Occurrence of
            Indo‐Pacific
            bottlenose dolphins (
            
              Tursiops aduncus
            
            ) off the Wild Coast of South Africa using photographic identification

AbstractWe investigated the abundance of Indo-Pacific bottlenose dolphins (Tursiops aduncus) along the south coast of South Africa, from the Goukamma Marine Protected Area (MPA) to the Tsitsikamma MPA, between 2014 and 2016. During this period, 662.3h of boat-based photo-identification survey effort was carried out, and the sighting histories of 817 identified individuals were used to estimate abundance using mark-recapture modelling. The selected open population model (POPAN) provided an estimate of 2,295 individuals (95% CI: 1,157-4,553) for the entire study area. A model estimate was produced for a subset of the study area, Plettenberg Bay, which could be compared with a past estimate for this location (2002-2003). The comparison suggested a 72.3% decrease in abundance, from 6,997 (95% CI: 5,230-9,492) in 2002-2003 to 1,940 (95% CI: 1,448-2,600) in 2014-2016. The decline in abundance was supported by a 72% reduction in mean group size for Plettenberg Bay between the periods. It is essential to be able to assess abundance changes at other locations to inform revision of T. aduncus conservation status in South Africa.

Download Full-text

Population structure of bottlenose dolphins (Tursiops aduncus) impacted by bycatch along the east coast of South Africa

Conservation Genetics ◽

10.1007/s10592-007-9379-y ◽

2007 ◽

Vol 9 (3) ◽

pp. 627-636 ◽

Cited By ~ 34

Author(s):

Ada Natoli ◽

Victor M. Peddemors ◽

A. Rus Hoelzel

Keyword(s):

South Africa ◽

Population Structure ◽

East Coast ◽

Bottlenose Dolphins ◽

Tursiops Aduncus

Download Full-text

Long-Term Demographic and Spatio-Temporal Trends of Indo-Pacific Bottlenose Dolphin (Tursiops aduncus) Bycatch in Bather Protection Nets off KwaZulu-Natal, South Africa

Frontiers in Marine Science ◽

10.3389/fmars.2020.542675 ◽

2020 ◽

Vol 7 ◽

Author(s):

Stephanie Plön ◽

Christine Erbe ◽

Sabine Wintner

Keyword(s):

South Africa ◽

Bottlenose Dolphin ◽

Bottlenose Dolphins ◽

Temporal Trends ◽

Long Term Effects ◽

Annual Fluctuation ◽

Tursiops Aduncus ◽

Kwazulu Natal ◽

The Impact

Bather protection nets have been in place off the coast of KwaZulu-Natal (KZN), South Africa, since the 1950’s. Besides sharks, they also catch a number of other marine vertebrates, including dolphins, the majority of which are Indo-Pacific bottlenose dolphins Tursiops aduncus. Previous analyses of dolphin bycatch in the nets indicated the potential impacts on the local populations, but a lack of information on population structure has to-date hindered a more detailed assessment. A recent re-assessment of the status and population delineations of T. aduncus off South Africa prompted a re-examination of demographic, spatial, and temporal patterns of its catches in bather protection nets over a 36-year period (January 1980 to December 2015). In total, 1169 dolphins were caught, including a slightly greater number of females and juveniles than other sex-classes, raising concern about the potential long-term effects on population demographics. More dolphins were caught off the North than the South coast. Temporal trends indicate that the bycatch during June and July every year (peak Sardine Run period) as a percentage of overall dolphin bycatch has been steadily decreasing from 39.8% in 1980 to 13% in 2015. A large inter-annual fluctuation can be seen, probably as a result of the inter-annual intensity of the Sardine Run. Although our results do not indicate a long-term decline of the individual populations as previously predicted, revised abundance estimates and data on the demographics and movement patterns of the animals are urgently required to accurately assess the impact of bycatch on the Indo-Pacific bottlenose dolphin populations off KZN and to advise conservation and management decisions going forward.

Download Full-text

Abundance of Indo-Pacific bottlenose dolphins (Tursiops aduncus) along the south coast of South Africa

PLoS ONE ◽

10.1371/journal.pone.0227085 ◽

2020 ◽

Vol 15 (10) ◽

pp. e0227085

Author(s):

O. Alejandra Vargas-Fonseca ◽

Stephen P. Kirkman ◽

W. Chris Oosthuizen ◽

Thibaut Bouveroux ◽

Vic Cockcroft ◽

...

Keyword(s):

South Africa ◽

Bottlenose Dolphins ◽

South Coast ◽

The South ◽

Tursiops Aduncus

Download Full-text

Cranial crassicaudiasis in two coastal dolphin species from South Africa is predominantly a disease of immature individuals

Diseases of Aquatic Organisms ◽

10.3354/dao03468 ◽

2020 ◽

Vol 139 ◽

pp. 93-102 ◽

Cited By ~ 3

Author(s):

MF Van Bressem ◽

P Duignan ◽

JA Raga ◽

K Van Waerebeek ◽

N Fraijia-Fernández ◽

...

Keyword(s):

South Africa ◽

Bone Development ◽

Bottlenose Dolphins ◽

Fatal Outcome ◽

Population Level ◽

Cape Coast ◽

Osteolytic Lesions ◽

Immune Mediated ◽

Significant Difference ◽

The Difference

Crassicauda spp. (Nematoda) infest the cranial sinuses of several odontocetes, causing diagnostic trabecular osteolytic lesions. We examined skulls of 77 Indian Ocean humpback dolphins Sousa plumbea and 69 Indo-Pacific bottlenose dolphins Tursiops aduncus, caught in bather-protecting nets off KwaZulu-Natal (KZN) from 1970-2017, and skulls of 6 S. plumbea stranded along the southern Cape coast in South Africa from 1963-2002. Prevalence of cranial crassicaudiasis was evaluated according to sex and cranial maturity. Overall, prevalence in S. plumbea and T. aduncus taken off KZN was 13 and 31.9%, respectively. Parasitosis variably affected 1 or more cranial bones (frontal, pterygoid, maxillary and sphenoid). No significant difference was found by gender for either species, allowing sexes to be pooled. However, there was a significant difference in lesion prevalence by age, with immature T. aduncus 4.6 times more likely affected than adults, while for S. plumbea, the difference was 6.5-fold. As severe osteolytic lesions are unlikely to heal without trace, we propose that infection is more likely to have a fatal outcome for immature dolphins, possibly because of incomplete bone development, lower immune competence in clearing parasites or an over-exuberant inflammatory response in concert with parasitic enzymatic erosion. Cranial osteolysis was not observed in mature males (18 S. plumbea, 21 T. aduncus), suggesting potential cohort-linked immune-mediated resistance to infestation. Crassicauda spp. may play a role in the natural mortality of S. plumbea and T. aduncus, but the pathogenesis and population level impact remain unknown.

Download Full-text