Birgus latro has significant conservation and socio-economic importance throughout its range, yet very little is known about its growth in its natural habitat. An extensive markrecapture program was undertaken on Christmas Island, Australia, in which over 1440 individual crabs were uniquely identified using passive integrated transponder (PIT) tags. Over 18% of the tagged population was recaptured at least once and remeasured, providing substantial information on growth of B. latro. Our results show that in its natural setting B. latro is a very slow-growing species. Individuals commonly experience conditions that result in zero or negative growth. Sex, size, and injury all strongly influence the crab's moult increment. Males approached zero growth at around 65 mm in thoracic length (TL), while growth in females started to plateau at around 50 mm TL. Injury frequently led to negative growth, particularly in individuals that had lost a claw and/or multiple limbs -presumably due to a loss of foraging opportunities or access to other resources and a redistribution of available energy into limb regrowth. Our study indicates that previous growth curves do not adequately describe the growth of B. latro in its natural setting and that individual crabs may live over 30 yr longer than previously predicted, with large crabs likely to be over 100 years old. This may have serious implications for the long-term conservation of the species in the face of continuing exploitation.
KEY WORDS: Birgus latro · Growth · Moult increment · Mark-recapture · PIT tag · ConservationResale or republication not permitted without written consent of the publisher Aquat Biol 19: 129-141, 2013 Robertson 1991) have attempted to maintain Birgus latro in captivity in order to monitor moult increment and moult frequency in a controlled environment. However, most studies on crabs > 30 mm thoracic length (TL) were deemed unsuccessful as crabs either did not moult before dying in captivity or the majority of moulted individuals had negative or zero growth. Smaller crabs held in captivity grew well, providing some good early growth information, but most studies terminated the experiments after 2.5 yr (Held 1963, Reese & Kinzie 1968, well before the crabs reached sexual maturity; believed to be at around 24.5 to 32 mm TL in females , 22.2 mm TL in males ) and at ca. 5 to 10 yr of age, as determined by the growth curve provided by Fletcher et al. (1990a).A number of mark-recapture studies have been undertaken on Birgus latro in an attempt to improve knowledge of their growth in a natural setting, but with limited success (see Drew et al. 2010 for a review). One of the primary problems with markrecapture programs has been the inability of the mark to be retained through ecdysis (Drew et al. 2012); external tags are lost during the moult process. Fletcher et al. (1989) attempted to alleviate the problem of retaining marks post-moult by using heat and freeze branding methods, enabling them to identify individual crabs for up to 3 yr. However, ...