Abstract
Overfishing of large predatory fish populations has resulted in lasting restructurings of entire marine food webs worldwide, with serious socio-economic consequences. Fortunately, some degraded ecosystems show signs of recovery. A key challenge for ecosystem management is to anticipate the degree to which recovery is possible. By applying a statistical food-web model, using the Baltic Sea as a case study, we show that under current temperature and salinity conditions, complete recovery of this heavily altered ecosystem will be impossible. Instead, the ecosystem regenerates towards a new ecological baseline. This new baseline is characterized by lower and more variable biomass of cod, the commercially most important fish stock in the Baltic Sea, even under very low exploitation pressure. Furthermore, a socio-economic assessment shows that this signal is amplified at the level of societal costs, owing to increased uncertainty in biomass and reduced consumer surplus. Specifically, the combined economic losses amount to approximately 120 million € per year, which equals half of today's maximum economic yield for the Baltic cod fishery. Our analyses suggest that shifts in ecological and economic baselines can lead to higher economic uncertainty and costs for exploited ecosystems, in particular, under climate change.
Highlights
Management of depleted fish stocks has traditionally been treated as a single species concern, primarily related to the level of exploitation [1]
We show that the pathway of ecosystem regeneration is, besides fishery management, conditionally dependent on the interaction of climate and human pressures and that the output of this interaction implies severe economic and societal costs
Our results show that the environmental conditions determine the level of achievable baselines and—what is most important in socio-economic terms—their degree of variability
Summary
Management of depleted fish stocks has traditionally been treated as a single species concern, primarily related to the level of exploitation [1]. Above the cod threshold P. acuspes is positively related to salinity (figure 3k), probably owing to its positive effect on reproduction and maturation [48] This result agrees with Casini et al [17] showing that the dynamics of zooplankton is being driven either by hydrography or sprat predation depending on the level of cod. We consider the Gotland Basin as representative of the Central Baltic Sea for the lower trophic levels and hydrographical conditions While acknowledging that this is a simplification of a complex system, we think the results provide new insight into the regeneration potential of the Baltic Sea. The last step of our analysis focused on the evaluation of the direct and indirect economic implications of an altered productivity of cod, the most important species in this regard (figure 2). These results indicate that the economic baseline shifted in parallel to the ecological baseline, but that the current conditions may not be able to support as many viable fishing units as before, and imply a higher uncertainty for fishermen
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