The Caspian Sea, the world’s largest inland body of water, hosts a diverse and commercially important fishery. Though landlocked, it functions ecologically as a massive lake, supporting approximately 115 native fish species, many of which are endemic. These populations include valuable commercial species that have supported the regional economies of the five bordering nations—Russia, Iran, Kazakhstan, Azerbaijan, and Turkmenistan—for centuries.
The Caspian Sea’s Unique Ecology
The Caspian Sea’s fish fauna is defined by its landlocked nature and its long, independent geological history. It is a remnant of the ancient Paratethys Sea, isolated from the world ocean about 5.5 million years ago. This isolation has led to a high rate of endemism, with over 60% of the fish species found exclusively in this basin.
The water body is characterized by widely varying salinity levels. The northern basin, which receives the vast majority of freshwater inflow from the Volga River, is nearly fresh (as low as 0.12 parts per thousand). In contrast, the deeper central and southern basins are brackish, averaging about 12 ppt, roughly one-third the salt concentration of the open ocean. This unique mix means that only species with strong osmoregulatory abilities, such as many gobies and crustaceans, have been able to thrive.
Endemic and Major Fish Species
The Caspian Sea is home to numerous commercially harvested and endemic species. The Caspian kilka, small pelagic fish related to sprats, represents the largest commercial catch by volume. These schooling fish form a foundation of the food web, serving as a primary food source for larger predators and the Caspian seal.
Another important endemic species is the Caspian kutum, a type of roach highly valued as food, especially along the Iranian coast. The sea also supports several species of Caspian shad and herring, which are important to local fisheries. Other well-represented families include gobies, which have diversified into numerous endemic species, and various types of carp, such as the common bream and zander.
The Critical Status of Caspian Sturgeon
The sturgeon group is the most economically significant fish in the Caspian Sea, historically accounting for the majority of the world’s wild caviar production. The basin is home to six species, including the Beluga sturgeon, the Russian sturgeon, and the Stellate sturgeon. These long-lived fish are anadromous, migrating from the sea into freshwater rivers, primarily the Volga and Ural, to spawn.
This life cycle makes them vulnerable to human impact, leading to a catastrophic decline, with natural stocks of certain species falling by as much as 99%. The construction of large dams along the Volga River severely restricted access to historical spawning grounds. This habitat destruction, combined with overfishing and poaching driven by the high value of caviar, has led to all five anadromous Caspian sturgeon species being classified as critically endangered.
Conservation Concerns and Future Outlook
The threats facing the Caspian Sea’s fish extend beyond overfishing and damming. Widespread industrial pollution, stemming from oil and gas exploration and the discharge of untreated waste, degrades habitats and weakens aquatic life. This deteriorating water quality contributes significantly to the crisis in biodiversity.
Climate change presents a serious long-term threat through its impact on sea levels. Increased evaporation and reduced river inflow are projected to cause the sea level to drop significantly, potentially by 5 to 10 meters. This would lead to the loss of vast shallow water habitats. This northern zone is crucial for the spawning of many fish species and would block access routes for sturgeon migrating up rivers. The five littoral states have acknowledged these issues, implementing a voluntary ban on commercial sturgeon fishing and attempting to coordinate management efforts to protect the ecosystem.