The ecosystem of the baltic sea has undergone dramatic changes, perhaps a regime-shift, during the last four decades. The Baltic Sea Herring SSB has declined to a third and weight-at-age has halved due to plankton prey deficits. The management objective of the herring is currently in the transition to a cautionary maximum sustainable yield (MSY). We modelled the main basin Baltic Sea herring under the currernt regime, and analysed the effect of a ercovery of the cod stock and the food availability as they were in the early 1980s. We recommend a target F MSY of 0.16, but with a recovery of the cod, recommended target F MSY is is 0.10. A simultaneous increase in both cod and food availability is estimated to increase the yield with 40% at the target F MSY is 0.20. We present functions to calculate F MSY and estimate the expected yield depending on the abundance of cod and food-availability. A retrospective application of our functions indicates over-fishing in the 1990s and early 2000s, and a net loss in yields with a landing value of about E440 Millions.
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