Squamomandibular Arthropathy in Indian Ocean Humpback Dolphins (Sousa plumbea) from South Africa, a Risk Factor for this Regionally Endangered Odontocete?
IAAAM 2019
Marie-Françoise Van Bressem1; Pádraig Duignan2*; Koen Van Waerebeek1; Stephanie Plön3
1Cetacean Conservation Medicine Group, Peruvian Centre for Cetacean Research, Museo de Delfines, Lima, Peru; 2Department of Veterinary Sciences, The Marine Mammal Center, Fort Cronkhite, Sausalito, CA, USA; 3Earth Stewardship Science Research Institute, Nelson Mandela University, Port Elizabeth, South Africa


Off South Africa, nearshore Indian Ocean humpback dolphins (Sousa plumbea), an IUCN listed endangered species with a declining population off the South African east coast, face several anthropogenic threats, including fisheries, pollution and shark nets deployed off the coast of KwaZulu-Natal (KZN).1,2 Documented diseases in this population include pneumonia, enteritis and lobomycosis.3 However, with the exception of Crassicauda spp.-associated bone lysis, pathology of the skull is mostly unknown in this species.4 To explore the diseases that may impact the health and welfare of S. plumbea, we carefully examined the skulls of 28 (14 immature, 14 mature) females and 46 (29 immature, 17 mature) males caught in shark nets along the coast of KZN in 1972–2016. Erosion and lysis of the mandibular fossa (squamomandibular joint - SMJ) were observed in nine (4 immature, 5 mature) or 32% of females and in 23 (14 immature, 9 mature) or 50% of males, aged between 2.5 and 21.5 years. Severity ranged from mild to severe, in which case numerous osteolytic lesions led to marked excavation on over 50% of the articular surface. Severe lesions were seen only in males and were already present in a 2.5 year-old individual. Other findings included lysis and osteitis of the mandibular ramus and maxillaries in four mature males, one immature male and an immature female, aged between 6 and 21.5 years. Dental abscesses are the suspected origin of these lesions. All affected specimens had also SMJ lesions. Altogether these results indicate that lesions of the jaws occur regularly in S. plumbea. Pathology of the SMJ has rarely been reported previously in cetaceans, although it is quite common in other marine mammal species.5,6,7 Together with the lytic lesions and osteitis, it is likely to cause morbidity and considerable pain, may compromise feeding and thus affect physical condition, especially when severe.


We kindly thank Dr. Greg Hofmeyr, Port Elizabeth Museum, for his help with logistics and facilitating access to specimens.

* Presenting author

Literature Cited

1.  Braulik GT, Findlay K, Cerchio S, Baldwin R. 2015. Assessment of the conservation status of the Indian Ocean humpback dolphin (Sousa plumbea) using the IUCN Red List criteria. In: Jefferson TA, Curry BE, eds. Advances in Marine Biology. 72:119–141pp, Oxford: Academic Press.

2.  Plön S, Cockcroft VG, Froneman WP. 2015. The natural history and conservation of Indian Ocean humpback dolphins (Sousa plumbea) in South African waters. In: Jefferson TA, Curry BE, eds. Advances in Marine Biology. 72:143–162, Oxford: Academic Press.

3.  Lane EP, de Wet M, Thompson P, Siebert U, Wohlsein P, Plön S. 2014. A systematic health assessment of Indian Ocean bottlenose (Tursiops aduncus) and Indo-Pacific humpback (Sousa plumbea) dolphins incidentally caught in shark nets off the KwaZulu-Natal Coast, South Africa. PLoS One. 9(9):e107038. doi: 10.1371/journal.pone.0107038.

4.  Van Bressem M-F, Duignan PJ, Van Waerebeek K, Raga JA, Plön S. 2018. Crassicauda spp. skull lesions in Indian Ocean humpback dolphins (Sousa plumbea) and Indo-Pacific bottlenose dolphins (Tursiops aduncus): implications for conservation. Poster presented to the African Marine Mammal Colloquium, Port Elisabeth, August 2018.

5.  Winer JN, Arzi B, Leale DM, Kass PH, Verstraete FJM. 2016. Dental and temporomandibular joint pathology of the walrus (Odobenus rosmarus). J Comp Pathol. 155:242–253. doi: 10.1016/j.jcpa.2016.07.005.

6.  Arzi B, Murphy MK, Leale DM, Vapniarsky-Arzi N, Verstraete FJ. 2015. The temporomandibular joint of California sea lions (Zalophus californianus): part 1 - characterisation in health and disease. Arch Oral Biol. 60:208–215.

7.  Ludolphy C, Kahle P, Kierdorf H, Kierdorf U. 2016. Osteoarthritis of the temporomandibular joint in the Eastern Atlantic harbour seal (Phoca vitulina vitulina) from the German North Sea: a study of the lesions seen in dry bone. BMC Vet Res. 14:150–164. doi: 10.1186/s12917-018-1473-5


Speaker Information
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Pádraig Duignan
Department of Veterinary Sciences
The Marine Mammal Center, Fort Cronkhite
Sausalito, CA, USA

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