Individual Fecundity of the Autumn Spawning Baltic Herring Clupea Harengus Membras L/Sugiskuderaime (Clupea Harengus Membras L.) Individuaalne Viljakus

Variability in reproductive investment is an important factor behind recruitment and population dynamics of fish. We investigated absolute individual fecundity (AF) of the currently depleted population of autumn spawning herring in the northern Baltic Sea over three sequential years (2008-2010). Fecundity of fish in relation to changes in individual body mass, individual body length, body condition factor, age, and gonadosomatic index was investigated. AF varied between 11 838 and 108 093 oocytes per fish and, as an average, varied insignificantly between years. AF was positively significantly related to fish length and weight, but not to age. In general, individuals with a higher condition factor (K) had a higher AF. However, the correlation with K was weak or non-significant in some cases. Relative fecundity of the fish was found to vary 24-33% between years, being significantly different in all three years. In addition, the obtained results on AF were compared with historical findings from 1959-1970, when the population was at a high level. Notable differences were found in the AF between the two time periods by age groups, while by weights AF remained the same. The results of the present study, together with ongoing additional biological and ecological investigations, will help to identify mechanisms that configure the fecundity and recruitment processes.