Low salinity and osmotic pressure keep Great White sharks out of the Black Sea

While Great White sharks are occasionally spotted in the Mediterranean, they are absent from the Black Sea. Despite a direct aquatic route via the Dardanelles, the Sea of Marmara, and the Bosphorus, several hydrological barriers prevent these apex predators from establishing a population in the region. The primary obstacle is the chemical composition of the water. Salinity in the Mediterranean ranges between 37-39 parts per thousand (ppt), whereas in the Black Sea, it drops to 17-18 ppt. For an oceanic fish evolved for high-density saltwater, this difference creates a severe osmotic load. "A sharp drop in osmotic pressure in freshened water forces cartilaginous fish to expend excessive energy to maintain their water-salt balance," zoologist Dmitry Melnikov told Pravda. Ru.