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Use of the Robust Design to Estimate Seasonal Abundance and Demographic Parameters of a Coastal Bottlenose Dolphin (Tursiops aduncus) Population

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  • Holly C Smith
  • Ken Pollock
  • Kelly Waples
  • Stuart Bradley
  • Lars Bejder

Abstract

As delphinid populations become increasingly exposed to human activities we rely on our capacity to produce accurate abundance estimates upon which to base management decisions. This study applied mark–recapture methods following the Robust Design to estimate abundance, demographic parameters, and temporary emigration rates of an Indo-Pacific bottlenose dolphin (Tursiops aduncus) population off Bunbury, Western Australia. Boat-based photo-identification surveys were conducted year-round over three consecutive years along pre-determined transect lines to create a consistent sampling effort throughout the study period and area. The best fitting capture–recapture model showed a population with a seasonal Markovian temporary emigration with time varying survival and capture probabilities. Abundance estimates were seasonally dependent with consistently lower numbers obtained during winter and higher during summer and autumn across the three-year study period. Specifically, abundance estimates for all adults and juveniles (combined) varied from a low of 63 (95% CI 59 to 73) in winter of 2007 to a high of 139 (95% CI 134 to148) in autumn of 2009. Temporary emigration rates (γ') for animals absent in the previous period ranged from 0.34 to 0.97 (mean = 0.54; ±SE 0.11) with a peak during spring. Temporary emigration rates for animals present during the previous period (γ'') were lower, ranging from 0.00 to 0.29, with a mean of 0.16 (± SE 0.04). This model yielded a mean apparent survival estimate for juveniles and adults (combined) of 0.95 (± SE 0.02) and a capture probability from 0.07 to 0.51 with a mean of 0.30 (± SE 0.04). This study demonstrates the importance of incorporating temporary emigration to accurately estimate abundance of coastal delphinids. Temporary emigration rates were high in this study, despite the large area surveyed, indicating the challenges of sampling highly mobile animals which range over large spatial areas.

Suggested Citation

  • Holly C Smith & Ken Pollock & Kelly Waples & Stuart Bradley & Lars Bejder, 2013. "Use of the Robust Design to Estimate Seasonal Abundance and Demographic Parameters of a Coastal Bottlenose Dolphin (Tursiops aduncus) Population," PLOS ONE, Public Library of Science, vol. 8(10), pages 1-10, October.
  • Handle: RePEc:plo:pone00:0076574
    DOI: 10.1371/journal.pone.0076574
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    Cited by:

    1. Manan Gupta & Amitabh Joshi & T N C Vidya, 2017. "Effects of social organization, trap arrangement and density, sampling scale, and population density on bias in population size estimation using some common mark-recapture estimators," PLOS ONE, Public Library of Science, vol. 12(3), pages 1-24, March.
    2. Violaine Dulau & Vanessa Estrade & Jacques Fayan, 2017. "Identifying key demographic parameters of a small island–associated population of Indo-Pacific bottlenose dolphins (Reunion, Indian Ocean)," PLOS ONE, Public Library of Science, vol. 12(6), pages 1-19, June.
    3. Krista Hupman & Karen A Stockin & Kenneth Pollock & Matthew D M Pawley & Sarah L Dwyer & Catherine Lea & Gabriela Tezanos-Pinto, 2018. "Challenges of implementing Mark-recapture studies on poorly marked gregarious delphinids," PLOS ONE, Public Library of Science, vol. 13(7), pages 1-27, July.

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