Birgus latro (Linnaeus, 1767)

Cumberlidge, Neil, Caro, Tim, Watson-Zink, Victoria M., Naruse, Tohru, Ng, Peter K. L., Orchard, Max, Rahayu, Dwi L., Wowor, Daisy, Yeo, Darren C. J. & White, Tim, 2022, Troubled giants: The updated conservation status of the coconut crab (Birgus latro), Raffles Bulletin of Zoology 70, pp. 1-21 : 15-17

CONSERVATION OF BIRGUS LATRO

Although conservation management plans (to different degrees) are in place in Japan, Taiwan, the Philippines, Indonesia, Guam, Vanuatu, Tuvalu, Funafuti Atoll, Christmas Island, Aldabra, Nuie, and the Tanzanian Islands, this species is nevertheless unprotected in the majority of its range. Most unprotected B. latro populations in the world are in long-term decline because crabs are captured frequently, and their numbers are slow to recover. That is, unregulated capture is not sustainable. Protection policies for B. latro should, therefore, take into account the slow recruitment and replacement rate of this slow-growing species. In addition, the successful conservation of B. latro populations needs to be a community-driven initiative that incorporates multiple stakeholders. Conservation measures aimed at sustainable harvesting include hunting bans, no-take areas, catch-size limits, minimum size limits, and a ban on the capture of egg-bearing females. Sustainably managing the populations of these charismatic crustaceans increases the opportunities for tourism, and will have a wider benefit for the whole of the local community.

Several municipalities in southern Japan enforce B. latro protection ordinances ( Table 4). In Miyakojima City, there are four protected areas with year-round bans on B. latro collection that have been in force since April 2014 ( Fig. 10 ). In other less-protected areas, the collection of ovigerous females (TL <8 cm and> 12 cm) is banned, and there is a three-month ban (1 June to 31 August) on the collection of all B. latro (penalty ~ US $950, ¥100,000). In Tarama Village ( Fig. 10 ), limits on the harvesting of B. latro have been in force since March 2010. There is a year-round ban on the collection of small crabs (TL <4 cm) and of ovigerous females, and a two-month ban (from 1 July to 31 August) on the collection of crabs of any size (penalty US $475, ¥50,000). In Ishigaki City ( Fig. 10 ), there are three protected areas with year-round bans on B. latro collection that have been in force since June 2014. In other less-protected areas, there is a ban on the collection of small males (TL <4 cm), large males (TL> 5.5 cm), and females of any size, and a nine-month ban (1 December to 31 August) on the collection of all B. latro (penalty ~ US $950, ¥100,000). In Kagoshima Prefecture, there is a year-round ban on the collection of crabs of any size (penalty ~ US $4,750, ¥500,000). On Naha, the availability of large B. latro (sold for US $30–40 each) has declined since the 1990s (most crabs now weigh less than 1 kg), and the open sale of live B. latro in plastic boxes to tourists has now stopped.

In Lyudao, Taiwan, B. latro has been legally protected by the Wildlife Conservation Law since 1995. Conservation strategies in Taiwan consist of protecting these crabs in their inland forest habitat and during their annual migrations to and from the coast, when they are shedding eggs in the sea, and when juveniles return to land ( Chen et al., 2004). Other conservation actions in Taiwan include captive breeding programmes and educating the community about the need to conserve these charismatic giant arthropods. On Guam, conservation measures aimed at protecting B. latro are enforced both in US military installations as well as in the other non-military parts of the island, and include limiting harvesting to crabs of a certain size and making it illegal to catch ovigerous females during the time of year when they are present in the population.

Christmas Island supports what is probably the world’s largest population of B. latro , most of which is carefully managed in the Christmas Island National Park (including The Dales and Hosnie’s Spring, which are both Wetlands of International Importance under the Ramsar Convention on Wetlands). Control measures on Christmas Island focus on the invasive yellow crazy ants that attack crabs, as well as measures aimed at the mitigation of road kills. In Nuie, large adult females (TL> 8 cm, around 14–15 years old) can be harvested, but small adult females (TL 2.5–3.5 cm) are protected because they make up 95% of the female population and produce 100,000–250,000 eggs when they spawn ( Helfman, 1973; Helagi et al., 2015).

The Northern Mariana Islands allow licensed harvesting of B. latro , but the bag is restricted to five large (TL 7.6 cm), non-egg-bearing adults a day, and to 15 crabs over the threemonth season from September to November. In Tuvalu, B. latro is protected in Funafuti Marine Conservation Area on Funafuti Atoll (33 km ²). In Indonesia, B. latro is protected under a regulation issued by the Minister of Environment and Forestry of the Republic of Indonesia, No. P.106/MENLHK/ SETJEN/KUM. 1/12/2018. However, hunting of B. latro is allowed in North Maluku Province with special permits that limit size and catch number.

Other conservation tools include careful mapping of B. latro habitat using remotely sensed electronic tracking of individual crabs, and mapping of suitable habitat cover ( Krieger et al., 2012; T. White, pers. obs.). On Palmyra Atoll, such tracking has already demonstrated a loss of the native forest habitat of B. latro , and has linked habitat loss to reductions in its population levels. Habitat monitoring could provide a better understanding of the population levels and conservation status of B. latro across its entire range if it were to be expanded to survey other parts of this range across the Indo-Pacific. Given that areas with perfectly suitable habitat may be devoid of crabs, the value of quantifying habitat may be more of a guide to how its availability has declined. If harvesting moratoriums are to be successful, there needs to be enough suitable, undisturbed habitat remaining for crabs to make a strong recovery.

Conservation measures. The following are possible conservation measures and recommendations for threatened populations of B. latro (not in order of priority):

• Establish community-based conservation initiatives aimed at protecting the species and its habitat.

• Establish sanctuaries to protect coastal and inland forest habitats with primarily native vegetation (as opposed to only Cocos palms).

• Close major B. latro migration routes and spawning areas to public access during the breeding season.

• Monitor and eradicate (or at least suppress) introduced species that impact B. latro populations.

• Monitor B. latro populations and carry out detailed research on crab ecology and genetics.

• In places where harvesting is legal, implement a closed harvesting season (together with a permit/licensing system), set very small bag limits, and ban the collection of egg-bearing females for at least part of the year.

• Where relevant, implement a ban on the export of B. latro .

• Introduce public awareness campaigns informing of the need to arrest declines in B. latro populations and habitat quality, and the need to restrict harvesting and regulate coastal land development.

• Recommend/propose adding B. latro to CITES Appendix III.

Figures

Fig. 10. Conservation actions for Birgus latro (Linnaeus, 1767) in Okinawa and Kagoshima Prefectures, Japan. A, the location of Okinawa and Kagoshima Prefectures. The collection of coconut crabs is regulated by legal protective ordinances in the entire Kagoshima Prefecture. B, detail of Okinawa Prefecture showing the islands where the collection of coconut crabs is regulated by legal protective ordinances, shown in red ovals (Tarama Village, Miyakojima City, and Ishigaki City). Islands shown in black ovals (Yonaguni Village, Taketoni Town, and Okinawa Island and its associated islands) do not have protective ordinances for coconut crabs.