Distribution and threats to coconut crabs on Unguja, Zanzibar

Abstract

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.

Meta‐ and subpopulation estimation with disparate data: coconut crabs in the Western Indian Ocean

“…Other sites with large population sizes (e.g. Matumbini KP, Fundo, Ngao and Kokota) are also being leased for investment (Hamad et al ., 2023) which involves removing large areas of native vegetation for hotel construction, and an influx of people. We are hopeful that this metapopulation estimate, unusual for an invertebrate (Caro, 2022), can be used by departmental officials charged with conservation of Zanzibari wildlife to actively limit development of island sites and establish additional protected sites for this and other coral rag species.…”

“…Coconut crab populations on most island archipelagos in the Western Indian Ocean are in steep decline or else extirpated (Cumberlidge et al ., 2022). Despite this, the species still survives on some coastal East African islands and on Unguja and Pemba, Zanzibar, although principally on outlying smaller islands off the Zanzibari coastline (Caro et al ., 2021; Hamad et al ., 2023). Here, our aim was to: Estimate the abundance and density of coconut crabs on the main island of Pemba and its outlying islands (Fig.…”

Interviews in ecology and conservation biology: A hidden treasure for the African ecologist

“…(e.g. Chakanyuka & Utete, 2022;Hamad et al, 2023;Matema et al, 2022;Wright et al, 2022). Pillay et al, 2022).…”