The Caspian Sea, the world’s largest inland body of water, prompts questions about its marine life. Its immense size, stretching approximately 1,200 kilometers from north to south and covering an area of about 371,000 square kilometers, leads many to wonder if creatures typically associated with oceans, such as sharks, inhabit its waters. This inquiry stems from its designation as a “sea” and its impressive scale. Its unique characteristics invite a closer look into its environment and the species it harbors.
The Caspian Sea’s Unique Environment
The Caspian Sea is the largest landlocked body of water on Earth, exhibiting characteristics of both a lake and a sea. It is an endorheic basin, meaning it has no natural outflow to the global oceans. This isolation is a fundamental factor shaping its distinct environment.
Its geological history explains its unique composition. The Caspian Sea is a remnant of the ancient Paratethys Sea, which was once connected to the world’s oceans millions of years ago. Over time, tectonic shifts and falling sea levels caused this ancient sea to become isolated, forming the landlocked basin seen today.
The Caspian Sea’s salinity differs from oceanic waters. While oceans typically have an average salinity of around 35 parts per thousand (ppt), the Caspian Sea’s average salinity is about 12 ppt. This brackish nature is due to significant freshwater inflow, which dilutes the salt content.
Salinity levels vary across the sea, with the northern, shallower parts being less saline due to river inputs. In contrast, the southern and eastern regions tend to be more saline. This blend of fresh and salt water creates an environment distinct from both freshwater lakes and marine habitats, influencing the types of life that can survive there.
The Answer: No Sharks, But Unique Life
Due to its lower salinity and landlocked nature, oceanic sharks do not inhabit the Caspian Sea. The specific physiological adaptations required for sharks to thrive in the high salinity of open oceans are not met by the Caspian’s brackish, enclosed waters. The absence of a connection to the world’s oceans prevents these species from migrating into the basin.
Despite the absence of sharks, the Caspian Sea is home to unique and endemic species. The Caspian seal (Pusa caspica) is the only marine mammal found exclusively here. These seals are one of the few seal species living in inland waters.
The sea is also known for its diverse sturgeon population, including Beluga, Russian, Persian, and Sevruga sturgeon. These fish represent a significant part of the Caspian’s biodiversity. Sturgeon species thrive in the Caspian’s brackish conditions, contributing to its distinctive ecosystem.
Beyond seals and sturgeon, the Caspian Sea supports various other fish species, including gobies, cyprinids, clupeids, herring, pike, and perch. While the overall number of species might be lower compared to oceans, a significant proportion of the animal life found here is endemic. This unique collection of species highlights the distinct evolutionary path taken by life within this colossal, isolated basin.