Abstract:
Coastal dolphin populations are indicators of environmental health and may be sensitive to
anthropogenic influences. An observed increase in lesions during routine necropsies of
dolphins prompted the first systematic health assessment of dolphins incidentally caught in
shark nets off the KwaZulu-Natal coast. A detailed standard dissecting and sampling
protocol for small cetaceans was developed for use in South Africa. Thirty five Indian Ocean
bottlenose dolphins (Tursiops aduncus) and five Indo-Pacific humpback dolphins (Sousa
chinensis), incidentally caught between 2010 and 2012, were subsequently evaluated by full
necropsy and sampling using this protocol.
All animals were considered to be in good nutritional condition, based on blubber thickness
measurements and muscle condition. A large proportion of dolphins had lesions with
parasitic aetiology, including pneumonia (34/40), bronchiolar epithelial mineralisation
(33/40), gastroenteritis (28/40), hepatitis (24/39); endometritis (11/26), capsular inflammation
of various abdominal and thoracic organs (30/40), and splenic capsular tags (18/40). Four
parasite species (Halocercus sp., Crassicauda sp., Brachycladiinae, and Xenobalanus
globicipitis) were recovered from six animals. Non-specific encephalomeningitis was found in
7/18 animals. Adrenal cortical hyperplasia (18/37,) possibly related to chronic stress, was
also found, as well as myocardial fibrosis (10/39). Pulmonary pneumoconiosis and lymph
node foreign material accumulation, possibly indicating exposure to polluted air, was seen in
three animals. Lesions suggestive of morbillivirus, Toxoplasma gondii, or Brucella spp.
tested negative on immunohistochemistry. The first confirmed cases of lobomycosis and
sarcocystosis in South Africa were found. Most lesions were mild, although their high and
apparently increasing prevalence may indicate a change in the host/parasite interface. This
may be attributed to anthropogenic factors, such as stress or environmental pollution,
suggesting degradation of the marine environment. This could also negatively impact human
populations associated with the marine environment.
The results indicate a need for continued health monitoring of coastal dolphin populations
and for further research into disease pathophysiology and anthropogenic factors affecting
these populations. This standard necropsy protocol will encourage a more complete health
investigation of incidentally caught and stranded cetaceans in the region and will assist in
expanding the current knowledge of diseases affecting dolphin populations in southern
Africa. Furthermore, we provide valuable information regarding the baseline of disease
affecting these populations, which may be used to determine and monitor temporal trends.
