Distribution and threats to coconut crabs on Unguja, Zanzibar.

Coconut crabs Birgus latro are listed as vulnerable by the IUCN due to habitat conversion and fragmentation as well as direct exploitation for human consumption. Here, we document the distribution of coconut crabs in 81 coastal wards (shehia) across the island of Unguja, Zanzibar, and its outlying islets using standardised interviews and night-time fieldwork. Coconut crabs are mostly absent from the main island of Unguja but are found on 14 of 22 small outlying islands. We matched the distribution on the main island to environmental, social and economic data at the ward level. Our analyses show that coconut crabs are more likely to be present in wards containing rocky as opposed to sandy coastlines, and less likely to be found in wards with hotels and urbanisation, a finding of broad relevance for coastal populations of other species. Our findings show that a new government initiative for economic improvement that encourages construction of hotels on small islets around Unguja needs considerable oversight to prevent threatening the long-term viability of this vulnerable species in one of its last areas in the Western Indian Ocean. In addition, full formal protection of this species will reduce further population fragmentation.