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Journal of Marine Biology
Volume 2014, Article ID 267917, 8 pages
Research Article

Correcting Positional Errors in Shore-Based Theodolite Measurements of Animals at Sea

1School of Biological Sciences, University of Canterbury, Christchurch 8140, New Zealand
2Department of Geography, University of Canterbury, Christchurch 8140, New Zealand
3Department of Biology, University of Toronto at Mississauga, Mississauga, ON, Canada L5L 1C6

Received 30 September 2013; Revised 3 December 2013; Accepted 9 December 2013; Published 22 January 2014

Academic Editor: Nobuyuki Miyazaki

Copyright © 2014 Ophélie Sagnol et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.


Determining the position of animals at sea can be particularly difficult and yet, accurate range and position of animals at sea are essential to answer a wide range of biological questions. Shore-based theodolite techniques have been used in a number of studies to examine marine mammal movement patterns and habitat use, offering reliable position measurements. In this study we explored the accuracy of theodolite measurements by comparing positional information of the same objects using two independent techniques: a shore-based theodolite station and an onboard GPS over a range of 25 km from the shore-based station. The technique was developed to study the habitat use of sperm whales (Physeter macrocephalus) off Kaikoura, New Zealand. We observed that the position accuracy fell rapidly with an increase in range from the shore-based station. Results showed that the horizontal angle was accurately determined, but this was not the case for the vertical angle. We calibrated the position of objects at sea with a regression-based correction to fit the difference in distance between simultaneously recorded theodolite fixes and GPS positions. This approach revealed the necessity to calibrate theodolite measurements with objects at sea of known position.