Fig. 1: Current physical environmental conditions of the Caspian Sea.

a Bathymetry of the Caspian Sea with a datum of −27.5 m against global mean sea level. b NASA Worldview satellite image of the Caspian Sea region showing typical winter ice coverage of the northern Caspian basin, which is the breeding habitat for the endemic Caspian seal (Pusa caspica). The pink polygon indicates the Caspian seal breeding Important Marine Mammal Area (IMMA; see Methods).