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Disentangling Conditional Effects of Multiple Regime Shifts on Atlantic Cod Productivity
  • Tommi Perälä,
  • Jeffrey Hutchings,
  • Esben Olsen
Tommi Perälä
University of Jyvaskyla

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Jeffrey Hutchings
Dalhousie University
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Esben Olsen
Institute of Marine Research
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Regime shifts are increasingly prevalent in the ecological literature. However, definitions vary, and many detection methods are subjective. Here, we employ an operationally objective means of identifying regime shifts, using a Bayesian online change-point detection algorithm able to simultaneously identify shifts in the mean and(or) variance of time series data. We detected multiple regime shifts in long-term (59-154 years) patterns of coastal Norwegian Atlantic cod (>70% decline) and putative drivers of cod productivity: North Atlantic Oscillation (NAO); sea-surface temperature; zooplankton abundance; fishing mortality (F). The consequences of an environmental or climate-related regime shift on cod productivity are accentuated when regime shifts coincide, fishing mortality is high, and populations are small. The analyses suggest that increasing F increasingly sensitized cod in the mid 1970s and late 1990s to regime shifts in NAO, zooplankton abundance, and water temperature. Our work underscores the necessity of accounting for human-induced mortality in RS analyses of marine ecosystems.