De Bruyn, P.J. NicoBester, Marthan NieuwoudtCarlini, Alejandro R.Oosthuizen, Wessel Christiaan2010-02-012010-02-012009-03De Bruyn, PJN, Bester, MN, Carlini, AR, Oosthuizen, WC 2009, ‘How to weigh an elephant seal with one finger: a simple three-dimensional photogrammetric application’ Aquatic biology, vol. 5, pp. 31–39. [http://www.int-res.com/journals/ab]1864-778210.3354/ab00135http://hdl.handle.net/2263/12817Several 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.enInter-Research. This article is embargoed by the publisher until March 2013.Mass estimationVolume estimationLife historyPhocidsSouthern elephant seal -- SizeBody sizePhotographyWeight (Physics) -- MeasurementPhotogrammetric picturesEstimation theory -- Computer programsArticle