An investigation has begun into the declining health of Adelaide’s Port River dolphins after a trick-turning male was found dead and two of his friends went missing.
Key points:
- The Port River dolphin population is believed to have halved from up to 40 members to about 20 in recent times
- Several dolphins are feared dead after showing poor health, with one dead male recovered on the weekend
- The SA Museum will perform a post-mortem this week as the government launches an investigation
After showing signs of emaciation and poor skin health, a 12-year-old dolphin known as Talulla — renowned for tail walking across the surface of the water — was found dead in the Adelaide Dolphin Sanctuary (ADS) on the weekend.
Two other Port River dolphins, Twinkle and Doc, are missing after presenting similar symptoms and are now presumed dead.
SA Department for Environment and Water (DEW) Minister David Speirs said he had ordered an investigation into the failing health of dolphins in the sanctuary.
“Given recent events, it is important that we take a closer look and we hope to learn more about the possible causes of death of the dolphins through necropsy [animal autopsy] procedures and further testing.”
Mr Speirs said the SA Museum was assessing the recent dolphin deaths and undertaking additional testing.
Dolphin numbers declining
The 118 square kilometre dolphin sanctuary encompasses the Port River and adjacent Barker Inlet, and stretches north into the Gulf of St Vincent to the Adelaide International Bird Sanctuary.
The Port River dolphins once numbered in their 40s, with about 30 remaining almost entirely in the river area, but in recent times the main river population has declined to about 10, with a further 10 coming and going from the gulf.
Whale and Dolphin Conservation volunteer and ADS researcher Marianna Boorman said she was deeply concerned about the dwindling population.
“We’ve had some terrible years with a number of calves dying,” she said.
Ms Boorman said boat strikes, fishing line entanglements and shark attacks were constant threats to the dolphins, but the reason behind the recent deaths was unknown, which made it “very worrying”.
“It’s certainly possible that pollution is causing the calves to pass away, but whether the pollution is being passed on in the mother’s milk, we don’t know enough about that,” she said.
She said the deaths could also be due to a virus, and if that was the case, “there’s not much we can do”.
“And all three dolphins [Talulla, Doc and Twinkle] were scavenging and picking up discarded scraps of fish, which was very concerning behaviour,” Ms Boorman said.
Necropsy held this week
A SA Museum spokeswoman said the post-mortem on Talulla would be undertaken this week, but an investigation into the cause of his death could take up to six weeks to finalise.
“Once the post-mortem has been completed, the museum will work with DEW and the University of Adelaide to analyse the findings and a report will be publicly available at this time,” the spokeswoman said.
Ms Boorman was also concerned that the leaking of hypersaline water at St Kilda, where it has killed mangroves and salt marsh, could be linked to the dolphins’ failing health because Talulla, Doc and Twinkle were known to spend a lot of time in the adjacent Barker Inlet.
Mr Speirs said consideration would be given to “inform further areas which may require investigation”.
“DEW will lead the investigation and will be seeking input from a dolphin expert reference group which is made up of independent, qualified veterinarians and experts with experience in the management of marine mammals, as well as researchers and other relevant government departments,” he said.
An entangled history
In 2019, a dolphin named Star died after becoming tangled in fishing line and having hooks in its throat for nearly three weeks.
Another dolphin, Marianna — named after Ms Boorman — was found dead in October last year, with a necropsy revealing he had most likely died due to blunt force trauma caused by a boat strike.
Doc himself had to be rescued from an entanglement just three days before he was last seen alive on July 27.
Ms Boorman said Doc started exhibiting ill-health symptoms in October last year and appeared to improve slightly before deteriorating again.
She said Talulla and Twinkle started showing symptoms about three weeks before they were last seen alive on July 7.
“It is very fortunate that Talulla’s body was able to be collected [for necropsy] because Doc’s and Twinkle’s bodies disappeared, so we sort of had no answers,” Ms Boorman said.
Many male dolphins in the ADS, such as Talulla, Twinkle and Marianna, have female names because it can take enthusiasts years to learn that a dolphin who might have originally appeared female was actually male.
‘They brought so much joy’
Ms Boorman said Talulla learnt how to tail walk from his mother, Wave, who was among other dolphins that learnt the skill from another dolphin, Billy.
Billy had returned to the Port River after being released from Marineland, a West Beach aquarium and wildlife park that closed in 1988.
“Talulla’s mum, Wave, used to do it regularly, and then Talulla started copying the behaviour, so it’s an amazing site to see and certainly spectacular when you see a dolphin walking backwards on its tail,” Ms Boorman said.
“We also knew Twinkle very well because we had to rescue him four times due to entanglements, and Doc was regularly seen playing around and people were able to watch them from the land at Garden Island.
In 2019, the state government reduced boating speed limits in key areas of the ADS, from unlimited speed to seven knots, and it is illegal to feed dolphins or discard fish litter in SA waters.
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