Dead Bunbury dolphins test negative for virus

The revelation that a measles-like virus killed some of the Swan River dolphins who died suddenly in 2009 has not shed any morelight on the deaths of dolphins in and around the Bunbury harbour since 2007.

Picture: Bunbury Dolphin Discovery Centre marine biologist Phil Coulthard with a Koombana Bay dolphin.

Scientists confirmed last week a morbillivirus infection killed at least two of the Swan River dolphins but samples taken from Bunbury dolphins tested negative for the virus.

Studies on the cause of death for the Swan River and Bunbury dolphins have been inconclusive, but the dolphins were reported to be covered in lesions or badly decomposed.

A combination of disease, highlevels of contaminants, human impacts such as fishing lines and rainfall events were blamed for the animals’ demise.

The eight dead Bunbury dolphins were all from a pod of 16 which lived in the Bunbury harbour and surrounding waters, including the Leschenault Estuary and Inlet and the Collie and Brunswick rivers.

Post mortem examinations at the time revealed there was no clear common cause of death between the Bunbury and the Swan River populations and that no critical levels of any contaminants were discovered in the Bunbury dolphins.

It has also been suggested reduced salinity in Bunbury’s waterways could have caused damage to the dolphins’ skin and increased their susceptibility to viruses.

Post-mortem analysis on the Bunbury dolphins revealed some were emaciated, some showed signs of bacterial infection, one dolphin had severe fungal pneumonia as well bacterial invaders and one dolphin had skin lesions.

Two juvenile dolphins showed signs of heavy parasitism which scientists said could be caused if the dolphin’s immune system was suppressed.

Marine biologist Phil Coulthard said it was always a concern and grounds for further study when there were animal deaths that exceeded natural mortality rates.

Mr Coulthard said environmental stressors and human induced problems in the waterways could have led to immune deficiency in the dolphins.

‘‘Their immune system is lowered and the animals lost the ability to fight infections,’’ he said.

Mr Coulthard said the cause of the dolphin deaths would likely be multi-factorial and it could be impossible to clearly define one factor.