[Note: It has been agreed that territorial waters of all six Black Sea countries constitute the 12-mile-wide aquatic strip along the coasts of the sea; marine boundaries of the countries coincide with the external (offshore) border of this strip. However, there are some areas where the sea runs deep inland (gulfs, bays, etc.), and in these places the 12-mile rule does not work. These water bodies are situated quite far from the state boundaries and constitute the so-called âinternal [marine] watersâ of the Black Sea countries.]
Habitat and Ecology
IUCN Red List Assessment
Red List Category
Red List Criteria
The Black Sea Short-beaked Common Dolphin subspecies, D. d. ponticus, is assessed as Vulnerable based on criterion A2cde. There is no estimate of overall population size but preliminary data for some parts of the basin suggest that it is currently at least several 10,000s, and possibly 100,000.
Generation time was not estimated for this subspecies but was assumed to be approximately 15 years following Taylor et al. (2007). Three generations therefore would be about 45 years.
The past 45-year period (three generations) includes circumstances that are relevant to criterion A, as follows:
(1) Large directed takes occurred during the years 1962-1983 before the ban on small cetacean hunting was declared in Turkey in 1983. Within that 22-year period, the total number of common dolphins killed was at least 159,000-161,000 but certainly greater because that range of values does not take account of catches in Romania (1962-66) or Turkey (before 1976 and after 1981) (see âThreatsâ).
(2) A mass mortality event of unknown cause occurred in 1990, involving at least 100s of dolphins.
(3) A mass mortality event caused by morbillivirus infection occurred in 1994, again involving at least 100s of animals.
(4) The Black Sea environment overall (including common dolphin habitat) and many of its indigenous animal populations (including common dolphin prey) have been increasingly degraded from the 1970s to the present, with a likely peak in the devastation caused by overfishing and habitat deterioration (including pollution and explosive growth of populations of invasive species) in the late 1980sâearly 1990s. These processes, taken together, have led to severe declines in prey populations.
A reduction in common dolphin population size of more than 30% (the threshold for Criterion A2cde) was inferred from a simple simulation in which the population was assumed to increase at a constant 4% per year and the direct removals were as indicated in paragraph (1) above. This simulation showed that a decline of about 36% in the last three generations would be required for the current population size to be about 100,000. Although the current population size may be larger, there is also reason to believe that the post-1962 removals were considerably larger than indicated.
Directed killing ceased in 1983 but degradation of habitat, prey depletion and epizootics have continued and these factors are not well understood.
The population size is unknown. Region-wide estimates based on strip transect surveys in the USSR (1967-1974; Zemsky and Yablokov 1974) and Turkey (1987; Ãelikkale et al. 1989) have been shown to be fundamentally flawed for a number of methodological analytical reasons so their use as indicators of absolute abundance is unwarranted (e.g., IWC 1992, Buckland et al. 1992). Nevertheless, it is generally recognized that for almost the first two-thirds of the 20th century, the abundance of common dolphins in the Black Sea was far higher than that of bottlenose dolphins, Tursiops truncatus ponticus, and harbour porpoises, Phocoena phocoena relicta (Tzalkin 1940, Kleinenberg 1956, Geptner et al. 1976).
Line transect surveys have been conducted recently to estimate common dolphin abundance in a few parts of the range (see Table 1 in attached PDF). The survey areas are small relative to the total range of the subspecies. Results suggest that current population size is at least several 10,000s, and possibly 100,000 or more.
By the mid 1960s, the population was depleted due to long-running overexploitation, which involved the killed of many 100,000s of common dolphins in the mid-20th century (IWC 1983; see âThreatsâ). The directed takes continued until 1983 when cetacean hunting finally ceased in Turkey. The numbers of animals taken were not recorded systematically or reliably, and therefore total removals have to be estimated indirectly. It can be inferred that the number of common dolphins was much reduced by the directed kills. It might be assumed that during the period from 1983-2005, the population was increasing. However, this may not be the case in view of mass mortality events (in 1990 and 1994) and the pronounced depletion of these dolphinsâ primary prey species during the same period. The population has not fully recovered, and in fact it may have recovered only very little, from the depletion caused by hunting. Further decline seems likely if degradation of the Black Sea environment continues.
Last century, the population was depleted because of directed takes. The total number of animals killed is unknown, but it was estimated that before the mid 1950s common dolphins comprised 94.8% of the total number of Black Sea cetaceans killed and processed in the former Soviet Union (Tzalkin 1940, Kleinenberg 1956). Based on this value, it was calculated that during the last five years of the cetacean fishery in the USSR and Bulgaria (1962-66), these two countries landed 121,395 common dolphins, while during the preceding 31 years (1931-61) a further 1,449,304 had been landed mainly by the USSR (Zemsky 1996). Between 1976 and 1981, D. d. ponticus was believed to account for 15-16% (or 37,500-40,000 individuals) of the Turkish catch, estimated for that period as 250,000 animals of all three species (IWC 1983).
Reduced prey availability has been considered an ongoing major threat to D. d. ponticus since the late 1980s (Bushuyev 2000). Of two mass mortality events that killed unknown but certainly large numbers of common dolphins in winterâspring 1990 and summerâautumn 1994 (Krivokhizhin and Birkun 1999), the latter was recognised as being the result of a morbillivirus epizootic (Birkun et al. 1999). However, both die-offs coincided with a drastic decline in the abundance of both principal prey species, anchovy and sprat, which has been blamed on overfishing, eutrophication (e.g. water hypoxia) and the explosive increase of the introduced ctenophore Mnemiopsis leidyi (Zaitsev and Mamaev 1997). The total commercial catch of anchovies declined by 12-fold (from 468,800 tonnes in the 1987-88 fishing season to 39,100 tonnes in 1990-91), while landings of sprat fell by a factor of nearly eight (from 105,200 tonnes in 1989 to 13,800 tonnes in 1993) (Prodanov et al. 1997). This correlation between large die-offs of Black Sea common dolphins and prey scarcity could signify that reduced prey availability compromised the health of the dolphins and increased their susceptibility to viral infection.
Other known threats (bycatch in pelagic trawls, parasitic invasions) are of secondary importance (at least at present).
The species D. delphis is listed globally as Least Concern by IUCN. At the same time, the Mediterranean population is listed as Endangered (see Bearzi et al. 2003), and concerns regarding the Black Sea population were expressed in the IUCN/SSC 2002-2010 Conservation Action Plan (Reeves et al. 2003).
Commercial killing of Black Sea common dolphins, as well as other Black Sea cetaceans, was banned in 1966 in the former USSR, Bulgaria and Romania, and in 1983 in Turkey. Black Sea states assumed certain international obligations to protect cetaceans as contracting parties to the Convention on Biological Diversity (CBD), Convention on the Conservation of Migratory Species of Wild Animals (CMS), Convention on the Conservation of European Wildlife and Natural Habitats (Berne Convention), Convention on the Protection of the Black Sea Against Pollution (Bucharest Convention), Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES), and the Agreement on the Conservation of Cetaceans in the Black Sea, Mediterranean Sea and Contiguous Atlantic Area (ACCOBAMS). The common dolphin is included in EC Directive No.92/43/EEC on the conservation of natural habitats of wild fauna and flora; D. delphis is listed in its Annex IV (Animal and Plant Species of Community Interest in Need of Strict Protection). In 2003 the IWC Scientific Committeeâs Sub-Committee on Small Cetaceans recommended that the Black Sea population should be managed for conservation as a distinct entity (IWC 2004).
The Strategic Action Plan for the Rehabilitation and Protection of the Black Sea (1996) envisages some special cetacean-oriented conservation and research actions. The common dolphin was included as Data Deficient in the Black Sea Red Data Book (1999). Nevertheless, it is listed as Endangered in the Provisional List of Species of Black Sea Importance, an annex to the Black Sea Biodiversity and Landscape Conservation Protocol (2002) of the Bucharest Convention. The regional Conservation Plan for Black Sea Cetaceans prepared in accordance with the ACCOBAMS International Implementation Priorities for 2002-2006 (Notarbartolo di Sciara 2002) was adopted by the 3rd Meeting of Parties to ACCOBAMS (Dubrovnik, Croatia, 22-25 October 2007).
On a national level, Black Sea cetaceans, including common dolphins, are protected by environmental legislation and governmental decrees. Action plans for the conservation of Black Sea cetaceans were produced in Ukraine (2001) and Romania (2003) but they have no legal effect at present. The common dolphin is listed in the Red Data Book of Ukraine. In Russia and Ukraine, Red Book inscription means appropriate monitoring and management programs should be implemented at state or national levels. Such a program has existed in Ukraine since 1999.
Relevance to Humans and Ecosystems
IUCN Red List Category
- IUCN (2008) Cetacean update of the 2008 IUCN Red List of Threatened Species.