Bulletin of the SFI 2 (156) 2002 - Variability of sprat peak spawning and larvae appearance timing in the southeastern Baltic Sea during the past six decades

Variability of sprat peak spawning and larvae appearance timing in the southeastern Baltic Sea during the past six decades
Bulletin of the Sea Fisheries Institute 2 (156) 2002, pp. 57-67

Elena Karasiova
AtlantNIRO, Dm. Donskoi 5, Kaliningrad, Russia

Key words: sprat, peak spawning timing, spawning activity shift, larva/egg ratio

Abstract.
Based on the analysis of historical (Mankowski 1950a, 1950b, 1951, 1955, 1959, Grauman 1969, 1970, 1972, 1980a, 1980b) and recent (STORE EU-project FAIR CT-98 3959) ichthyoplankton data, the seasonal dynamics of the Baltic sprat egg and larval abundance in the Gdansk Deep were considered for different time periods: late 1940s - early 1950s; late 1960s - mid 1970s; late 1990s. The percentage ratio of larvae to egg abundance was also estimated for these periods.
Significant differences between these periods were revealed in larva peak timings and larva/egg ratio values. The latter declined drastically towards the late 1990s. The possible influences of factors such as increases in surface water temperature, oxygen depletion in the Baltic Sea, age structure changes and increases in the larva dispersion rate are discussed.