In March and April, 2013 a significant, marine mortality event occurred off the coast of South Australia. Large numbers of fish, mostly small-bodied benthic species, were found dead in the water or washed up on beaches. Concurrently over 30 dolphins deaths were reported.
Post mortem examination of fish revealed evidence of stress and physical gill damage, sufficient to impede respiration. Stress and opportunistic bacterial infection are considered the likely cause of fish deaths. Although public concern was high, underwater observations indicated that only a small percent of fish populations were affected.
It is postulated that unusually high water temperature (3-5°C above the historic average), was the primary factor in this fish mortality event. The plume of warm water across the State corresponded with the kill locations. High levels of harmful, but non-toxic, algae (Chaetoceros coarctatus) were observed in water samples and likely contributed to fish mortalities.
The dolphin deaths were primarily reported in Gulf St Vincent and carcasses were but concentrated along the Adelaide coastline. Almost all dolphins were juvenile or neonatal bottlenose dolphins (Tursiops aduncus). Necropsy findings varied but bruising, lymphadenopathy, lungworm, and lung consolidation were common. Bronchioalveolar pneumonia with multinucleated giant cells, suggesting a viral aetiology, was observed in some samples. Aspergillus spp. fungal hyphae were also seen in necrotic lesions in some lung, heart and brain tissues. Morbillivirus was identified by PCR and immunohistochemistry in 6 of 6 lung samples examined.
The investigations involved cooperative effort from multiple government and non-government agencies and clearly demonstrated the value in this approach. In addition to the co-authors’ organisations, the contributions from the Australian Marine Wildlife Research and Rescue Organisation and the EPA are acknowledged.
This is the first time morbillivirus has been identified in dolphins in SA waters and the first event of this scale in Australia. At this point in the investigation the relationship between the dolphin deaths and the fish deaths, if any, has not been determined.