Scenario for Reacting to a Possible Outburst of Mnemiopsis in the Caspian Sea in 2001 and Beyond

Considering that the alternatives are: (1) do nothing and wait and see or (2) introduce a species of animal to control Mnemiopsis by predation, a choice to be made by the Caspian country governments in consensus, the participants of the Mnemiopsis workshop in Baku 24-27 April 2001, after due consultation, concluded that before an alien species is introduced, a proposal for introduction should be developed containing the purpose and objective of the introduction, the stages in the life cycle proposed for introduction, a detailed analyses of the potential impacts on the aquatic ecosystem of the proposed introduction, etc.) A rapid and independent review of the proposal should be made by a group of experts on biological invasions, with adequate knowledge of Mnemiopsis. They should be led by the FAO guidelines on the precautionary approach on inland fisheries and species introduction. The advisory group should be composed of experts from the Caspian countries and of international experts, under the aegis of the CEP.

Mnemiopsis may expand in the Caspian in 2001 or later at a rate sufficient to reach levels that could critically endanger the current functioning of the ecosystem and pose grave risks of extinction to a range of species, mainly invertebrates, but also fish (kilka and other species) and ultimately the Caspian seal. Loss of biodiversity as well as economic loss may result.

The participants of the meeting consider that a benchmark for action should be defined. Should such a threshold be met in the future, immediate and appropriate steps should be taken. Best available information on Mnemiopsis in the Caspian (i.e., sighting of isolated individuals between 1995 and late 1999; a first peak locally reaching 460 grams per meter squared g/m² in autumn 2000) suggests that, by analogy with the pace of events in the Black Sea, there might be an increase of Mnemiopsis in the Caspian in late 2001, leading to levels of biomass in excess of what the ecosystem can absorb without major damage.

The benchmark proposed is 1 kilogram, plus or minus 10 percent per meter squared (1 kg +/- 10 % /m²) (wet weight, uncorrected for net effects); this was the same level found in the Black Sea in 1988. The participants recommend that such biomass values should be measured at a number of fixed stations, at least two in each Caspian country, where sampling would be conducted on a regular basis, monthly or seasonally but especially in summer, using a standardized net method. The threshold should be reached at more than one station to make sure that it is not accidental and it should be followed by a replication of sampling as well. Immediately upon recording this threshold value the review and advice of the group of experts mentioned above should be sought, but an ad hoc proposal could already be worked out.

As to which species to introduce, two options were discussed: Beroe and Peprilus. Both have advantages and problems, but it was concluded that, although Peprilus, if successfully introduced, might become a new resource, knowledge on its biology is currently too fragmentary to consider it an option. Beroe ovata was therefore considered the best choice.