Biologists want to repopulate German rivers with sturgeon. A test batch of aquarium-raised fish has already been re-introduced and a school of fish will likely be released in the Oder River this autumn.
By Philip Bethge
Seen from above, the young sturgeon resemble little prehistoric sharks. They splay their rounded fins as if they were little wings and glide elegantly through the water using their pointed tails. The only things that don’t seem to fit into the picture are the yellow plastic bands attached to their angular dorsal fins.
“We’ve marked the fish so we can identify them later,” says Frank Kirschbaum as he adeptly scoops one of the sturgeon from the water and runs his finger over its archaic-looking bone plates, which line the narrow, 30 centimeter (12 inch) body like an ornamental strip. The sturgeon gasping for oxygen in Kirschbaum’s hand is one year old. In a few weeks, it may be drawing oxygen from the Oder River.
Kirschbaum is a fish specialist at Berlin’s Leibniz Institute of Freshwater Ecology and Inland Fisheries (IGB). He’s pursuing an ambitious species-protection project along with his colleague Jörn Gessner and Polish researchers. “We’re planning Europe’s largest practical experiment in sturgeon re-population,” Gessner says. The scientists want to set some 6,000 young fish free in the Oder by 2008. That would herald the return of sturgeon to Germany’s rivers.
“You could find sturgeon virtually anywhere in this country as recently as a century ago,” says Henning von Nordheim from Germany’s Federal Nature Conservation Agency, which has invested about €2 million ($2.6 million) in the sturgeon program. “The sturgeon is the product of 200 million years of natural history, (and) we want this charismatic animal to feel at home in our rivers again.”
A primordial fish
The sturgeon is one of those rare creatures that have survived virtually unchanged since the time of the dinosaurs. Most of the sleek, bony-sided fish spend the greater part of their lives in the sea, like salmon, and migrate upriver only to mate. They’re threatened with extinction worldwide, but 27 varieties of sturgeon still live in the world’s rivers, including the Hausen variety, which can weigh up to a ton and yields the best Russian caviar.
The Elbe, the Weser, the Oder and other German rivers feeding the North Sea and the Baltic once belonged to the fish’s habitat. As recently as 1888 fishermen on the Elbe managed to catch about 3,500 sturgeon, including massive specimens weighing between 60 and 70 kilograms, or 132 and 154 pounds. (The fish can reach a length of up to six meters, or 20 feet.) But the 20th century thinned their population. Factories and sewage from the cities polluted the rivers; modern weirs prevented the fish from reaching their spawning grounds. The last German sturgeon was seen in the Eider, a small river in Germany’s Schleswig-Holstein region, in 1969. Since then, sturgeon has been considered extinct in Germany.
Now researchers at Berlin’s IGB want the fish repatriated. This project looks promising, at least along the Oder, which feeds the Baltic Sea. The Atlantic sturgeon (Acipenser oxyrhyncus) migrated to the Baltic about 1,000 years ago, displacing the European variety, and adopted the river between Germany and Poland as its natural home. This proved to be a stroke of luck for the biologists, because Atlantic sturgeon still live in the tens of thousands in North America.
The young fish at the IGB in Berlin were imported from across the Atlantic. They travelled to Europe via Canada as fertilized eggs. In some cases the scientists even transported fully grown sturgeon: Twenty of the massive gilled creatures flew to Frankfurt airport on Air Canada last April. IGB researchers had caught them in St. John’s River in southern Canada, then transported them to Halifax airport across a distance of 600 kilometers (373 miles).
Back from extinction
These fish now swim in aquariums in the Regional Center for Agriculture and Fishery in the Baltic Sea town of Born. They’ve grown to a length of almost two meters (6.6 feet). “We hope they’ll soon be ready to spawn,” says Gessner. “Then we want to start breeding young sturgeon for the Oder ourselves.”
Repopulating the Elbe and Weser Rivers will be more difficult. Both North Sea tributaries were once dominated by the European variety of sturgeon (Acipenser sturio). Unlike its Atlantic counterpart, the European variety is now extremely rare. The Gironde River, near Bordeaux, France, is the only place where an estimated 2,000 of the European variety still exist. “That’s the only variety suitable for repopulating the North Sea tributaries,” says Kirschbaum. “Anything else would mean falsifying the historical situation.”
Kirschbaum imported some of these fish from France in 1996. Sixteen adult sturgeon born in the Gironde now populate the IGB aquariums. Taking care of these demanding creatures is no easy task, though; they refuse to touch regular food. Every day, Kirschbaum has to feed his primordial gourmets five kilograms (11 pounds) of imported French prawns.
But it pays off. Kirschbaum discovered eggs in one of his female sturgeon early this year. The discovery was a sensation. It’s been 10 years since scientists last saw young sturgeon in the Gironde. “If we can breed them, that would be an enormous success,” says Kirschbaum. Repopulating the Elbe, at least in theory, would then be possible. The question is whether migrant fish can navigate the river. “There’s a weir near the town of Geesthacht on the Elbe,” Kirschbaum says. The weir blocks the route the sturgeon would follow to reach their spawning ground. The weir, in fact, was built to let salmon cross it. “But it won’t work for sturgeon,” says Kirschbaum.
Not enough for caviar
So the scientists, for now, have pinned their hopes on the Oder. They consider the river sufficiently unspoiled to attempt repopulation. “Since 1997, we’ve done research to find out whether there still are spawning grounds in the Oder or any of its tributaries,” says Gessner. The researchers found a number of gravelly sections of riverbed provided with a strong current, the kind sturgeon need to deposit their eggs — most of them in the Polish river Warta. Local fishermen have been informed, too: Proposals have been developed to change their net-pulling techniques in order to avoid trapping the sturgeon, which live mainly close to the river bottom.
The researchers eventually want to attach ultrasonic devices to all these fish and follow them by boat. They’ve tested the method in the Peene, a little river in West Pomerania — since July they’ve observed the behavior of 15 young, ultrasonic-equipped sturgeon there.
Now the IGB scientists are waiting for the right moment to release sturgeon into the Oder. They had been focused on a date in April, but the plan fell through at the last minute because of a political quarrel over expanding the river’s usefulness as a commercial waterway.
Now, though, the signs are favorable again. Some sturgeon could be placed in the Oder as part of preliminary tests in late fall. The river itself would stand to benefit, say the biologists. “If we restore the sturgeon’s habitat, the whole ecosystem will improve,” says Kirschbaum. Typical river fish such as barbs and rock herring could follow the sturgeon back to the Oder.
But it will take some time before the project’s success can be gauged. Sturgeon need 10 to 15 years to grow sexually mature. Only then can they return to their native rivers to spawn. “It would be a sensation if even a few of those fish survive that long and then find their way back to the Oder,” says Gessner.
Anyone looking forward to buying Baltic Sea caviar, though, will be disappointed. Sturgeon roe from Europe used to be a gourmet specialty, Gessner admits — “but if some of our sturgeon come back and a fisher catches one of them, that will hardly be enough to give birth to a new industry.”