WŁODZIMIERZ Grygiel and Mirosław
Sea Fisheries Institute, Kołłątaja 1, 81-332 Gdynia, Poland
Key words: herring, sprat, sex ratio, length distribution, southern Baltic basins.
The sex ratio of spring-spawning herring and sprat in the southern Baltic were analyzed. The study material was collected in the pre-spawning and early spawning seasons from 1980-2000 primarily from research catches in the Polish Exclusive Economic Zone. A clearer numerical share of females was noted among sprat than among herring with regard to the natural ageing of the fish and increasing length. In most of these instances, the correlation was statistically significant. The increase of the share of females in length classes was marked n in herring above 21.5 cm and in sprat above 12.0 cm; all the females from these length classes spawned. The numerical prevalence of males over females was noted primarily among the smallest length classes. The average numerical share of herring females in the 1990s did not exhibit a significant change from that in the 1980s; however, the share of sprat females increased both in the Bornholm Basin from 48.4 to 54.4% and in the Gdańsk Basin from 50.3 to 52.6%. In comparison with herring, the differences in the sex ratio of sprat from the Bornholm and Gdańsk basins were clear.