During a 2013 field project in Gansbaai, South Africa we collected valuable data for over 6 months on the unique dorsal fin notch pattern and length of white sharks (Carcharodon carcharias). Combining two non-invasive methods like dorsal fin photo ID (see Andreotti et al. 2014) and parallel laser photogrammetry, we succeeded to measure (and re-measure) individual white sharks in both the summer (inshore) and winter (around Deyer Island & Geyser Rock) area.
This projected resulted in the following scientific publication:
Leurs, G., OโConnell, C. P., Andreotti, S., Rutzen, M., & Vonk Noordegraaf, H. (2015). Risks and advantages of using surface laser photogrammetry on free-ranging marine organisms: a case study on white sharks Carcharodon carcharias. Journal of Fish Biology, 86(6), 1713โ1728. doi:10.1111/jfb.12678
Abstract
This study employed a non-lethal measurement tool, which combined an existing photo-identification technique with a surface, parallel laser photogrammetry technique, to accurately estimate the size of free-ranging white sharks Carcharodon carcharias. Findings confirmed the hypothesis that surface laser photogrammetry is more accurate than crew-based estimations that utilized a shark cage of known size as a reference tool. Furthermore, field implementation also revealed that the photographer’s angle of reference and the shark’s body curvature could greatly influence technique accuracy, exposing two limitations. The findings showed minor inconsistencies with previous studies that examined pre-caudal to total length ratios of dead specimens. This study suggests that surface laser photogrammetry can successfully increase length estimation accuracy and illustrates the potential utility of this technique for growth and stock assessments on free-ranging marine organisms, which will lead to an improvement of the adaptive management of the species.
Paper is available at Wiley Online Library.
