Bohdan Draganik and Iwona Psuty-Lipska
Sea Fisheries Institute, Kołłątaja 1, 81-332 Gdynia, Poland

Key words: trawl fishery, flounder, flatfish, catch per unit effort (CPUE), target species, by-catch, Baltic Sea.

Abstract. The results of multidimensional statistical analyses of catch records from cutters which operated in Polish sea areas between 1993 and 2000 indicated that fishing ground was the factor which most influenced variability in the cutter catch rate. These results confirmed differences between the fishing grounds in the Gulf of Gdańsk and the Bornholm Basin. The results of composition analyses of Polish flatfish catches confirmed that flounder dominated and that plaice and brill contributed less than 6%. The catch rate index for flounder was simply assumed to be the same as that for flatfish. The catch rate used to calculate the cutter catch rate index was selected based on four thresholds (>10, >25, >50 and >85%) of the percentage of flatfish in individual hauls. The flatfish catch rate in Polish sea areas grew as the threshold of flatfish occurrence in the hauls increased. Cutter size did not influence the catch rate in statistical sub-division 26 (Gulf of Gdańsk), and the flounder stock in this area is best described by the rate index of 17 m cutters. In sub-divisions 24 and 25 the most representative rate indexes were for 25 m cutters.