First record of the Chinese mitten crab, Eriocheir sinensis H. Milne Edwards, 1853 (Crustacea: Brachyura: Varunidae) from Lake Ladoga, Russia

A special survey has been conducted to record the distribution of Chinese mitten crab, Eriocheir sinensis in the eastern Gulf of Finland basin (Baltic Sea). An illustrated questionnaire/registration form was distributed among the commercial fishermen. The survey indicated a significant increase in the abundance of adult crabs in 2003 migrating downstream in the Neva River, the connecting channel between the Gulf of Finland and Lake Ladoga. On October 25, 2005, the Chinese mitten crab was reported from Taypolovsky Bay, Lake Ladoga and this is the first confirmed record from Europe’s largest lake.


Introduction
The Chinese mitten crab Eriocheir sinensis H. Milne-Edwards 1853 (for date of authority and taxonomy see Clark 2006) was first recorded from the Aller River, Germany, Europe in 1912, probably as a result of an accidental introduction from ships' ballast water.In 1926 this invasive species was found on the German coast of the Baltic Sea, as a possible consequence of active migration via the Kiel Canal (Gollasch 1999).The Chinese mitten crab is considered to be unable to reproduce in freshwater and in the Baltic Sea.However it was frequently found in high numbers from some rivers and estuaries along the southern Baltic coast (Normant et al. 2000(Normant et al. , 2002)), and the eastern Gulf of Finland, i.e. the Neva River, the largest tributary to the Baltic Sea, since 1980 (Panov et al. 2003).
Eriocheir sinensis was first recorded from the freshwater ecosystems of the Lake Ladoga basin in the late 1990s from the Vuoksa River (Panov et al. 2003).The specimen may have migrated either from the Lake Saimaa District or from Lake Ladoga.Lake Saimaa is connected with the eastern Gulf of Finland by the Saimaa Canal, and since 1999 records of E. sinensis from this area were reported by Pienimäki and Leppäkoski (2004).Lake Ladoga, the largest European lake, is connected with the eastern Gulf of Finland via the Neva River and Neva Bay (easternmost part of the Gulf of Finland) (Figure 1), but to date there have been no confirmed records of E. sinensis from Lake itself.

Methods
Since 2002, when there were numerous records of E. sinensis caught in fishing nets in the Russian coastal waters of the eastern Gulf of Finland, a special survey has been conducted in this region using an illustrated questionnaire/ registration form, which was distributed among the commercial fishermen.The registration forms included photos of male and female crabs and scheme of measurements of crabs in order to make it user-friendly for fishermen (Annex 1).

Results and discussion
The survey indicated a significant increase in the abundance of E. sinensis adult crabs in 2003 migrating, most likely, downstream in the Neva River and the Neva Bay.Geo-referenced records of E. sinensis in the eastern Gulf of Finland basin in 2002-2005 are present in the Annex 2. On October 25, 2005, the first Chinese mitten crab was reported from Lake Ladoga.The adult male was captured in fishing nets, Taypolovsky Bay (Figure 1), 60˚37.9'N, 30˚32.2'E. The crab measured: carapace width 57 mm, carapace length 53 mm, and body weight 81 g (Figure 2).
Most likely, this migrating individual entered Lake Ladoga from the Burnaya River, a lower part of the Vuoksa River, and was trapped in the gillnet while moving towards the Neva River and eastern Gulf of Finland as part of regular seasonal migration of adult crabs to the western Baltic or North Sea for reproduction.In 1997 one individual of E. sinensis was found in the lower Burnaya River, close to the location of the first record of this species in the Lake Ladoga (Figure 1).
Eriocheir sinensis is the second crustacean invader recorded in Lake Ladoga, the first being the Gmelinoides fasciatus Stebbing.During the last two decades this Baikalian amphipod has successfully become established in littoral communities of the lake (Panov 1996).Consequences of recent mass invasion of Chinese mitten crab in freshwater ecosystems in the Lake Ladoga basin is not clear and require further study.

5.
Name of recorder: Date of filling the form:

Figure 1 .
Figure 1.Location of Chinese mitten crab records in the eastern Gulf of Finland area.Asterisk indicate location of the first confirmed record in Lake Ladoga.Dashed line indicated the Saimaa Canal

Figure 2 .
Figure 2. How to distinguish sexes in crabs A -male B -female