Formation regularities of Baltic sprat year class abundance at the early ontogenetic stages

Abstract

Early estimation of sprat (Sprattus sprattus balticus) year-class is given based on the quantitative calculations using the eggs and larval abundances. The main reproductive centres for eggs (Bornholm Deep, Baltic Sea) and larvae (Gotland Deep, Baltic Sea) are determined. Their importance depends on the hydrological regime and spawining stock abundance. Sprat eggs and larval dynamics are considered according to the areas and the periods of years (1968-1970, 1971-1974, 1975-1977, 1978-1980), during which the winter severity, hydrological conditions, spawning stocks and spawning efficiency were different. The factors, causing low abundance of sprat year-classes during warm-water period (1971-1977) are analyzed.