Olavi Kaljuste and Tiit Raid
Estonian Marine Institute, Mäealuse 10a, EE-12618 Tallinn, ESTONIA

Key words: Baltic sprat, sex ratio, maturity ogive, north-eastern Baltic Sea, Gulf of Finland.

Abstract. The sex ratio and maturity ogive of Baltic sprat were investigated in ICES Subdivisions 28, 29 and 32 for the 1980-1985 and 1995-2000 periods. The mean share of females in sprat catches has been slightly above 50% in the north-eastern Baltic Sea for the last two decades. The mean share of females in sprat catches increased in the Gulf of Finland but decreased in ICES Sub-division 29 in the 1990s. It was revealed that approximately 90% of sprat mature at the age of 2 and the fraction of mature fish at the age of 3 is about 95%. The maturation of age group 1 shows high variability which ranges from 6 to 60% depending on area and year. The maturity ogive indicated that sprat matured earlier in age groups in the 1990s as compared to the 1980s. The relatively higher winter air temperatures observed in the 1990s can be at least partly responsible for this phenomenon.