FEATURE CREATURE
FEATURE CREATURE INDIAN OCEAN HUMPBACK DOLPHIN (SOUSA PLUMBEA) FEATURE IUCN RED LIST 2017 PHOTOGRAPHY DR. ADA NATOLI
RED LIST CATEGORY & CRITERIA: ENDANGERED Scientific Name: Sousa plumbea Synonym: Delphinus plumbeus (G. Cuvier, 1829) Common Names: English: Indian Ocean Humpback Dolphin French: Dauphin à bosse Afrikaans: Boggelrugdolfyn Arabic: Dukhs Hindi: Fukariyo, Gada/Gad/Gaadha reda, Goonu, Kadal ongi, Kadal panni, Paru vedan, Sori vedan, Thella thoralu TAXONOMIC NOTES Sousa plumbea has been recognised as a species since taxonomic revision of the genus Sousa in 2014 (Committee on Taxonomy 2014, Jefferson and Rosenbaum 2014). Previously this species was lumped with the Indo-pacific humpback dolphin (Sousa chinensis) but animals occurring in the Indian Ocean from South Africa to India are now recognised as taxonomically distinct from those that occur further east, based on genetics, skeletal morphology, external morphology and colour. There is uncertainty about the taxonomic affinities of the humpback dolphins that occur 24
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in the Bay of Bengal and future studies will confirm whether S. plumbea actually occurs east of the southern tip of India. JUSTIFICATION In the places where studies have occurred, Indian Ocean Humpback Dolphin subpopulations were found to be small: always fewer than 500 and generally fewer than 100 individuals in discrete, or semi-isolated areas. Humpback dolphins have one of the most specific habitat preferences and restricted distributions of any marine megafauna, and both of these characteristics are well known to reduce the resilience of species to environmental change and anthropogenic threats and to increase their extinction risk (Davidson et al. 2011, Dulvy et al. 2014, Purvis et al. 2000). Indian Ocean Humpback Dolphins are concentrated in coastal waters within 2 km of shore and they are often sighted only a few hundred metres from land. This distribution places them in exactly the same location as the majority of small-scale fishing effort prevalent throughout their range in the same nearshore habitat. As a result, humpback dolphins encounter large numbers of coastal
gillnets and are at high risk of entanglement. High and clearly unsustainable mortality rates have been reported from several areas and frequent encounters with fishing gear can be inferred from the high degree of scarring and injury – for example, 41% of individuals in Pemba, Tanzania bore gear-related scars (Braulik unpub. data). Although information on population size, threats and mortality is available only for portions of the species range, there are strong reasons to suspect and infer that the threats will be similar or possibly even more intense elsewhere. The deaths of only 4.2 individuals per year from a population of 100 would result in a 50% decline (Moore 2015). The available evidence on the studied subpopulations in South Africa and all indications from elsewhere in the range suggest that mortality rates are consistently at or above the rate that would result in a 50% decline in 75 years (three generations). The species’ preferred habitat and small populations overlap in both space and time with several ubiquitous and pervasive threats that are increasing in severity, leaving no refuges for these dolphins. The