AB 5:31-39 (2009) - doi:10.3354/ab00135
How to weigh an elephant seal with one finger: a simple three-dimensional photogrammetric application
P. J. Nico de Bruyn1,*, Marthán N. Bester1, Alejandro R. Carlini2, W. Chris Oosthuizen1
ABSTRACT: Several studies have developed photogrammetric techniques for indirect mass estimation of seals. Unfortunately, these techniques are often narrowly delineated for specific field scenarios or species. Many require sophisticated, custom-designed equipment or analytical tools, limiting their applicability. We aimed to devise a photogrammetric technique for accurate volume/mass estimation of seals under a variety of field scenarios without manipulation of the animal and with minimal equipment. We used Photomodeler Pro 3-dimensional modelling software to estimate the mass of 53 weighed southern elephant seals Mirounga leonina. The method is centred on animal volume estimation in relation to the 3-dimensional area around it, rather than features of the animal itself, an approach that liberates limitations associated with earlier studies. No morphometric body measures are required for such volume/mass estimation. We offer predictive equations that allow high confidence in mass estimates relative to measured mass (95% confidence interval of mean deviation from measured mass is from ±1.34 to ±3.83% depending on the field scenario). A single photographer with a measuring stick and non-customised digital photographic equipment can use this technique to determine the mass of an elephant seal anywhere in the field with the push of a button.
KEY WORDS: Southern elephant seal · Mass estimation · Volume estimation · Body size · Field method · Photography · Life history · Phocids
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Cite this article as: de Bruyn PJN, Bester MN, Carlini AR, Oosthuizen WC (2009) How to weigh an elephant seal with one finger: a simple three-dimensional photogrammetric application. Aquat Biol 5:31-39