Reproductive ecology of Baltic sprat and its application in stock assessment
Sprat is an important ecological key species in the Baltic Sea. Temporal and spatial variability in reproductive traits of Baltic sprat was investigated in relation to biotic and abiotic parameters. The seasonality of important spawning traits were analysed. Models of sex ratio and maturity at length were established. The ovarian dynamics in relation to postovulatory follicles (POF) were described with the major finding that the degeneration of POF equals the spawning interval. A temperature dependent model on Baltic sprat egg development was established. All obtained results were finally used to implement the Daily Egg Production Method (DEPM) to the Baltic sprat stock. The knowledge obtained by the present thesis will serve as basis to (i) enhance existing assessment methods and to test alternative indices for sprat stock reproductive potential, (ii) implement alternative assessment methods and (iii) further investigate the population dynamics and ecology of Baltic sprat.
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