عنوان مقاله [English]
نویسندگان [English]چکیده [English]
Sturgeon are considered one of the most valuable fishes of the world that migrate to the rivers leading to the Caspian Sea, including the Sefirud River, to spawn. In the post this river was known as the reservoir for millioms of sturgeon larvae, but at present due to illegal fishing in the river and the construction of the Tarik Dam, Manjil Dam and the Sangar Dam in the migratory raoute of these fishes and so also the decrease in the water flow of this river, it is lossing its popularity. In order to study the natural reproduction of sturgeon in the river, an attempt to find larvae of different species of sturgeon was made from 19 May, 1996 to 13 June 1996. Six sampling stations were located from the begining of the Sangar Dam as far as the sea shore (about 40 Km) for this purpose. Different methods of catch were employed including beach seine nets (mesh size 1, 4 and 8mm). “CALO” a local fishing effort (mesh size 4mm) and conical nets (mesh size 1 and 4 mm). On the whole out of 268 times that nets were cast, 1853200 Km of the study area was survey and totally 514500 fishes belonging to the fallowing species were caught. Liza aura tus, Chalcalburnus chalcoides, Varicorhinus capoeta, Cobitis sp. Esox lucius, Silurus glanis, Abramis baranta, Carassius auratus, Cyprinus carpio, Tinca tinca, Stizostedion lucioperca , Alosa caspia , Syngnathus nigrolineatus, Barbus sp. , Anthemia boyeri, Pungitius platygaster and Gobius sp. No larvae of sturgeons were observed during this study. Although 218 brood fishes were caught in the Sefirud River in 1996, due to fishing pressure, illegal fishing, deterioration of spawning grounds and restrictions in the migratory route resulting from the construction of dams, no signs of natural reproduction were observed in the Sefirud River. Therefore it can be concluded that even if natural reproduction did take place in the Sefidrud River, the incidences were very low.