Fish of the Bulgarian Coastal Waters

Kamen Prodanov, Kristina Dencheva, and Ludia Ivanov

Summary

This paper discusses the ichthyofauna inhabiting the Bulgarian Black Sea coast throughout the year, both seasonally and episodically. This includes 46 families and 126 species; some of these, however, are known only on the basis of a single specimen, which raises doubts about their real presence in Bulgaria's Black Sea waters.

The species list used in this study contains 5 families that were not listed in "Fishes of the Bulgarian Black Sea coast" (Stoyanov et al., 1963). The representatives of these families inhabit coastal lakes or river mouths, but do not range into the Black Sea. According to the systematic list of FAO "Fisheries Statistics," which has been used since the end of 1987, the families Cybiidae and Thunnidae are related to the Scombridae. For the same reasons, Moronidae is now separated from Serranidae and Scophthalmidae from Bothidae. The two new families are Congridae and Merlucciidae.

The classification of Rass (1987) is accepted in the present list. It is based on the catalog of fishes in the northeast Atlantic Ocean and the Mediterranean (Clofnam, 1973). For the reasons mentioned above, 23 species (freshwater fishes from the coastal lakes) have been removed from Stoyanov et al.'s (1963) list of the Bulgarian ichthyofauna, which included 135 species, while 14 species have been added.

The table and map that accompany the species list show the areas of origin of the species, the character of their reproduction, and their most important biological characteristics (population numbers, migrations, etc.). The data indicate that the fish fauna of the Bulgarian coastal waters is formed to a considerable extent of seasonal migrants that winter in the Sea of Marmora or at the Anatolian coast of Turkey.

On the basis of calculations of fish mortality rates, it is concluded that the Bulgarian fishing industry takes an insignificant part of the total quantities of anchovy, Black Sea shad, horse mackerel, turbot, and whiting; sprat, however, are the exception to this finding. At the same time, the fishing industries of Turkey and the former Soviet Union have in some years over-harvested and, to a great extent, reduced the populations of these species.

Measures to protect different fish species from over-exploitation are described. It is concluded that both eutrophication and pollution (with oil products, heavy metals, chlorine compounds and other contaminants) are increasing in the sea, and that previous steps to protect fish populations have not yielded the desired results. The populations of most species have fallen sharply, especially after the rapid growth of the new ctenophore species Mnemia maccradyi (Mnemiopsis leidiy). Delays in the prohibition of bottom trawling, which ruined the biotic communities of the sea bottom and in so doing affected the link between the benthic and pelagic communities, have also contributed to declines in fish populations.

Effective fishing regulations on the Bulgarian Black Sea coast are urgently needed, as are international conventions to protect the sea and the large tributary rivers (Danube, Dnestr, Dnepr, etc.) from pollution. It is recommended that a Black Sea Commission be created to determine catch quotas for the intensively exploited fish species, with a view toward rational utilization of their populations.

A Brief History of Research on the Fish of the Black Sea Coast

Studies of the fish fauna in the Bulgarian Black Sea coastal waters began in the early 1920s. There was at the time no specialized marine scientific institute in Bulgaria. Consequently, these early studies were descriptive in nature and gave only a rough idea of the flora and fauna in the Bulgarian coastal waters (Drensky, 1923).

The monograph Fish in Bulgaria (Drensky, 1951) describes some species that have been identified only on the basis of single specimens, such as Squalus blainvillei (Risso), Acipenser nudiventris (Lovetzky), and Lichia amia (L); single specimens of these have been caught in different years near Sozopol and Varna. The species Conger conger (L) and Serranus cabrilla (L) are also extremely rare. The species Alosa caspia bulgarica (Drensky) = Alosa alosa bulgarica (Drensky) and Alosa alosa macedonica are, according to this author, members of a single geographical race of Alosa alosa. Drensky, however, following Vinciguerra (1921), assumed that all three geographical races were individual species. The monograph described 16 species of the Gobiidae family which were attributed to the genus Gobius.

In 1932, the Marine Biology Station and Aquarium was established in Varna. Its first director was the prominent Bulgarian zoologist G. Paspalev. In the same year the Experimental Ichthyological Station was established in Sozopol. The Russian scientist A. Nechaev, the best educated ichthyologist of the time, was appointed as its director. His research provided the first data on the migration and size distribution of bonito, mackerel, horse mackerel, mullets, and other species. After his retirement in 1941, these studies were discontinued until 1954, with the exception of sprat data collected by S. Stoyanov.

In 1954, the Marine Biological Station and Aquarium and the Experimental Ichthyological Station (the latter was moved to Varna in 1948) were integrated to lay the beginnings of the first Bulgarian scientific marine institute, to be known as "The Scientific and Research Institute of Fishery and Fish Industry - Varna." The name was subsequently subject to multiple changes, as reflected in the titles of the proceedings in which the studies of the institute scientists were published. After the establishment of this institute, more extensive studies of fish taxonomy and biology were carried out. In 1963, the book Fish of the Black Sea (Bulgarian Coast) by Stoyanov et al. was published. This book provided descriptions of 135 species in 49 families. Of these, 23 species were representatives of the fresh water ichthyofauna inhabiting the coastal lakes or the mouths of rivers running into the Black Sea. The taxonomic list of fish did not, however, include the six rare species described by Drensky (1951), mentioned above. In addition, in this classification the Gobiidae family contained 19 representatives in 9 genera.

Georgiev (1966) carried out a revision of the Gobiidae family representatives, describing 23 species. The new species, with respect to those specified in Fish of the Black Sea, were Gobius buccichi (Steindachner), Neogobius platyrostris (Pallas), Neogobius kessleri (Gunther) and Benthophiloides stellatus (Sauvage). The two latter species are representatives of the fresh water ichthyofauna, inhabiting the Danube and some coastal lakes.

Manolov (1970) described 11 fish species of the Sparidae family. As compared to the 8 species described in Fish in the Black Sea, the new species were Dentex dentex (L), Pagellus erythrinus (L), Diplodus vulgaris (Geoffrey St.-Hilaire) and Oblada melanura (L). The author noted in his paper that "within some 10 or 14 years we were able... to compile a collection of all the known Sparidae in our ichthyofauna (except Lithognatus mormyrus)".

Bearing in mind that Stoyanov, in Fish of the Black Sea, was the first to report the species Pagellus mormyrus = Lithognathus mormyrus, which had not been detected a second time for more than 10 years, it may be concluded that this is an extremely rare species. This is valid to the same degree for the species Dentex dentex, Diplodus vulgaris, Lithognathus erythrinus, and Oblada melanura. Prodanov and Chachev (1987) reported the capture of a single immature specimen of Merluccius merluccius (L) in front of Sozopol during bottom trawling for sprat. It is evident, from these observations, that a certain part of the ichthyofauna along the Bulgarian Black Sea coast consists of extremely rare species that occasionally visit the Bulgarian coastal waters.

The taxonomic status of the species in the family Gobiidae is very complicated, as there are multiple intermediate forms between individual species. Electrophoresis has proven the existence of hybrid forms between allied species. According to Dobrovolov (unpubl. data), a persistent inhabitant of the Bulgarian coastal waters is the species Neogobius cephalargoides Pinchuk, which is closely akin to Neogobius cephalarges and Neogobius ratan. Hence, they are often mistaken.

As a result of the important research of many Bulgarian ichthyologists (Stoyanov, Nikolov, Georgiev, Ivanov, Kolarov, Kolemanova, Karapetkova, Prodanov, Mikhailov, Daskalov, etc.) the major biological features of the commercial species - reproduction, growth in length and mass with age, population dynamics, rate of exploitation, and so forth - have been established. Periodic or continuous monitoring has been conducted on many features of the Black Sea ichthyofauna: the size, age, and sexual composition of the catch of sprat, anchovy, horse mackerel, whiting, bonito, mackerel, bluefish, shad, mullets, gobies, turbot, and other species; the dynamics of catch and fishery pressure (Ivanova); and the ichthyoplankton (eggs and larvae) and structure of the fish population along the Bulgarian coast (Dobrovolov and Dobrovolova). As a result of these studies, concepts were elaborated to provide for the rational exploitation of fish resources (Ivanov, Prodanov, Kolarov). During recent years, studies have been carried out to determine the effects of anthropogenic contamination of the Black Sea on the number of the most important fish species (sprat, horse mackerel, whiting, anchovy, etc.). These species have decreased dramatically, particularly after the rapid spread of the new ctenophore species Mnemia maccradyi.

In these studies, ever-increasing priority has been given to the adoption of an ecological approach. This has also been stimulated by the structure of the Institute of Oceanology, which, in addition to the sections of Marine Biology and Ecology, has well developed sections of Marine Physics, Marine Chemistry, Marine Geology, Marine Geochemistry, Submarine Equipment and Technology, as well as laboratories of Oceanographic Instrumentation and Marine Facilities. All of this allows the Institute to carry out integrated research on board the Scientific Research Vessel Akademik, which is equipped with the most up-to-date navigation and hydroacoustic instrumentation. However, under the present economic situation the lack of funding has become a problem, and the seasonal scientific expeditions of the SRV Akademik have been temporarily cancelled.

Gaps in Knowledge

The spawning status of the rare fish species found in Bulgarian coastal waters is unclear. Data indicates that many of them are spawning in the northwestern part of the Black Sea. However, this has not been proven for the Bulgarian coastal waters, although most of these species are thermophilic, migrating from the south to the north. The reason is that no regular investigations are carried out in the Bulgarian coastal waters to establish the presence of ichthyoplankton species or the population of the new fish generation. This is especially true for rare species, species whose populations are too low to support fishing, or species that are otherwise of little fishing significance.

During the last three years (1990-1993) no representative data on the amounts of catches or on fishing operations have been gathered. This has prevented researchers from making precise calculations of the population dynamics of the species subject to intensive fishing.

The measures for protection of the Black Sea from pollution and for regulating fishing are not coordinated. The Agreement for Fishing in Black Sea (1960) and other measures to regulate fishing and to conduct scientific investigations have involved Bulgaria, Romania, and the former Soviet Union, but Turkey has not participated. In the General Council for Mediterranean Fishing, the former Soviet Union was not represented.

Since 1990, investigations of the food base and the biomass dynamics of the new ctenophore species have been intermittent due to the lack of funds for surveys using the vessel Akademik. No studies have been undertaken to determine the influence on the fertilized fish eggs and larvae of the different metabolites during phytoplankton blooms.

Taxonomic Status

The taxonomic status of the fish in the Bulgarian part of Black Sea has not been firmly established. Appendix 1 gives the contemporary taxonomic status of the marine and brackish water fish found at different times in the Bulgarian Black Sea waters. The nomenclature adopted by Rass (1987), which is based to a great extent on the catalog of the northeast Atlantic and Mediterranean fish (1973), has been used. For the sake of consistency with the Yearbook of Fisheries Statistics of the FAO and the General Council of Fisheries in the Mediterranean (GFCM Statistical Bulletin, 1989), the Sea wolf (D. labrax) has been deleted from the Serranidae family and included in the Moronidae family. In addition, the Cybiidae and Thunnidae families have been assigned to Scombridae. For the same reason, the Scophithalmidae family has been separated from the Bothidae family.

In Appendix 1, the older non-matching names of the families and species from Fish in the Black Sea are indicated in parentheses underneath the newer name. The list does not include freshwater fish of the coastal lakes and river mouths that do not occur in the Black Sea. For this reason, 23 species have been removed from Stoyanov et al.'s 1963 list, which comprised 49 families and 135 species. The 23 deleted species belong to 5 families: Cyprinidae (17 species), Cobitidae (2 species), Siluridae (1 species), Esocidae (1 species), and Percidae (2 species). Hence, the list of families has been reduced from 49 to 44, as the families Cybiidae, Thunnidae, and Scombridae are integrated into one family, and the Moronidae and Scophthalmidae have been separated from, respectively, the Serranidae and Bothidae families. The two new families in Appendix 1 are Congridae (Drensky, 1951) and Merlucciidae. Thus, the total number of families is 46. They comprise 126 species. Of the 14 new species, 8 were described by Drensky (1951), 2 by Georgiev (1966), 2 by Manolov (1970), one by Prodanov and Chachev (1987), and one by Dobrovolov (to be published). There is no mention of the very rare visitors from the Mediterranean to the Bulgarian coastal waters, such as mackerel (Scomber scombrus L.) and anchovy (Engraulis encrasicolus). The first of these species differs from the common small mackerel form of the Marmara and Black Sea. Neither is the Azov anchovy (E. encrasicolus maeoticus), which in particular seasons reaches the Bulgarian coast, mentioned.

Species Characteristics

Of the 126 species listed in Appendix 1, 24 are Pontian relicts, 9 originate from the Atlantic, and 93 are Mediterranean emigrants. Catadromous fish are represented by 1 species, and anadromous fish by 8 species. Approximately 62 species in the Bulgarian waters migrate towards the shore and back, while about 64 migrate from south to north and back. The total number of species with pelagic spawn is 66, though 27-29 species spawn in the Bulgarian sea waters: 17-19 in the offshore area and 10 in the open waters. Forty-nine species spawn in bottom waters; 41-42 spawn in the Bulgarian sea waters, all of them in the near offshore area. There are 3 viviparous species. Two breed along the Bulgarian coast: one in the near offshore strip, and the other in more open waters. One species spawns by attaching eggs in capsules in the offshore area. Of the 7 species in which males bear the spawn in special nursing bags or in pre-anal body cavities, 6 inhabit the near offshore area and one lives in more open waters. Six species spawn in the autumn-winter season; all the rest spawn in the spring-summer months. As was mentioned, most of the fish spawn in the near offshore area, rendering them very vulnerable to water contamination.

Status of the Black Sea Coastal Zone and Fisheries

Despite recent corrective measures, the stocks of most species and groups of fish have tended to diminish, as reflected in their catch by decades in the sea (Table 1) and in lakes (Table 2) from 1941-1990. Possible reasons for these declines include the rapid rate of exploitation, the contamination of the waters, and the changes in the Black Sea ecosystem as a whole. In the coastal lakes, which in the past had been frequented by as many as 20-30 marine and brackish water species, the hydrological and hydrochemical conditions have changed dramatically. Since 1962, Mandrensko Lake has been turned into a reservoir and Bourgasko Lake has been isolated and no longer receives sea water inflow. The latter lake has subsequently become polluted with waste water and oil products. The small Dyavolsko wetland was drained and the area of Pomoriysko Lake (lagoon) was greatly reduced. Blatnishko Lake has been turned into a reserve. A new navigation channel was dredged from the sea through Varna and Beloslav Lakes. The life in the latter lake is almost entirely extinct due to pollution from the chemical plants in Devnya.

As regards the Bulgarian Black Sea zone as a whole, we assume provisionally that it had been relatively clean up to the year 1970. At that point, eutrophication began to affect the sea. This period has been characterized by structural and functional changes in the ecosystem, due to which local and widespread algae blooms are becoming more frequent and of ever-increasing intensity, duration, and extent. These blooms are frequently followed by oxygen deficiency and the perishing of bottom-dwelling and mud fish species, especially in the near offshore area.

Table 1: Bulgarian mean annual catches of commercial fishes in Black Sea during 1941-1990 (in tons).

Species or groups of fishes 1941-50 1951-60 1961-70 1971-80 1981-90 1990 Only
Squalis acanthias, spiny dogfish 0.1 2 1 12 56 16
Raja clavata, ray 1.1 7.4 45 2 + +
Acipenseridae, Sturgeons 1 10 43 40 12 +
S. sprattus phalericus, sprat 795 1468 1030 7551 11619 2650
Alosa kessleri pontica, pontic shad 112 129 41 49 26 17
Engraulis encrasicolus ponticus, anchovy 225 162 177 134 168 +
Belone belone euxini, garfish 10 9 6 0.4 + -
Merlangius merlangus euxinus, whiting - - - 161 + +
Mugilidae, mullets 33 68 28 11 8 1
Atherina boyeri, silverside (Boyer's sand smelt) 17 9 + + + +
Dicentrarchus labrax, common bass 0.1 0.2 + - - -
Pomatomus saltator, bluefish 21 69 230 30 8 6
Trachurus mediterraneus ponticus, pontic horse mackerel 480 499 444 1108 777 164
Centracanthidae, pickerels 11 103 + + + -
Mullus barbatus ponticus, striped mullet 14 10 2 0.2 + -
Sarda sarda, bonito 653 1152 945 20 25 17
Thunnus thynnus, great tuna 1.5 0.4 + - - -
Scomber scombrus, pontic mackerel 966 543 452 + - -
Xiphias gladius, swordfish 0.1 0.2 + - - -
Gobiidae, gobies 98 34 25 23 28 14
Psetta maeotica, turbot 69 234 334 172 12 -
Platichthys flesus luscus, European flounder 0.3 0.8 0.3 0.2 + +
Other fishes 16.8 68.7 173.7 69.2    
Total 3525 4477 3977 9383 12799 2898

Overharvesting

In the Bulgarian zone, the last 10 to 15 years have witnessed reduced occurrences both in a majority of the year-round inhabitants and in species that migrate between the south and the north.

The stocks of the generatively Marmarian and trophically Black Sea mackerel (Scomber scombrus L.) dramatically dropped, almost to the point of extinction, after 1969. The stocks of bonito (Sarda sarda L.) in the Bulgarian zone, which once were substantial in the October-December period, sharply diminished in 1970. This anomaly continues to this day. Meanwhile, along the Turkish Black Sea coast and in the Sea of Marmara, the stocks of this species, despite a definite drop, continue to be relatively abundant.

The situation with the bluefish (Pomatomus saltator L.) is similar. Since 1970 its numbers have stayed relatively high in the Sea of Marmara and along the Turkish Black Sea coast, but in Bulgarian waters it occurs only in small quantities. Judging by the catches (Table 3), the horse mackerel stock along the Bulgarian coast has stabilized, but its dynamics in 1990-92 demonstrated a downward trend.

Especially disturbing, and occurring for the first time, has been the sizable depression of Black Sea anchovy stocks. This species was almost absent in the 1989-1991 Bulgarian catch. According to unofficial data, the anchovy catch of the Black Sea nations in 1991 dropped to about 5% of the average annual catch of 1980-1989.

The greatest stock and catch in the Bulgarian zone is represented by the sprat. This stock of this species has also shown a downward trend, especially in 1990-91. There has been some recovery since the autumn of 1992. The decline in catch, however, has been greater than the decline in stocks. The Bulgarian sprat catch in 1990 (2650 tons) dropped to about 14% of the 1981 catch (18,880 tons). About 49% of this decline is attributed to declines in the stocks, while about 51% is due to the decline in fishing activity.

Table 2. Mean annual catches of marine and brackish water fishes in Bulgarian coastal lakes (in tons)

Species or family of fishes 1941-50 1951-60 1961-70 1971-80 1981-90
S. sprattus phalericus and Clupeonella cultriventris, (sprat and common kilka) 16 7 + + +
Mugilidae, mullets 84 189 113 7 2
Atherina boyeri, silverside (Boyer's sand smelt) 27 16 + + +
Gobiidae, gobies 40 40 97 21 8
Platichthys flesus luscus, European flounder 27 53 + + +
Other fishes 5 1 + + +
Total 199 306 210 28 10

The exploitation rate of fish stocks by the Bulgarian fishery industry is far below the minimum tolerable standards. According to Ivanov (1970), from 1963-65 the instantaneous fishing mortality (Fex) rate of the mackerel stocks from all Black Sea countries had been 0.445, while from the Bulgarian fishery alone, 0.042. For the Danube shad (Alosa kessleri pontica) from 1963-79 this rate has been 0.99 for all Black Sea countries, and 0.035 for the Bulgarian fishery alone (Ivanov and Beverton, 1985). The Fex is higher for the turbot (Psetta maeotica). The mean value of Fex for the 1956-78 period had been 0.57 (Ivanov and Karapetkova, 1979; Ivanov and Beverton, 1985). This figure, however, included the turbot catch by Turkish fishermen in the Bulgarian zone. Supposing their catch had been twice that of the Bulgarians, the Fex would split as follows: Bulgarian fishery - 0.19, Turkish fishery - 0.38.

The most heavily exploited species is the sprat. For sprat, the tolerable value of F is 0.43 (Ivanov, 1989; Prodanov, 1989). In the period 1976-82 the actual value of F had been considerably lower than the theoretical tolerable value. Nevertheless, the sprat stock began to decline, with some oscillations. Since 1989 fishing pressure has dropped sharply, but the sprat stock is still below its 1978-82 level.

The low exploitation rate of fish stocks by the Bulgarian fishery is confirmed by data on the commercial fish catch in the Black Sea countries (Table 3). At the same time the exploitation of fish stock in over-wintering locations in the Sea of Marmara and along the Anatolian and the Caucasus Black Sea coasts is very heavy and is exceeding the tolerable standards for some species.

The depression of the Black Sea anchovy stocks in 1989-1992 is due to both deteriorating ecological conditions and excessive harvesting of this species (Shlyakhov et al., 1990). Together these have resulted in a reduction of the reproductive stock. Ivanov and Mikhailov (1991) have also shown by means of modelling that increases in the Fex in over-wintering locations lead to strong reductions in the surviving reproductive stock. It has also been shown that instituting a 50-100% ban on fishing of the youngest age group (0+ years of age) in November-April would significantly increase the total stock and would increase the reproductive stock several times over. The improved quality of the larger anchovies would compensate for the reduction in the catch at over-wintering locations. These theoretical results provide evidence of the need for the Black Sea countries to reach agreement on regulation of the fisheries.

Table 3. Mean annual catches of commercial fishes from all Black Sea countries in subarea of 37.8.0 GFCM in 1980-1989 (in tons)

Species or family of fishes Bulgaria Romania Turkey Former USSR Total
Sprattus sprattus phalericus 13011 5479 - 50824 69332
g. Alosa, shad 25 592 688 299 1604
g. Engraulis, anchovy 188 3716 269408 183162 456474
Merlangius merlangus euxinus, whiting * 30 1403 15330 2445 19208
Pomatomus saltator, bluefish 10 2 14870 3 1488
Trachurus mediterraneus ponticus, pontic horse mackerel 842 1190 79444 5727 87203
Sarda sarda, bonita 25 - 16720 - 16745
Pleuronectiformes, flatfish 21 8 2261 1238 3927

Notes: * this catch represents 50% from Bulgarian catch of "other fishes"

Bulgaria has recently adopted a number of restrictions in order to preserve the fish of the Bulgarian Black Sea area from over-exploitation.

Species Minimal Length (in cm) By-catch (%)
1 Huso huso 170 0
2 Acipenser guldenstadti colchicus 110 0
3 Acipenser stellatus 100 0
4 Psetta maeotica 35 5
5 Alosa kessleri pontica 16 8
6 Mugilidae (in sea only) 20 20
7 Trachurus mediterraneus ponticus 10 20
8 Scomber scombrus 15 20
9 Sprattus phalericus 6 40
* Fishing of Acipenser nudiventris is absolutely banned.

Pollution

In terms of water quality, the Black Sea has a small pollution acceptance capacity and faces an added handicap in the presence of hydrogen sulphide under its surface oxygen layer (in the Bulgarian zone, the bottom fish down to 90 m and pelagic and mud fish down to 100-130 m occur rarely). The Bulgarian zone accepts pollutants not only from its own coast, but to an even greater extent from other regions. These pollutants come mainly from the northwest, where the waters of the large rivers pour into the sea. According to Konovalov (1992), the Black Sea is contaminated annually by some 100 thousand tons of oil derivatives, 40-50 thousand tons arriving via the Danube. Contamination with heavy metals and other chemical compounds is considerable (Marine Pollution '90, 1990). In addition to river-borne pollutants, the Black Sea also receives a great deal of pollution via the atmosphere from the industrial centers of Europe and the former Soviet Union. The Bulgarian Black Sea zone also receives pollutants of domestic origin, the most significant being emitted from chemical plants at Devnya and Bourgas, which lie 30 and 10 km from the seashore respectively.

From the Danube, the Black Sea annually receives 60 tons of mercury, 240 tons of cadmium, 4000 tons of lead, and 900 tons of chromium. Copper contamination of the Black Sea is about 2-3 times greater than that of the Mediterranean. The contamination of the basin with different chemical substances - including DDT and other insecticides, hexacyclohexane (HCH), polyvinylchlorides (PVC), and polychlorinated biphenyls (PCBs) - is also strong. The rivers Danube, Dniepr, Dniester, and South Bug annually pour from 1200 to 5000 tons of pesticides into the Black Sea. According to UNEP, the most dangerous substances for living organisms are radionuclides and mercury, followed by the pesticides and other heavy metals (UNEP, 1986a,b,c). Compared to the Mediterranean, the Black Sea is also much more heavily burdened with phosphates and nitrates, especially if only the oxygen zone is considered. According to Konovalov (1992) the quantities of these substances are as follows:

  Mediterr. Sea Baltic Sea Black Sea
Phosphates
tons 384606 82415 153842
tons/km3 0.102 3.8 (0.19) 0.286
Nitrates
tons 1093-2187 234.4-468 437.5 -875
tons/km3 0.291 -0.582 10.85 -21.0 8.1 -16.2*
(Note: * Phosphorus and Nitrogen quantities in proportion to the Black Sea oxygen zone volume)

The parenthesized value 0.19 is the predicted quantity of phosphates in the Baltic Sea after the International Programme for Phosphorus Control on the Baltic is implemented.

As is well known, the greatest effect upon marine ecosystems is exerted by the phosphates, nitrates, and potassium compounds which cause eutrophication of water bodies (Vollenweider, 1976). In this respect, the most affected part of the Black Sea is the northwest. As considerable quantities of nutrients - especially nitrogen and phosphorus - are imported by the large rivers Danube, Dniepr, Dnestr, and South Bulgare, they are carried to the Bulgarian shore by the typical currents within the sea basin.

Changes in the Black Sea Ecosystem

As a result of all these environmental changes, serious shifts have occurred in the Black Sea ecosystem in the last 20 years. The ecosystem has also been affected by the delayed ban on bottom trawling, which destroys the seabed communities and affects the links between the benthic and pelagic components of the system.

The major changes in the Black Sea ecosystem can be briefly summarized as follows:

As has been noted, the ichthyofauna along the Bulgarian coast is comprised to a great extent of migrating fish species from the Sea of Marmara, the Anatolian Turkish coast, and the northwest part of the Black Sea. Pollution and excessive harvesting of fish populations in those regions will result in further declines in the occurrence and species diversity of the ichthyofauna inhabiting the Bulgarian Black Sea coast throughout the year, seasonally, or occasionally. The adverse effects of pollution will likely increase by the end of the century due to the expected decrease in precipitation, which will further diminish the water exchange in the Black Sea and will reduce the self-purification capacities of the basin.

Recommendations

In consideration of all of the above, the following major recommendations are offered:

Appendix 1. Species Composition of the Ichthyofauna in the Bulgarian Black Sea Waters

Family, species, subspecies Pontic relicts Boreal-Atlantic relicts Mediterranean immigrants
1 2 3 4
I. Squalidae      
1. Squalus acanthias L., spiny dogfish - + -
2. Squalus blainvillei (Risso), dogfish - + -
II. Rajidae      
3. Raja clavata, ray - + -
III. Dasyatidae (Trigonidae)      
4. Dasyatis pastinaca (L.) (Trigon pastinaca L.) common stingray - + -
IV. Acipenseridae      
5. Huso huso L., great sturgeon + - -
6. Acipenser nudiventris Lovetzky, spiny sturgeon + - -
7. A. guldenstadti colchicus Marti, russian sturgeon + - -
8. A. sturio L., common sturgeon + - -
9. A. stellatus Pallas, starred sturgeon + - -
V. Clupeidae      
10. Sprattus sprattus phalerieus (Risso) (S.s.sulinus (Antipa)), sprat - + -
11. Sardinella aurita Valenciennes, round sardinella - - +
12. Sardina pilchardus (Walbaum) (S.p.sardina (Risso)), European pilchard - - +
13. Clupeonella cultriventris (Nordm.), common kilka + - -
14. Alosa kessleri pontica (Eichwald), pontic shad + - -
15. Alosa caspia nordmanni Antipa, caspian shad + - -
16. Alosa caspia bulgarica (Drensky), Drensky shad + - -
17. Alosa brashnikovi maeotica (Grimm) (A.kessleri pontica var.), Brazhnikov's shad + - -
18. Alosa fallax nilotica (Geoffroy), twaite shad - - +
VI. Engraulidae      
19. Engraulis encrasicolus ponticus Aleks., pontic anchovy - - +
VII. Salmonidae      
20. Salmo trutta labrax Pallas, pontic salmon - + -
VIII. Anguillidae      
21. Anguilla anguilla (L.), European eel - + -
IX. Congridae      
22. Conger conger (L.), Conger eel - - +
X. Belonida      
23. Belone belone euxini Gunter, garfish - - +
XI. Gadidae      
24. Gaidropsarus mediterraneus (L.), shore rockling - - +
25. Merlangius merlangus euxinus (Nordm) (Odontogadus merlangus euxinus (Nordm.), whiting - + -
XII. Merluccijdae      
26. Merluccius (L.), European hake - - +
XIII. Gasterosteidae      
27. Gasterosteus aculeatus L., tree-spined stickleback - + -
28. Pungitius platygaster (Kessler) (P.platygaster (Kessler), nine-spined stickleback + - -
XIV. Syngnathidae      
29. Hippocampus ramulosus Leach (H. hippocampus microcoronatus (Slastenenko), short-nosed seahorse - - +
30. Nerophis ophidion L., straight-nosed pipefish - - +
31. Syngnathus abaster Risso (S.nigrolineatus Eichwald), black-striped pipefish - - +
32. S. phlegon schmidti Popov (S. schmidti Popov), Atlantic pipefish - - +
33. S. tenuirostris Rathke, narrow-snouted pipefish - - +
34. S. typhle L. (S. t. argentatus Pallas), broad-nosed pipefish - - +
35. S. variegatus Pallas (S. rubescens Risso), wide-nosed pipefish - - +
XV. Sphyraenidae      
36. Sphyraena L., European barracuda - - +
XVI. Mugilidae      
37. Mugil cephalus L., common gray mullet - - +
38. Lisa aurata (Risso) (Mugil auratus Risso), leaping gray mullet - - +
39. Liza saliens (Risso) (Mugil saliens Risso), leaping gray mullet - - +
40. Lisa ramada (Risso) (Mugil ramada Risso), thin-lipped mullet - - +
XVII. Atheniridae      
41. Atherina boyeri Risso (A.mochon pontica (Eichwald)), Boyer's sand smelt - - +
42. Atherina hepsetus L., Mediterranean sand smelt - - -
XVIII. Zeidae      
43. Zeus faber L., St. Peter's fish - - +
XIX. Serranidae      
44. Serranus scriba (L.), lettered perch - - +
45. Serranus cabrilla (L.), comber - - +
XX. Moronidae (Serranidae)      
46. Dicentrarchus labrax (L.) (Morone labrax (L.)), common bass - - +
XXI. Pomatomidae      
47. Pomatomus saltator (L.) (P.saltatrix (L.), bluefish - - +
XXII. Carangidae      
48. Trachurus mediterraneus ponticus Alleev, pontic horse mackerel - - +
49. Trachurus L. (T.t.trachurus (L.)), common scad - - +
50. Lichia amia (L.), leer fish - - +
XXIII. Sciaenidae      
51. Umbrina cirrosa (L.) (Sciaena cirrosa L), bearded umbrine - - +
52. Sciaena umbra L. (Corvina umbra (L.)), brown meagre - - +
XXIV. Sparidae      
53. Boops boops (L.), bogue - - +
54. Dentex dentex (L.), dentex - - +
55. Diplodus annularis (L.) (Sargus annularis (L.)), annular bream - - +
56. Diplodus sargus (L.) (Sargus (L.)., white bream - - +
57. Diplodus vulgaris (Geoffroy St.-Hilaire), two banded bream - - +
58. Lithognathus mormyrus (L.) (Pagellus mormyrus (L.)), sand steembras - - +
59. Pagellus erythrinus (L.), pandora - - +
60. Puntazzo (Gmelin) (Charax puntazzo (Cetti)), sharp-snouted sparus - - +
61. Sarpa salpa (L.) (Boops salpa (L.)), bamboo fish - - +
62. Sparus aurata L. (Aurata (L.)), gilthead bream- - - +
63. Spondyliosoma cantharus (L.) (Cantharus (L.)), black bream - - +
64. Oblada melanura (L.) - - +
XXV. Maenidae      
65. Spicara flexuosa Rafinesque (Maena chryselis (C.V.)), saddled bream - - +
66. Spicara maena (L.) (Maena (L.)), common pickarel - - +
67. Spicara smaris (L.) (Maena smaris (L.)), plotched pickarel (stripped mullet) - - +
XXVI. Mullidae      
68. Mullus barbatus ponticus Essipov, high body pickarel - - +
XXVII. Pomacentridae      
69. Chromis (L.), blunt snouted mullet - - +
XXVIII. Labridae      
70. Symphodus tinca (L.) (Crenilabrus tinca (L.), blue damselfish - - +
71. Symphodus ocellatus (Forsskal) (Crenilabrus ocellatus Forsskal), long striped wrasse - - +
72. Symphodus cinereus (Bonnaterre) (Crenilabrus griseus L.), axillary wrasse - - +
73. Symphodus roissali (Risso) (Crenilabrus quiquemaculatus Bloch), cork wing - - +
74. Ctenolabrus rupestris (L.), gold sinny - - +
XXIX. Trachinidae      
75. Trachinus draco L., greater weever - - +
XXX. Uranoscopidae      
76. Uranoscopus scaber L., common stargazer - - +
XXXI. Blenniidae      
77. Blennius pavo Risso, peacock blenny - - +
78. Blennius sanguinolentus Pallas, Black sea blenny - - +
79. Blennius tentacularis Brunnich, tentacled blenny - - +
80. Blennius zvonimiri Kolombatovic, Zvonimir's blenny - - +
81. Blennius sphynx Valenciennes (B.sphinx Val.), sphynx blenny - - +
82. Coryphoblennius galerita (L.), montagn's blenny - - +
XXXII. Ophidiidae      
83. Ophidion rochei Muler, snake blenny - - +
XXXIII. Ammodytidae      
84. Gymnammodytes cicerelus (Rafinesque) (Ammodytes cicerellus Rafinesque), smooth sand lance - - +
XXXIV. Callionymidae      
85. Callionymus risso Le Sueur (Callionymus belenus (Risso), datted dragonet - - +
86. Callionimus pusillus Delaroche (C.festivus Pallas), Delaroch's dragonet - - +
XXXV. Scombridae      
87. Scomber scombrus L. (S.s.ponticus Zambr.), pontic mackerel - - +
88. Scomber japonicus Houttuyn (Pneumatophorus colias (Lowe)), japan mackerel - - +
89. Sarda sarda (Bloch), bonita - - +
90. Thunnus thynnus (L.), great tunny - - +
91. Euthynnus alleteratus (Rafinesque), little tunny - - +
XXXVI. Xiphiidae      
92. Xiphias gladius L., swordfish - - +
XXXVII. Gobiidae      
93. Aphya minuta (Risso), transparent goby - - +
94. Bentophiloides brauneri Beling et Iljin, Brauner's goby + - -
95. Chromogobius quadrivittatus (Steindachner) (Relictogobius kryzhanovski Ptschelina), Steindachner's goby - - +
96. Gobius bucchichi Steindacher, Buchich's goby - - +
97. Gobius cobitis Pallas, giant goby - - +
98. Gobius niger L., black goby - - +
99. Gobius ophiocefalus Pallas, grass goby - - +
100. Gobius paganellus L., rock goby - - +
101. Knipowitschia georghievi Pinchuk (Knipowitschia longicaudata (Kessler), lagoon goby + - -
102. Mesogobius batrachocephalus (Pallas), toad goby + - -
103. Neogobius cephalarges (Pallas), mushroom goby + - -
104. Neogobius fluviatilis (Pallas), monkey goby + - -
105. Neogobius gymnotrachelus (Kessler) (Mesogobius gymnotrachelus (Kessler), goad goby + - -
106. Neogobius melanostomus (Pallas), round goby + - -
107. Neogobius platyrostris (Pallas), guban goby + - -
108. Neogobius ratan (Nordmann), ratan goby + - -
109. Neogobius cephalargoides Pinchuk, Pinchuk's goby + - -
110. Neogobius syrman (Nordmann), syrman goby + - -
111. Pomatosshistus caucasicus (Kawrajski) Berg (Knipowitschia caucasia Kawrajski), lagoon goby + - -
112. P.marmoratus (Risso) (Pomatoschistus microps (Kr_yer), marbled goby - - +
113. P.minutus elongatus (Canestrini) (Pomatoschistus minutus Pallas), sand goby - - +
114. Proterorhinus marmoratus (Pallas), tube nosed goby + - -
XXXVIII. Scorpaenidae      
115. Scorpaena porcus L., small scaled scorpion fish - - +
XXXIX. Triglidae      
116. Trigla lucerna L., yelow gurnard - - +
XL. Bothidae      
117. Arnoglossus kessleri Schmidt, sea bach - - +
XLI. Scophthalmidae (Bothidae)      
118. Psetta maeotica (Pallas) (Rhombus maeoticus (Pallas), turbot - - +
119. Scophthalmus rhombus (l.) (Rhombus rhombus (L.)), brill - - +
XLII. Pleuronectidae      
120. Platichthys flesus luscus (Pallas) (Pleuronectes flesus luscus (Pallas), European flounder - + -
XLIII. Soleidae      
121. Solea nasuta (Pallas), snouted scole - - +
XLIV. Echeneididae      
122. Echeneis naucrates L., slender sucker fisch - - +
XLV. Gobiesocidae      
123. Lepadogaster lepadogaster lepadogaster (Bonnaterre) (L. gouani Lacepede), cornish sucker fish - - +
124. Lepadogaster candolei Risso (L.de candollii Risso), connemara clingfish - - +
125. Diplecogaster bimaculata euxinica (Mugroci) (Lepadogaster bimaculatus Penant), two-spotted clingfish - - +
XLVI. Lophiidae      
126. Lophius piscatorius L., angler - - +
Total 24 9 93

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