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Relative abundance and size of coastal sharks derived from commercial shark longline catch and effort data

Authors

  • J. K. Carlson,

    Corresponding author
    1. NOAA Fisheries Service, Southeast Fisheries Science Center, 3500 Delwood Beach Drive, Panama City, FL 32408, U.S.A.
      Tel.: +1 850 2346541; email: john.carlson@noaa.gov
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  • L. F. Hale,

    1. NOAA Fisheries Service, Southeast Fisheries Science Center, 3500 Delwood Beach Drive, Panama City, FL 32408, U.S.A.
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  • A. Morgan,

    1. Florida Program for Shark Research, Florida Museum of Natural History, University of Florida, Gainesville, FL 32611, U.S.A.
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    • Present address: Tree of Life Woodworking and Design, P. O. Box 454, Belfast, ME 04915, U.S.A.

  • G. Burgess

    1. Florida Program for Shark Research, Florida Museum of Natural History, University of Florida, Gainesville, FL 32611, U.S.A.
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Tel.: +1 850 2346541; email: john.carlson@noaa.gov

Abstract

In the north-west Atlantic Ocean, stock assessments conducted for some commercially harvested coastal sharks indicate declines from 64 to 80% with respect to virgin population levels. While the status of commercially important species is available, abundance trend information for other coastal shark species in the north-west Atlantic Ocean are unavailable. Using a generalized linear modelling (GLM) approach, a relative abundance index was derived from 1994 to 2009 using observer data collected in a commercial bottom longline fishery. Trends in abundance and average size were estimated for bull shark Carcharhinus leucas, spinner shark Carcharhinus brevipinna, tiger shark Galeocerdo cuvier and lemon shark Negaprion brevirostris. Increases in relative abundance for all shark species ranged from 14% for C. brevipinna, 12% for C. leucas, 6% for N. brevirostris and 3% for G. cuvier. There was no significant change in the size at capture over the time period considered for all species. While the status of shark populations should not be based exclusively on abundance trend information, but ultimately on stock assessment models, results from this study provide some cause for optimism on the status of these coastal shark species.

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