Quantifying predation on Baltic cod early life stages

Predation on cod eggs by sprat and herring is known to be one of the processes influencing reproductive success of the Eastern Baltic cod, and has been reported to have contributed to lack of recovery of the stock in the 1990s. This study quantifies the predation on cod eggs in the Bornholm Basin, the major spawning area of cod in the central Baltic Sea, in the 1990’s in comparison to the second half of the 2000s. The analyses involve estimating daily consumption rates of predator populations, which are then compared with corresponding daily egg production rates. As a methodological advancement compared to earlier studies, spatially resolved information on predator distribution and abundance is utilized in quantifying predator stock size. This resulted in more realistic consumption estimates in relation to overall egg production, compared to earlier studies that consistently overestimated predation pressure by clupeids. Our results suggest a generally lower predation pressure on cod eggs in the mid- to late-2000s, due to a combination of reduced predator abundance and lower daily rations by individual predators