Plankton effect on cod recruitment in the North Sea

Abstract

The Atlantic cod (Gadus morhua L.) has been overexploited in the North Sea since the late 1960s and great concern has been expressed about the decline in cod biomass and recruitment1. Here we show that, in addition to the effects of overfishing1, fluctuations in plankton have resulted in long-term changes in cod recruitment in the North Sea (bottom-up control). Survival of larval cod is shown to depend on three key biological parameters of their prey: the mean size of prey, seasonal timing and abundance. We suggest a mechanism, involving the match/mismatch hypothesis2, by which variability in temperature affects larval cod survival and conclude that rising temperature since the mid-1980s has modified the plankton ecosystem in a way that reduces the survival of young cod.

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Figure 1: Long-term monthly changes (1958–1999) in the plankton index (as the first principal component, 33.78% of the total variability), resulting from analysis of the table years–months × biological indicators.
Figure 2: Relationships between plankton fluctuations and cod recruitment (one-year-olds) at lag one.
Figure 3: Plankton changes (1958–1999) and their consequences for larval/juvenile cod survival.

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Acknowledgements

We are grateful to all past and present members and supporters of the Sir Alister Hardy Foundation for Ocean Science whose sustained help has allowed the establishment and maintenance of the CPR data set in the long term. The main support of this work was from UK DEFRA, and both the French PNEC Art 4 and IFB ‘Biodiversité et changement global’ programmes. Consortium support for the CPR survey is provided by agencies from the following countries: UK, USA, Canada, the Faroe Islands, France, Ireland, the Netherlands, Portugal, the IOC and the European Union. We thank the owners, masters and crews of the ships that tow the CPRs on a voluntary basis.

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Correspondence to Grégory Beaugrand.

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Beaugrand, G., Brander, K., Alistair Lindley, J. et al. Plankton effect on cod recruitment in the North Sea. Nature 426, 661–664 (2003). https://doi.org/10.1038/nature02164

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