Indian Ocean humpback dolphin (Sousa plumbea) movement patterns along the South African coast

Abstract

The Indian Ocean humpback dolphin was recently uplisted to 'Endangered' in the recent SouthAfrican National Red List assessment. Abundance estimates are available from a number of localized study sites, but knowledge of movement patterns and population linkage between these sites is poor. A national research collaboration, the SouSA project, was established in 2016 to address this key knowledge gap. Twenty identification catalogues collected between 2000 and 2016 in 13 different locations were collated and compared.2. Photographs of 526 humpback dolphins (all catalogues and photos) were reduced to 337 individuals from 12 locations after data selection. Of these, 90 matches were found for 61 individuals over multiple sites, resulting in 247 uniquely, well-marked humpback dolphins identified in South Africa.3. Movements were observed along most of the coastline studied. Ranging distances had a median value of 120 km and varied from 30 km up to 500 km. Long-term site fidelity was also evident in the data. Dolphins ranging along the south coast of South Africa seem to form one single population at the western end of the species' global range.4. Current available photo-identification data suggested national abundance may be well below previous estimates of 1000 individuals, with numbers possibly closer to 500. Bearing in mind the poor conservation status of the species in the country, the development of a national Biodiversity Management Plan aimed at ensuring the long-term survival of the species in South Africa is strongly recommended. At the same time, increased research efforts are essential, particularly to allow for an in-depth assessment of population numbers and drivers of changes therein.5. The present study clearly indicates the importance of scientific collaboration when investigating highly mobile and endangered species.

South Africa’s newly approved marine protected areas have increased the protected modelled habitat of nine odontocete species

“…Their predicted distribution is very patchy and could be related to the limited presence data available for both species, resulting in the poor predictive ability of the ensemble models. The literature suggests that both of these species occur in warmer waters, inshore of the Agulhas Current, with their most westerly distribution limits being west of Cape Agulhas (Best 2007, Vermeulen et al 2018. Our results do indicate this, but because bathymetry was the variable that primarily described their distribution, there are a few small pockets of predicted distribution for both species farther up the west coast, past False Bay.…”

“…The Indo-Pacific humpback dolphin is the only endangered odontocete species in South Africa (Vermeulen et al 2018). The results from our study indicate that the coastal east and south coast MPAs (Fig.…”

Another dolphin in peril? Photo‐identification, occurrence, and distribution of the endangered Indian Ocean humpback dolphin (Sousa plumbea) in Algoa Bay

“…For example, a BMP has previously been implemented for the most endangered species in South Africa, the African penguin Spheniscus demersus (DEA, ). Conservation management options for humpback dolphins along the South African coastline have been highlighted already, including the development of a BMP (Vermeulen et al, ). These include the following recommended actions.…”

“…It is possible that not all of the individuals have been accounted for as a result of movement of individuals between Algoa Bay and the neighbouring areas, such as St Francis Bay, located about 90 km away (Karczmarski, Winter, et al, ; Bouveroux, unpublished data). A recent study focusing on the movement patterns of humpback dolphins along the entire South African coastline has revealed that significant movements of individuals can occur, over distances ranging from 30 to 500 km (Vermeulen et al, ). Poor‐quality photographs and individuals that have less distinctive markings could have also decreased the re‐sighting rate.…”

Estimates of abundance and change in abundance of the Indo-Pacific bottlenose dolphins (Tursiops aduncus) along the south coast of South Africa

“…While T. aduncus was recently assessed to be Near Threatened in South Africa [16], the S. plumbea is currently Endangered at the national level on account of the small size of the population and apparent decline, exacerbated by its fragmented distribution with considerable movement within the bioregions [59,60]. Expanding the current MPAs or identifying new conservation areas has been recommended for S. plumbea in South Africa [60]. Given the sympatry of the two species, such measures could also address certain conservation needs for T. aduncus ; e.g.…”