GROWTH OF THE COCONUT CRAB BIRGUS-LATRO IN VANUATU

Aspects of the growth of the coconut crab were investigated in the northern islands of Vanuatu where they form a major cash crop. Moult behaviour and growth increment were studied in enclosures but with limited success: under these conditions, small crabs moulted and grew but larger crabs generally did not increase in size. Further information on moult increment from free-ranging individuals was obtained from freeze- and heat-branded crabs and from crabs excavated from their moulting burrows. Moult frequency was estimated from monthly field assessment of the moult stage of individual crabs. The moult increment, as a percentage of initial size, can be expressed by the formula% increment = a-bx, where x is the premoult thoracic length (mm), a and b are 13.4 and 0.176 for male crabs and 14.0 and 0.28 for females. An L∞ of ≈80 mm thoracic length (TL) was predicted for males and 50 mm for females; both estimates approximate the maximum sizes observed in the field. Adults appeared to moult only once per year, during the winter dry season, but juveniles (< 30 mm TL) moulted more frequently. The calculated growth rate indicates that > 10 yr is required to reach the legal size for sale in Vanuatu and longevity may surpass 40 yr. The significance of these population characteristics on the exploitation of coconut crab stocks is discussed. © 1990.