Over the past 10 to 12 years the Volga-Caspian basin has been the scene of ecological catastrophe. Things are going from bad to worse: the populations of the Russian sturgeon (Acipenser guldenstadti) and the great sturgeon, or beluga (Huso huso), have been as good as wiped out. While between 1952 and 1990 total annual catches of these fish did not go below 7 thousand tons (in a range of 7.16 to 16.77 thousand tons), the 1998 catch totaled a mere 890 tons: namely, 620 tons for the Russian sturgeon, 200 tons for the stellate sturgeon (Acipenser stellatus), and 70 tons for the beluga. In 1999, the overall catch of the Russian sturgeon, which is the main object of commercial fishing, was down to 357 tons. This downtrend is attributed to the contraction of natural spawning-grounds due to high dams put up across the Volga, environmental pollution, decreasing river drainage, and to poaching which has been up in the last few years. Research scientists of the N.I. Vavilov Institute of General Genetics (RAS) have come up with yet another explanation. Here's what its director, Academician Yuri Altukhov, has told our correspondent Igor Goryunov.
-While not denying the negative effect of the commonly cited factors on the sturgeon population, you name yet another cause. What is it?
- Our Institute offers the following explanation of the disaster. It is related to... the good performance offish hatcheries in the Northern Caspian. As a result, there came a dramatic rise in the fry population and, as a consequence of that, a fish population optimum for the local ecosystem was out of joint - fodder gave out, hence the downtrend.
Our institute has been involved with a similar vexations problem ever since 1968, as we tried to see what could be done to save the salmon population in the Far East. Studying the biological and genetic condition of the Pacific salmon (genus Oncorhynchus), we came up against a paradox: the number of fry was up, whole the catches went down. The blame was put on Japanese fishermen hunting for salmon on the high seas and thus causing damage to our shoals. A close scientific look into the heart of the matter, however, revealed other, more serious causes.
Now, in its work a fish hatchery follows a beaten track: it is common knowledge that fish always return to their native river for spawning. So the idea to overproduce fry that, on maturing, would get back to their native waters seemed excellent.
At first the results were staggering indeed. Like it was in a small stream, the Kalinka, in Sakhalin, about four kilometers long: under natural conditions one never caught above 10 thousand salmon a year there; but with the commissioning of a fish hatchery the annual catches shot up to hundreds of thousands.
Inspired by such results, fish-breeders of the Far East would turn out as many as 800 mln young fish a year. What the fish-breeders failed to see, however, was that the fodder reserve of the ocean was
Dependence between the output of fry and commercial catches of the Russian sturgeon in the Volga-Caspian basin from 1955 to 1998 when fish hatcheries were all too active. Dot numbers denote birth years of non-overlapping generations.
not infinite, and it came to be exhausted rather soon. The feed shortage sends the mortality rate of the fry up, and the overall fish population declines as a result. In other words, the catch volume depends on a medium where commercial shoals offish are living. If you want to up their numbers, go ahead and give them feed enough!
\\e made a thorough study of data on the fry let out and on the annual commercial catches over a long period, and determined optimal volumes of young fish production for Sakhalin's hatcheries. The annual output of fry had to be cut by 250 min fish, we said. From 1985 on, as one started acting on our recommendations, came a recovery
- What was the situation like with the sturgeon fish ? Was their population going down too because of the overproduction of fry?
- In those days we had other fish to fry - we had trouble enough with the salmon fish and could not get down to the sturgeons. But we were anxious about things in the Volga-Caspian basin too. What spurred us to attack this problem was a report by the director of the Caspian Research Institute of Fishing - it was made a few years ago at a session of the Interdepartmental Ichthyological Commission set up by the RF State Committee for Fishing, the Ministry for Natural Resources and the Russian Academy of Sciences. Presented in this report were plots depicting increases in fry production and in sturgeon catches. Initially both curves showed a parallel increase; but then the curve for catches nosedived, while that for young fish production kept rising.
This is what we learned from our study of statistics on the annual output of fry at Volga-based fish hatcheries (in a period from 1955 to 1994) and on the annual catches (from 1932 to 1992) - these very data we got from the RF Committee for Fishing: like with the salmon fish, the young sturgeon production optimum was off. And our subsequent studies showed that to keep the population of sturgeon shoals in the North Caspian basin at a maximum, no more than 12 min young fish should be put out every year. But since the early 1970s more than 44 mln sturgeon fry have been let out on the average. And if we take the three sturgeon species, the figure will top 100 min. The fry ate heavily into the fodder reserve, and in the mid-1980s the degradation process of the sturgeon population set in.
- Well, one did not talk about the sturgeon population until the scope of poaching went out of all proportion... ?
- No, I wouldn't say that. In 1984 the total catch of the Russian sturgeon was 12 thousand tons; in 1986 the figure was down to 10 thousand. This decline continued: less than 8 thousand tons in 1990. and just about 4 thousand in 1991. True, at that time poachers were not as loose as they are now.
Yet another factor argues for our hypothesis - that the overproduction of fry was the chief cause of the degradation of the Russian sturgeon population, and this is the mass-scale stratification of muscle tissue in the Caspian sturgeon registered in the late 1980s.
This phenomenon was put down to many causes, including chemical contamination of water and mutational processes. But that period, in 1987 and 1988, offered favorable ecological conditions for the sturgeon owing to a higher level of the Caspian and abundant freshets.
As to mutational processes, he who tries to relate them to the muscle tissue stratification does not know anything about genetic variability. It's a long-established fact: the rate of spontaneous mutation is at 10 -5 -10 -6 genes per generation. In addition, 99 percent of new mutations is immediately eliminated by natural selection. And so mutant sturgeon individuals could never grow up to adulthood.
The muscle tissue stratification problem was solved after all - by the Severtsev Institute of Ecology and Evolution Problems (Russian Academy of Sciences). Electron microscopy of sturgeon muscle showed dystrophy developing during spawning migrations. The point is that in this period the sturgeon is off food and subsists on the inner reserves of protein. Such reserves must have been down to a minimum due to the fodder shortage in the late 1980s; so the organism digested proteins both of the muscles and of the connective tissue, and that led to muscle degeneration.
Yet another explanation is worked a good deal - a drop in the population of the Russian sturgeon is attributed to a low runoff of the Volga-basin rivers. But having analyzed data of the RAS Institute of Water Management, we saw that late in the 1980s the water regime was quite favorable for sturgeon fish, and it could in no way be responsible for a decrease in their numbers.
The chief conclusion of our inquiry is this: it was the overproduction of fry at fish hatcheries that could be the principal cause of the degradation of the Russian sturgeon in the Volga- Caspian basin. The same is true of the beluga and starred (stellate) sturgeon population.
Knowing the "culprit" now, we should go ahead and set things right. Fortunately, the sturgeon fish have many overlapping generations, so there is hope for rehabilitation of their shoals. But this is a long and difficult process.
- So we are not going to feast on sturgeons in the years to come ?
- Well, things are not as hopeless as that. Sturgeon fish can be bred artificially, in nursing ponds, where one can raise spawning shoals and have young fish grow to marketing condition. All this involves extra expenses, sure, which one could have otherwise avoided by heeding to scientists and their advice.
Prepared by Igor GORYUNOV
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