Migration patterns of sterlet (Acipenser ruthenus, Linnaeus 1758) in the Middle Danube assessed by 1 year acoustic telemetry study

The sterlet (Acipenser ruthenus, L.) is the last of the five native sturgeon species historically inhabiting the Middle and the Upper Danube. Its population has undergone a large decline, mainly due to the degradation of key habitats, the spawning and feeding grounds, the construction of migration barriers, over-fishing and poaching. Generally, no information is available about sterlet migration patterns and how they are triggered. Our results, based on direct observations by acoustic telemetry, suggest that sterlet seem to migrate when the water temperature is above 12 degrees C. No pattern is visible in sterlet migrations in connection with the water level. The restricted one-year life of implanted transmitters does not allow to separate the effects of highly correlated water temperature and the length of the day on sterlet migration. The sterlet tends to spend from three to seven months in the feeding area, from 6 to 8 months in the wintering area and around 2-4 weeks in the spawning area. There is a need for further confirmation of the exact location of these habitats in the Middle Danube. A description of the migration patterns and identification of environmental cues affecting its migration are an important part of effective sterlet conservation and management.