A systematic health assessment of two dolphin species by-caught in shark nets off the KwaZulu-Natal Coast, South Africa

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.