The entirety of the whitefish stocking material (343 830 specimens) released into the Puck Bay in 1997-1999 was marked by immersion in alizarin red (S) in order to assess the share of natural reproduction of whitefish in this basin. Analyses of the presence of markers in whitefish otoliths from the 1997-1999 year-classes caught from 1999 to 2002 in the Puck Bay and Reda River indicated that from 6.2 to 12.8% of the fish were the result of natural spawning. Marker retention was still sufficiently visible even four years after marking.

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