One tagged sterlet, 180 kilometers and information exchange across the Danube

Sometimes, valuable information about sturgeon movement starts with something as small as a tag, but it becomes meaningful when the right people connect the pieces.

In August, a fisherman working with the MonStur in the Danube team from the University of Belgrade - Institute for Multidisciplinary Research (IMSI) encountered several sterlets (Acipenser ruthenus) as bycatch in the Danube, upstream from Bogojevo, Serbia. The fish, weighing around one kilogram each, were released back into the river. One of them carried a T-bar tag. There was no photograph, but the fisherman recalled a code that appeared to begin with “MOHOSZ”.

The observation was shared within the MonStur partnership. Colleagues from Széchenyi István University (SZE) in Hungary recognised MOHOSZ as the abbreviation of the Hungarian Angling Association and contacted the organisation to trace the fish. The answer they received revealed part of its journey.

The sterlet had been released into the Danube at Madocsa (Hungary), at river kilometer 1542, on 21 April 2026. Less than four months later, it was encountered near Bogojevo, approximately 180 kilometers downstream from its release location.

This was not the first long-distance encounter involving a tagged sterlet. A few weeks earlier, another specimen had been found near Komárom, Hungary, after being released near Baja - approximately 280 kilometers upstream from its release location.

The Bogojevo encounter illustrates why cooperation across the Danube is so important. A fisherman in Serbia noticed a tag and reported it to Serbian researchers. Through the MonStur partnership, the observation reached colleagues in Hungary, who were able to connect it with stocking records held by another organisation. As a result, a single encounter could be linked to information collected months earlier and hundreds of kilometers away, held by another country and another institution.

This is precisely the kind of connection that our project aims to strengthen.

Sturgeons know no country borders and no institutional boundaries. One tagged sterlet cannot tell us the whole story, but when relevant observations are shared, they become valuable pieces in the bigger puzzle of understanding and protecting the Danube’s sturgeons.