Distribution and growth of juvenile Atlantic sturgeon released into the Drwęca and Wisłoka rivers (Poland)

The Atlantic sturgeon, Acipenser oxyrinchus oxyrinchus Mitchill, has been considered to be an extinct species in the Baltic Sea for many years. A program to restore it to the Vistula basin was initiated in 2006 using cultured fish. This paper presents data regarding the distribution of juvenile Atlantic sturgeon released into the Drwęca and Wisłoka rivers (Vistula drainage). Tag returns from juvenile Atlantic sturgeon were few at just 3.15% for fish released into the Drwęca and 0.85% for those released into the Wisłoka. Information obtained from stocking the Drwęca River was used to analyze the distribution and growth of juvenile Atlantic sturgeon. These fish were caught most frequently in the Gdańsk Bay and the mouth of the Vistula River. Catches were made from March to December with two periods of much more abundant catches in July and October. The size of the fish released had an impact on the daily total length growth rate and the period of time between fish release and recapture, the mean of which ranged from 177 to 362 days, at a minimum of 10 and a maximum of 664 days. Absolute juvenile fish growth increased along with the period of time the fish spent in open waters; however, this period had no impact on daily body length growth rates.