The solution of transnational environmental problems in the field of the protection of threatened species and conservation biology directly depends on the level of international communication, which can significantly decrease due to differences in Red Lists and Red Data Books of different levels. In order to identify the similarities and differences in approaches to the assessment of
national Red Lists and Books of the Baltic Sea region countries (Russia, Denmark, Germany, Lithuania, Finland, Poland and Sweden) with the IUCN Red List, a comparative analysis was carried out. It was determined that the level of discrepancy between Red Data Lists and Books varies considerably,
with differences in the scales of species categories, species lists and categories. Most of the threatened species at the national level are not listed under the IUCN Red List, while species in a more stringent category at the national level prevail (37% and 3% on average, respectively). However, national Red Lists and Red Data Books do not take into account the global trend of the risk of extinction of species. The percentage of species with insufficient information to define a category at the national or global level ranges from 6% to 28%. These discrepancies make it difficult to exchange data on threatened
species and create a unified database with information on protected species at different levels and, therefore, reduce the effectiveness of biodiversity conservation activities at regional and international
levels. The results also demonstrate that countries have an international responsibility to conserve a species, and the cases identified can provide useful additional information to guide a national conservation strategy.