Could seals prevent cod recovery in the Baltic Sea?
Brian R MacKenzie1, Margit Eero, Henn Ojaveer
1National Institute for Aquatic Resources, Technical University of Denmark-Aqua, Charlottenlund, Denmark.
Plos One
|May 17, 2011
Summary
Baltic Sea cod populations face challenges from exploitation and climate change. Simulation shows cod can recover with reduced fishing and stable salinity, but lower salinity impacts biomass and yields.
Area of Science:
- Marine Ecology
- Fisheries Science
- Population Dynamics
Background:
- Fish populations, including Baltic Sea cod (Gadus morhua), are impacted by human activities (exploitation, eutrophication, habitat alteration) and climate change.
- Population recovery is occurring in changing ecosystems, influenced by factors like predator resurgence (grey seal, Halichoerus grypus) and climate shifts.
Purpose of the Study:
- To investigate the potential recovery and 21st-century development of a depleted Baltic Sea cod population.
- To assess the combined impacts of increased grey seal predation, fishing management targets, and changing salinity on cod population dynamics.
Main Methods:
- Utilized simulation modeling to project cod population trends under various environmental and management scenarios.
- Incorporated factors such as increased seal predation, fishing levels aligned with management plans, and altered salinity levels (stable vs. 15% lower).
Main Results:
- Under stable salinity and increased seal predation, cod populations could recover to levels significantly above the long-term average.
- A 15% reduction in salinity, alongside similar seal and fishing pressures, would still support a cod fishery but with reduced biomass and yields.
- Seal predation had a lesser impact on cod recovery compared to exploitation levels and salinity changes.
Conclusions:
- Dual management objectives for recovering both seal and cod populations are feasible.
- Successful cod recovery and sustainable fisheries depend critically on managing exploitation and salinity.
- Climate change impacts on cod recruitment remain a key uncertainty for achieving recovery goals.
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