article · Frontiers in Marine Science
Indian Ocean humpback dolphins along South Africa's Garden Route face mounting pressure from human coastal activities, with the national population numbering fewer than 500 individuals. Using photo-identification surveys carried out between March 2014 and June 2015, Bayesian open-population models were applied to records of 65 identified dolphins to estimate local abundance and group structure. The surveys indicated an estimated 89 individuals in the region, representing roughly one fifth of the total South African population. The animals occurred most consistently in the western section of the study area, particularly within the Goukamma marine protected area, and formed small groups. Further historical analysis of records from Plettenberg Bay showed a local population decline from an average of 112 dolphins in 2002 and 2003 to around 60 to 70 individuals in 2014 and 2015, mirroring broader regional trends.
Coastal development threatens marine ecosystems worldwide, placing vulnerable species at severe risk. For the endangered Indian Ocean humpback dolphin, robust estimates of population size and trends are critical to guide effective environmental management. Documenting regional abundance and a sustained decline highlights the need for targeted conservation planning and reinforces the value of marine protected areas.
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Human development is placing growing pressure on coastal ecosystems worldwide. Coastal dolphins are consequently exposed to a range of anthropogenic threats, yet for many species, limited knowledge of population size and dynamics hinders effective conservation planning. Four species of humpback dolphin ( Sousa spp.) inhabit shallow coastal waters globally, and all are threatened by human activities. Along the South African coast, the endangered Indian Ocean humpback dolphin ( Sousa plumbea ) occurs in a small, declining population whose abundance is thought to be fewer than 500 individuals. Here, we estimate the abundance and group structure of this species along the Garden Route on South Africa’s south coast. We conducted photo-identification surveys from March 2014 to June 2015 and fitted a Bayesian open-population (Jolly-Seber) model to encounter histories of 65 identified individuals. Dolphins were encountered most consistently in the west of the study area, particularly inside the Goukamma marine protected area, and never in large groups. We estimated that approximately 89 individuals occurred in the study area over the survey period, representing around one-fifth of the latest abundance estimate for the species in South Africa. We also analyzed intermittently collected photo-identification data from Plettenberg Bay, a subset of the study area, to evaluate temporal changes in local abundance. This suggested a decline in abundance over comparable 12-month periods, from a posterior mean of 112 individuals in 2002/03 to approximately 60–70 individuals in 2012/13 and 2014/15, consistent with declines reported elsewhere across the species’ range. This study underscores the importance of the Garden Route region for conservation of this species and provides a valuable baseline against which future population change can be assessed.
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DOI: 10.3389/fmars.2026.1904659
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