Movement and habitat use of juvenile Atlantic sturgeon in the Wisłoka River (southern Poland)

The aim of conducting the study was to describe the habitats and the movements of juvenile Atlantic sturgeon, Acipenser oxyrinchus oxyrinchus Mitchill, in the Wisłoka River. Radio telemetry methods were used to identify migration rates and the sites where sturgeon stopped during the day. In the 2009-2010 period, 25 juvenile sturgeon equiped with radio telemetry transmitters were released into the Wisłoka; most of them left the river from two to seven days later. In 2009, the sturgeon covered from 0 to 45.3 km, while one year later in 2010 they covered from 0.1 to 54.1 km; the mean migration rates in these two years did not differ significantly statistically (P>0.05). The sturgeon migrated at a mean rate of 0.84 BL (standard body length) s^-1 in 2009 and at 0.94 BL s^-1 in 2010. No statistically significant dependence was noted between migration rate and the size of the sturgeon. The sturgeon were most frequently located in areas with slow-flowing waters, and least frequently in riffle. In both habitats, the sturgeon stopped at deep locations most frequently in river channels, depressions formed beneath submerged tree trunks, or in whirl areas. The greatest fraction of bottom sediments in these places was sand (56-58%) followed by gravel (33-35%). The results presented in the present paper indicate that juvenile sturgeon migrate quickly from the Wisłoka to the Vistula rivers.