Caspian Sea Environment

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THE PRESENT RATE OF MORTALITY OF THE CASPIAN SEALS CANNOT CONTINUE INDEFINITELY WITHOUT A DANGER OF EXTINCTION

An international team of scientists, working as part of the Caspian Environment Programme's Ecotoxicology Project (ECOTOX), has recently concluded that canine distemper virus (CDV) infection was the primary cause of the epizootic of the Caspian seals. Microscopic lesions, characteristic of canine distemper, were found in the seal tissues and infection with CDV was confirmed by serological and molecular methods. These findings in seals from several geographically dispersed regions of the Caspian Sea provide strong evidence that CDV infection was the primary cause of the epizootic. Other environmental factors may have contributed to the deaths, including pollution from land-based sources, warm winter temperatures, which inhibited ice formation, and so on.

Further studies are underway to determine the origin, spread, remedial actions and danger of extinction of the Caspian seals:

Origin - not identified, but either domestic or feral dogs, wild canids (such as wolves in the north Caspian), or both. We need to investigate characterise the strain of CDV in the domestic, feral & wild canid populations before we can say any more on this.

Spread - any form of contact, apparently - touching, coughing, etc. maintenance of the virus in population may be complex as to how the virus is maintained in the population, apparently causing periodic mass outbreaks. It is not clear at present why or how the virus is apparently continuing from one year to the next, and why the survivors do not appear to be developing immunity. Pollution, especially from pesticides such as DDT (known to be at high levels in Caspian seals) will reduce the seals' immunity to infection - possibly this may contribute to the population failing to develop an immunity. However, CDV is a highly pathogenic virus and cause illness even without an added pollution problem. CDV infection may sometimes be sub-acute - i.e. just occur at a low level in an animal - and this low-grade infection may also cause reduced immune response. The bacterial and parasitic infections we found in CDV-infected animals could therefore be partly due to immune suppression either by the CDV itself, or by pesticide pollution, or both. Another effect of organochlorine contamination (DDT, PCB etc) as well as causing immunosuppression is that it reduces fertility. Fecundity of Caspian seal adult females investigated in the past few years has been less than 30%. At present we need to know more about the population size of the Caspian seal - overall and in different areas of the Caspian - as well as contaminant levels in the seals - to begin to understand the epidemiology of the virus. If possible we need to get some tissues preserved from Caspian seals in the past, to see if the virus is detectable from earlier years.

Remedial actions - unfortunately a wildlife vaccine is still some way off, though work is ongoing to develop an effective vaccine. Possible measures to alleviate the problem would be to reduce other stresses on the seals as much as possible, by:

Campaigning to eliminate pollution of the Caspian by pesticides (especially DDT), and other organochlorine contaminants (such as PCBs);
Stop all hunting of Caspian seals;
Reduce bycatch of seals in fisheries.

One noticeable feature of all the dead and dying seals during this epidemic has been their emaciated condition. This may be simply a consequence of the virus. However, there is also a possibility that some of the seals have difficulty in finding sufficient food. If possible, the status of fish stocks, especially of kilkas, throughout the Caspian should be monitored to see if there might be a shortage of food available for the seals. If this were the case, it could exacerbate the problem by weakening their condition. If kilka stocks should be found to be low, action should be taken to reduce fisheries pressure to allow the stocks to recover. All of these remedial actions should be on an international/pan-Caspian basis.

Danger of extinction of the Caspian seal -we do not have updated figures on the present population size of the Caspian seal. However, the present rate of mortality, together with other pressures on the seal, obviously cannot continue indefinitely without a danger of extinction. Moreover, we already mentioned the effect of organochlorine contamination, which as well as causing immunosuppression reduces fertility. Fecundity of Caspian seal adult females investigated in the past few years has been less than 30%. This problem would obviously contribute to a population decline.

For further information, please contact:

Dr. Susan Wilson
Tara Seal Research Centre, 7 Millin Bay Road, Portaferry, Northern Ireland BT22 1QD
Fax: +44 (0)28 42728600
E-mail: suewilson@marinelife.demon.co.uk

Elina Farmanova
Caspian Environment Programme, Programme Coordination Unit, Room 108, Government Building, 40 Uzeir Gadjibekov Street, Baku 370016 Azerbaijan,
Phone: + (99412) 97 17 85, 93 80 03
Fax: + (99412) 97 17 86
E-mail: efarmanova@caspian.in-baku.com

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