Future fishing potential of cod and herring under climate change in the Western Baltic Sea

Abstract Climate change and the associated changes in environmental conditions are major challenges for sustainable fisheries management. Scientific advice needs to take modifications in stock productivity into account to safeguard healthy stocks, and to secure viable fisheries, which provide economic and social benefits. We include temperature-dependent stock-recruitment relationships into an ecological-economic multispecies optimization model for major Western Baltic fisheries. Climate-driven temperature increase negatively impacts stock productivity of cod and herring, the two most important fish stocks in the area. We combine three climate change scenarios (RCP4.5, RCP8.5, constant climate) with two management scenarios, namely multispecies maximum sustainable yield (MMSY), and multispecies maximum economic yield (MMEY), to explore the potential future development of key fisheries indicators. Spawning stock size, catch potential, fishery profits as well as total economic surplus are evaluated in the short-, medium-, and long-term. Western Baltic herring shows potential for stock recovery and commercial exploitation under all investigated scenarios, but only if allowed for an initial stock rebuilding moratorium. Accordingly, all models suggest a total fishing ban for herring of 4 years, before exploitation can restart. Catch opportunities for cod are less optimistic. Given climate change, catch levels will stay below 5.000 tons (historically 40.000 tons), even under optimal management. Differences between RCP 4.5 and RCP 8.5 become obvious from mid-century onwards. Acknowledging climate change in the scenarios strongly changes optimal management (and management outcomes) as compared to assuming a constant climate. Ignoring this might trigger overexploitation. Under climate change, MMEY management is superior to MMSY management in terms of stock size, catch, and total economic surplus, but would result in lower fishing mortality.