About dolphins

THE BLACK SEA CETACEANS
 
In the Black Sea are found three species of cetaceans from two families: Dolphins (Delpninidae) and Porpoises (Phocoenidae).
 
 

Black Sea common dolphin (Delphinus delphis ponticus)

Обикновен делфинConservation status:
In Bulgaria: Biological Diversity Act – Appendix III; International: IUCN Red list – VU (Vulnerable); Bern Convention – Appendix II; CITES – Appendix II; The Habitats Directive 92/43/EEC – Appendix IV.
The subspecies D. d. ponticus is suggested on the base of  morphological characteristics, later on criticized as insufficient. However, the comparative analyses using skull morphometric measurements and DNA analyses suggest that some diversity exists between the Black Sea and the Mediterranean common dolphins. Up to now it could not be defined with certainty, but it seems that the genetic exchange between the Black Sea and the Mediterranean Sea is rare or almost none. Therefore the subspecies is recognized at this stage.
 
Distribution:
Practically, it is found in all the oceans and seas of the tropics. The distribution area of the Black Sea common dolphins covers almost the entire Black Sea, including the territorial waters and the exclusive economic zones of Bulgaria, Georgia, Romania, Rusia, Turkey and Ukraine, as well as the internal sea waters of Ukraine at Karkinitsky Bay and Turkey, including Bosphorus and Marmara Sea, although for the last two a taxonomic survey and genetic research are needed to confirm that they belong to the Black Sea subspecies. The common dolphins are not found in the Sea of Azov and generally avoid the Kerch Strait, although a single live stranding was recorded there in 1994 during the morbillivirus epizootic. There is no reliable information on the presence of the species in the Dardanelles that connects Marmara and Aegean Sea, as there are no reliable evidences of migrations of common dolphins across the Turkish straits.
 
Population:
Total size of the population in the Black Sea is unknown. It is generally recognized that during the first two-thirds of the 20th century the numbers of the common dolphins in the Black Sea have been much higher than those of the Black Sea bottlenose dolphins (Tursiops truncatus ponticus) and the harbour porpoises (Phocoena phocoena relicta). The estimates of the population size based on line transect surveys in some parts of the Black Sea suggest that the present size of the population is at least several tens of thousands of individuals as it is possible to reach over 100 000 individuals.
 
Biology and ecology:
The body is elongated, torpedo-shaped. The rostrum (the beak) is clearly distinctive. The dorsal fin is big, triangular, tipped and slightly arched backwards. The coloring of the body is dark grey to black on top, whitish underneath, with light grey, yellowish or white patch on both sides in the form of horizontally hourglass or infinite sign. In his mouth the dolphin has numerous sharp teeth. Their number is 80-120 on the lower and upper jaw. The form is conic as with the bottlenose dolphin, but differs from it in the smaller size and much larger number.
It is found mainly in open water, but sometimes it also enters the coastal waters following the seasonal gatherings and mass migrations of the small pelagic fish species. The Black Sea subspecies is the smallest representative of the species worldwide: the average length is 1,5-1,7 m (maximum 2,0 m) for the adult females and 1,7-1,8 m (maximum 2,2 m) for the adult males. The weight is 50-55 kg, maximum 100 kg. Females reach sexual maturity at the age of 2-4 years, while males at 3-4 years.
The average life span is 20-22 years, with possibility to reach even more (25-30 years). The breeding season usually is in the late autumn or early spring as reaches its peak in July-August. The annual share of pregnant females is calculated on 46-75%, depending on the length of the interval between births, which is 1,3-2,3 years. The pregnancy lasts 10-11 months, giving birth to one infant. The lactation period lasts 14-19 months, but the infants feed on mother’s milk only during the first 5-6 months of their life.
The preferred food consists of small pelagic fish forms large shoals – anchovy (Engraulis encrasicolus ponticus) and sprat (Sprattus sprattus). 11 species of fish in total are registered in the food spectrum: pipefishes (Syngnathidae spp.), whiting (Merlangius merlangus euxinus), mullets (Liza spp.), red mullet (Mullus barbatus ponticus), bonito (Sarda sarda), shad (Alosa spp.), bluefish (Pomatomus saltatrix), scad (Trachurus spp.), garfish (Belone belone), mackerel (Scomber scombrus), wrasses (Labridae spp.), blennies (Blennidae spp.). The daily consumption is about 4-10 kg.
 
Threats:
There are two pathogens known to be the reason for mass mortality resulting in limitation of the population: the lung nematode (Skrjabinalius cryptocephalus) and unidentified morbillivirus. An epidemic, caused by morbillivirus is registered in July-September 1994, going along with washed ashore diseased individuals. Another reason for the decrease of the population is reduction of the food resource, caused by fishing and by the introduced species ctenophore Mnemiopsis leidyi.


Black Sea bottlenose dolphin (Tursiops truncatus ponticus)

Бутилконос делфин, афалаConservation status:
In Bulgaria: Red book – vulnerable VU [D1]; Biological diversity act – Appendix II and III. International: IUCN Red list – EN (endangered); Bern convention – Appendix II; CITES – Appendix II, Bonn convention – Appendices I and II; Habitats directive 92/43/EEC – Appendices II and IV.
The bottlenose dolphins in the Black Sea are recognized as separate subspecies that differs morphologically from the populations in Atlantic and the Pacific Ocean. The Black sea population is also differentiated genetically from the other populations of the bottlenose dolphin in the eastern and western Mediterranean Sea and the northeast Atlantic Ocean and this evidence confirms the nomination of the subspecies T. t. ponticus.
 
Distribution:
Practically, it is found in all the oceans and seas on the temperate and tropical latitudes. The Black Sea subspecies is found in the Black Sea, the Kerch strait and the south part of the Sea of Azov and probably (due to lack of genetic evidences) the Sea of Marmara with the Bosphorus and the Dardanelles. There is a series of observations of the bottlenose dolphin entering the big rivers – for example Danube, Dnieper.
The bottlenose dolphins are found in the entire shelf zone of the Black Sea as in some cases they are found far in the open sea. Usually, they gather in large groups during the autumn, winter and spring on comparatively small territory south of Crimea between Sarych cape and Kherson cape.
The migration routes need to be explored in more detail, particularly in the region of the Turkish straits, which serve as the only relation for genetic exchange between the Black Sea and the Mediterranean populations.
 
Population:
The total number of the population in the Black Sea is unknown. For a larger part of the 20thcentury the bottlenose dolphin is considered to be the lowest number species from the three Black Sea cetaceans.
The estimates of the population size based on line transect surveys in some parts of the Black Sea suggest that the present size of the population is at least several thousand individuals.

Biology and ecology:
The body is dark grey on top and white underneath. The rostrum (beak) is short, the lower jaw – protruding forward. The dorsal fin is big and triangular, arched backwards. The teeth are conic, much bigger than those of the common dolphin. Their number is significantly smaller: 36-52 on each jaw. The bottlenose dolphin is the biggest representative of the cetaceans in the Black Sea, reaching length of up to 3,3 m (usually 1,9-2,5 m) and weight of up to 300 kg. Lifespan is up to 25-30 years, but has comparatively low fertility. The females become sexually mature at the age of 5-6 years or even later and the males at the age of 8-12 years.
The breeding season is year-long as the most active periods are the spring and the early summer. The pregnancy lasts 12 months and most often gives birth to one infant. The period of birth is from 2-3 to 6 years. The lactation period is 4-18 months. These reproduction characteristics of the bottlenose dolphins seem to be the main natural factor limiting the increase of the population.
The bottlenose dolphins are mainly piscivorous in the Black Sea, feeding on benthic species as well as pelagic species with different sizes. 16 species of fishes in total are described as plunder on the Crimean and Caucasian shores: turbot (Psetta maxima maeotica), thornback ray (Raja clavata), whiting (Merlangius merlangus euxinus), golden grey mullet (Liza aurata), leaping mullet (Liza saliens), flathead grey mullet (Mugil cephalus), anchovy (Engraulis encrasicolus ponticus), red mullet (Mullus barbatus ponticus), bonito (Sarda sarda), black scorpion fish (Scorpaena porcus), corb (Umbrina cirrosa). Within the last years the introduced species far-east mullet (Mugil soiuy) is an important food resource in the Northern Black Sea in Crimean waters. The daily consumption is 6-32 kilos.
 
Threats:
After the total prohibition on commercial killing of cetaceans in the Black Sea from 1983, the main threat to the species caused by human activity is the bycatch (accidental entanglement in fishing nets) mainly caused by turbot fishery.


Black Sea harbour porpoise (Phocoena phocoena relicta)

Морска свиня, муткурConservation 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.