season is mainly during the summer as the females can become pregnant almost every year as the pregnancy lasts 9-22 months and usually gives birth to one infant in the period from May until August. The lactation period is 4-6 months, after that the infants start feeding on small benthic species (mainly gobies) and mass pelagic species of fish (anchovy, silverside). The daily ration for the adults is about 3-5 kg.
The life span of the Black Sea harbour porpoise is not very clear, but probably is similar to this of the harbour porpoises in the north Atlantic – 7-8 years, maximum 15 years. It lives in small groups (average 4-6 individuals). Larger groups are formed at mass gatherings of fish. It swims slowly, close to the surface, rarely jumps over the water. The coastal, relatively shallow waters (0-200m) on the entire perimeter of the Black Sea over the continental shelf are typical distribution area of the harbour porpoise, although there are observations in open waters with depth of 450-2,170m. It does not avoid waters with low salinity and transparency, in some cases can be observed in brackish bays, lagoons, estuaries and deltas of big rivers.
Significant numbers of the species migrate every spring through the Kerch strait to the Sea of Azov and return during the winter. Migrations through the Bosphorus to the Sea of Marmara and back are very likely to happen. Probably, the two seas should be identified as the most important breeding and feeding sites of the Black Sea population. On the other hand the Sea of Azov and the Sea of Marmara can be defined as a critical habitat due to the intensive shipping traffic, the intensive fishing and pollution.
The most significant wintering sites are the southeast Black Sea including the south territorial waters of Georgia and probably the east territorial waters of Turkey. These regions are well known wintering sites for the population of the anchovy (Engraulis encrasicolus ponticus) in the Black Sea and the Sea of Azov, which is main food of the harbour porpoise during the cold months. Probably the larger part of the Black Sea population of the harbour porpoise is gathered in this region every year.
The ecology of the Black Sea harbour porpoises is unusual. It is due to the high level of geographic isolation of their habitat, relatively low salinity, the significant seasonal temperature fluctuations and the presence of a large amount of water without oxygen saturated with hydrogen sulphide below 100-250 m. At least 14 species of fishes are described as part of the diet of the species, as four species are considered most significant: anchovy (Engraulis encrasicolus ponticus), sprat (Sprattus sprattus), whiting (Merlangius merlangus euxinus) and gobies (Gobiidae).
Threats:
The species is most threatened by entanglement in fishing nets for turbot (bycatch). Based on different bycatch studies highest share is definitely that of porpoises - about 90 % of all cases. The pollution of the environment with persistent organic pollutants is another threat for the Black Sea population as studies have revealed levels of POPs in the porpoises blubber is higher compared to other regions. The reduction of the food resource is caused by the fishing and another negative factor is the invasive species ctenophore Mnemiopsis leidyi. Significant, but not very frequent natural cause, limiting the Black Sea population is the mass mortality due to pulmonary infection caused by the nematodes Halocercus taurica and H. ponticus.
The harbour porpoise is a marine mammal with relatively short life, but with higher level of reproduction in comparison with the rest of the cetaceans in the Black Sea. The males and females reach sexual maturity probably at the age of 3-4 years. The breeding season is mainly during the summer as the females can become pregnant almost every year as the pregnancy lasts 9-22 months and usually gives birth to one infant in the period from May until August. The lactation period is 4-6 months, after that the infants start feeding on small benthic species (mainly gobies) and mass pelagic species of fish (anchovy, silverside). The daily ration for the adults is about 3-5 kg.
The life span of the Black Sea harbour porpoise is not very clear, but probably is similar to this of the harbour porpoises in the north Atlantic – 7-8 years, maximum 15 years. It lives in small groups (average 4-6 individuals). Larger groups are formed at mass gatherings of fish. It swims slowly, close to the surface, rarely jumps over the water. The coastal, relatively shallow waters (0-200m) on the entire perimeter of the Black Sea over the continental shelf are typical distribution area of the harbour porpoise, although there are observations in open waters with depth of 450-2,170m. It does not avoid waters with low salinity and transparency, in some cases can be observed in brackish bays, lagoons, estuaries and deltas of big rivers.
Significant numbers of the species migrate every spring through the Kerch strait to the Sea of Azov and return during the winter. Migrations through the Bosphorus to the Sea of Marmara and back are very likely to happen. Probably, the two seas should be identified as the most important breeding and feeding sites of the Black Sea population. On the other hand the Sea of Azov and the Sea of Marmara can be defined as a critical habitat due to the intensive shipping traffic, the intensive fishing and pollution.
The most significant wintering sites are the southeast Black Sea including the south territorial waters of Georgia and probably the east territorial waters of Turkey. These regions are well known wintering sites for the population of the anchovy (Engraulis encrasicolus ponticus) in the Black Sea and the Sea of Azov, which is main food of the harbour porpoise during the cold months. Probably the larger part of the Black Sea population of the harbour porpoise is gathered in this region every year.
The ecology of the Black Sea harbour porpoises is unusual. It is due to the high level of geographic isolation of their habitat, relatively low salinity, the significant seasonal temperature fluctuations and the presence of a large amount of water without oxygen saturated with hydrogen sulphide below 100-250 m. At least 14 species of fishes are described as part of the diet of the species, as four species are considered most significant: anchovy (Engraulis encrasicolus ponticus), sprat (Sprattus sprattus), whiting (Merlangius merlangus euxinus) and gobies (Gobiidae).
Threats:
The species is most threatened by entanglement in fishing nets for turbot (bycatch). Based on different bycatch studies highest share is definitely that of porpoises - about 90 % of all cases. The pollution of the environment with persistent organic pollutants is another threat for the Black Sea population as studies have revealed levels of POPs in the porpoises blubber is higher compared to other regions. The reduction of the food resource is caused by the fishing and another negative factor is the invasive species ctenophore Mnemiopsis leidyi. Significant, but not very frequent natural cause, limiting the Black Sea population is the mass mortality due to pulmonary infection caused by the nematodes Halocercus taurica and H. ponticus.