Identification of individual coconut crabs, Birgus latro, on the basis of the pattern of grooves on the carapace

Abstract

We identified individual coconut crabs, Birgus latro, on the basis of photographic matching of the grooving patterns on the carapace. The photographic matching was performed using 336 front cephalothorax photographs obtained during night searching (capture and release) from 2006 to 2012 in Ocean Expo Park, southern Japan. Grooving patterns were visually matched on the basis of the distribution, form, and number of grooves. We determined that 99 individuals were captured and photographed twice. The period between release and recapture ranged from 2 to 2224 days. The grooving pattern on the carapace was unchanged, even when there were more than 1500 days between release and capture. In addition, captive crab maintained the same grooving pattern through four molts. Therefore, photographic matching of carapace grooving patterns is a useful technique for long-term individual identification. Crabs identified using this method are safer to consume than those tagged using invasive tagging methods, including passive integrated transponder tags. Photographic matching is also a useful way to identify individuals in the harvested population.