Application of laser photogrammetry on C. carcharias in natural environment

Most morphometric methods of investigation used on large marine organisms are intrusive, as they involve the capture or the killing of the animal. In the last decade new methods and new technologies have been developed able to supply the same morphometric data avoiding contact with the animal. The result of these efforts was the introduction also in the ecological field of laser photogrammetry. Photogrammetry is a non-invasive remote sensing technique that uses digital photography or images to measure objects or, in the case of animals, morphometry. Laser photogrammetry uses two laser beams, parallel to each other, to obtain the real dimensions of a body starting from a digital image. The objective of the present study is to provide a contribution to the definition and validation of the method for the study of white sharks. Data were collected during XIV° Scientific Expedition in South Africa (2017) managed by Centro Studi Squali and Unical to study the behaviour of Carcharodon carcharias. We proceeded to create a system suitable for the study of the white shark, being careful to the problems highlighted in the literature. The realized instrument was equipped with two filming means, in this way the attention was focused on two aspects: the real effectiveness of laser photogrammetry and the efficiency of using a reflex camera compared to an action-cam. The tool made allowed to obtain valid data. From these, estimates of the total lengths of the samples encountered were obtained by processing the frames considered valid using an appropriately defined protocol. The results obtained by the two imaging systems were compared with each other and with the data derived from the visual estimation (traditionally used not invasive method). The comparison of results allowed some indications regarding the effectiveness of the new morphometric measurement system and its degree of reliability.