Neonatal and female reproductive pathology, trauma and demographics of Indo-Pacific humpback dolphins (Sousa chinensis) and Indo-Pacific finless porpoises (Neophocaena phocaenoides) stranded in Hong Kong

Abstract

Material and data collected from post-mortem examinations of stranded odontocetes provide a unique method of assessing the demographics and health of free-ranging populations non-invasively. Existing studies in Hong Kong have focused on quantitative and temporal studies of environmental pollutants and were not carried out from a veterinary perspective, with little being known about the pathology and pathogens affecting local odontocetes.

In this research, records and necropsy samples of 269 stranded odontocetes in Hong Kong over the period 2007–2014 were examined to acquire additional knowledge about the health of the two resident species, the Indo-Pacific humpback dolphin (Sousa chinensis) and the Indo-Pacific finless porpoise (Neophocaena phocaenoides) and the processes that may impact their reproductive success. Updated demographic parameters and spatio-temporal characteristics of the population of strandings were obtained. An increase in the number of Indo-Pacific finless porpoise cases was noted during the study period. Evaluation of neonates showed that in Indo-Pacific humpback dolphins this age category was overrepresented. Spatially, clusters of cases were seen in Sha Chau and Lung Kwu Chau Marine Park and Tai O Bay, consisting predominantly of neonates. Cases were reviewed for changes attributable to trauma, and a gradual increase in cases of human interaction over the study period was observed. Lungworm prevalence was higher in the human interaction cases compared to non human interaction cases. Among the human interaction trauma cases, females were overrepresented, and this overrepresentation was more pronounced in the Indo-Pacific humpback dolphins juvenile subadult and adult group. Fetal and neonatal characteristics were identified. Pathological changes of the female reproductive system, including mammary glands and neonates were described. Three pathogens (bacterial, viral and parasitic) previously unreported in local odontocetes were described. In Indo-Pacific finless porpoises Brucella ceti was detected by PCR in a neonate's brain and in milk samples. In Indo-Pacific Humpback dolphins genital mucosal lesions were reported and a gammaherpesvirus was detected. It was discovered that the parasitic nematode Crassicauda sp. predominantly affects sexually mature females. The resulting lesions from parasitic mastitis, in some cases accompanied by nodules and abscesses were considered severe enough to interfere with normal lactation. Based on findings from 12S ribosomal DNA analysis, it was demonstrated that the same Crassicauda parasite affects both species. This parasite was morphologically identified as Crassicauda fuelleborni. The Indo-Pacific humpback dolphin is reported here as a new host for the genus Crassicauda and these findings represent a new geographical record for this parasite in the South China Sea. The additional knowledge on diseases in two species of odontocetes provided here can assist veterinarians working with live stranded cetaceans, increasing the chances of successful rehabilitation. The present study demonstrates that diseases and pathogens, along with anthropogenic trauma impact the reproductive health and calf raising outcome and conceivably the population viability of Hong Kong odontocetes. Future conservation measures spatio-temporally targeting mother and calf pairs and the areas they utilise will address the vulnerabilities of this demographic group highlighted in this thesis and therefore increase the sustainability of the population of threatened odontocetes in Hong Kong.