(…) The Black Sea harbour porpoise, P. p. relicta, qualifies for listing as Endangered (EN) based on criteria A1d and A4c,d,e. The basis for inferences and suspicions leading to that assessment is summarised below.
The estimated generation time is around 9-10 years (see main text of workshop report), thus three generations for the Black Sea harbour porpoises would be 27-30 years.
There are no estimates of unexploited or present total population size, although the available information suggests that present abundance is at least several thousands.
The following information from the last three decades is relevant to the proposed classification. However, it is important to note that very high levels of direct and incidental mortality occurred for a long period before then (from the 1830s and throughout the 20th century) and this undoubtedly would have dramatically reduced the population prior to the 1970s (IWC, 2004).
(1) Large directed takes occurred during the years 1976-1983 before the ban on small cetacean hunting was declared in Turkey in 1983. Within that period, the total number of harbour porpoises killed was at least 163,000-211,000. Illegal direct killing of unknown numbers continued in some parts of the Black Sea until 1991.
(2) Regionally extensive incidental mortality of porpoises in bottom-set gillnets is roughly estimated to have been in the thousands annually through the 1980s. The scale of this mortality almost certainly increased in the 1990s-2000s owing to the rapid expansion of illegal, unreported and unregulated fishing in the Black Sea.
(3) A major mass stranding/mortality event occurred in the Azov Sea in August 1982 as a result of an explosion at a gas-extraction platform. More than 2,000 porpoises were found on shore following this event.
(4) Two other mass stranding/mortality events occurred in 1989 and 1990, attributed to the combined effects of parasitic and bacterial infections. Although difficult to quantify, the mortality of porpoises is believed to have been in the thousands.
(5) Periodically (most recently in November 1993), natural mass mortality events occur as a result of ice entrapment in the Azov Sea. Although no direct estimates are available, these can result in the deaths of several tens or more animals.
(6) There has been general and ongoing degradation of the Black Sea environment (including harbour porpoise habitat) and biodiversity during the 1970s-2000s, with perhaps the most serious period in the late 1980s–early 1990s due to a combination of overfishing, water pollution, eutrophication, demersal fish die-offs caused by hypoxia and the population explosion of harmful alien species. This degradation almost certainly has resulted in a decline in the abundance and quality of harbour porpoise prey.
(7) The harbour porpoise was considered extinct in the Mediterranean Sea until 1997, when a specimen stranded alive in the northern Aegean Sea; a few further strandings and sightings have occurred in that limited area since then.
EN: A1d. A reduction in population size of 70% over the past 30 years is inferred based on paragraphs (1) and (3) above, i.e. the directed takes and, to a lesser degree, the accident in 1992 (considered ‘actual exploitation’ in the context of IUCN criteria). These causes were clearly reversible and understood and they have ceased. Despite the absence of abundance estimates for the initial part of the 30-year period, the suspected decline of 70% is based on inferences from a crude extrapolation based on the annual removal levels in the Turkish fishery: a reduction of 70% implies that the population in 1976 must have been at least 233,000-302,000, whereas a reduction of 50% (threshold for Vulnerable) would require a population size of at least 326,000-422,000. The latter seems unrealistic given the duration and intensity of past exploitation.
EN: A4c,d,e. A reduction in population size of >50% over a 30-year period that includes both the past and the future is inferred based on the above paragraphs except (1) and (3). During this period, although direct killing has ceased, the other known or suspected causes of decline (bycatch, habitat degradation, prey depletion, epizootics and adverse climatic circumstances) have not ceased. (…)