|Scientific Name:||Theodoxus transversalis|
|Species Authority:||(Pfeiffer, 1828)|
|Red List Category & Criteria:||Endangered B2ab(ii,iii,iv) ver 3.1|
|Assessor/s:||Solymos, P. & Feher, Z.|
|Reviewer/s:||Tomovic, J., Vavrova, L., García, N., Seddon, M., Nichols, C. & Cuttelod, A.|
This species has a restricted area of occupancy (AOO) of about 80 km². Due to the loss of habitats and subpopulations in Hungary, this species is considered to be severely fragmented and there is a continuing decline in the area of occupancy, quality of habitat and number of subpopulations. It is therefore considered to be Endangered (EN B2ab(ii,iii,iv)).
It is also assessed as Endangered (EN B2ab(ii,iii,iv)) for Europe and the countries of the EU27.
|Range Description:||This species is distributed along the Danube River system including the Tisza (Tisa, Theiss) River system. Its geographical range includes Germany, Austria, Slovakia, Hungary (Rába, Hernád, Bódva, Upper-Tisza), Serbia (Juzna Morava, Velika Morava and Nisava), Bulgaria (Danube, Zlatna Panega), Romania and Croatia.
In Romania, Sirbu (2001) notes that the most extensive range was in the Tisa Basin, including Mures (Maros) river and tributaries of the Olt River (mostly in the middle sectors however, by the 1960s the range had declined to a few localities from the specified area). Surveys over the last 20 years have shown the disappearance from the whole of the Mures and Olt Rivers and from all sites in Transylvania. It is also no longer found in the Crit River basin and in Marannret region.
The last record in Slovakia is from 1999 (Danube River), and the species is probably extinct from the Hungarian section of the Danube also.
Native:Bulgaria; Croatia; Germany; Hungary; Serbia (Serbia, Serbia)
Possibly extinct:Romania; Slovakia
|Range Map:||Click here to open the map viewer and explore range.|
|Population:||There are only a few known subpopulations (less than 20). Some of them are in good condition (e.g. Bódva in Hungary and Zlatna Panega in Bulgaria), but most of them are threatened by pollution and the invasive Theodoxus fluviatilis species. There are long term monitoring results in Hungary and two of the Hungarian populations (Tisza and Hernad) are close to extinction. Population size decline has been observed in 50% of the Hungarian populations. There are no data on population size in other countries. It is however probable that soon subpopulations along the whole Danube section will be extinct and only some fragmented sub-populations will remain in some tributaries.|
|Habitat and Ecology:||This is a fluvial species, it occurs in rivers associated with solid surface.|
|Major Threat(s):||Habitat decline has been observed in parts of the species range. This is due to domestic and industrial pollution, competition from the non-native species Theodoxus fluviatilis and changes in the hydrological regime through dams.|
|Conservation Actions:||This species is listed by the Annexes II and IV of the European Union Habitat and Species Directive (EUHSD). It is also protected in Hungary on a national level. Population and habitat monitoring combined with a water management plan is recommended.|
|Citation:||Solymos, P. & Feher, Z. 2011. Theodoxus transversalis. In: IUCN 2013. IUCN Red List of Threatened Species. Version 2013.2. <www.iucnredlist.org>. Downloaded on 13 December 2013.|
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