Indian Ocean humpback dolphin in the Menai Bay off the south coast of Zanzibar, East Africa is Critically Endangered

Abstract

Abstract Cetaceans occupying coastal habitats are at high risk of impact from anthropogenic sources which can cause direct mortality or affect long‐term health. Monitoring and detecting change require long‐term studies and reliable funding, not always available especially in developing countries. Management and conservation of cetaceans must therefore use precautionary methods that allow assessment from limited data sources to identify risk of, and prevent, species extirpation or extinction. IUCN Red List criteria for regional populations was applied to the population of Indian Ocean humpback dolphins (Sousa plumbea) resident in Menai Bay Conservation Area off the south coast of Zanzibar, East Africa which is subjected to unsustainable entanglement rates in gillnet fisheries and unregulated tourism activities. Photographic identification surveys were conducted in 2015 to generate a new abundance estimate from capture–recapture analysis. Mortality estimates were calculated using available data from 1999 to 2002 and a population viability analysis was conducted based on population, species and genus specific parameters. The 2015 abundance estimate for humpback dolphins was 19 (95% CI 14–25) non‐calf individuals, representing a 63% reduction in abundance since 2002. The population viability analysis baseline scenario predicted chance of extinction at 0.996 (SE 0.002) with the median time to extinction at 36 years. Sensitivity analysis suggested that population recovery would only be possible with a complete prevention of bycatch mortality. The population met the threshold for Critically Endangered for all criteria which could be directly assessed. This conservation assessment highlights the requirement for immediate management action to eliminate bycatch of humpback dolphins to prevent the local extinction of the species.