Spatial and interannual variability in Baltic sprat batch fecundity

Absolute and relative batch fecundity of Baltic sprat (Sprattus sprattus balticus S.) during peak spawning time was investigated for several years over the last two decades by applying the hydrated oocyte method. Batch fecundity was analysed for three important spawning areas of sprat in the central Baltic Sea, namely the Bornholm Basin, Gdansk Deep and Southern Gotland Basin. Environmental parameters such as hydrography, fish condition and stock density were tested in order to investigate the observed variability in sprat fecundity. Absolute batch fecundity was found to be positively related to fish length and weight. Significant differences in absolute and relative batch fecundity of Baltic sprat among areas and years were detected, and could partly be explained by hydrographic features of the investigated areas. A non-linear multiple regression model taking into account fish length and ambient temperature explained 70% of variability in absolute batch fecundity. Oxygen content and fish condition were not related to sprat batch fecundity. Additionally, a negative effect of stock size on sprat batch fecundity in the Bornholm Basin was revealed. The obtained data and results are important to assess the stock reproductive potential of this important Baltic fish stock.