Use of the robust design to estimate seasonal abundance and demographic parameters of a coastal bottlenose dolphin (Tursiops aduncus) population

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

doi:10.1371/journal.pone.0076574

Use of the robust design to estimate seasonal abundance and demographic parameters of a coastal bottlenose dolphin (Tursiops aduncus) population

PLoS One. 2013 Oct 9;8(10):e76574. doi: 10.1371/journal.pone.0076574. eCollection 2013.

Authors

Holly C Smith¹, Ken Pollock, Kelly Waples, Stuart Bradley, Lars Bejder

Affiliation

¹ Murdoch University Cetacean Research Unit, Centre for Fish, Fisheries and Aquatic Ecosystems Research, School of Veterinary and Life Sciences, Murdoch University, Perth, Australia ; Marine Science Program, Nature Conservation Division, Department of Environment and Conservation, Perth, Australia.

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.

Publication types

Research Support, Non-U.S. Gov't

MeSH terms

Animal Migration
Animals
Bottle-Nosed Dolphin*
Data Collection
Female
Male
Population Dynamics
Seasons*
Statistics as Topic / methods*

Grants and funding

This project was financially and logistically supported by the partners of the South West Marine Research Program. These include Bemax Cable Sands, BHP Billiton Worsley Alumina Pty Ltd, Bunbury Dolphin Discovery Centre, Bunbury Port Authority, the City of Bunbury, Cristal Global, Department of Environment and Conservation, Iluka, Millard Marine, Naturaliste Charters, Newmont Boddington Gold, South West Development Commission and WA Plantation Resources. HS was supported by a Murdoch University scholarship. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.