Dolphin deaths - frequently asked questions
Date posted: 07 May 2013
What is the current situation with dolphin mortalities?
Test results and observations made during the post mortem examinations point strongly to dolphin deaths having been caused by an outbreak of dolphin morbillivirus.
What is dolphin morbillivirus?
Dolphin morbillivirus is one of a family of viruses that includes distemper in dogs and measles in humans. In dolphins, it is known to cause brain and lung infections and suppress immunity, leading to secondary infections. It has been found previously in overseas dolphin populations and in Queensland and Western Australia.
How is it transmitted?
Dolphin morbillivirus is transmitted by close contact between dolphins, including between mothers and newborns. It cannot be transmitted to humans. It is unlikely that the disease would be able to survive in the environment, outside an animal, for any significant length of time.
How many dead dolphins have been found?
Thirty-three dolphins have been found along the South Australian coast since 1 March. Twenty-eight of these have been found in the Gulf St Vincent bioregion, three in Spencer Gulf and two in the South East. The most recent finds were juvenile dolphins at Port Clinton on 5 May and Stansbury on 7 May.
Where have dead dolphins been found?
Dolphins have been found at Middleton, Maslin Beach, Seacliff, Sellicks Beach, O’Sullivans Beach, Grange, Port Noarlunga, Hallett Cove, Outer Harbor, North Haven, West Beach and the Port River, at Stansbury, Port Julia and Port Broughton on Yorke Peninsula, Danger Point and Canunda in the South East and at Brownlow Beach, Kingscote and Strawbridge Point on Kangaroo Island.
What do we know about the dead dolphins?
Most of the dolphins that have been identified are Indo-Pacific bottlenose dolphins , although at least two are short-beaked common dolphins. The age of the dolphins ranges from birth to young adult.
What has been found in the dead dolphins?
Sixteen dolphins have been examined to date. Six have tested positive for dolphin morbillivirus, including two examined by the University of Adelaide’s Veterinary School. Some results of laboratory examinations are still pending Many of the animals have pneumonia associated with parasite burdens (lung worm) and disseminated fungal infections. This suggests the animals have been stressed and may have had impaired immune systems at the time of death. This is characteristic of viral diseases.
Why haven’t all the dolphins been examined?
The inter-agency team looking into the dolphin deaths has concentrated on the carcasses found in Gulf St Vincent, as this is where the highest concentration of deaths has occurred. The dolphins recovered in the South East and in Spencer Gulf will be examined at a later date.
Five of the dolphins reported dead could not be recovered and therefore could not be examined.
What about the dolphin calf from the Port River?
Mimo, the Port River dolphin calf, was collected on 16 March. His behaviour appeared to be abnormal from birth, so his death may well have been unrelated to those of the others. The pathology results from his post mortem examination have not yet been received.
If you think the deaths are caused by morbillivirus, why have so few dolphins tested positive?
Not all of the dead dolphins were able to be tested for viruses because the carcasses were too decomposed. The others do show signs that are consistent with the secondary infections common in dolphins suffering from morbillivirus.
Are the dolphin deaths linked to the fish deaths?
The recent fish deaths have been linked to an algal bloom. We do not fully understand the predisposing causes of morbillivirus infection in dolphins, but the outbreak may be linked to the same warmer-than-usual water temperatures that caused the bloom.
Are dolphins dying because of the desalination plant?
Nothing surrounding the deaths of the dolphins points to any link to the desalination plant. Salinity levels in the gulf are not at a level that would be considered dangerous. Also, dead dolphins have been found well away from the desalination plant, where salinity levels are absolutely normal.
What tests are being carried out and where have samples been sent?
Most of the dolphins that have been recovered have been examined at the South Australian Museum by a collaborative group of pathologists, veterinarians and biologists. The dolphins examined at the museum are photographed and measured, then undergo a full post-mortem. Many samples are collected, including liver, kidney, brain, muscle, heart, blubber, stomach contents and urine. The samples collected for pathology will be studied immediately using a variety of tests such as histology, bacteriology and toxicology.
Other samples will be available for future studies if the need arises. In addition, all the bodies will be macerated and the skeletons examined in detail at a later date.
PIRSA is supporting the South Australian Museum and DEWNR with the dolphin mortalities, with the Chief Veterinary Officer assisting with port mortems and pathology diagnostics.
The University of Adelaide has also examined two dolphins. Tissue samples from these and from the South Australian Museum cases have been forwarded to the Australian Animal Health Laboratory at Geelong for virus studies.
Why are the results taking so long?
Most of these tests are undertaken in Australia but the toxicity tests are to be undertaken in New Zealand. Therefore it takes a significant amount of time to get full sets of results back.
What results have been received?
Laboratory testing has identified dolphin morbillivirus in tissues from five animals, and changes consistent with a virus infection were also seen in some tissues.
Tests for algal toxins in the dolphins were negative. Microscopic examination of tissues has been completed on some dolphins and the findings indicated that the animals had pneumonia. Some also had inflammation of the brain (encephalitis). Fungi were identified in some of the affected tissues.
When will more results be available?
Post mortems are still being undertaken, so the results will come in gradually over the next three or four weeks.
Surely this isn’t a normal situation?
The numbers of dead dolphins we have seen in the Gulf St Vincent bioregion is an unusual occurrence, which is why comprehensive testing is required to determine what is actually happening. This is the first time dolphin morbillivirus has been seen in South Australia.
Is this mortality event going to impact on dolphin populations?
At this stage it does not seem that the number of dead dolphins will impact the population of bottlenose dolphins living in the bioregion.
There is no precise number of how many dolphins live in the Gulf St Vincent region but it may be as many as a few thousand. Natural mortality of dolphins occurs regularly. However, the current observed dolphin mortalities are unusual. The Indo-Pacific bottlenose dolphin is protected by law but it is not a threatened species.
What do I do if I find or see a dead dolphin?
Contact the Adelaide Dolphin Sanctuary on (08) 8240 0193.
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