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RESEARCH ARTICLE
Contents Vol 35(4)

Coping with variation in aerial survey protocol for line-transect sampling

Jeff Laake A D , Richard J. Guenzel B , John L. Bengtson A , Peter Boveng A , Michael Cameron A and M. Bradley Hanson C
+ Author Affiliations
- Author Affiliations

A National Marine Mammal Laboratory, Alaska Fisheries Science Center, National Marine Fisheries Service, Seattle, WA 98115, USA.

B Wyoming Game and Fish Department, Laramie, WY 82070, USA.

C Northwest Fisheries Science Center, National Marine Fisheries Service, Seattle, WA 98112, USA.

D Corresponding author. Email: jeff.laake@noaa.gov

Wildlife Research 35(4) 289-299 https://doi.org/10.1071/WR07065
Submitted: 8 June 2007  Accepted: 12 December 2007   Published: 27 June 2008

Abstract

Altitude and flight speed affect detection probability and they typically vary during the course of most aerial surveys. We demonstrate how these sources of variation can be accommodated with covariates in a line-transect analysis using data from a pronghorn (Antilocapra americana) survey in Wyoming and a survey of Antarctic ice seals (Lobodon carcinophaga, Leptonychotes weddellii, Hydrurga leptonyx, Ommatophoca rossii). We also show how the likelihood for binned distance data can be modified to allow for variation in altitude. As an alternative, we develop an estimator for aerial line-transect sampling based on vertical angles rather than distance. With a small simulation study, we show that our estimators are unbiased and are preferable to using biased estimators based on fixed-distance intervals derived from average altitude.


Acknowledgements

The seal survey was supported by National Science Foundation grant OPP-9815961 to Bengtson, Boveng and Laake. The Wyoming Game and Fish Department has been instrumental in the development and implementation of distance sampling in pronghorn management by providing continued support for the development of improved methodology. We thank Devin Johnson, Rod Hobbs, Gary Duker, Jim Lee, Richard Barker and an anonymous reviewer for suggesting improvements to the manuscript.


References

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Appendix 1 Contd. 
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