Beluga (sturgeon)

• 1. Introduction

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  The beluga sturgeon, Huso huso, holds a record that was set in 1827 in the Volga estuary: a single female weighing 1,571 kilograms and stretching 7.2 metres. That fish was not a monster or an aberration. It was simply an old beluga, doing what belugas do, which is grow. They never stop growing, not for a century if they are given the chance. That is the first thing to understand about this animal. The second is that almost no one is giving them the chance anymore. Wild beluga populations have been pushed to the edge of extinction by overfishing and poaching, and the International Union for Conservation of Nature now classifies the species as critically endangered. How does the largest freshwater fish in the world end up on the brink? What is it about this creature that made humans pursue it so relentlessly? And what is left to save?

• 2. A Body Built for the Ages

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  Among all living bony fishes, Huso huso rivals the ocean sunfish as the most massive and trails only the giant oarfish, Regalecus glesne, in length. It also competes with the great white shark and the Greenland shark for the title of largest actively predatory fish. These are extraordinary comparisons, and the beluga's body reflects that extraordinary status. Its skeleton is only partially made of bone; much of it remains cartilaginous, an ancient trait shared across the sturgeon family. The skin carries no scales in the conventional sense. Instead, rows of bony plates called scutes run along the body in five longitudinal series, including dorsal, lateral, and ventral arrangements. The dorsal fin alone carries between 48 and 81 soft rays. The rostrum is conical and packed with sensory pits on both surfaces, helping the fish detect prey in dark or murky water. The mouth is crescent-shaped, large, and protractile, meaning it can be thrust forward to engulf prey with extraordinary speed. As a beluga ages, that mouth shifts from a position on the underside of the head toward an almost frontal position, and the snout, which in juveniles accounts for nearly half the head, shortens to between one-third and one-quarter by adulthood. The oldest individuals become stocky, with massive heads and enormous mouths that reflect decades of continuous growth.

• 3. The Long Migration

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  Beluga sturgeon are anadromous, meaning they live in salt water but travel into rivers to breed. The distances involved are staggering. At one time, individuals could migrate up to 1,000 kilometres upriver to reach spawning grounds. Some travelled as far as 1,700 kilometres upstream in the Danube system, while others stopped just 100 kilometres inland. The difference between individuals is not arbitrary. Spawning biology in the Danube co-evolved alongside the formation of the Danube valley itself, producing survival strategies that vary dramatically across the species. The autumn entry into the river begins a two-stage journey: the fish overwinter in the river and then move to spawn in spring, once the substrate and water-flow conditions meet their requirements. Females reach sexual maturity between 16 and 22 years of age; males do so earlier, between 12 and 16. Once they spawn, they do not return every year. The cycle repeats every four to seven years. Females deposit their eggs on gravel at depths ranging from 4 to 40 metres. The eggs are sticky and adhesive, anchored to the clean hard substrate. Hatchlings emerge at 11 to 14 millimetres in length. Ten to fourteen days later, once the yolk sac is absorbed, they reach 18 to 20 millimetres. Those small fish then make their way back toward the sea, covering up to 60 kilometres per day.

• 4. What a Beluga Eats

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  Fish make up roughly 73 percent of an adult beluga's diet, but the species takes a wide range of prey depending on size, location, and life stage. Juveniles smaller than 40 centimetres in the Caspian Sea feed mainly on small schooling fish of the genus Clupeonella. As they grow to between 40 and 280 centimetres, gobies from the family Gobiidae become the primary target. The largest individuals shift to mullets, shad of the genus Alosa, and even other sturgeons, including Acipenser ruthenus. In the brackish waters of the Ponto-Caspian basin, the preferred prey shifts to genera including Alosa, Aspius, and Engraulis. Rivers and estuaries bring a different menu: migrating spawners eat cyprinids including common carp and roach, as well as pike-perch. Adults are not limited to fish. Molluscs, crustaceans, aquatic birds, and even young Caspian seals appear in the diet. The now-extinct Adriatic population appears to have relied heavily on cephalopods in marine and brackish water, including common cuttlefish and European squid, alongside fish from several families. Prey is not chewed. The beluga's protractile mouth creates suction powerful enough to draw the prey in almost instantly.

• 5. The Price of Caviar

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  Beluga caviar is considered a delicacy worldwide, and the demand for it has driven the species toward extinction. The female's roe has been fished intensively for generations, and that pressure has come at a biological cost that the species is poorly equipped to absorb. Belugas reproduce slowly. Females do not spawn until they are at least 16 years old, and they return to spawn only every four to seven years. Fishing and poaching have systematically removed the largest, oldest, and most reproductively capable individuals from the population. The result is that natural reproduction has been nearly eliminated in many parts of the historic range. Overfishing has been so severe that the average lifespan of wild beluga is now unknown; no specimens have been recorded living past their 56th year, even though the species is capable of surviving more than 100 years. The fish's air bladder is also commercially valuable. It is used to produce isinglass, a high-grade clarifying agent. The flesh, though not as celebrated as the caviar, is a hearty white meat with some similarity to swordfish. Almost every part of the animal has found a market, which has made protection extremely difficult.

• 6. Dams, Pollution, and a Shrinking World

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  The Iron Gate dam on the Danube and the Volgograd Dam on the Volga have blocked the historic spawning routes that beluga relied on for millennia. Before dam construction, individuals could travel up to 1,000 kilometres upriver. Today, access to those distant upstream grounds is effectively cut off. Very few wintering and spawning sites for sturgeon are known to remain in the lower Danube, and none are documented in the upper reaches. The problem extends beyond blocked passages. Pollution from oil extraction, industrial discharge, agricultural runoff, and sewage degrades the quality of the habitat the fish do reach. Because belugas live for decades, they accumulate pesticide contamination over time, reducing reproductive success and generating broader health problems. Their range has contracted sharply. Historically the species inhabited the Caspian Sea, the Black Sea, the Adriatic Sea, the Sea of Azov, and all the rivers connecting those bodies of water. Today the Adriatic population is considered extinct. The Danube is now the only river within the European Union where naturally reproducing sturgeon populations persist at all.

• 7. Efforts to Bring Them Back

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  Since 2015, an official captive breeding programme has operated in Italy using beluga sourced from the Azov Sea. In 2019, hundreds of young microchipped beluga and 60 tagged subadults were released into the Po river following the construction of a fish ladder on the Isola Serafini dam, as part of the EU-funded Life Ticino Biosurce project. The goal is to rebuild the Adriatic population, which has been gone long enough that the fish releasing into the Po are, in effect, colonists in a river that once held their ancestors. In Bascom, Florida, Sturgeon Aquafarms became in July 2016 the first facility in the world to obtain a permit exemption allowing the sale of beluga sturgeon and its caviar in the United States. Since 2017 the company has contributed more than 160,000 fertilized eggs to repopulation efforts in the Caspian Sea region. A World Wildlife Fund crowdfunding campaign funded the release of more than 7,000 three-month-old beluga sturgeons into the Danube River in Bulgaria. Legal protections are layered: the species is listed under Appendix III of the Bern Convention, under CITES Appendix II, and under the U.S. Endangered Species Act. The United States banned imports of beluga caviar and other beluga products from the Caspian Sea on the 6th of October 2005. Yet in 2021, two men in Grindu, Ialomita, in Romania were caught trying to move a 140-kilogram, 2.5-metre beluga in a wagon, a reminder that laws alone have not closed the gap between protection and reality.