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Rapid noninvasive field estimation of body length of female elephant seals ( Mirounga leonina )
Author(s) -
Sanvito Simona,
Sanvito Roberto,
Galimberti Filippo
Publication year - 2019
Publication title -
marine mammal science
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.723
H-Index - 78
eISSN - 1748-7692
pISSN - 0824-0469
DOI - 10.1111/mms.12525
Subject(s) - southern elephant seal , elephant seal , seal (emblem) , sea lion , harbor seal , geography , archaeology , zoology , biology , fishery , computer science , documentation , programming language , phoca
Body size is an important correlate of physiology, life history, and ecology of animal species (Bonner 2006, Schmidt-Nielsen 1984). Body size estimation is an important component of research on social behavior (Pelletier et al. 2006), parental investment (Wheatley et al. 2006), foraging ecology (Hassrick et al. 2013) and conservation (Berger 2012). There is an increasing tendency to use noninvasive methods to study wildlife, to reduce the impact on the subjects’ welfare (Pauli et al. 2010). Most noninvasive body size measurement methods are based on photogrammetry (Berger 2012). An important drawback of those methods is that they are based on pictures and, therefore, cannot produce size estimates in the field. The measurement of pictures usually requires manual processing and, even when automated processing is possible, extensive manual clean up and validation is required. The processing of pictures can be very time consuming, and requires specialized software in the case of 3D photogrammetry (de Bruyn et al. 2009). We used photogrammetry to study various aspects of southern elephant seal (Mirounga leonina) male biology, including reproductive effort (Galimberti et al. 2007), vocal communication (Sanvito et al. 2007a), and secondary sexual traits (Sanvito et al. 2007b). Application of photogrammetry to female elephant seals was problematic, because photogrammetry required a scale to be placed in the picture, and females were more difficult to be approached than males, due to their smaller size, greater sensitivity to disturbance, and gregariousness. We explored other photogrammetric options without success. In particular, we tried the parallel lasers method (Durban and Parsons 2006), but we were not able to obtain reliable measures because parallel lasers work well on flat targets, where the measurement is taken on the same plane where the lasers point, while in the case of elephant seals it was difficult to target the lasers on the middle axis of the subjects. Moreover, parallel lasers needed to be pointed exactly perpendicular to the measurement plane, and this was not an easy task in field work conditions.