The Caspian Sea is the largest enclosed body of water on earth. Covering a surface area of around 436 000 km² and being situated in a natural depression, the Caspian Sea receives its inflowing freshwater from nearly 130 rivers. The main rivers are Volga (241 km³), Kura (13 km³), Terek (8.5 km³), Ural (8.1 km³) and Sulak (4 km³) contributing to over 90% of the Caspian’s freshwater inflow. Thus, these rivers form a critical part of the overall Caspian ecosystem. As the Caspian Sea has no outlet to the world oceans, the inflow of these rivers largely determines the level of the Caspian Sea which is currently nearly twenty-seven meters below MSL.
The coastlines of the Caspian are shared by the five Caspian littoral states, namely Azerbaijan, I.R. of Iran, Kazakhstan, Russian Federation and Turkmenistan. The Caspian Sea is commonly divided into three parts, the North, Middle and South Caspian Sea. The border between the northern and middle part runs along the edge of the North Caspian shelf (the Mangyshlak threshold), between Chechen Island and Cape Tiub-Karagan at Fort Shevchenko. The border between the middle and southern part runs from the Apsheron threshold connecting Zhiloi Island in the west to Cape Kuuli in the east. While the North Caspian Sea with an average depth of only 6.2 m is rather shallow, the middle part has an average depth of 190 m and the South Caspian Sea reaches a maximum depth of 1 025 m. The Caspian differs from most other large inland water bodies in its meridian orientation and 1 200 km length resulting in extreme continental climate in the North and sub-tropical climate in the South. The range of climatic conditions that prevail around the Caspian Sea has lead to a significant degree of biological diversity. This is further enhanced by the existence of extensive wetland systems such as the deltas of the Volga, Ural and Kura rivers and the Kara-Bogaz-Gol. The range of salinity around the Caspian sustains freshwater ecosystems in the deltas and estuaries of the Caspian influents, oligohaline ecosystems in the Northern Caspian (salinity between 0.5 and 5 grams/liter), mesohaline ecosystems in the Middle and Southern Caspian and hyperhaline ecosystems in the Kara-Bogaz-Gol, where water salinity is higher than 40 grams per liter.
The isolation of the Caspian basin for over two million years and its climatic and salinity gradients has created a unique ecological system with more than 400 species endemic to the Caspian Sea. There are 115 species of fish, of which some are anadromous migrating from the Caspian up the rivers to spawn. The Caspian sturgeon and the rare fresh water seal are among the most famous species indigenous to the Caspian. In fact, more than 90 % of the world resources of sturgeon originate from the Caspian Sea. The vast river system and extensive wetlands attract millions of migrating birds and are the habitat of diverse flora and fauna.
The Caspian basin is rich in commercially developable hydrocarbon deposits. But the increasing number of oil and gas producing industries as well as hydrocarbon productions and exports constitute serious environmental threats. Years of intensive oil production and refining at industrial sites has polluted ground water, led to widespread oil-mingled soil and the discharge of toxic drilling mud into the Caspian Sea. Moreover, the large rivers polluted with industrial wastes, heavy metals and sewage flowing into the Caspian Sea contribute to the impairment of the habitat of so many species. The mass mortality of more than 3 000 Caspian seals and various species of fish in 2000 was caused by a high amount of toxic substances discovered in the carcass.
Today, Caspian biota is threatened by over-exploitation, habitat destruction and pollution. The traditional Caspian sturgeon fishery is well-known for its caviar production. In recent years, however, the Caspian region has witnessed a serious decline in fish stocks. More efficient fishing methods combined with over-fishing and extensive poaching, dam constructions, introduction of invasive species as well as increased pollution are relevant factors contributing to the dramatic decline.
Being the first regional legally binding instrument signed by all five Caspian littoral states, the Framework Convention for the Protection of the Marine Environment of the Caspian Sea serves as an overarching framework laying down the general requirements and the institutional mechanism for environmental protection in the Caspian region.