Recently, the east coast of Australia has seen a dramatic increase of Risso’s dolphin (Grampus griseus) strandings. As of February 2015, there have been 21 strandings, involving 22 animals spread over New South Wales (NSW), Victoria and Tasmania. All animals have been in poor body condition and have ranged in both age and gender. The Tasmanian strandings are of particular significance, as prior to 2014, there has only been a single documented case of a Risso’s dolphin stranding (K. Carlyon, personal communication, February 6, 2015). The objective of the report was to provide a descriptive epidemiological study of Australian Risso’s dolphin strandings from August 2014 to February 2015.
Primary collection of stranding data were compiled by National Parks and Wildlife in NSW, Department of Environment, Land, Water and Planning in Victoria and Department of Primary Industries, Parks, Water and Environment in Tasmania. Full autopsies were performed on ten animals by veterinarians and others by wildlife officers where possible. Tissue samples were collected and sent off for histopathology and other testing either fixed in 10% formalin or as fresh specimens.
There seems to be no clear pattern to explain the sudden rise of Risso’s dolphin strandings. Pathological abnormalities have been limited and where present have not been consistent between events. One animal (out of six) tested positive for toxoplasmosis, none (out of four) for Dolphin Morbillivirus and none (out of one) for Brucella. Four animals showed evidence of cerebral inflammation.
Based on pathological findings, an infectious cause to these strandings appears unlikely and perhaps greater focus should be placed on underlying ecological issues affecting the changing distribution of Risso’s dolphins such as increasing water temperatures, shifting prey distribution and/or environmental contamination. Genetic testing would beneficial but difficult to interpret due an incomplete DNA database for this species.