Shifting dynamic forces in fish stock fluctuations triggered by age truncation?

Authors

  • TRISTAN ROUYER,

    1. Centre for Ecological and Evolutionary Synthesis (CEES), Department of Biology, University of Oslo, PO Box 1066 Blindern, N-0316 Oslo, Norway
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  • GEIR OTTERSEN,

    1. Centre for Ecological and Evolutionary Synthesis (CEES), Department of Biology, University of Oslo, PO Box 1066 Blindern, N-0316 Oslo, Norway
    2. Institute of Marine Research, Gaustadalléen 21, 0349 Oslo, Norway
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  • JOËL M. DURANT,

    1. Centre for Ecological and Evolutionary Synthesis (CEES), Department of Biology, University of Oslo, PO Box 1066 Blindern, N-0316 Oslo, Norway
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  • MANUEL HIDALGO,

    1. Centre for Ecological and Evolutionary Synthesis (CEES), Department of Biology, University of Oslo, PO Box 1066 Blindern, N-0316 Oslo, Norway
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  • DAG Ø. HJERMANN,

    1. Centre for Ecological and Evolutionary Synthesis (CEES), Department of Biology, University of Oslo, PO Box 1066 Blindern, N-0316 Oslo, Norway
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  • JONAS PERSSON,

    1. Centre for Ecological and Evolutionary Synthesis (CEES), Department of Biology, University of Oslo, PO Box 1066 Blindern, N-0316 Oslo, Norway
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  • LEIF CHR. STIGE,

    1. Centre for Ecological and Evolutionary Synthesis (CEES), Department of Biology, University of Oslo, PO Box 1066 Blindern, N-0316 Oslo, Norway
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  • NILS CHR. STENSETH

    1. Centre for Ecological and Evolutionary Synthesis (CEES), Department of Biology, University of Oslo, PO Box 1066 Blindern, N-0316 Oslo, Norway
    2. Institute of Marine Research, Department of Coastal Zone Studies, Flødevigen Research Station, N 4817 His, Norway
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Tristan Rouyer, tel. +47 22 85 50 78, fax +47 22 85 40 01, e-mail: rouyer.tristan@bio.uio.no

Abstract

Accumulating evidence shows that environmental fluctuations and exploitation jointly affect marine fish populations, and understanding their interaction is a key issue for fisheries ecology. In particular, it has been proposed that age truncation induced by fisheries exploitation may increase the population's sensitivity to climate. In this study, we use unique long-term abundance data for the Northeast Arctic stock of cod (Gadus morhua) and the Norwegian Spring-Spawning stock of herring (Clupea harengus), which we analyze using techniques based on age-structured population matrices. After identifying time periods with different age distributions in the spawning stock, we use linear models to quantify the relative effect of exploitation and temperature on the population growth rates. For the two populations, age truncation was found to be associated with an increasing importance of temperature and a relatively decreasing importance of exploitation, while the population growth rate became increasingly sensitive to recruitment variations. The results suggested that the removal of older age classes reduced the buffering capacity of the population, thereby making the population growth rate more dependent on recruitment than adult survival and increasing the effect of environmental fluctuations. Age structure appeared as a key characteristic that can affect the response of fish stocks to climate variations and its consequences may be of key importance for conservation and management.

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