WŁODZIMIERZ Grygiel
Sea Fisheries Institute, Kołłątaja 1, 81-332 Gdynia, Poland

Key words: bottom trawl calibration experiments, alternate hauls, CPUE, length distribution, southern Baltic fishes.

Abstract.
A statistically significant dependence was confirmed between variables - the CPUE of hauls repeated at the same places and times and the CPUE of first (prime) hauls, made with a TV-3#930 cod bottom trawl, using the alternate hauls method. In November 2002 and 2003 the average CPUE (except for sprat) in the southern Baltic Sea was higher in first hauls than in second (repeated) hauls by 39% for cod, 50% - herring, 17% - flounder, 59% - other species and 28% - all species.