Another Port River dolphin found dead as the interim report struggles to identify a cause

A third dolphin has been found dead inside the Adelaide Dolphin Sanctuary, but despite showing similar symptoms to other dead or missing mammals, a temporary investigation is nowhere near finding the cause.

A four-year-old dolphin known to enthusiasts as Squeak or Mimo was found dead late Sunday near Fletcher’s Slip on the Port River.

Squeak was the latest Port River dolphin to show signs of weight loss and illness after his older brother, Hunter, had to be euthanized due to serious ill health.

A 12-year-old dolphin known as Tallulla – known for its tail that crosses the water surface – was found dead in August.

Director of the Department of Environment and Water Conservation and Wildlife (DEW) Lisien Loan told ABC Radio Adelaide all the dolphins had shown similar symptoms and suffered a “really rapid decline”.

Two other dolphins, named Twinkle and Doc, are also believed to have died after showing similar symptoms earlier this year before disappearing, and a sixth dolphin washed up dead on Semaphore Beach during July.

A dolphin rises vertically above the water
The late Talulla was among those who had learned the tail walk.(Delivered by: Marianna Boorman)

The root cause elusive

The Port River dolphins are a treasured tourist attraction, and the deaths prompted DEW Minister David Speirs to launch an investigation into their failing health in August.

Ms Loan said autopsies, or autopsies, of the dolphins had found that the dolphins all suffered from infections and diseases that affected their health with varying degrees of severity.

Two of the dolphins, Hunter and Doc – taken before he disappeared – were found to have been exposed to Brucella, a zoonotic bacterium that could result in dolphin abortions, male infertility, neurobrucellosis, cardiopathies, bone and skin lesions and death.

two dolphins swim close to shore in a river while a child watches
Doc and Twinkle swim near a Port River spectator in August before disappearing.(Delivered by: Marianna Boorman)

Investigators said broader monitoring was needed to see if it had a negative impact on the dolphin population, especially in terms of calf mortality.

The 118-square-mile dolphin reserve includes Port River and adjacent Barker Inlet and extends north into St. Louis. Vincent Bay to the Adelaide International Bird Sanctuary.

The Port River dolphins once numbered in the 40s, and about 30 were almost exclusively left in the river basin.

In recent times, the population of the main river has dropped to about 10, with another 10 coming and going from the bay.

Test to continue

Testing will also continue for environmental toxins, including biotoxins and other factors that may contribute to weakened immunity, including water quality, toxicology, pathology and marine ecosystems.

Ms Loan said veterinary pathologists on the investigation team were eager to continue looking for a disease or neurological condition that could cause weight loss and lead to other infections.

This included data on dolphin deaths worldwide in an attempt to “pinpoint or narrow down what we might be looking for”.

A little girl and a little boy stand on the bank of a river mouth and watch a dolphin flip through the water
Several dolphins around Adelaide have learned to go after a trained dolphin that has been released into the wild.(ABC News: Mahalia Carter)

Despite escaping hypersalt water at nearby St Kilda, which has killed mangroves and salt marshes since late last year, Ms Loan said it was unlikely to be a factor due to the size of the body of water involved. .

She said the affected dolphins appeared to be those that lived in and around the Port River tidal estuary and lived within a “very small home area”.

“That’s why they’re well known by the community down there, because they tend to be in the inner Port River area around Garden Island and do not tend to move too far from there,” Ms Loan said.

“We have a lot of other dolphins using the sanctuary that also come in and out of the bay.”

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