In short:

The deaths of resident dolphins from the Port Adelaide River in 2021-2022 prompted an extensive investigation.

No single cause was uncovered, but low genetic diversity and some inbreeding is believed to make them more susceptible to disease.

What’s next?

Toxicological investigations are continuing, including into the cumulative effects of exposure to pollutants.

Two years after several much-loved dolphins renowned for performing tricks in the Port Adelaide River died, the local population seems to have stabilised despite researchers being no clearer as to what killed them.

Six male dolphins named Doc, Hunter, Twinkle, Tallula, Namor, Squeak, and an unnamed female dolphin at a nearby beach, died between June 2021 and March 2022, having quickly deteriorated with a condition that left them emaciated. 

Another dolphin, Ripple, disappeared in September 2022 after appearing sick in late August, leaving her calf, Rocket, orphaned.

Talulla, now deceased, learnt the act of tail walking from his mother, Wave.(Supplied: Marianna Boorman)

Local dolphin expert Mike Bossley lobbied from the mid-1990s to protect the region’s residential marine mammals before Adelaide Dolphin Sanctuary (ADS) was put in place in 2005.

He said the 2021-22 deaths were caused by “an unknown wasting-type disease”.

“Five or six animals died very quickly, but there haven’t been any of those now for getting on two years, so things have stabilised,” Dr Bossley said.

He added that while it was too early to know for sure, the current crop of calves was “nearing their weaning stage and so far they’re looking good”.

Mike Bossley has been studying the local dolphins for more than 30 years.(ABC Radio Adelaide: Malcolm Sutton)

About 20 resident bottlenose dolphins live in the Port Adelaide River estuary and the adjacent Barker Inlet, although transient dolphins come and go from the Gulf of St Vincent as well.

The resident dolphins are renowned for culture in animal behaviour, having learnt tricks like tail-walking from a former dolphin, Billie, that spent two weeks in a former dolphinarium after being rescued from a polluted marina.

Investigation launched

In response to the deaths, the state government, under former environment minister David Speirs, launched an extensive investigation using a multi-agency group of researchers in 2021.

A Department for Environment and Water spokesperson said that while testing could not determine a single common link behind the deaths, it was likely “multiple factors in combination” led to each individual death.

The investigation into dolphin deaths in the ADS report pointed out they lived within a heavily industrialised environment containing “legacy pollutants” at the end of one of SA’s busiest shipping ports and most urbanised catchments.

This meant they were at an increased threat from waterfront industry, noise pollution, and high recreational water uses than offshore populations in SA.

The Port River dolphins are a popular tourist attraction for the area.(ABC Radio Adelaide: Malcolm Sutton)

The spokesperson said the investigation uncovered some new insights into the population with the size of the spleen in several animals found to be smaller when compared to other wild populations.

“Several male ADS dolphins had not reached the expected sexual maturity for their age when compared to other wild SA populations,” he said.

Another dolphin had been exposed to the bacteria, brucellosis, which is known to cause abortions and infertility in domestic livestock.

“This result is significant because it is the first detection of the bacteria in an SA dolphin,” the spokesperson said.

The report added there was low genetic diversity and some inbreeding in ADS dolphins, which could make them more susceptible to disease due to low variation of immune-related genes.

Fishing restrictions

In October 2023, PIRSA banned the use of fishing lines within 50 metres of a dolphin sighted within the Port Adelaide River, south-east from Pelican Point to the southern breakwater at St Kilda.

It also banned the use of fishing hooks larger than 56 millimetres in shank length and 23mm gape.

Hunter, who was euthanased in 2021, shows off to passing fishers.(Supplied: Jenni Wyrsta)

The restrictions were put in place for 12 months while permanent regulations were developed.

Authorities said they rescued about one dolphin every year from being entangled with fishing line.

Despite the rescues, the report stated only one had died as a result of entanglement since 1987.

Doc, presumed dead, had previously been freed from entanglement.(Supplied: Marianna Boorman)

Several dolphins in the past have been intentionally killed by humans, including animals that had been shot, speared, and stabbed.

The report stated there had been a decline in intentional killings since the ADS was implemented in 2005, although there had been several unintentional killings, such as from boat propellers.

It said toxicological investigations were continuing, including into the cumulative effects of exposure to pollutants.

The report found further research was also required into the potential effects of endocrine-disrupting chemicals in sediments and water.

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