Summary 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°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.

In the past, sturgeons played an important role in commercial and recreational fisheries in the Danube River and its tributaries. Human impacts in the Danube River Basin coupled with exploitation of sturgeon stocks led to all species being either locally extinct, critically endangered or of unknown status. Sterlet (Acipenser ruthenus, Linnaeus 1758) is the last known sturgeon species occurring in the upper and middle Danube; however, the population of this species is considered unbalanced and decreasing since the beginning of the twenty‐first century. The decline of sturgeon stocks has been noted before owing to their economic importance. With commercial fisheries being forbidden in the Slovak section of the Danube River, there is generally no information available about the status of what is considered a local population. Databases containing recreational catch of sterlet (2003–2018) and historical records of commercial harvest (1961–1990) were used to describe the trend in the weight and number of sterlet caught over the following years. Modelling indicated that the number of fish caught each year appears to be lower, while the average weight of each individual is increasing. This might suggest that the population is ageing. Although older individuals can contribute a great deal more to spawning because they produce a greater number of eggs, several problems are apparent. The number of spawners might be decreasing as a result of bycatch or fishing, their ability to spawn might be obstructed, or annual recruitment may fail owing to unpredictable events. Although restocking programmes are in place to help maintain the sterlet population in the Danube River, their efficiency seems to be drastically low. In fact, restocking could be of little value unless studies on the availability of key habitats are conducted and their protection and restoration are ensured.

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