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RESEARCH ARTICLE
Contents Vol 35(4)

Detectability of penguins in aerial surveys over the pack-ice off Antarctica

Colin Southwell A C , Charles G. M. Paxton B and David L. Borchers B
+ Author Affiliations
- Author Affiliations

A Australian Antarctic Division, Department of the Environment, Water, Heritage and the Arts, 203 Channel Highway, Kingston, Tas. 7050, Australia.

B School of Mathematics and Statistics, University of St Andrews, North Haugh, St Andrews KY16 9SS, Scotland, UK.

C Corresponding author. Email: colin.southwell@aad.gov.au

Wildlife Research 35(4) 349-357 https://doi.org/10.1071/WR07093
Submitted: 13 July 2007  Accepted: 20 March 2008   Published: 27 June 2008

Abstract

Knowledge of penguin abundance at regional and circumpolar scales across the Southern Ocean is important for the development of ecosystem models and to estimate prey consumption by penguins to assess potential competition with fisheries’ operations. One means of estimating penguin abundance is to undertake aerial surveys across the pack-ice surrounding Antarctica where penguins forage. However, it has long been recognised that aerial counts and resultant abundance estimates are likely to be negatively biased unless detectability is estimated and taken into account. Mark–recapture line-transect methods were used to estimate the detectability of penguin groups resting on ice floes during helicopter surveys over the pack-ice off Antarctica. Group size had the greatest effect of several measured covariates on detectability. Despite a concerted effort to meet the central assumption of conventional line-transect sampling (all objects on the transect line are detected), this was close to being achieved by single observers only in the case of the occasional very large group of >20 penguins. Emperor penguins were more detectable than Adélie penguins. Although observers undertook an extensive simulation training program before the survey, overall they improved in their ability to detect penguin groups throughout the survey. Mark–recapture line-transect methods can provide less biased estimation than conventional line-transect methods in aerial survey applications. This improvement comes with some costs, including the need for more demanding data-recording procedures and the need to use larger, more expensive aircraft. These additional costs will often be small compared with the basic cost, but the gain in terms of improved estimation may be substantial.


Acknowledgements

We are grateful to Helen Achurch, Julie Barnes, Robyn Delaney, Mark Fletcher, Michael Heinze, Matt Herne, Yuzuru Hyakatake, Lisa Meyer, Fiona McNight, Tim Page, Melissa Sharpe, Dave Taylor, Rick Van Veen and Sarah Way for their diligence and enthusiasm as aerial observers. We also thank Kelvin Cope for engineering support, pilots Adrian Pate and Brian Hole for helicopter support, Tony Hanson and his crew for ship support, and Rob Easther and Gerry Nash for coordination of aerial and ship work. We thank two anonymous reviewers for their helpful comments.


References

Borchers D. L. (1996). Line transect abundance estimation with uncertain detection on the trackline. Ph.D. Thesis, University of Capetown.

Borchers, D. L. , Zucchini, W. , and Fewster, R. (1998). Mark–recapture models for line transect surveys. Biometrics 54, 1207–1220.
| Crossref | GoogleScholarGoogle Scholar | Buckland S. T., Anderson D. R., Burnham K. P., Laake J. L., Borchers D. L., and Thomas L. (2001). ‘Introduction to Distance Sampling: Estimating Abundance of Biological Populations.’ (Oxford University Press: Oxford.)

Butterworth, D. S. , and Borchers, D. L. (1988). Estimates of g(0) for minke schools from the results of the independent observer experiment on the 1985/86 and 1986/87 IWC/IDCR Antarctic assessment cruises. Report of the International Whaling Commission 37, 301–333.
Laake J. L., and Borchers D. L. (2004). Methods for incomplete detection at distance zero. In ‘Advanced Distance Sampling’. (Eds S. T. Buckland, D. R. Anderson, K. P. Burnham, J. L. Laake, D. L. Borchers and L. Thomas.) pp. 108–189. (Oxford University Press: Oxford.)

Laake, J. , Dawson, M.J. , and Hone, J. (2008). Visibility bias in aerial survey: mark–recapture, line-transect or both? Wildlife Research 35, 299–309.
| Crossref | GoogleScholarGoogle Scholar | Thomas L., Laake J. L., Strindberg S., Marques F., Borchers D. L., Buckland S. T., Anderson D. R., Burnham K. P., Hedley S. L., and Pollard J. H. (2001). ‘Distance 4.0.’ (Research Unit for Wildlife Population Assessment, University of St Andrews: St Andrews, UK.)

Van Franeker, J. A. , Bathmann, U. V. , and Mathot, S. (1997). Carbon fluxes to Antarctic top predators. Deep-Sea Research. Part II, Topical Studies in Oceanography 44, 435–455.
| Crossref | GoogleScholarGoogle Scholar | Wood S. N. (2006). ‘Generalized Additive Models: an Introduction with R.’ (Chapman and Hall: Boca Raton, FL.)