Measuring Hammerhead Sharks with Lasers

Although we published this paper already two (almost three, geez!) year ago, I think it is a paper worth sharing here as well. Together with Craig O’Connell (O’Seas Conservation Foundation) and a whole expedition team we set out to try a novel technique to non-invasively identify and measure great hammerhead sharks (Sphyrna mokarran). The technique has previously been used on whale sharks and large terrestrial species as African elephants and on captive western lowland gorillas.

Now we combined this technique with dorsal fin identification (as is done in dolphins and white sharks), to see if laser photogrammetry is a viable tool to study growth of these endangered sharks. Practically this means, that you score a photo of the shark’s dorsal fin first, after which a second researcher projects the lasers on the side of the body once the shark approaches and shoots a full-body shot. The shark can than be identified using the pattern of notches on the posterior margin of the dorsal fin, and can be measured using the fixed lasers as a scale on the photo. Read more about the paper in the abstract or by downloading the full paper.

O’Connell, C. P., & Leurs, G. (2016). A minimally invasive technique to assess several life-history characteristics of the endangered great hammerhead shark Sphyrna mokarran. Journal of Fish Biology88(3), 1257–1264.

A dorsal-fin photo-identification technique paired with a non-invasive parallel laser photogrammetry technique was used to non-invasively identify individual Sphyrna mokarran over time. Based on the data collected over a duration of 59 days, 16 different S. mokarran (mean±s.d. pre-caudal length: 220⋅82±13⋅66 cm; mean±s.d. cephalofoil width: 71⋅38±7⋅94 cm) were identified using dorsal-fin photo-identification, with a mean±s.d. shark re-sighting frequency of 4⋅05±3⋅06 at-sea days. The results illustrate a high S. mokarran sighting rate and therefore, the utilization of parallel laser pho- togrammetry and dorsal-fin photo-identification may be a plausible multi-year approach to aid in non-invasively determining the growth rate and inter-annual site fidelity of these animals.