Growth of the coconut crab Birgus latro estimated from mark-recapture using passive integrated transponder (PIT) tags

Abstract

Determination of the growth pattern of a harvested species is an important step toward a proper assessment and suitable management of the stock. Although coconut crab Birgus latro populations in most regions have been severely depleted, few reliable biological data are available. We assessed the growth of B. latro using a mark-recapture method based on the use of passive integrated transponder (PIT) tags on Hatoma Island, located southwest of Okinawa, Japan. Of 781 crabs tagged (337 males, 444 females; 14.89 to 58.03 mm thoracic length [ThL]), 17 males and 20 females were recaptured. The application of PIT tags provided field data for growth of individuals for up to 2326 d and confirmed that coconut crabs molt during the winter dry season on Hatoma Island. The curves relating ThL with age, estimated from data of 29 crabs that had spent one or multiple winter dry seasons at liberty, showed that the coconut crab is an extremely slow growing species, with males showing much higher mean asymptotic ThL (69.87 mm) than females (42.79 mm). The Brody growth coefficient (K) was 0.061 yr −1 for males and 0.091 yr −1 for females. This study is the first to provide growth estimates of wild coconut crabs based on markrecapture over multiple years. Potentially long-lived, slow growing species such as coconut crabs may be susceptible to overharvesting, and a cautious approach is recommended to the determination of resource management regimes for B. latro.

Site fidelity and population structure of blue land crabs (Cardisoma guanhumi Latreille, 1825) in a restricted-access mangrove area, analyzed using PIT tags

“…According to these authors, this island is a refuge for this species due to the lack of natural predators and there is little catch for consumption. The same was observed by Sato et al [33], which found a ratio of 3:1 for males in B. latro.…”

“…Recently, tagging with PTs was used for several species of crustaceans, such as M. rosenbergii and C. magister [29], P. camtschaticus [30,31], U. cordatus [32], B. latro [33] and C. guanhumi [18,34], but studies using this method for land crabs are still scarce. The loss of PIT tags observed in some individuals in this study did not influence our population size calculations, since all animals with heat scars were considered, and loss of heat scars was considered to be zero for this study period.…”

“…More recently, PIT (Passive Integrated Transponder) tagging was used for several crustacean species: Macrobrachium rosenbergii and Cancer magister [29]; Paralithodes camtschaticus [30,31]; Ucides cordatus [32]; Birgus latro [33] and Cardisoma guanhumi [18,34]. The latter studies investigated large-scale spatial displacement and abundance of individuals at different sites in Puerto Rico.…”

Working with, not against, coral-reef fisheries

“…It may be the case that the populations of coconut crabs in the wild do not grow fast enough to supply the local human population, let alone the international market. Females reach sexual maturity in 9 yr in the wild (Sato et al 2013).…”

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

“…Fletcher et al (1989) reported that marking with heat branding has been useful for identifying coconut crabs. Passive integrated transponder (PIT) tags have also been applied to the coconut crab Sato et al, 2013). In addition, Krieger et al, (2012) used GPSbased telemetric studies to examine their migration behavior.…”