Where did the largest river fish - Beluga, 4 meters long, go?

2024 Author: Seth Attwood | [email protected]. Last modified: 2023-12-16 15:55

Even some 100 years ago, fabulous fish by modern standards were caught in the Volga: weighing up to 1, 2-1, 5 tons and more than 4 meters long. And these are not at all tales of fishermen, but confirmed scientific facts. These were huge belugas, which had not been seen in the Volga for a long time, and the few representatives of this species that remained in our days bear little resemblance to their great ancestors.

But what happened to the largest freshwater fish on the planet? Why did it almost disappear, and those few individuals that remained, with their modest size do not at all resemble the largest freshwater fish on the planet?

Belugas belong to the sturgeon family and live in the basin of the Caspian, Black and Azov seas. This fish belongs to anadromous species that live in the seas, but go into rivers to reproduce. The population of the Caspian beluga spawns in the Volga, Ural, Kura, Terek, and the Azov beluga spawns in the Don River. The Black Sea beluga lives off the coast of Ukraine, Bulgaria and Romania, therefore it spawns in the Danube, Dnieper and Dniester. Back in the middle of the last century, the beluga population lived off the coast of Italy in the Adriatic Sea, but today this species of sturgeon is not found there.

Belugas are predatory fish that feed on small aquatic organisms, molluscs, larvae and crustaceans at a young age, and when they reach venerable age and size, they switch to larger prey - river fish. Belugas are real long-livers, as they can live up to 100 years. But this is not the only record for these fish. The fact is that belugas grow all their lives, that is, by the size of the fish, you can roughly determine its age. Well, the famous 4-meter beluga specimen, which was caught at the beginning of the last century in the Volga, most likely was close to its centenary.

But 4-meter giants are records of bygone days, in our time there are no such belugas. Those belugas that today swim in the waters of the Caspian and the Black Sea are extremely small in number, despite the fact that the species is listed in all the Red Data Books that are possible. Several factors led to such a deplorable situation, but the main culprit in such a plight of the beluga, of course, is a person.

Intensive fishing and pollution of river and sea waters led to a catastrophic population decline in the 20th century. The situation was worsened by the construction of numerous hydroelectric power plants on the largest rivers in Europe, which were not equipped with fish-passing mechanisms, which did not allow fish to go upstream to their usual spawning grounds. Volga, Kama, Kura, Don, Dnieper and Dniester - all of them were blocked by dams of hydroelectric power plants, which deprived beluga whales of most of their spawning grounds.

Another important feature that influenced the sharp decline in the population is the very long maturation period of the beluga. It takes a very long time for the beluga to reach reproductive age. Males of the Caspian beluga are capable of breeding no earlier than 13-18 years old, and for females this figure reaches 16-25 years. Thus, in order for the beluga to grow up and be able to leave offspring, a very long time must pass.

The fact that the beluga needs to be saved, especially the population of the Sea of Azov, which is in a more deplorable state compared to the Caspian beluga, became clear back in the middle of the 20th century. They began to breed beluga in special nurseries, release eggs and fry into the Sea of Azov. This made it possible to stabilize the situation a little, but the volumes released were not enough to maintain and increase the population size.

The current state of the species is of serious concern to ichthyologists. The weight of most of the belugas caught over the past 20-30 years does not exceed 300 kilograms, and the age of these fish is no more than 40-50 years. If in the middle of the XX century in the Volga there were about 25 thousand belugas going for spawning, then at the beginning of the XXI century their number did not exceed 5 thousand. It remains to be hoped that ecologists and fish farming specialists will be able to preserve this amazing species of fish and belugas of incredible sizes will again be found in the Volga.

In "Research on the state of fishing in Russia" 1861 reports on a beluga caught in 1827 in the lower reaches of the Volga, which weighed 1.5 tons (90 poods)

Ichthyologist's comment:

As a professional ichthyologist (Department of Ichthyology, Moscow State University), I will allow myself to comment on the article. In fact, the main reason for the sharp decline in sturgeon numbers is precisely the cascade of dams.

The point here is that sturgeons have a very pronounced phenomenon of "homming", i.e. the desire to return to spawn in the places where these fish were once born. And there are so-called "races" that do not rise to spawn at the same time. Well, let's say, one "race" spawned earlier in the Tver province, and so it started the spawning run earlier, and those "races" that spawned in the middle reaches of the Volga went to spawn later. But the fact is that more than 90% of sturgeon spawned in places that are now located above the first dam of the cascade.

Fish passages for sturgeon are practically useless, because this fish is archaic and has a very primitive nervous system. A vivid example - if you feed the fish in the same place in the aquarium, after opening the aquarium lid, they will soon develop a conditioned reflex, and will begin to swim to the feeding site as soon as the lid is opened, without even waiting for the bark to be brought in. But with sturgeons, this situation does not work - the fish will not learn and will not respond to raising the lid, and every time the aquarist introduces food, the sturgeon begins to "twist circles" around the aquarium, looking for food by smell. And even if they always feed in one place, sturgeon fish will not remember this, and each time they will search for food again.

It's the same with fish passages - the sturgeon can go to spawn only in those ways that were mastered during millions of years of evolution. Sturgeons will never use the fish ladder (well, perhaps, single specimens and purely by accident).

But there is also a downside to the coin - if all the dams are now demolished, the sturgeon population has recovered relatively quickly. Moreover, economically, it is probably more profitable to sell caviar than to supply electricity from hydroelectric power plants (which, by the way, can be replaced by nuclear power plants, without losing productivity).