Huchen

The huchen is endemic to the Danube basin in Europe where the remaining population is threatened primarily by river damming, resulting in habitat fragmentation and loss through river impoundment and disruption of the longitudinal continuity of rivers, cutting away fish from its spawning grounds, with overfishing and fisheries mismanagement as an additional issue in many areas. Damming and all these other problems are especially visible in the Balkans.[4][1]

The upper reaches of the Danube basin, rivers and tributaries contain almost all of the recent population. This includes:

• In Austria: the Inn river, the upper Drava, with the lower Gail in Carinthia, the Pielach, in Styria the upper Mur.
• In Germany: middle and lower Inn, Isar (especially in Munich)

In the Balkans huchen still appears in following river systems:

• In Slovenia: in the headwaters of Sava and its tributaries.
• In Croatia: in the upper and middle course of Kupa.
• In Bosnia and Herzegovina: in the upper and middle Una, with the upper and middle Sana; the upper and middle Vrbas, with the lower and middle Vrbanja; the main channel of the Bosna lost its population due to degradation of its waters, its banks and riverbed, but its four main tributaries, the Krivaja, the Fojnička, the Lašva and the Željeznica, are still important habitats; one of the most important huchen habitats in the Balkans and Europe is the Drina, with its numerous tributaries, especially the Lim, the Tara and the Ćehotina, and smaller ones, the Bistrica, the Prača, and the Drinjača;
• In Serbia: the Lim.
• In Montenegro: the Lim, with the Lake Plav, the Ćehotina, and the Tara.

Some of these habitats, especially in the Balkans, are endangered with planned, or already implemented plans for construction of new dams and hydroelectric power plants, such as on the Lim in Serbia, or like in case of the river Piva in Montenegro and Bosnia and Herzegovina, whose respective populations were completely wiped out since mid 20th century.[3]

In some cases rehabilitation of parts of the habitat is attempted, through restoration of the river course. Such positive example is the part of the course of the river Inn, with some 30 km (19 mi)-long stretch around the Bavarian town of Mühldorf was rebuilt and renaturalized and the huchen has returned in recent years.[5]

It has been introduced to other major river basins elsewhere on the continent and even North Africa, to rivers in Morocco, but these populations are not self-sustaining.[1] Some evidence suggest that in historic times the huchen has also been found in the neighboring Dniester basin. Huchen sometimes successfully establish in accessible natural lakes, like glacial Lake Plav which is the source of the Lim river in Montenegro, one of the major huchen habitats in the Balkans. However, the species sometimes survives even when cut off from the rest of the population in big dam reservoirs on mountain rivers, such as reservoirs on the Drina in Bosnia, or Lake Czorsztyn in Poland, as long as competitive and/or allochthonous predator species are not introduced into the newly created lakes.[6]

The huchen reaches about 1.5 m (4 ft 11 in) in length and more than 50 kg (110 lb) in weight.[7] The average length is between 60 and 120 centimetres (24 and 47 in). The huchen has a slender body that is nearly round in cross-section. On the reddish brown back are several dark patches in an X or crescent shape, but most distinctive feature is its head, which is larger than in other salmonides (longer and wider), with large elongated mouth. Smaller fish feed on the larvae of water insects or on insects dropped into the water; the larger individuals are predators of other species of fish and other small vertebrates.

This permanent freshwater salmonid spawns in April, once water reaches a temperature of 6 to 9 °C (43 to 48 °F). For spawning, the huchen migrates up the river and enters small and shallow affluents, where females excavate depressions in the gravel into which they deposit their eggs, then a male releases a cloud of sperm and the female then covers the eggs with sand.[16] Larvae hatch 30 to 35 days after fertilization.

A large Inn River huchen (1913)

There is a considerable effort to produce huchen fry commercially and to reintroduce the species into the wild with moderate to good success. This requires catching the adults just before spawning and keeping them in special tanks. Fry are released in appropriate places once they have reached 4 to 10 cm (1.6 to 3.9 in).[17]