An improved mark-recapture method using passive integrated transponder (PIT) tags in Birgus latro (Linnaeus, 1767) (Decapoda, Anomura)

The effectiveness of Passive Integrated Transponders (PIT tags) was investigated in the robber or coconut crab, Birgus latro. A pilot study was conducted in Chumbe Island, Zanzibar, and a definitive study on Christmas Island, Indian Ocean. No mortality or adverse behaviour was recorded as a result of PIT tagging. On Christmas Island 1150 crabs were tagged in 2009 and 2010. In the period to April 2011, 169 crabs were recaptured, some up to four times. Of these, 67 had moulted before recapture. Approximately equal numbers of each sex were marked, and recaptured. Tag loss was estimated at ~5%. Alternative sampling protocols using grid and transect searches were tested. They produced different results in terms of sampling efficiency and sex ratio: sampling protocol must be considered when interpreting data.PIT tagging in Birgus is a promising method for long term population studies. It promises low tag loss and good recapture rates in comparison with previous studies.