Short answers, pulled from the story.
The largest confirmed beluga sturgeon was a female caught in 1827 in the Volga estuary, weighing 1,571 kilograms and measuring 7.2 metres in length. Claims of fish reaching 10 to 12 metres and weights of up to 3,000 kilograms exist but remain disputed and unconfirmed. Beluga sturgeon grow throughout their entire lives and can survive more than 100 years.
The International Union for Conservation of Nature classifies the beluga sturgeon as critically endangered due to heavy overfishing and poaching, primarily driven by demand for beluga caviar. Dam construction has blocked historic spawning migrations, and pollution has degraded habitat throughout the species' range. These pressures have removed the oldest, most reproductively capable individuals and nearly eliminated natural reproduction in much of the historic range.
Beluga sturgeon are found primarily in the Caspian Sea and Black Sea basins, and in rivers including the Danube. Historically they also inhabited the Adriatic Sea and Sea of Azov, but the Adriatic population is now considered extinct. The Danube is the only river within the European Union where naturally reproducing sturgeon populations remain.
The United States Fish and Wildlife Service banned imports of beluga caviar and other beluga products from the Caspian Sea on the 6th of October 2005, after listing the beluga sturgeon under the U.S. Endangered Species Act.
Beluga sturgeon are anadromous, migrating from the sea into rivers to deposit sticky eggs on gravel at depths of 4 to 40 metres. Males reach sexual maturity at 12 to 16 years; females do so at 16 to 22 years. After the first spawning, individuals return to breed only every four to seven years.
A captive breeding programme established in Italy in 2015 uses beluga from the Azov Sea to support the extinct Adriatic population. In 2019, hundreds of microchipped juveniles and 60 tagged subadults were released into the Po river following construction of a fish ladder on the Isola Serafini dam. Sturgeon Aquafarms in Bascom, Florida, has provided more than 160,000 fertilized eggs to the Caspian Sea region since 2017, and a World Wildlife Fund crowdfunding campaign funded the release of over 7,000 young beluga into the Danube in Bulgaria.