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Seasonal occurrence and population structure of the broadnose sevengill shark Notorynchus cepedianus in coastal habitats of south-east Tasmania

Authors

  • A. Barnett,

    Corresponding author
    1. Tasmanian Aquaculture and Fisheries Institute, Marine Research Laboratories, University of Tasmania, Private Bag 49, Hobart, TAS 7001, Australia
    2. CSIRO Marine Research, GPO Box 1538, Hobart, TAS 7001, Australia
      Tel.: +61 03 6227 7275; email: adam.barnett@utas.edu.au
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  • J. D. Stevens,

    1. CSIRO Marine Research, GPO Box 1538, Hobart, TAS 7001, Australia
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  • S. D. Frusher,

    1. Tasmanian Aquaculture and Fisheries Institute, Marine Research Laboratories, University of Tasmania, Private Bag 49, Hobart, TAS 7001, Australia
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  • J. M. Semmens

    1. Tasmanian Aquaculture and Fisheries Institute, Marine Research Laboratories, University of Tasmania, Private Bag 49, Hobart, TAS 7001, Australia
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Tel.: +61 03 6227 7275; email: adam.barnett@utas.edu.au

Abstract

Research longline sampling was conducted seasonally from December 2006 to February 2009 to investigate the occurrence and population structure of the broadnose sevengill shark Notorynchus cepedianus in coastal areas of south-east Tasmania. Notorynchus cepedianus showed a consistent temporal trend in seasonal occurrence in Norfolk Bay characterized by high abundances in summer to near absence in winter. This pattern was less pronounced in the Derwent Estuary, where fish were still caught during winter. The absence of smaller total length (LT) classes (<80 cm) from the catches suggests that N. cepedianus are not using these coastal habitats as nursery areas. Of the 457 individuals tagged, 68 (15%) were recaptured. Time at liberty ranged from 6 days to almost 4 years and all but one of the recaptures were caught in its original tagging location, suggesting site fidelity. The large number of N. cepedianus in these coastal systems over summer indicates that these areas are important habitats for this species and that N. cepedianus may have a significant influence on community dynamics through both direct and indirect predator–prey interactions.

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